Session GP1 - Poster Session IV.
POSTER session, Tuesday afternoon, November 12
Grand Ballroom CDE, Rosen Centre Hotel

[GP1.001] Education and Outreach

[GP1.002] A Plasma Science Education Laboratory for K-16 Students and Teachers

In the Summer 2002, a major new science education laboratory was created at PPPL. The new laboratory significantly increasing our educational opportunities for teachers and students at all levels, both locally and nationally, especially for those that are underrepresented in math, science, and technology. Recent collaborations include partnerships with The Lewis School, a private school of grades 6-12 for “learning different” students (redesigning their physics and physical science curricula), Douglass College (programs designed for undergraduate and high school women interested in math, science, or engineering) and the science museum The Franklin Institute (creating teacher and student plasma workshops for their educational programs). The Plasma Science Education Laboratory is more than 3600 sq. ft. and is designed as a laboratory and a classroom, with the general lab space easily changed depending upon the type of use. The flexible layout allows for a unique combination of curricula design and direct plasma education. Small rooms are set aside for advanced projects. Other activities in the laboratory include research with small plasma sources, typically a DC glow discharge, that pairs an advanced high school student with an undergraduate physics major. Research topics include high speed video imagery and analysis of classroom plasmas (Jacob’s ladder, plasma ball), investigations of plasmas that mimic biological systems, creation of new plasma sources for classroom use.

[GP1.003] Promoting Pre-College Science Education

The Fusion Education Program, with support from DOE, has begun its 9th year of dynamic interactions between scientists, teachers, and students. The program has continued to grow in the number and kind of available educator workshops, scientist-student interactions, and supplemental curricular materials. In addition, student visits to see the DIII-D facility continue to be an integral part of the program. The content of our educator workshops has grown to include energy, radiation and radioactivity, fusion and plasma science, in-depth use of Excel software in the classroom, solar science, and the electromagnetic spectrum. During the previous year, workshops on some of these topics were given to teachers at the national APS/DPP, NSTA, and AAPT meetings, as well as at local meetings, such as the UCLA Three R's of Science workshop, the annual CSTA meeting, and STEP II in Riverside, CA. Scientists and engineers have had more than 4000 students participate in off-site activities through our Scientist in the Classroom program. New materials available for teaching and the overall program status will be presented.

[GP1.004] Educational Outreach at the MIT Plasma Science and Fusion Center

At the MIT PSFC, student and staff volunteers work together to increase the public's knowledge of fusion science and plasma technology. Seeking to generate excitement in young people about science and engineering, the PSFC hosts a number of educational outreach activities throughout the year, including Middle and High School Outreach Days. The PSFC also has an in-school science-demonstration program on the theme of magnetism. As ``Mr. Magnet," Technical Supervisor Paul Thomas brings a truck-load of hands-on demonstrations to K-12 schools, challenging students to help him with experiments. While teaching fundamentals of magnetism and electricity he shows that science is fun for all, and that any student can have a career in science. This year he reached 82 schools -- 30,000 teachers and students. He has recently expanded his teaching to include an interactive demonstration of plasma, encouraging participants to investigate plasma properties with audiovisual, electromagnetic, and spectroscopic techniques. He has also developed a workshop for middle school on how to build an electromagnet.

[GP1.005] Coalition for Plasma Science (CPS) Education and Outreach Activities

The Coalition for Plasma Science (http://plasmacoalition.org/, CPS@plasmacoalition.org) is a group of institutions, organizations, and companies joining forces to increase awareness and understanding of plasma science and its many applications and benefits for society. Ongoing CPS educational activities include: (1) Construction and maintenance of a web site featuring "A Teacher's Guide to Plasma Science on the Web," a page that links to a wide range of plasma-related education sites, most of them analyzed for consistency with national science standards. The web site also directs visitors to our "Plasma Page," a brief, clear summary of plasma-related news; (2) Preparation of two-page articles on a wide range of plasma topics, including lighting, fusion, and space plasmas; and (3) Printing and distribution of an educational brochure entitled "Plasmas are Everywhere." The audience for these activities is primarily nontechnical, and includes students, teachers, and policy makers.

[GP1.006] CPEP Fusion/Plasma Physics Education Materials/Activities

The Contemporary Physics Education Project (CPEP) is a not-for-profit organization of teachers, educators, and physicists (see http://cpepweb.org) whose goals include the development and implementation of teaching materials about contemporary physics topics for introductory courses. To this end, the CPEP Fusion/plasma group has produced the teaching chart, "FUSION-Physics of a Fundamental Energy Source" and ancillary materials including an Instructors' Manual and a packet of classroom activities. To promote effective classroom use of its educational materials, CPEP presents workshops for high school and college teachers. These workshops have been sponsored by or held in conjunction with various organizations including; the APS/DPP, the AAPT-PTRA program, the AAPT, the Space Science Institute, the American Nuclear Science Teachers Association, The Allegheny Intermediate Unit, and the University of Pittsburgh at Greensburg. The chart is available in wall-size, poster-size and student notebook-size, and has been translated into six languages. Laminated versions of the poster and notebook size charts are also available as well as an overhead transparency of the chart. For more information, visit the CPEP/Fusion website (http://FusEdWeb.llnl.gov/CPEP/Chart.html). Many of these topics will also be presented at T. P. Zaleskiewicz's invited talk, "A CPEP Primer for Education/Outreach to the Classroom," in the Education and Outreach session.

[GP1.007] A Plasma Science Class for High School Students

The Fusion Division of the Center for Energy Research at the University of California, San Diego hosted a 3-week long, in-residence plasma science class entitled ``Radiant Plasmas: from Neon Lights to Nuclear Fusion" during July 2002 as part of the Academic Connections program at UCSD. The class consisted of 3 girls and 6 boys (4 seniors, 4 juniors, and 1 sophomore) from across the US and had a wide range of educational experience since the only prerequisite was a course in Algebra. The students were exposed to a number of hands-on activities developed by CPEP and supplemented with activities that drew on the local strengths of the PISCES program, the Center for Astrophysics and Space Sciences, and the GA Fusion Education Project. We will discuss the specifics of the student's activities, the relative effectiveness of each, and some ideas for developing this prototype class into an offering for a more general high school audience.

[GP1.008] Fusion Education Physical Models for Students and Teachers

Interactive classroom visits by scientists and engineers in the ``Scientist in the Classroom" program and educator workshops led by Fusion Education team members continue to be the catalyst in the development of low cost, age appropriate, understandable physical demonstration models for use in classroom and workshop environments. Physical models developed for these interactive settings are based on topics in plasma science and technology, vacuum, thermodynamics, light, and electricity and magnetism. The physical models are actual hands-on devices students use to observe specific phenomena. One example uses a piston, a sealed volume, and a vacuum chamber to illustrate the ideal gas law. Another example uses liquid nitrogen to explore how temperature affects changes in states of matter, and, as a third example, magnets are used on simple plasma devices to illustrate the effects a magnetic field has on moving, charged particles. The details of these models will be presented. Three very successful ``build-it" days have been sponsored that enable teachers to build these physics models for use in their own classrooms.

[GP1.009] The Wonders of Physics

The Wonders of Physics (WOP) has been the University of Wisconsin's primary physics outreach since 1984. Utilizing faculty and staff of the plasma group, a typical WOP presentation covers the six areas of classical physics in a way designed to make science interesting. A special emphasis is placed on plasmas and fusion science. Every February, Clint Sprott gives six WOP presentations on the UW-Madison campus. He has given over 150 standing-room-only shows, to a total audience of over 50,000. These annual February shows are videotaped and distributed nationwide. In 1990, a Lecture Kit was developed and is also distributed nationwide. A mobile version of WOP, the Wonders of Physics Traveling Show (WPTS) was created in 1988. Over 725 WPTS presentations have been given to nearly 100,000. In 2001, Roger Feeley, the principal WPTS presenter, gave 134 presentations, to over 15,000. WPTS has traveled to nineteen states and provinces, and has been an active participant in APS DPP education and outreach activities since 1996.

*Supported by DoE

[GP1.010] Integrated Computer Controlled Glow Discharge Tube

An “Interactive Plasma Display” was created for the Princeton Plasma Physics Laboratory to demonstrate the characteristics of plasma to various science education outreach programs. From high school students and teachers, to undergraduate students and visitors to the lab, the plasma device will be a key component in advancing the public’s basic knowledge of plasma physics. The device is fully computer controlled using LabVIEW, a touchscreen Graphical User Interface [GUI], and a GPIB interface. Utilizing a feedback loop, the display is fully autonomous in controlling pressure, as well as in monitoring the safety aspects of the apparatus. With a digital convectron gauge continuously monitoring pressure, the computer interface analyzes the input signals, while making changes to a digital flow controller. This function works independently of the GUI, allowing the user to simply input and receive a desired pressure; quickly, easily, and intuitively. The discharge tube is a 36” x 4”id glass cylinder with 3” side port. A 3000 volt, 10mA power supply, is used to breakdown the plasma. A 300 turn solenoid was created to demonstrate the magnetic pinching of a plasma. All primary functions of the device are controlled through the GUI digital controllers. This configuration allows for operators to safely control the pressure (100mTorr-1Torr), magnetic field (0-90Gauss, 7amps, 10volts), and finally, the voltage applied across the electrodes (0-3000v, 10mA).

[GP1.011] Effect of Dipole Perturbation on a Good Confining Surface Near X Point

We analyze effects of dipole perturbation on a good magnetic surface of a single null divertor tokamak using the method of maps developed by Punjabi and Boozer /1/. Unperturbed fields are represented by the Symmetric Simple Map /2/. Effects of high MN perturbation are represented by the Dipole Map (DM) /2/ given by: x_n+1 = x_n+2\delta s^3x_n[(y_n-y_s+s) / [x_n+1^2+(y_n-y_s+s)^2]^2], y_n+1 = y_n+\delta s^3x_n[[(y_n-y_s+s)^2-x_n+1^2] / [x_n+1^2+(y_n-y_s+s)^2]^2] The good surface is x_0=0 and y_0=0.952873. We start with the strength of perturbation, \delta=0, increase it slowly, and observe how the surface changes. The results will be presented. This project is supported by the QEM network NASA Sharp Plus program and by DE-FG02-02ER54673. The work is done on the FUSION1 server under Profs. Ali and Punjabi

1. Punjabi A., Verma A. and Boozer A., Phys. Rev. Lett., 69, 3322 (1992) 2. Ali H., Punjabi A. and Boozer A., Dipole Map for Single-null Divertor Tokamak, 2002 International Congress on Plasma Physics, Manly, Australia.

[GP1.012] Effects of Low MN Perturbation on a Good Confining Surface Near X Point

Here we analyze effects of low MN perturbation on a good magnetic surface of a single-null divertor tokamak. We use the method of maps developed by Punjabi and Boozer /1/. Effects of low MN perturbation is represented by the Low MN Map /2/ given by: y_n+1=y_n+2k\x_n-ky_n[1-y_n-\deltacos(2\pin/N_p)][1+\deltacos(2\pin/N_p)]\, x_n+1=x_n-ky_n[1-y_n-\deltacos(2\pin/N_p)]-ky_n+1[1-y_n+1-\deltacos(2\pin/N_p)]. The k value is fixed at 0.3. The good surface is x_0=0 and y_0=0.965. We start with the strength of low MN perturbations \delta=0, increase it slowly, and observe how the surface changes. The results are presented in this paper. This work is supported by the QEM Network NASA SHARP PLUS program and DE-FG02-02ER54673. The research is done under the mentorship of Profs. Halima Ali and Alkesh Punjabi. The FUSION1 Sun Station 10 server is used for this work.

1. Punjabi A., Verma A. and Boozer A., Phys. Rev. Lett., 69, 3322 (1992) 2. Punjabi A., Ali H. and Boozer A., Phys. Plasmas, 4, 337 (1997)

[GP1.013] Undergraduate Posters

[GP1.014] Electrostatic spray experiment at Prairie View Aamp;M University

Electrostatic spray device originally developed at Princeton Plasma Physics Laboratory, has been rebuilt and started operation at Prairie View AM University. The device consists of a capillary needle with a high voltage applied to it, that sprays a cone of charged oil droplets of around one micron radius into a vacuum tank. The distribution of charges with respect to droplet radius is measured by means of a quadrupole mass filter and a charge detector. Our goal is to reproduce past experiments with Octoil, which revealed the multi-peak character of the charge distribution, and make further improvement by using other types of liquids and smaller diameter needles.

[GP1.015] Vacuum Control System for Operating the Field Reversed Configuration Experiment (FRX-L) for Magnetized Target Fusion

We describe a vacuum interlock and control system, which will be used to operate the Field Reversed Configuration (FRX-L) experiment for the Magnetized Target Fusion program at LANL. FRX-L has high voltage pulsed power components; so all control systems must be optically isolated. The vacuum system must be remotely controlled and needs safety and operational interlocks. We use Real Time version of LabView as a programmable logic controller (PLC) to monitor and control the status of all the vacuum hardware. The hardware includes: valves, gas feeds, pressure gauges, power disconnects and a variety of other functions. The major goal of the increasingly complex vacuum control system is to replace the relay operated components with an easily programmable computer technology. This allows us freedom to reconfigure parts of the experiment without changing out hardware.

[GP1.016] Constructing a Bolometer Array Diagnostic for the FRX-L Plasma

The Field Reversed Experiment – Liner (FRX–L) is a plasma experiment in which deuterium gas will be preheated in a Field Reversed Configuration (FRC) magnetic bottle. Once preheated to 100-300 eV, the plasma target will be translated into a thin-walled cylindrical metal cylinder (liner). As the liner implodes due to the application of a large current, the fusion fuel will be adiabatically compressed to fusion conditions. The overall concept is called Magnetized Target Fusion (MTF). The entire process, from plasma formation to compression, will occur within twenty-five microseconds. Because plasma energy losses can prevent the attainment of fusion conditions it is imperative to quantitatively determine these losses. We will build a plasma diagnostic, called bolometry, to measure the total radiative energy losses. Three and twenty element time resolved silicon p-n junction photodiodes, obtained from International Radiation Detectors INC., will initially be mounted axially on the FRX-L to determine these radiative energy losses as a function of time. Diagnostic designs and construction will be presented, along with initial measurements and plans.

[GP1.017] Field Reversed Configuration Interchange Stability vs.\ Pressure Profiles and Shape

The field reversed configuration (FRC) is a possible high-beta magnetic confinement scheme for fusion that has not been studied in as great of depth as the tokamak configuration. Using a Grad-Shafranov solver, developed and based on MATLAB® finite element tools, we calculate free boundary, numerical MHD equilibria of FRCs. The local interchange mode stability is a good indicator of the stability of other pressure-driven modes in FRCs, and it is readily calculated in this program. We seek to identify possible regimes of favorable MHD stability for FRC. We will show and discuss FRC interchange stability as a function of pressure profile and flux surface shape, including non-standard FRCs, such as doublet shaped FRCs.

[GP1.018] Methods For Analyzing Temperature Pertubations From Pulsed Heating

Heat transport by electrons in tokamak plasmas is currently a subject of intense study. Transport analysis using power balance analysis does not allow one to separate heat convection and conduction, but this can be accomplished using the dynamic response of the electon temperature from periodic heat pulses. The plasma response is analyzed using the linearized Braginski equation. On the DIII-D tokamak, localized electron cyclotron heating (ECH) is used to generate a train of heat pulses which is monitored using electron cyclotron emission. Two different methods have been implemented for the analysis of periodic temperatue perturbations: the fast Fourier transform (FFT) and a Fourier series using the modulation frequency of the ECH and its harmonics. The Fourier series technique holds promise for smaller uncertainty estimates. The expected dependance of the temperatue perturbations in space and time has also been studied using numerical simulations of the heat pulses in realistic toroidal geometry. The results of the simulations will be compared to experimental measurements to determine the salient features of the model.

[GP1.019] Perturbation Techniques for Distinguishing Between Conduction and Convection in Electron Heat Transport

Obtaining an effective description of electron heat transport within tokamak plasmas is a long-standing problem. The separate effects of heat conduction and convection are not discernible from radial power balance analysis alone. The high power electron cyclotron heating (ECH) system on the DIII-D tokamak is a useful tool for studying heat transport because it locally increases the electron temperature. Modulating the ECH power at frequencies between 25 and 300~Hz produces a series of heat pulses in the plasma that are observed using electron cyclotron emission (ECE). Analytic solutions of the Braginskii energy conservation equation are obtained for various model assumptions, including slab and cylindrical geometries, conductive and convective transport, and damping terms. The analytic solutions are fit to the Fourier analyzed ECE data to determine the salient transport properties of the electron channel. Software tools are developed to compare multi-harmonic data to the models.

[GP1.020] Investigation of the EHO Phenomenon in DIII-D Plasmas

In recent experimental campaigns, a phenomenon known as the edge harmonic oscillation (EHO) has been observed in a variety of DIII-D plasmas. The EHO is an edge phenomenon that exhibits a structured magnetic field oscillation on the plasma edge. There has been a strong correlation observed between the EHO phenomenon and a type of H-mode operation known as Quiescent H-mode (QH-mode) during counter injected beam discharges. Quiescent refers to the notable absence of Edge Localized Modes (ELMs) during QH-mode operation. This ELM free H-mode behaviour provides a strong motivation for developing a physics understanding of the EHO and QH-mode phenomena. Results will be presented of an investigation of the physics of the EHO using computational methods for large scale data processing. The methods used will be described and their relevance to other related physics problems will be discussed.

[GP1.021] Numerical Study of Resistive Wall Mode Stabilization by Differentially Rotating Wall

Stabilization of the resistive wall mode (RWM) by non-uniform rotation of an external wall has been studied. The MARS [1] stability code, which solves for the stability of the RWM, is modified to include a toroidally rotating wall with poloidally different rotational velocities. Growth of the RWM is due to leakage of the magnetic flux of the unstable mode ``coherently" through the resistive wall. It is expected that with sufficiently large differential rotation speed on the resistive wall, this ``coherency" will be destroyed and the RWM stabilized. The dynamics of the plsma with differentially rotating wall are compared to that with uniform rotating wall. Initial application of the modified code verifies results by J.B.\ Taylor, et al. [2]. Further application to general plasmas with more equilibrium properties and profiles willbe presented.\par \vspace0.15em [1]~A.~Bondeson, et al., Phys.\ Fluids B 4, 1889 (1992).\par [2]~J.B.\ Taylor, et al., Phys.\ Plasmas 8, 4062 (2001).

[GP1.022] Plasma Diagnostics for Plasma Polymer Coatings Used in Fabrication of Thin Wall CH Shells for Direct Drive OMEGA Cryogenic Experiments

High aspect ratio CH shells, \approx1~\mum thick, 9001~\mum diameter, are crucial for the success of the cryogenic direct drive inertial confinement fusion (ICF) experiments at the OMEGA laser facility at the University of Rochester's Laboratory for Laser Energetics (LLE). Plasma polymer coatings are currently used in fabrication of such shells, which can be made substantially stronger by altering parameters. High strength is important for inherently fragile high aspect ratio shells. The plasma characteristics used in the deposition process were studied in order to determine a correlation between the plasma parameters and the strength of shells. Several plasma processing parameters such as deposition pressure, power and relative and absolute gas flow rates were varied. The plasma was studied using several techniques such as optical emission spectroscopy, Langmuir probe diagnostics, and mass spectrometry. These diagnostic results were then correlated with direct measurements of the target strength (burst testing and buckle testing) and permeability to determine the ideal parameters for creating the strongest and most permeable ICF targets.

[GP1.023] Numerical Calculations of the Coulomb Logarithm in an Expanded Electron Density and Temperature Space

The Coulomb logarithm is a fundamental parameter in the study of non-equilibrium plasmas because it directly relates to energy and momentum relaxation. Traditionally, it is calculated by considering the mean momentum transfer between two charged particles whose interaction is described by a Debye-Hückel potential. While this model is valid over a broad range of electron density and temperature, its applicability is limited. For example, in high-density plasmas, such as those involved in inertial confinement fusion, three-body interactions become significant. Also, in low-temperature plasmas, such as those found in the tokamak edge, the recombination of ions and electrons into neutral atoms will render the electron screening approximation invalid. In both of these examples an adjusted two-body potential can account for the additional physical effects. Thus, we developed numerical methods for calculating the Coulomb logarithm for an arbitrary potential. These calculations will allow us to quantify the extent to which traditional calculations differ from results predicted by more advanced physical models.

This work is performed under the auspices of the U.S. Department of Energy and the Lawrence Livermore National Laboratory under Contract Number W-7405-ENG-48.

[GP1.024] Isolating the Effects of the Moving Ends of a Collisionless Non-neutral Plasma, or "Landau Damping of a Manhole Cover"

In an effort to understand and isolate the effects of the moving ends of a spheroidal, collisionless, non-neutral plasma we model the situation as ideal gas particles in a cylinder under a plate which is perturbed from an equilibrium height. We have developed a numerical simulation that implements this model. The simulation conserves total energy to within machine precision, and the physics is simple enough that it is feasible to model as many as 100 million particles or more over many seconds of simulation time. The simulation shows good agreement with a linear theory of Landau damping for the system. The effects of non-linear saturation are evident in the simulation and match the predictions of a Fermi map resulting from an analytic approximation for the orbits of the trapped particles. As a consequence of this non-linear saturation, very low amplitude perturbations (\sim0.1%) are necessary so that a long linear damping phase may be observed in the simulation. At such low amplitudes large numbers of particles (\sim10^6) are needed to accurately model the damping rate of the system. We discuss the results of the numerical simulation and agreement with theory.

[GP1.025] Development Of An Electron Beam Transmission Window For Use In A KrF Laser

A silicon (Si) based electron beam transmission window is to be produced for use in a KrF laser system in support of inertial fusion energy technology. Silicon is the material of choice because of its low Z value and high structural integrity. The window separates the lasing medium from an electron beam source while allowing the electron beam to pass through. The window must meet certain requirements set by the characteristics of the laser and must be able to withstand the hostile environment presented by the lasing medium and electron beam source. This environment includes KrF gas, \geq1500 gauss magnetic fields, large exposure to x-rays, and a \DeltaP of 2 atm. Materials, structures, and cooling systems for the window are determined theoretically based on the requirements of the system. Empirical tests for the window are set up to simulate the actual environment it will operate in. Results of these empirical tests are discussed. Various design changes are considered to enhance the structural integrity of the Si windows and relieve stresses at the edges due to thermal expansion. This work is supported by the Naval Research Laboratory (NRL) in collaboration with the Princeton Plasma Physics Laboratory (PPPL).

[GP1.026] Quiet Time Neutral Atom Imaging of the Terrestrial Magnetosphere: MENA Observations

Carried into space in 2000 aboard the IMAGE spacecraft, the Medium Energy Neutral Atom (MENA) imager has provided the first ever images of neutral atom emission from the Earth's magnetosphere at energies below 20 keV. Recently, Scime et al. [2002] demonstrated that the plasma ion temperature can be remotely determined from MENA data during storm intervals. However, the dim emission between storm intervals precludes such analysis for the quiet time magnetosphere. In this work, we will describe a new algorithm designed to add together quiet time neutral emission intervals from long time periods of the IMAGE mission, i.e., different seasons of the orbit. The algorithm corrects for the changing field of view of the MENA instrument as the orbital plane precesses in local time. We will also describe a second algorithm that is used to correct the MENA data for the effects of neutral atom scattering in the thin carbon foils used in the instrument. Images of the quiet time structure of the inner magnetosphere will be presented and discussed in terms of contemporary models of the Earth's magnetosphere.

[GP1.027] ANALYSIS OF DUST CLOUD PERTURBATIONS IN A DC GLOW DISCHARGE

Potential profiles of dust clouds in a plasma can be studied by applying known voltage perturbations. The dust clouds are suspended in a direct current glow discharge plasma with pressures ranging from 100 to 300 mTorr. The anode and cathode bias voltages are 220 and –230 V, respectively. Measurements of particle transport are obtained using the particle image velocimetry (PIV) technique. Two experiments are performed to characterize the impact of applied perturbations on the suspended dust clouds. One experiment involves the use of a probe to apply a voltage pulse to the plasma in order to perturb the dust cloud. Using the PIV system, velocity measurements of the cloud are made and correlated to the known voltage pulse. A second experiment involves the interactions of dust clouds. A wire is placed between the two clouds and is pulsed with a known voltage to allow the dust clouds to interact with each other. The velocity profiles of the dust clouds are measured and correlated with the known voltage pulse.

[GP1.028] Effects of Temperature Anisotropy and Shear Flow on Ion-Cyclotron Instability of a Magnetized Plasma

Recent numerical investigations of a plasma in a uniform magnetic field with ion temperature anisotropy, field-aligned flow, and perpendicular one-dimensional shear have shown that the growth rate of ion-acoustic waves and their dispersion relationship can be significantly affected by temperature anisotropy and shear. In this work we have investigated the effects of thermal anisotropy on shear modified ion-cyclotron waves. The ion-cyclotron instability growth rate is a strong function of ion temperature anisotropy [Spangler et al., 2000]. We have examined the threshold for ion-cyclotron instability growth at small values of parallel shear. The effect of ion temperature anisotropy on the instability threshold is discussed for a range of propagation angles (k_z/k_y) and normalized perpendicular wave numbers (k_y*rho).

[GP1.029] Glow Discharge Cleaning for LDX

The Levitated Dipole Experiment (LDX) has completed construction of its glow discharge cleaning (GDC) system. GDC will be used before first plasmas in LDX, as well as between experimental operations, to eliminate all impurities from the vacuum vessel. The glow is created by a movable anode probe inserted through a flange on the underside of the vessel. The anode is biased with up to 1kV with respect to the vessel wall with 12kW DC power available for plasma formation. Away from the anode, a biased tungsten filament will be installed to aid in discharge breakdown and reduce the likelihood of arcing[1]. The filament may also be used for preionization during experimental operations. GDC will be implemented with deuterium gas followed by a shorter period of helium gas. A reduced conductance pumping path will be incorporated into the vacuum system in order to better control pressure during GDC operation. The completed design and initial tests of the GDC system will be presented. [1] H.W Kugel, W. Blanchard, G. D'Amico, R. Gernhardt, and T. Provost, "NSTX Filament Preionization And Glow Discharge Cleaning Systems", PPPL Report (2000).

[GP1.030] Imaging Electron Plasmas in a Partially Toroidal Trap

A phosphor screen imaging detector has been implemented for diagnosing electron plasmas in the Lawrence Nonneutral Torus(M.R.\ Stoneking, et al)., Phys.\ Plasmas, 9, 766 (2002)., a partially toroidal trap. The electron plasma has n\approx 10^6cm^-3 and is confined by a toroidal magnetic field of 200G. The plasma has major radius 43cm and minor radius 4.5cm. Trapping times up to 300\mus have been obtained. Because the plasma is trapped in a `C'-shaped partial torus, it can be dumped onto a detector located in the portion of the torus excluded from the trap. Previous experiments involved dumping the plasma onto an array of 17 collecting patches to provide information on the distribution of charge in the trap. Greatly improved spatial resolution has been achieved using a newly constructed phosphor screen and CCD camera. Temporal evolution of the charge distribution is observed by dumping the plasma after different holding times. This work is supported by the U.S.\ Department of Energy and Lawrence University.

[GP1.031] Teaching Physics and Engineering with an Interactive Plasma Display

The goal of this project is to use an interactive, computer controlled demonstration that teaches the properties of plasma to students ranging from middle school to college. The plasma source is similar to a basic discharge tube, but it is bigger in size and primarily computer controlled. The demonstration includes a vacuum and flow meter that regulates how dense the gas is inside the tube. The setup also includes an computer controlled electromagnet which pinches the plasma. By demonstrating the properties of plasma with the model, we will be enhancing people’s knowledge about plasma physics. This knowledge will spark the interest of the public and make plasma more recognized. Our initial curriculum is associated with the Plasma Academy Program that reaches out to underrepresented high school students.

[GP1.032] Grassroots Advancement Plasma Physics: The Creation of a Dc Glow Discharge Tube for a high school classroom

The objective of the project is to create a safe, affordable, portable, computer interactive, and multifunctional DC glow discharge tube for use in a typical high school physics classroom. Our goal is to use this device not only to capture and cerate interest in plasma physics but as a tool to engage students in an active exploration of a variety of physics topics. We present the design, operation and labs created with our discharge tube. We are creating a selection of labs ranging from current/voltage relationships to spectroscopy that can be done on our setup. We have evaluated the vacuum chamber material- glass vs. plastic, our electrode spacing- a fixed vs. variable, external electronics with an emphasis on the power supply, safety and ease of use. Our design is an accessible 6 inch long tube with an inner diameter of 2 inches, which attains low pressure of about 20- 40 mTorr and is computer interactive.

[GP1.033] Bio-plasma physics: Measuring Ion Transport Across Cell membranes with Plasmas

A recent theoretical publication in the American Journal of Physics [1] investigates a mathematical model of plasma double layers, and their applicability to understanding ion transport across cell membranes. Cell membranes have selective permeability to the transport of different charged particles, similar to ion and electron movement across a double layer in a plasma. An existing voltage difference between the cells internal cytoplasm and the external bio-plasma causes a double layer to form between the cytoplasm and the bio-plasma. We present our design of a plasma created in a vessel with two distinct cross sections, similar to the model mentioned in the paper. When two plasmas of different cross sectional areas are considered, a double layer in the plasma forms on the interface between the two separate volumes. We use a Langmuir probe to evaluate plasma parameters such as electric potential, electric field, and charge density in the areas inside and surrounding the plasma double layer. These are used to show the similarity between charge transport across a plasma double layer, and ion transport across a cell membrane.

[GP1.034] Plasma Filament Investigations Using High Speed Video Imaging

A Jacob’s Ladder apparatus and a plasma ball are two tools that are used to study plasmas in an educational setting. However, much of the physics behind these beautiful plasmas remains unknown or not well studied. A new way to examine these plasmas is through high-speed video imaging. We used a Canadian Photonic Labs’ Mega Speed 1000 camera to view behavior such as the filament’s movement, fragmentation, or recombination with other filaments, at over 8,500 frames per second. Analyzing our movies in slow motion, and through the aid of image processing software, we are able to trace each step of this behavior and quantify values such as filament brightness and thickness. Along with spectroscopic techniques, we infer basic plasma parameters and attempt to fully explain the physics controlling each source.. The results of this study are presented as well as a number of high speed movies.

[GP1.035] Particle-In-Cell Simulation of Heavy Ion Beam Propagation through a Plasma

The propagation of a high-current finite-length ion charge bunch through background plasma is studied. Simulation code has been developed in the past to calculate the degree of charge and current neutralization of the ion beam pulse by the background plasma. The code uses fully electromagnetic, relativistic particle-in-cell (PIC) algorithms. The code has been upgraded to account for additional sources of electrons in plasma. The emitting electrodes and gas ionization by beam ions has added. The effects of additional electron sources on charge neutralization are studied.

This work has been supported by the National Undergraduate Fellowship Program.

[GP1.036] A lithium deposition system for tokamak devices*

The production of a lithium deposition system using commercially available components is discussed. This system is intended to provide a fresh lithium wall coating between discharges in a tokamak. For this purpose, a film 100-200 Å thick is sufficient to ensure that the plasma interacts solely with the lithium. A test system consisting of a lithium evaporator and a deposition monitor has been designed and constructed to investigate deposition rates and coverage. A Thermionics 3kW e-gun is used to rapidly evaporate small amounts of solid lithium. An Inficon XTM/2 quartz deposition monitor then measures deposition rate at varying distances, positions and angles relative to the e-gun crucible. Initial results from the test system will be presented.

*Supported by US DOE contract #DE-AC02-76CH-03073

[GP1.037] The Effects of a Magnetic Field on Parametric Excitation of Surface Waves in Liquid Gallium

The Liquid Metal Experiment (LMX) at the Princeton Plasma Physics Laboratory is designed to study magnetohydrodynamic (MHD) effects on driven waves in liquid gallium under the influence of a magnetic field. Previous work with LMX has measured the dispersion relation in the case of one-dimensional surface waves propagating in the directions perpendicular and parallel to the magnetic field. Damping was found only in the case of propagation parallel to the field(Fox, W. 2001. Magnetohydrodynamic Surface Waves in Liquid Metal). Senior Thesis, Princeton University.. Parametrically driven waves have been studied since the time of Faraday and in many types of media including granular, ferromagnetic, and colloidal(Rabinovich, M.I. et al. 2000. The Dynamics of Patterns.) World Scientific Publishing Co. Pte. Ltd. Singapore.. The goal of this work is to examine the case of parametric excitation of a liquid metal in the presence of a magnetic field parallel to the unperturbed surface. Various boundary conditions and orientations will be studied.

[GP1.038] Measurements of Torque and Spindown in Couette Flows

Accretion disks are formed when interstellar gas accretes onto a central massive object such as a black hole or star. The effects of viscosity and hydrodynamic processes fail to explain the outward transport of angular momentum necessary for the fast accretion. Magnetorotational instability (MRI) has been regarded as the dominant mechanism, but has not yet been realized in the laboratory. It is hoped that MRI will be observed utilizing an applied external magnetic field and two concentric rotating cylinders to create a differential angular velocity in liquid gallium. Before this is possible, however, certain characteristics of the setup must be examined in water. For example, due to rigid boundaries on the top and bottom, Eckman circulation competes with MRI for outward angular momentum transport. The torque coupling between the two rotating cylinders can be used to characterize Eckman effects. This will establish "background noise" due to the existing angular momentum transport mechanisms for the MRI in the liquid gallium experiment. Additionally, the Eckman effect can be determined by measurements of time scale of spindown by pressure sensors. Detailed experimental results and comparison to theory will be presented.

[GP1.039] Spectral Analysis of Lower Hybrid Magnetic Fluctuations in the Magnetic Reconnection Experiment

Magnetic reconnection, the topological annihilation and reconnection of magnetic field lines, is a crucial process occurring in both astrophysical and laboratory plasmas evident in solar flare creation and magnetically confined fusion. The Magnetic Reconnection Experiment (MRX) directly observes the reconnection process in a laboratory setting, focusing on a wide array of electrostatic and magnetic instabilities. One class of micro instabilities, which may be described as electromagnetic Lower Hybrid Drift Instabilities (LHDI)(P. Yoon et al., Phys. Plasmas, vol.9, 1526 (2002)), is currently under scrutiny as a source of explanation for fast reconnection (anomalous resistivity). The objective of the present study is to use spectral analysis techniques to find coherence lengths for the observed magnetic fluctuations to better characterize their linear and nonlinear behaviors. Detailed results will be presented together with comparisons with theoretical predictions.

[GP1.040] Hodogram Analysis of Magnetic Fluctuations in the Lower-Hybrid Frequency Range in the Magnetic Reconnection Experiment (MRX)

Magnetic reconnection, a topological change of magnetic field lines, is thought to play an important role in governing the processes of solar flares as well as the particle dynamics of the Earth's magnetopause. Studies have shown the Sweet-Parker model's rate of reconnection to be too slow to describe the fast reconnection rate observed experimentally. Several theories have been proposed to explain this discrepancy, among them a modified Sweet-Parker model involving anomalous resistivity caused by electromagnetic microinstabilities. Recently, magnetic fluctuations in the lower-hybrid frequency range (\sim10 MHz) have been detected in the current sheet in MRX. A 3-component magnetic probe is being built in order to measure the direction of propogation of these fluctuations using hodograms. Hodograms are constructed by mapping the time evolution of the magnetic field vector at one point in space. A perfectly coherent wave will form a plane; the normal vector of this plane is the direction of propogation of the wave. Detailed results of the hodogram analysis will be presented.

[GP1.041] Investigation of Energetic Electron Production by Ultraintense Laser Ionization of Highly Stripped Atoms

It has recently been predicted that GeV electrons can be produced by ultraintense laser ionization of highly stripped atoms [S.Gu and A.Starace, Phys.Rev.Lett. 88, 245003 (2002)]. This acceleration process is investigated by numerically integrating the relativistic electron equations of motion in which the bound state of the electron is approximated as a classical Keplerian orbit. The ionization of an electron from 22-times ionized vanadium by a laser pulse of intensity 10^21 W/cm^2 is used as a representative case. The dependence of the ejected electron energy on ion charge, laser amplitude, and laser pulse shape is examined.

[GP1.042] INVESTIGATION OF PSOC FOR POSSIBLE USE IN THE GROUND FAULT MONITOR FOR THE NATIONAL COMPACT STELLARATOR EXPERIMENT

Programmable system on Chip (PSoC) micro controller technology, a fairly new concept, enables designers to select from a variety of peripheral building blocks that can be configured to suit specific application needs. System functionality, which includes analog and digital building blocks, such as amplifiers, filters, counters and timers, is configured via development software. This system configuration is then downloaded to configure the micro controller. PSoCs include features such as; a sea-of-gates area that allows the user to implement special peripheral functions, 8, 16 or 32 bit CPU, 8 to 16Kbytes of flash memory and SRAM. PSoCs will be investigated for future use in upgrading a Ground System Monitor (GSM) for use on the National Compact Stellarator Experiment. The Ground System Monitor is used to provide Ground Loop and Ground Fault detection in real-time, during installation, maintenance and machine operation. It also assists in determining fault cause and location. PSoCs are a prime candidate for use in upgrading the GSM because they might enable functionality to be located at the sensor, which would lead to enhanced system performance. PSoC use would also lower system cost by reducing part count and simplifying system design.

[GP1.043] Modeling plasmons and photons in complex, periodic lattices

We present the continued evolution of Curly3d, a finite element code for solving the vector Helmholtz equation in a periodic lattice. New developments in Curly3d which are of particular interest for analyzing optical properties in such lattices are discussed: (1) the capability to compute the curl of a vector field of the lattice and by extension the Poynting flux throughout (2) the implementation of algorthims to allow for the lattice to have inhomogenuous and anisotropic dielectric and permeability properties on an arbitrarily small scale (i.e. on the order of a single element). Curly3d uses these new features coupled with its flexibility due to its implementation in the Python scripting language to analyze complex geometries. Calculations are performed on materials with local negative dielectric and permeability characteristics and presented with the necessary implications of the results.

[GP1.044] A Mapping Model for Magnetic Fields with q-profile Variations Typical of Internal Transport Barrier Experiments

Recent studies of ion and electron transport indicate that the safety factor profile, q(r), affects internal transport barrier (ITB) formation in magnetic confinement devices [1, 2]. These studies are consistent with experimental observations that low shear suppresses magnetic island interaction and associated stochasticity when the ITB is formed [3]. In this sense the position and quality of the ITB depend on the stochasticity of the magnetic field, and can be controlled by q(r). This study explores effects of the q-profile on magnetic field stochasticity using two-dimensional mapping techniques. Q-profiles typical of ITB experiments are incorporated into Hamiltonian maps to investigate the relation between magnetic field stochasticity and ITB parameters predicted by other models. It is shown that the mapping technique generates results consistent with these predictions, and suggested that Hamiltonian mappings can be useful as simple and computationally inexpensive approximation methods for describing the magnetic field in ITB experiments. 1. I. Voitsekhovitch \textitet al. 29th EPS Conference on Plasma Physics and Controlled Fusion (2002). O-4.04. 2. G.M.D. Hogeweij \textitet al. Nucl. Fusion. 38 (1998): 1881. 3. K.A. Razumova \textitet al. Plasma Phys. Contr. Fusion. 42 (2000): 973.

[GP1.045] Experimental observation of dynamical energy flow in SSX-FRC

The Swarthmore Spheromak Experiment (SSX) studies the dynamics of magnetic reconnection during the collision of two spheromaks with opposing helicities. Colliding, the spheromaks’ opposing helicities cancel each other, leaving the plasma in a Field-Reversed Configuration (FRC), which we observe to be stable for about 30 \mu s. To observe the energy released in the merging process, we use a soft x-ray diagnostic and a Mach probe. The x-ray diagnostic is comprised of photodiodes, shielded from ions and electrons by permanent magnets, and shielded from low-energy light by thin metallic foils, including Al, In, Mo, Ti, Zr. Since each filter has a different soft x-ray passband, the brehmstraalung curve can be roughly reconstructed, which yields information about the temperature and density in the reconnection region. Preliminary data correlate with the magnetic dynamics of the spheromak collision and resulting FRC. In particular, soft x-rays are observed in conjunction with the reconnection event, and in conjunction with FRC instabilities. A new Mach probe simulation is used to calibrate our Mach probe, which will measure the bulk ion flow velocity in SSX pending its completion. Preliminary results from a prototype Mach probe show M = 0.2-0.5.

[GP1.046] Experimental observation of an FRC in SSX-FRC

Measurements of magnetics in the Swarthmore Spheromak Experiment (SSX) indicate the formation of a field reversed configuration (FRC) after the merger of two spheromaks inside a 0.5 m flux conserver. The FRC retains some of the toroidal field characteristic of spheromaks, but the poloidal fields of the two spheromaks reconnect, linking the two spheromaks together. The FRC is stable for several Alfvén times. The magnetics are measured with 12 magnetic probes distributed throughout the chamber, each of which measure the magnetic field at 8 locations with 1 inch spacing along the probe. The FRC meta-equilibrium is modeled with a code by M. J. Schaffer and J. A. Leuer that solves Grad-Shafronov equilibria. Preliminary analysis indicates a correlation between soft x-ray emissions and FRC formation.

[GP1.047] Fully 3D Measurement of reconnecting magnetic field structure in SSX

A high resolution (2 cm) magnetic probe array has been developed to investigate the three dimensional magnetic reconnection of two spheromaks in the Swarthmore Spheromak Experiment (SSX). The magnetic field vector is measured at a grid of 5 x 5 x 8 points during each shot with 800 ns time resolution, allowing visualization of the unique dynamics of each reconnection event as a 3D ``movie''. Multiplexing electronics are used to allow this high volume of information to be while minimizing the number of costly digitizer channels. The magnetic field geometry in SSX is not well described by existing 2D reconnection models due to the asymmetry of the machine geometry and the intrinsic curvature of spheromak fields. Consequently, these measurements hope to lend insight into the fully 3D reconnection that occurs in the solar corona (which has similar |B| and density to SSX). Non-2D effects observed in SSX reconnection include out-of- reconnection-plane components in the magnetic field and in the pressure gradient.

[GP1.048] Linear wave spectrum associated with collective neutrino-plasma interactions

The linear wave spectrum associated with collective neutrino-plasma interactions is investigated. Weak electric and magnetic fields, E_w = -\,\nabla n - c^-1\, \partial_t\Gamma and B_w = \nabla\times \Gamma, defined in terms of neutrino or plasma densities n_\nu or n_e (acting as scalar potentials) and neutrino or plasma flux densities \Gamma_\nu or \Gamma_e (acting as vector potentials), are introduced into the neutrino-plasma fluid dynamics through a variational principle derived by Brizard, Murayama, and Wurtele [Phys. Rev. E 61, 4410 (2000)]. Space-charge waves supported by a magnetized (or unmagnetized) electron-positron plasma in the presence of a electron neutrino-antineutrino medium are shown to be capable of breaking the CP symmetry of the neutrino-antineutrino medium, with potentially important cosmological implications for the evolution of the Early Universe.

[GP1.049] Numerical modeling of the Madison Dynamo Experiment.

Growth, saturation and turbulent evolution of the Madison dynamo experiment is investigated numerically using a 3-D pseudo-spectral simulation of the MHD equations; results of the simulations will be compared to results obtained from the experiment. The code, Dynamo (Fortran90), allows for full evolution of the magnetic and velocity fields. The induction equation governing B and the curl of the momentum equation governing V are separately or simultaneously solved. The code uses a spectral representation via spherical harmonic basis functions of the vector fields in longitude and latitude, and fourth order finite differences in the radial direction. The magnetic field evolution has been benchmarked against the laminar kinematic dynamo predicted by M.L. Dudley and R.W. James (M.L. Dudley and R.W. James, Time-dependent kinematic dynamos with stationary flows, Proc. R. Soc. Lond. A 425, p. 407 (1989)). Power balance in the system has been verified in both mechanically driven and perturbed hydrodynamic, kinematic, and dynamic cases. Evolution of the vacuum magnetic field has been added to facilitate comparison with the experiment. Modeling of the Madison Dynamo eXperiment will be presented.

[GP1.050] Numerical simulations of attosecond x-ray strobe light produced by colliding laser pulses

Femtosecond x-ray pulses can be produced by Compton scattering with bunched relativistic electrons. In the present scheme, relativistic electrons are strongly bunched at the laser second harmonic by the intense ponderomotive pressure induced by a co-propagating, linearly polarized, drive laser pulse. A second probe laser pulse then interacts with the bunched electron beam, causing Compton scattering and attosecond x-ray pulse production. This is studied in detail by way of a fully relativistic, three-dimensional (3D) code using the 3D electromagnetic fields for the drive laser and modeling the probe laser pulse by its photon density. Retardation effects are also taken into account to properly simulate the x-ray propagation from the interaction point to a detector.

This is partially supported under the auspices of the US DoE by LLNL under contract No. W-7405-ENG-48, and by the NUF student program.

[GP1.051] Comparison of Fluctuation Levels in the Inboard and Outboard Scrape-Off-Layers of the Alcator C-Mod

Because of the large cross-field particle fluxes found in the Alcator C-Mod SOL, most of the main plasma recycling occurs at the wall, not at the divertor. Edge turbulence is believed to be a principle cause of this large particle flux to the outer wall. Several current theoretical simulations predict that the turbulence is ballooning in character and has a magnitude in the inboard SOL significantly less than that in the outboard SOL. To test these hypotheses, two radial arrays of toroidal views are used to measure local emission fluctuations in the SOL near the mid-plane; one inboard, the other outboard. Each array views a respective region in front of a gas puffing nozzle (D_2 or He). Any three views can be selected simultaneously and filtered for an emission line corresponding to the gas species. These intensity fluctuations are used to infer the level of density fluctuations. Our results give a 1-D fluctuation profile for rho(=dist. from the LCFS) from 0 to ~20mm for both the inner and outer SOL. The fast (500 KHz) digitization rate ensures that the sampling rate is large compared to the frequency and structure-velocity domains of the turbulence.

[GP1.052] Laboratory Space and Astrophysics

[GP1.053] A Laboratory Plasma Experiment for Studying Magnetic Dynamics of Accretion Disks and Jets

Spheromak formation in our planar coaxial gun experiment is remarkably similar to MHD theories of accretion disk jet formation. The ideal Ohm's Law E + U \times B = 0 relates the electric field E and plasma velocity U. In an accretion disk, the accreting matter wraps up the magnetic field and induces an E-field between star and disk. In the experiment, an applied E-field produces toroidal plasma rotation above the gun electrodes. In both cases, magnetic helicity is injected into the plasma. In our experiment we have observed three distinct \alpha_gun-dependent plasma configurations(S.~C.~Hsu and P.~M.~Bellan, Mon.\ Not.\ R.\ Astron.\ Soc.~334), 257 (2002). (where \alpha_gun is the force-free parameter applied at the gun), each of which has a potential analog with observed features of accretion disks and jets, including (1)~the collimation of plasma, (2)~internal ``knotty'' jet structure, and (3)~disk flaring, respectively. These observations suggest the relevance of magnetic helicity injection and plasma relaxation to astrophysical jet formation, structure, and dynamics. We are obtaining direct quantitative measurements of magnetic field, localized values of \alpha in the plasma, and plasma bulk flow velocities via Doppler broadened emission spectra. We will present this data along with quantitative analysis of our observed plasma regimes. Implications for astrophysical jets will be discussed.

[GP1.054] Interaction of arch shaped plasma with dipole magnetic field in a solar prominence simulation experiment

Solar prominence evolution has been simulated in a laboratory experiment at Caltech [1]. The solar gun produces a small arch-shaped plasma in a cylindrical vacuum chamber (1.4 m diameter, 2.0 m long) that is much larger than the plasma, so that wall effects are unimportant. We are constructing a new version of this experiment whereby the expanding arch-shaped plasma is made to collide with a pre-existing dipole field produced by a permanent magnet or coil. This is meant to simulate the interaction of a solar prominence with a dipole magnetic field. Measurement of net torque and force exerted on external fields by the expanding plasma is expected to provide useful information related to the sun-earth connection. Evolution of plasma will be recorded by a high speed CCD camera. Soft X-ray diodes with different filters and electrostatic probes will also be used. Preliminary experimental results on the interaction of the simulated solar prominence with the dipole field will be presented. \vspace0.2in [1] J. F. Hansen and P. M. Bellan, Astrophys. J., 563, L183, (2001)

[GP1.055] Connections between laser hydrodynamics experiments and astrophysics

Recent and ongoing experiments have studied mechanisms that affect the evolution of supernovae, supernova remnants, and related systems. These experiments are designed to be well scaled from astrophysical systems to the laboratory. The experiments and some of the astrophysical systems involve time-dependent flows with very large Reynolds number. In contrast, numerical viscosity limits computer simulations of these phenomena to a Reynolds number of order 1000. Using our own experiments and other work in fluid dynamics as a guide, we will explore the implications for astrophysical systems. The key question is whether the astrophysical systems might evolve into a turbulent state that the computer simulations cannot reproduce. The US DOE and NASA supported this work.

[GP1.056] Nonlinear Rayleigh Taylor Hydrodynamics on the Omega laser

We will show calibrated images from experiments to study the development of the Rayleigh Taylor instability at a decelerating interface, a mechanism that affects the evolution of supernovae, supernova remnants, and related systems. These experiments are designed to be well scaled from astrophysical systems to the laboratory. They begin by using the laser to drive a strong shock into a target material. After the laser ends, a rarefaction overtakes the shock, forming a blast wave. The blast wave shocks a structured interface, which then decelerates. We have explored the development of Rayleigh Taylor from initial 2D perturbations with one, two, or 8 modes present, and from initial 3D, single-mode perturbations. There are indications in the data of bubble merger and possibly of the onset of turbulence.

[GP1.057] Radiative shocks in gas on the Omega laser

A number of astrophysical systems involve radiative shocks that collapse spatially in response to the energy lost through radiation. This is believed to produce thin, dense, unstable shells. We have begun experiments on the Omega laser intended to produce such collapsing shocks and to study their evolution. The experiments use the laser to accelerate a thin slab of Be, which becomes a piston that drives a shock through 1.1 atm of Ar gas at ~ 100 km/s. The shock is predicted to collapse. Experiments are in preparation that will detect the dense layer and also the radiative precursor in front of the shock. We will report their results.

[GP1.058] Omega Hydrodynamic Experiments that Simulate Jets in Supernova Explosions

Recent observations of core collapse supernovae provide increasing evidence that supernova explosions are intrinsically asymmetric. An explosion model based on the assumption that bipolar, non-relativistic jets form during core collapse predicts an efficient ejection of a highly asymmetric supernova envelope and helps in understanding many of the observations (Khokhlov, et. al. ApJ 524, L107, 1999). Since the complex numerical hydrodynamic simulations of these jets require validation, we have designed a series of hydrodynamically-scaled jet experiments on the Omega laser at the University of Rochester. The jet in these experiments is formed by the laser ablation of the end of a cylinder of aluminum or magnesium that is imbedded in a gold washer. The plug is allowed to accelerate through a vacuum region in the washer and then enters into low-density foam as a jet. Several time-dependent transmission images are obtained by irradiating two large disks of titanium or silver that backlight the jet. In the supernova jet calculations, some of the material is accelerated to higher velocities in the equatorial plane (perpendicular to the bipolar jet) by a Mach ring formation. To study this effect, we have fielded experiments that create a Mach ring by the collision of two plates of aluminum that have been accelerated towards each other into a CH plastic. The Mach ring forms in the CH plastic and several radiographs were obtained. We will compare the jet and Mach ring data to simulations done with the LANL RAGE, the AWE NYM/PETRA, and the NRL ALLA codes.*This work is performed under the auspices of the U. S. Department of Energy by the Los Alamos National Laboratory Laboratory under Contract No. W-7405-ENG-36, Lawrence Livermore National Laboratory under Contract No. W-7405-ENG-48, the Laboratory for Laser Energetics under Contract No. DE-FC03-92SF19460, the Office of Naval Research, and the NASA Astrophysical Theory Grant.

[GP1.059] Study of Magnetorotational Instability and MHD Surface Waves in Liquid Gallium

Two liquid gallium experiments have been constructed in PPPL to study basic MHD physics related to astrophysics and fusion sciences. The first experiment focuses on laboratory studies of the magnetorotational instability (MRI) in a rotating gallium disk or a short Couette flow geometry. The MRI has been proposed as a dominant mechanism for fast angular momentum transport in electrically-conducting accretion disks ranging from quasars and X-ray binaries to cataclysmic variables and perhaps even protoplanetary disks. Experiments using a prototype water disk has revealed importance of Ekman circulation, consistent with 2D hydrodynamic simulations. A revised design using multiple rings at each end of the flow are being implemented. The second experiment focuses on MHD surface waves in a large liquid gallium pool. It has been found that the damping rates of driven 1D surface waves propogating along a magnetic field are consistent with linear theory. The parametric excitation of 2D surface waves is being studied to elucidate effects of a horizonally imposed magnetic field on the dynamics of pattern formation. Detailed results will be presented for both experiments and implications to astrophysics and to the liquid metal wall concept in fusion reactors will be discussed.

This work is supported by DoE.

[GP1.060] Laboratory simulation of supernova shockwave propagation

High Mach number shockwaves were launched in laboratory plasmas to simulate supernova shockwave propagation through an interstellar medium. Shockwaves were created by focusing a high power infrared (1064 nm) pulsed laser onto the tip of a metal pin. Laser energies ranged from 2.0 J to 146.8 J. The pin was located in a vacuum chamber backfilled with a gas representing the interstellar medium. Both xenon and nitrogen gas were used, to study the effect with or without radiative preheating ahead of the shock. The typical gas pressure was 0.7 kPa. Some shockwaves were allowed to interact with a wire array (0.2 mm wire diameter with 3 mm spacing placed 20 mm from pin). The shock was backlit with a green (532 nm) laser, to deduce shock structures and densities from Schlieren and interferometry image. Emission spectroscopy data in the near ultraviolet range were also obtained to infer electron temperatures ahead of and behind the shock. Preliminary results indicate that the shock velocity follows the Taylor-Sedov blast wave relation. No shock instabilities were observed in either xenon or nitrogen, including when the wire array was present to perturb the shock (perturbations were observed to oscillate but dampen out). Earlier work in this field has reported unstable shockwaves in xenon, which is different from our result. Further data analysis is underway, and results will be presented.

[GP1.061] Observation of a threshold velocity to produce a radiative-precursor shock

Many astrophysical systems, such as supernova remnants and jets, produce radiative-precursor shock waves. In a radiative-precursor shock, radiation from the shock ionizes and heats the medium ahead of it. An important goal of this effort is to produce an experiment that can be modeled by an astrophysical code without implementing laser absorption physics into it. In this experiment, the laser-irradiation conditions are chosen so that the driven shock will produce an observable radiative precursor. We observe the radiative precursor by using absorption spectroscopy. These observations allow us to determine the temperature profile in the precursor. The length and temperature of the radiative precursor are observed to vary as the laser irradiance, and hence shock velocity, is varied. These measurements indicate there is a minimum shock velocity to produce a radiative precursor.

Work supported by the U.S. Department of Energy both directly and through the Lawrence Livermore National Laboratory

[GP1.062] Measurement of magnetic reconnection outflow and rapid heating in Laboratory experiment

Laboratory experiments of magnetic reconnection have been developed in the TS merging devices at University of Tokyo using two colliding tokamaks and spheromaks with co- and counter-helicities[1]. Magnetic reconnection outflow and ion rapid Heating (reached 10km/s as outflow speed and 100eV as ion temperature) have been measured in these experiments. The purpose of this study is to find the conversion mechanism from magnetic energy to ion kinetic / thermal energy and also to find some engineering application of this phenomenon. In order to solve ion acceleration process, we are now developing the following diagnostics: vector tomography method by use of spectral Doppler shift[2] and calculation of 2-D ion velocity by use of 2-D magnetic field data for ion velicity measurement, and new local measurement method by use of faraday cup and conventional Doppler broadening method for ion temperature measurement. These results will be compared with those of MHD and particles simulations to evaluate the ion acceleration properties of magnetic reconnection. This ion acceleration effect is now being used to generate non-thermal plasmas for new applications of magnetic reconnection. [1]Y. Ono et al. Phys. Rev. Letts. 76, 3328 (1996). [2]A. Balandin et al. Local ion plasma temperature from Doppler broadening: method and computer simulation.

[GP1.063] Temporal Variation of Sounding Rocket Langmuir Probe Contamination*

A novel technique for removing surface contaminants from a sounding rocket spherical Langmuir probe has been developed in the NRL Space Chamber Laboratory. Contamination layers present on probe surfaces can skew the collected data, resulting in the incorrect determination of plasma parameters. Despite careful cleaning procedures prior to launch, probe surfaces can become coated with layers of adsorbed neutral gas in less than a second when exposed to atmosphere. Our laboratory tests show that by heating the probe from the interior using a small halogen lamp, adsorbed neutral particles can be removed from the probe surface, allowing accurate plasma parameter measurements to be made. We present data indicating the effective times required for decontamination and any subsequent recontamination in the absence of heating under a variety of plasma and neutral gas conditions.

[GP1.064] Experimental verification of the shear-modified ion-acoustic instability

The shear-modified ion-acoustic instability has been experimentally verified in double-ended Q-machine barium plasma containing shear in the magnetic-field-aligned (parallel) ion drift. The ion distribution function f(X,Vz) was measured directly and non-perturbatively with laser induced fluorescence. Measurements of the wave frequency (in the lab frame) and the wave-vector components show that, in the presence of shear, the wave phase velocity (in the ion frame) is greater than the ion-acoustic speed and out of the strong ion landau-damping regime. Measurements of the parallel electron drift yield values lower than the excitation threshold predicted by homogeneous theory but large enough for inverse electron landau damping to provide the free energy for the wave. We emphasize the ramifications on the mode properties of positive and negative values of shear. A quantitative comparison between experimental results and theoretical predictions is presented. Work supported by NASA and NSF. Useful discussions with V. Gavrishchaka and E. Scime are acknowledged.

[GP1.065] On the role of ion-temperature anisotropy on the propagation of shear-modified ion-acoustic waves

Oblique ion-acoustic waves, excited by the combination of magnetic-field-aligned (parallel) electron drift and sheared parallel ion flow, are investigated in magnetized laboratory plasma that is characterized by ion-temperature anisotropy. Direct measurements of the parallel and perpendicular ion temperatures, parallel and perpendicular ion drift velocities, electron temperature and parallel electron drift velocity, parallel and perpendicular wavevector components, and mode frequency and growth rate are used to document an observed correlation between ion-temperature anisotropy and wave-propagation angle. Experimental measurements show that anisotropy significantly influences the propagation angle. These results support the ion-acoustic wave interpretation of broadband waves in the auroral energization region where shear and anisotropy are known to exist and may have ramifications for many space plasmas in which anisotropy exists in the electron-temperature or ion-temperature.

[GP1.066] Planned Observation of Rotationally-Driven Interchange Instabilities in a Laboratory Dipole Plasma.

A hot-filament bias control system and diagnostic imaging system have been installed in the Collisionless Terrella Experiment. The bias control system is designed to change electric potential of the plasma confined by a dipole magnetic field, thus inducing azimuthal E\timesB flows and exciting centrifugally-driven Rayleigh Taylor instabilities. Both axisymetric and nonaxisymmetric radial electric fields can be applied with array of tungsten filaments, enabling study of plasma convection cells, as well as instabilities caused by a combination of B field curvature and centrifugal drives simultaneously. Diagnostic imaging system consisting of 96 gridded particle energy analyzers, is situated at one of the poles of the dipole electromagnet. It will be used to directly measure the phase-space dynamics and reconstruct plasma flows. In addition, multiple floating potential probes will be used to measure the global structure of observed modes. Finally, a fully self-consistent numerical simulation will offer comparison with experimental observations of mode structure, plasma flows and instability growth and saturation.

[GP1.067] Design of the Rotating Wall Machine

The Resistive Wall Mode (RWM) is an external kink mode limiting the operational boundaries of toroidal magnetic confinement. For a system of magnetized plasma surrounded by two conducting walls, one rotating with respect to another, stability of the RWM has been predicted at a critical rotation rate. The Rotating Wall Machine has been constructed to test this hypothesis in several screw pinch configurations. Initially, the kink will be studied in a "no-wall" limit, where the plasma column is surrounded by 200 mm diameter, 43" long glass cylinder. Subsequently, two copper cylinders replace the single cylinder, the outer one rotating poloidally around the stationary inner cylinder. Finally, a manifold of poloidally-flowing liquid sodium replaces the outer cylinder. The sodium models a flowing liquid metal (e.~g.~, lithium). Stabilization by the liquid wall will be compared to the solid conductor. Additionally, the configuration of the plasma column, formed by a nineteen gun hex array, can be modified to excite different kink instabilities. This work is supported by US DoE DE-FG02-00ER54603.

[GP1.068] Experimental Approach and Diagnostics for the Rotating Wall Machine

A new screw pinch experiment is under construction to study stabilization of the resistive wall mode (RWM) using differentially rotating shells. The experiment consists of a magnetized cylindrical plasma column surrounded by two concentric copper shells, the outer rotating with respect to a stationary inner shell. An ideal kink unstable with a stationary shell boundary can theoretically be stabilized with sufficient differential rotation of the double shell geometry. Flexible control of the current density and safety factor profiles is provided by a plasma gun array, which also sources the plasma. The key RWM diagnostic is a 2D array of radial magnetic field sensors on the outer surface of in the inner copper shell, designed with sub-Gauss sensitivity. The array is constructed using flexible printed circuit film technology to provide simple installation and accurate alignment. Magnetic sensors inside the inner shell will be used to discriminate the slowing growing RWM from possible resistive (e.g., tearing) instabilities. The first phase experiment will examine the RWM for a variety of conditions without the second rotating shell, followed by the addition of the rotating shell and re-examination of the RWM behavior. A third phase experiment where the rotating copper shell is replaced by a flowing liquid sodium shell is under design. This work is supported by US DoE DE-FG02-00ER54603.

[GP1.069] Magnetic and Velocity Field Diagnostics in the Madison Dynamo Experiment

The Madison Dynamo Experiment is used to study magnetic field generation and magnetohydrodynamic (MHD) turbulence in a 1 m diameter, spherical vessel filled with liquid sodium moving at speeds 15 m/s. Liquid sodium is well modeled by the equations of MHD. These equations determine the evolution of the magnetic and velocity fields. An array of Hall probes (6 in the theta, 11 in phi) measures the radial component of B on the surface of the sphere. This measurement completely determines the multipole expansion of the vacuum magnetic field and is representative of the internal poloidal magnetic field near the surface. Linear arrays of Hall probes mounted within thermowells are used for measuring the internal magnetic field. We propose to measure the velocity field of the sodium using ultrasonic techniques. High temperature ultrasonic transducers mounted on the surface of the sphere can be used to measure the line-of-sight velocity of the sodium.

[GP1.070] Magnetic Eigenmodes in the Madison Dynamo Experiment

A spherical dynamo experiment has been constructed at the University of Wisconsin's liquid sodium facility. The goals of the experiment are to observe and understand magnetic instabilities driven by flow shear in MHD systems, investigate MHD turbulence for magnetic Reynolds numbers of 100, and understand the role of fluid turbulence in current generation. Magnetic field generation is only possible for specific flow geometries. We have studied and achieved simple roll flow geometries in a full scale water experiment. Results from the water experiment have guided the design of the sodium experiment. The experiment consists of a 1 m diameter, spherical stainless steel vessel filled with liquid sodium at 110 Celsius. Two 100 Hp motors with impellers drive flows in the liquid sodium with flow velocities of 15 m/s. A gaussian grid of 66 Hall probes on the surface of the sodium vessel measure the generated external magnetic field. Hall probe feed-thru arrays measure the internal field. A pair of magnetic field coils produce a roughly uniform field inside the sphere with a centerline field strength of 100 gauss. Preliminary investigations include measurements of the turbulent electromotive force and excitation of magnetic eigenmodes.

[GP1.071] Study of the Stark Broadening of Balmer Lines In a High Density FRC Plasma

The Field Reversed eXperiment Liner (FRX-L) is a target injector for Magnetized Target Fusion (MTF) experiments. MTF is a novel approach to achieving fusion conditions in a high-density plasma. A low temperature, high density Field Reversed Configuration (FRC) plasma is formed in the FRX-L. The FRC will then be translated to a chamber where it will be adiabatically compressed in a liner to fusion conditions.

When hydrogen is placed in an external electric field, broadening of its spectral lines can be observed due to the Stark Effect. In a high-density plasma, this broadening can be related to both the temperature of the plasma and its electron density. Moreover, asymmetries are present in the Gaussian structure of the individual spectral lines. As the electron density increases a shift of this asymmetry toward the red end of the spectrum can be observed. This phenomenon is most obvious in the H_\beta line corresponding to a wavelength of 4861.3 angstroms.

Utilizing an eight-channel spectrometer, I will be observing the region surrounding the H_\beta line in the emission spectrum of the FRC plasma in the FRX-L. Using this data, I can construct an intensity curve allowing to predict the electron density and temperature of the FRC plasma by comparison to previous experimental data.

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[GP1.072] Basic Plasma Physics

[GP1.073] Exact Closures of Vlasov-Poisson

It has long been known that closures to moment descriptions of Vlasov-type systems may be generated by requiring a moment at a given order to depend in a specified manner on the previous moments. We consider such closures in the case of the Vlasov-Poisson system which exactly model the underlying Vlasov dynamics. The essential premise is that a prescribed closure must generate a solution to moment equations at all orders. This leads to an important constraint which is associated with the invariance of solutions under a re- scaling of the phase space coordinates. At second order, this constraint alone determines that the exact closure is the well-known water bag closure. At third and higher orders, the constraint determines that closures may be expressed in natural coordinates, which are functions of the lower order moments, as the product of a scaling factor and a function which satisfies a set of nonlinear differential equations. The solutions to these differential equations are generated by an algebraic system, and at third order the solution is presented explicitly.

[GP1.074] Covariant Lagrangian for guiding/oscillation center plasma

Four-dimensional electromagnetic fields/potentials and eight-dimensional Lagrangian particle dynamics are used to formulate a covariant variational principle for Vlasov-Maxwell plasma. Covariant Lie methods are used to transform to a guiding-center description for slowly-varying field, with attention to boost- and gyrophase-invariance. Small-amplitude field perturbations are treated by wave-eikonal methods, and lead to covariant ponderomotive Hamiltonian and linear susceptibility. Noether methods lead to energy/momentum/stress and spin/angular momentum conservation laws.

[GP1.075] The quantum acceleration of particles by fast potential fluctuations

The reaction rate and other rates proportional to the contact probability between two particles can be quantified using the two body schrodinger equation. The processes are complicated by the presence of the plasma potential fluctuation. To estimate the modification of the reaction rate in the plasma, time varying potential is considered. The potential parameters which can significantly change the reaction rate are identified and the amount of the change in the rate is calculated for the specific type of the potential.

[GP1.076] NONLINEAR WAVE-PARTICLE INTERACTION FOR STEADY STATE ELECTROSTATIC WAVES*

Here a perturbation analysis is performed for nonlinear steady state electrostatic waves in the x-t space. The treatment developed in previous paper^1, in order to treat steady state conditions instead of boundary value problem. In our analysis we consider collisionless plasmas and the nonlinear unideimensional Vlasov equation is treated by a perturbation analysis in the x-t space, instead of the k-ømega space. Our analysis leads to the calculation of the space echo amplitude, which can be better compared with the experiments, than the usual echo time evolution^2. The meaning of the essential singularity around v=0 is discussed. Nonlinear corrections to the usual Landau camping has been also found. This corrections has been calculated in the case of Lagmuir waves and ion sound waves. The nonlinear corrections are also calculated for the usual Landau damping case, considering Maxwellian distributions, and for two stream instabilities.

* Work supported by The Royal Society-Fonacit grant.

1 P.Martin, Phys. FLuids \underline17, 384 (1974). 2 R.D. Hazeltine and F. L. Waelbroeck, "The Framework of Plasma Physics" (Perseus Books, Reacding Massachussetts, 1998), pp.193-195

[GP1.077] Dynamics and stability of nonuniform m-fold symmetric nonneutral plasma equilibria

Nonuniform, large aspect ratio, m-fold symmetric nonneutral plasma equilibria (nonuniform V-states) can be conveniently excited by adiabatic nonlinear synchronization (autoresonance) with external time dependent perturbations, passing through resonances with initially axisymmetric plasma columns having a sharp edge radial density profile [1]. Here, we discuss the problem of stability of these equilibria. We shall show that nonuniform m=2 V-states remain stable after the external synchronizing perturbation is switched off. Free m=3 and 4 states, in contrast, are destroyed via three-wave decay process. The negative feedback approach can stabilize this instability. Experimentally, we have shown that elliptical vortices can be created with ellipticities exceeding five. We shall also discuss excitation and stability of hollow nonaxisymmetric V-states by adiabatic synchronization approach. [1] L. Friedland and A. Shagalov, Phys. Fluids, 14 (September 2002). Supported by US-Israel Binational Science Foundation (Grant 1998474) and by INTAS (Grant 00-02-17179).

[GP1.078] Dynamic Electrical Conductivity In A Bumpy Cylinder

The equilibrium electrical conductivity in a bumpy cylinder magnetic field is given by the Spitzer electrical conductivity modified by neoclassical effects due to collisions of untrapped particles carrying the flow with immobile trapped particles. Neoclassical effects are introduced in a fluid moment approach through the parallel viscous force B \cdot \nabla \cdot \pi. In this work we explore the dynamical (ømega \sim \nu_e) electrical conductivity using a combination of a deductive Champan-Enskog-like procedure(J.P. Wang and J.D. Callen, Phys. Fluids B4), 1139(1992); ibid 5, 3207 (1993). and an eigenmode expansion procedure similar to that developed previously(C.T. Hsu, K.C. Shaing and R. Gormley, Phys. Plasmas 1), 132 (1994) for determining the time-dependent kinetic response and consequent parallel viscosity closure moment in the low (banana) collisionality regime. Progress will be presented on the appropriate reduced kinetic equation and the frequency-dependent parallel viscosity and electrical conductivity in a bumpy cylinder magnetic field.

[GP1.079] Effect of drifts on rotation braking and resonant-field penetration in tokamaks

Rotation braking has recently been shown to play a critical role in wall-mode destabilization on the DIII-D tokamak. It is also known to lead to error-field penetration in low density discharges, and constitutes an important operational limit for present day as well as next-step devices. Despite the fact that plasma rotation perpendicular to the field is typically comparable to diamagnetic rotation, the theory of rotation braking has so far only been developed within the context of magnetohydrodynamics (MHD). Here we consider the effect of drifts and electron parallel thermal streaming on the electromagnetic torque caused by externally imposed resonant perturbations. These perturbations may be either error fields or rotating magnetic perturbations deliberately imposed to stabilize a mode or induce rotation. Our results are summarized by torque curves showing the variation of the imposed torque with plasma rotation frequency. Two key non-MHD effects are the formation of current channels due to the variation in the AC conductivity with distance to the resonant surface, and the splitting of the Alfvén resonance due to the drifts. In certain frequency regimes, drift wave excitation may also play a role in determining the plasma response.

[GP1.080] Kinetic MHD Simulation

A fully kinetic quasi-neutral plasma simulation model is presented that can easily be cast as an upgrade to existing nonlinear MHD simulations. Maxwell's equations, neglecting the displacement current, are solved along with the generalized Ohm's law. The one-fluid momentum equation is replaced by calculating ion and electron flow directly using a delta-f particle method. The generalized Ohm's law can be solved exactly using ion and electron flow and electron pressure. No ion pressure or higher moments (other than electron pressure) are needed for closure. The model has been implemented in a 1D simulation and benchmarked with linear theory. Keeping only ions and neglecting the electron pressure in the Ohm's law, the model includes Alfven waves, whistler waves and electron inertia effects. An outline of the model will be presented along with results from the 1D simulation. Progress on a 3D implementation in NIMROD and a gyrokinetic formulation of the model will be discussed.

[GP1.081] Simulation of Alfvenic Phenomena of Short Transverse Scale

An electromagnetic, particle-in-cell code with finite axial boundaries is used to investigate the spatio-temporal evolution of large amplitude shear Alfvèn waves whose characteristic dimension across the magnetic field is on the order of the electron skin-depth. In this regime significant parallel electric fields arise that allow the interaction with background electrons. Presently this interaction is considered to be a key process in the formation of auroral beams. For cold ions and small amplitudes the wave packets launched from a finite size antenna are found to follow the characteristic pattern associated with Alfvèn-wave cones. As the amplitude is increased the nonlinear interaction with the electrons causes a filtering of the perpendicular k-spectrum leading to broad perpendicular structures which are collimated in the parallel direction. The effect of hot ions on these interactions is investigated as well as the behavior resulting from a single-mode exciter.

[GP1.082] Random walk and electron energy gain in microwave electric fields: gaseous breakdown revisited

Random walk and electron energy gain in microwave electric fields leading to breakdown of a gas are studied theoretically and by numerical simulation with collision and phase randomized. The square law dependence of the random walk given by N \propto (\Lambda/\lambda)^2, where N is the average number of collisions encountered by an electron, \Lambda is the characteristic diffusion length and \lambda is the mean free path, is strictly valid only for free diffusion or for a weak field approximation (v \cong v_th, where v is the velocity attained from the field and v_th is the thermal velocity). This can explain breakdown phenomena at limited pressure regimes satisfying ømega/\nu << 1, where ømega is the wave frequency and \nu is the electron neutral collision frequency. More accurately, the electron random walk under the impressed wave electric field has to be considered consistently to yield breakdown electric fields. The numerical simulation yields a readily usable emperical relation; N \propto Log(1+ \sqrt\Lambda/\lambda) which can be used to obtain breakdown fields over a wide pressure regime covering either side of the collision frequency transition (ømega = \nu).

[GP1.083] ITG driven intermittent behaviour with a flux-tube toroidal model

In order to understand the mechanism of anomalous transport and transport barrier formation related to the sheared plasma flow generation due to toroidal ion-temperature-gradient (ITG)-driven turbulence, two-dimensional flux-tube model has been employed.

In the previous studies, we have presented the low-order mode-coupling model composed of 18 ordinary defferential equations [1] for the Horton-Choi-Tang model [2, 3]. It has been shown that ELM (edge localized mode)-like intermittent behaviour is generated by the interaction between the growth of ITG mode and the shear flow generation to suppress the ITG mode.

For the linear phase, the behaviour in the flux-tube model well agrees with that in 18 ODE model.

In the poster, behaviour in the nonlinear phase of toroidal ITG mode will be discussed.

References: [1] K. Takeda, S. Hamaguchi and M. Wakatani, Plasma Phys. Control. Fusion 44, A487 (2002) [2] W. Horton, D. -I. Choi and W. Tang, Phys. Fluids 24, 1077 (1981) [3] G. Hu and W. Horton, Phys. Plasmas 4, 3262 (1997)

[GP1.084] A New Toroidal Plasma Experiment for Basic Collisionless Plasma Physics

A new toroidal device, TORPEX, is under construction at CRPP-EPFL to investigate basic collisionless plasma phenomena, including wave-particle interaction, transport processes and magnetic reconnection. Major and minor radius are R=1m and a=0.2m. The toroidal magnetic field is of the order of 0.1T. A poloidal coil system can generate magnetic field from purely vertical to a cusp configuration. Different plasma production schemes are possible, including ohmic tokamak discharge and ECRH at 2.45GHz. Plasmas of different gases will be created with n\simeq10^17 m^-3 and T_e\simeq20 eV. Internal electrostatic and magnetic probes and electrostatic energy analyzers will be employed for reconstructing static and fluctuating electric and magnetic field, and the electron dynamics. Active optical methods such as laser-induced fluorescence will be applied to determine the ion response. The first campaigns will focus on the physics of turbulent transport, in particular on the relationship between the turbulence properties (frequency and wave-number spectra) and the plasma transport characteristics (diffusion, zonal flows, etc.).

[GP1.085] Spontaneous Alfvénic Fluctuations in a Large Nonuniform Plasma Column

Experiments designed to study the effects of both field-aligned and cross-field gradients on the spontaneous generation of Alfvénic fluctuations in a cylindrical plasma column were performed in the LAPD device at the Basic Plasma Science Facility at UCLA. These experiments are pertinent to processes occurring in natural plasmas with multiple gradient scale-lengths and currents carried by fast electrons. It is found, in general, that drift-Alfvén waves in the frequency range of .1 f_ci exist in regions of steep cross-field density gradients. In the uniform magnetic field case, broadband shear Alfvén waves are found everywhere in the plasma but are limited in bandwidth, extending only up to about .7 f_ci. This limit appears to be associated with the presence of a global plasma mode with frequency near .7 f_ci. In the presence of an axial magnetic field gradient, the bandwidth of broadband shear noise increases, extending up to the local ion cyclotron frequency, but the amplitude across the entire band is reduced. The effect of a short scale cross-field density gradient embedded in a larger-scale gradient on these general features is also presented.

[GP1.086] Comparison of Emissive Probe and Plugged Probe measurements of low frequency plasma fluctuations

The fluctuations of the floating potential \tilde\Phi_F of a usual Langmuir probe are generally not a good measure for the fluctuations of the plasma potential \tilde\Phi_P. The amplitude of the floating potential fluctuations is usually much higher and the phase between plasma potential and floating potential can be forged by temperature fluctuations, i.e the fluctuation induced transport estimated as \Gamma=\tilden\tilde\Phi_F is not reliable. In low density plasmas the Emissive probe is a well established technique for the direct measurement of the plasma potential and its fluctuations. A novel probe for plasma fluctuation measurements in a magnetised plasmas with T_i<

[GP1.087] Ion Collection by a Sphere in a Flowing Plasma --- Mach-Probe Calibration

The spatial distribution of collisionless ions collected by a spherical object of radius much larger than the Debye length, in a flowing plasma, is calculated using a particle-in-cell code. The results provide the first rigorous theoretical calibration of a ``Mach probe'' in a plasma with negligible magnetic field. They are also applicable, for example, to spacecraft-plasma interactions. Ion to electron temperature ratios 0.1

[GP1.088] Phase-space resolved ion-wave fluctuations

We report observations of both thermal and externally driven ion-wave fluctuations observed using laser induced fluorescence in a singly ionized Argon plasma column of length 2.5m and diameter 0.1m. The ions are nominally at a temperature of 0.6eV and the electrons 2 eV. Small variations in the ion distribution function have a considerable effect on the character of the ion-acoustic/electrostatic ion cyclotron waves observed in the experiment.

Fluctuations are detected by calculating the cross-power between the fluctuations observed in two separate light collection systems that have orthogonally intersecting optical axis. This makes it possible to go beyond the limit imposed by photon statistics on band-width and dynamic range.

[GP1.089] Low frequency instability stimulated by the resonant absorption of a short microwave pulse

One possibility for efficient transfer of electromagnetic energy into a plasma is to use the so-called resonant absorption which occurs when a p-polarized electromagnetic wave is incident obliquely in nonuniform plasma. This process is characterized by the efficient conversion of an electromagnetic wave to electrostatic one near the critical plasma density, where the frequency of the incident wave is equal to the local plasma frequency. One of the results of resonant absorption process consists of the modification of the distribution function of plasma particles, which could switch plasma into a non-equilibrium state and, consequently, can stimulate some instabilities in the resonance region. In this work we represent our experimental studies of collisionless low frequency instabilities of a positively-biased electrode stimulated by the resonant absorption of a short microwave pulse in an unmagnetized plasma.

We have observed intense RF oscillations in the circuit of an electrode immersed into an inhomogeneous non-isothermal (T_e / T_i \sim 10) laboratory plasma after the plasma was irradiated by a short (\tau < 100ns) microwave pulse. These oscillations are observed only at the electron saturation current (i.e. when the electrode is biased positively with respect to the plasma). The oscillations with their characteristic frequencies below the ion plasma frequency Ømega_p are detected in the vicinity of the resonance region only when the pulse duration is in the order of an ion plasma period (\tau \approx 2\pi / Ømega_p). We have measured that the resonant absorption of such short microwave pulse efficiently accelerates considerable part of plasma ions; thus we believe that the observed oscillations, which persist after the pump microwave is turned off, are generated by the interactions between the accelerated ions and the background plasma.

[GP1.090] DYNAMICS OF A SUPERSONIC PLUME IN A MAGNETIZED PLASMA*

A particle-in-cell code is used to investigate the dynamics and evolution of a microscopic density plume moving through a background, magnetized plasma at supersonic speed. The characteristic dimension of the plume across the magnetic field is on the order of the electron skin-depth and it is ten times in the parallel direction. In the cases investigated the plume density and temperature are comparable to those of the background plasma. When the initial velocity is along the confinement field a complex sequence of events give rise to a long-lived, dipolar current system surrounding a region of net charge associated with the plume ions. A key feature in the evolution is the ballistic expansion of electrons originally belonging to the plume. Quasi-static magnetic fields are created ahead and behind the plume center of mass and develop oscillatory structures. The increasing axial compression of background electrons eventually evolves into a density shock that trails the gentle expansion of the plume ions. When the initial velocity is across the magnetic field additional features arise due to the compression of the magnetic field lines. In this case multiple filamentary structures are generated as the plume is modulated by the ion cyclotron motion across the magnetic field.

* Sponsored by ONR and NSF

[GP1.091] Expansion of a laser-produced plasma embedded in an ambient magnetized background plasma

The expansion of a dense (initially, n_lpp/n_0>>1) laser-produced plasma (lpp) into an ambient magnetized background plasma (He, Ne n=2\times10^12~cm^-3, 17~meters long, 80~cm diameter, B_0z=.5-1.5~kG) capable of supporting Alfvén waves has been studied in the LAPD (LArge Plasma Device). In particular, the initial diamagnetic expulsion of the background field for a supersonic expansion has been investigated using a 3-axis inductive probe. The resulting impulse to the background field and induced current profiles are mapped spatially and temporally for each case. It has been found that the presence of a background plasma allows for complex currents to be created which in turn radiate, among others, Alfvén and Lower Hybrid waves. The dynamics of particle motions toward and away from the \textitlpp are compared to the case where the target is struck in vacuum.

* Work supported by the U.S. Department of Energy and the Office of Naval Research.

[GP1.092] Lower hybrid wave generation by a laser-produced plasma

The expansion of a dense, laser-produced plasma (lpp) into a uniform, low-density plasma has been observed to generate a spectrum of lower hybrid waves. The experiment is conducted in the upgraded Large Plasma Device ( LaPD) at UCLA. A 3/4-inch Aluminum target rod is immersed within a background Neon plasma, with plasma parameters: n_e=2\times10^12cm^-3, T_e=5eV, B_0=500-1500G, length=17m, radius=30cm. The target is struck with a NdYAG laser (1J, 7ns pulse) focused to a spot size of less than one millimeter. The ions in the lpp (with energies of several keV) are initially unmagnetized and propagate across the background field. The electrons, however, remain magnetized and jet away from the point source of the laser impact in a field-aligned burst. The measured electric field spectra as a function of angle are consistent with a finite line source of lower hybrid waves, with one end fixed at the laser impact site. We present these spectra, correlation measurements, and an estimation of the coupling efficiency of laser power into wave energy.

[GP1.093] Experiments on and observations of intense Alfvén waves in the laboratory

There are many situations, which occur in space (coronal mass ejections, supernovas), or are man-made (upper atmospheric detonations) in which a dense plasma expands into a background magnetized plasma, that can support Alfvén waves. The \textbfLArge \textbfPlasma \textbfDevice (\textbfLAPD) is a machine, at UCLA, in which Alfvén wave propagation in homogeneous and inhomogeneous plasmas has been studied. We describe a series of experiments which involve the expansion of a dense (initially, n_lpp/n_0>>1) laser-produced plasma into an ambient highly magnetized background plasma capable of supporting Alfvén waves. The interaction results in the production of intense shear and compressional Alfvén waves, as well as large density perturbations. The magnetic fields of the waves are obtained with a 3-axis inductive probe. Spatial patterns of the magnetic fields associated with the waves and density perturbations are measured at over 10^4 locations. The wave generation mechanism is due to currents from fast electrons which leave the \textitlpp and field aligned return currents provided by the plasma to neutralize space charge. Dramatic movies of the measured wave fields and their associated currents will be presented. *Work supported by the ONR, and DOE/NSF.

[GP1.094] A Fast-Ion Source for LAPD

To measure the fast-ion transport as a function of gyroradius, a 3-cm diameter, 17~MHz, \sim 80~W, \sim 3~mA, argon source is under development for use in the LArge Plasma Device (LAPD). In tests on the Irvine Mirror, the source performs reliably when oriented either parallel to the magnetic field or at an oblique angle and in either a CW or pulsed mode of operation. A radial energy analyzer measures the profile of the 200-500~eV beam. Laser-induced fluorescence (LIF) of cold 3d^2G_9/2 argon metastables excited by the source is readily measured but the hot argon ions in the beam itself are more difficult to detect. In preliminary tests on LAPD, the source operated successfully. Planned physics experiments include measurements of collisional fast-ion diffusion and fluctuation-induced transport.

[GP1.095] Quasi-neutrality Breaking of a Plasma Hole Structure

Formation of plasma hole (vortex with a cylindrical density cavity) has been observed in a rotating magnetized plasma. The density of core region is one tenth of that of ambient plasma, and the density transition takes place in a thin layer of the order of several ion Larmor radii. The flow structure has been measured by using a directional Langmuir probe. The velocity field forms a monopole vortex with a sink in its center, which is identified as a dissipative vortex (Burgers vortex). Potential measurement revealed that the bell-shaped potential (\sim5T_e) is localized in the core region, producing the exceptionally intense electric field compared to ordinary laboratory plasmas, and resulting in the quasi-neutrality breaking. From the analysis of Poisson's equation with the experimental data, the normalized charge difference in the core plasma is 10^3 times higher than that of ambient plasma. It is found that the electron rich layer is present, forming the interface between the core and the ambient plasma.

[GP1.096] Convective radial transport in a linear magnetized plasma column and fast infrared imaging of plasma turbulence

The transition to turbulence of strongly nonlinear low frequency unstable waves obtained in a new magnetized plasma device is studied. The device consists in a large multipolar plasma chamber (1.4m diameter, 1 m length) connected to a cylinder (40 cm diam., 1m length) and a half-torus (40 cm diam., 0.61 m large radius). The linear and curved columns are surrounded by 50 solenoid coils producing a magnetic fied intensity lower than 0.04T. The linear magnetized plasma columns is unstable when a floating grid is inserted between the source chamber and the plasma column. The main control parameter is the negative biasing of the plasma source. Strongly nonlinear coherent waves are recorded. In order to study the detailed mechanism of the destabilization of the waves, the diameter of the column is restricted to 15 cm at the entrance of the column. Coherent modes still exist in that case and the plasma density is slowly decaying to the wall of the cylinder in the shadow of the limiter. A conditional sampling method exhibits the spiral structure of the unstable modes: the plasma is convected radially by centrifugal effect and a spiral arm structure is recorded. This leads to the clear evidence that the unstable modes are due to the centrifugal instability induced by the rotation of the plasma due to the existence of a radial electric field. The fast imaging of the fluctuations is obtained using a square array of 64 photodetectors coupled to 64 transient digitizers (200 ksamples/s). The near infrared radiation of metastables argon ions is modulated by the electron fluctuations. The spatial structure of regular modes is recorded and the transition to turbulence is studied. The implications in the diagnostic of the convective transport in the SOL of tokamaks are discussed.

[GP1.097] NSTX

[GP1.098] NSTX Research Aimed at High Beta, Long Pulse Operations: Recent Results and Plans

Central to achieving long-pulse, high-beta plasmas in NSTX is integrating the results of topical research in MHD, transport, heating, current drive and boundary physics. For example, the high-performance plasmas recently achieved demonstrate the effectiveness of MHD wall stabilization, which depends on the profiles and thus the transport. Wall stabilization studies are part of a broader set of MHD research on beta limiting modes and the possible influences of fast ion-induced instabilities. Confinement research includes systematic studies of core thermal and particle transport in L- and H- modes, and of turbulence near and at the plasma boundary. Current drive requirements and possibilities for future devices are being assessed through studies of HHFW physics, EBW emission, non-inductive startup and analysis of the bootstrap current. Boundary research includes studies of heat flux scaling and mitigation, and assessment of particle control requirements. Recent research results, and how they form the basis of a plan for research on NSTX that carries through the middle part of this decade, will be discussed.

[GP1.099] Confinement Studies of Auxiliary Heated NSTX Plasmas

Rapidly developing diagnostic, operational and analysis capability is enabling detailed studies of local transport in high beta plasmas in the National Spherical Torus Experiment (NSTX) produced by neutral beam injection (NBI; up to 7 MW, 100 keV) and High Harmonic Fast Wave (HHFW) heating (up to 6 MW). These studies are motivated in part by the observation of energy confinement times in NBI-heated discharges that exceed, by more than a factor of two, expectations based on the ITER-89P scaling expression. Profile measurements of the electron density, electron and ion temperatures and impurity ion rotation, and other measurements permit analysis of the transport coefficients in these discharges. Results from these experimental studies and supporting theoretical analysis will be described in the areas of ion particle transport and ion and electron thermal transport with both NBI and HHFW heating.

This work is supported by DoE Contract No. DE-AC02-76CH03073

[GP1.100] Initial Neutral Particle Analyzer Measurements of Energetic Ion Distributions in NSTX Plasmas

The Neutral Particle Analyzer (NPA) diagnostic on NSTX utilizes a PPPL-designed E||B spectrometer which measures the energy spectra of H and D simultaneously with 39 energy channels per mass species with a time resolution of 1 msec. The calibrated energy range is E = 0.5-150 keV and the energy resolution varies from 3 - 7 The NPA measures Maxwellian spectra of residual H to obtain ion temperatures and measures the energetic ion spectra produced by injection of up to 100 keV D neutral beams into a D plasma. The NPA views across the co-injection paths of the three neutral beam sources on NSTX. Recent implementation of horizontal scanning capability for the NPA over a sightline tangency range of 92 cm to -15 cm has enabled measurement of the anisotropic energy distribution of the beam ions. Initial measurements of these distributions are presented and compared with TRANSP simulations of the observed NPA spectra. A rich variety of energetic ion behavior resulting from magnetohydrodynamic (MHD) activity is observed in NSTX. For example, onset of an n = 2 mode leads to relatively slow decay of the energetic ion population (E ~ 5 - 100 keV) and consequently the neutron yield. The effect of reconnection events differs from that observed for MHD modes. In this case, prompt loss of the energetic ion population occurs on a time scale of * 2 msec and a precipitous drop in the neutron yield occurs. Variations in the MHD-induced energetic ion behavior with the NPA ‘pitch angle’ will be discussed.

[GP1.101] Characteristics of the Neutron Emission from NSTX during High Power Neutral Beam Injection

Recent high power, long pulse and high current operation on NSTX has resulted in a record neutron emission rate of ~6e14n/s with many discharges exceeding initial predictions of 2e14n/s1. This increased performance is due primarily to recent re-alignment of some of the poloidal field coils, which has reduced the error fields and decreased MHD activity. Conclusive comparisons of the neutron emission with orbit code predictions of fast ion loss fractions has been previously hampered because of the large scatter in the data caused by the onset of MHD.2 Reliable comparisons of the neutron emission with parameters such as plasma current, toroidal field strength, neutral beam power and neutral beam angle of injection are now being obtained. These neutron emission data will be used in conjunction with data from the neutral particle analyzer, fast loss ion probe and diamond detector to study the confinement of energetic ions during high-power neutral beam heated discharges including the effects of MHD events such as sawteeth and IREs. Future improvements in the neutron detection system will also be discussed. 1 NSTX Project Requirements Document, 7/10/96 2 Confinement of Dilute Population of Beam Ions in stable NSTX plasmas. RSI, 2002 HTPD Conference(submitted)

[GP1.102] Neutral beam ion loss measurements in NSTX plasmas

The loss of 80 keV D neutral beam ions from NSTX plasmas has been measured with a Faraday cup probe for a wide range of conditions. When Ip exceeds 800 kA, loss rates are below the 3 microA/sq cm noise level of the diagnostic, except during MHD activity. However, losses are clearly observable when the beams inject during the current ramp up or ramp down, and when Ip is below 800 kA. Then the measured loss rate depends strongly on the distance between the plasma edge and the vessel wall at the outer midplane (the outer gap). In order to understand whether these quiescent losses are due to classical prompt orbit losses, we are adding the beam ion source distribution to an orbit following code. It will then calculate the expected detector signal from the measured plasma magnetic equilibrium and beam deposition profile. Comparisons between the classically calculated loss to the probe and the measurements will indicate whether any effects other than prompt loss are important in NSTX. In addition, we are installing a scintillator based beam ion loss diagnostic that will provide energy and pitch angle resolution of the losses.

[GP1.103] Confinement of Dilute Populations of Beam Ions in Stable NSTX Plasmas

Short \sim3 ms pulses of 80 keV deuterium neutrals are injected into NSTX. The jump in neutron emission during the pulse is used to infer prompt losses of beam ions. The decay of the neutron emission following the blip is compared to the expected classical deceleration to detect losses on a 10~ms timescale. Beam-ion loss detectors at the wall and neutral particle measurements also diagnose the beam behavior. The beams inject at three different tangency radii from nearly perpendicular to nearly tangential. The confinement is studied as a function of tangency radius, plasma current (between 0.4-1.0~MA), and toroidal field (between 2.0-4.5~kG). In the absence of MHD, the neutron data show the expected dependencies on beam angle and plasma current. The temporal evolution of the neutron and neutral particle signals are consistent with Coulomb scattering rates. The confinement is insensitive to the toroidal field despite large values of \rho\nabla B/B, so any effects of non-conservation of the adiabatic invariant \mu are smaller than the experimental error. The measured losses at the plasma wall are more sensitive to the shape of the plasma than the total losses inferred from the neutron signals. The neutron data agree with the predictions of the TRANSP code.

[GP1.104] Neutral Beam Driven Neoclassical Transport in NSTX

We re-examine the particle and heat flows driven by neutral beam injection in tokamak plasmas. These appear as inward pinches for co-injection and outward for counter injection. We derive the parallel friction and heat friction forces exerted on the thermal species by the energetic beam ions by extending the early analysis of Callen, et al. [1], which are then used as external forces in the moments formulation of neoclassical transport in NCLASS [2]. NCLASS is based on the multiple species treatment of Hirshman and Sigmar [3]. Of particular interest is the ion energy flux driven by the heat friction term. It scales as the beam energy, while the particle and electron heat terms scale as the thermal plasma temperature. In NSTX the high beam energy to plasma temperature ratio may lead to a net negative ion heat flux with strong co-injection. Limtations to the theory, such as the large fast ion orbit size relative to the radius of the flux surface, are discussed. Comparisons are made with earlier works by Hinton and Kim [4] and Stacey [5], who evaluated only the beam-thermal friction.

[1] J.D. Callen, et al, 5th IAEA, Tokyo (1974), Vol 1, 645 [2] W.A. Houlberg, K.C. Shaing, S.P. Hirshman, M.C. Zarnstorff, Phys. Plasmas 4 (1997) 3230 [3] S.P. Hirshman, D.J. Sigmar, Nucl. Fusion 21 (1981) 1079 [4] F.L. Hinton, Y.-B. Kim, Phys. Fluids B 5 (1993) 3012 [5] W.M. Stacey, Phys. Fluids B 5 (1993) 4505

[GP1.105] Dependence of Resistive Wall Stabilization on Equilibrium Configuration in NSTX^1

The dependence of the NSTX high \beta operating window as a function of current peaking (parameterized by l_i) and total pressure peaking, F_p \equiv P(0)/

, has been studied both experimentally and theoretically. Discharges within an operating window of 4.0 < \beta_N < 6.5 have been produced in NSTX. Operation in excess of 25% above the computed no-wall \beta_N-limit for n=1 kink/ballooning modes has been achieved in lower single null plasmas with l_i \simeq 0.73 and pressure peaking factor F_p \simeq 2.0. Record values for both \beta_N \geq 6.5 and \beta_N/l_i \geq 9.5 with I_p \simeq (0.8\div0.9) MA and B_T \simeq 0.45 T were produced in H-mode NBI heated discharges. Plasmas in this range exhibit resistive wall modes, or faster growing ideal modes leading to \beta collapse. \beta_N-limits are reduced but their separation \delta(\beta_N) is increased as l_i is reduced. \beta_N-limits increase and their separation increases as F_p is reduced due to enhanced coupling of the kink mode to the stabilizing passive structure. Global mode structures are computed for typical H-mode type plasmas (F_p \simeq 2.1) while in L-mode type plasmas (F_p > 3.2) the modes are more internally localized. ^1USDOE Contracts: DE-FG02-89ER53297; DE-AC02-76CH03073.

[GP1.106] Resistive Wall Mode Characteristics in the Spherical Torus^*

Instabilities similar to the resistive wall mode (RWM) in the advanced tokamak have been observed in high beta plasmas in the National Spherical Torus Experiment. As in more conventional aspect ratio plasmas, the instability that is observed in saddle loop signals measuring locked n=1 mode activity, occurs only at sufficiently large normalized beta, and correlates with rapid toroidal rotation damping. However, the mode can become less prominent at the highest normalized beta (up to 6.5). In addition, the locked mode signature of the RWM is less apparent or non-existent at higher toroidal field operation (Bt > 0.4T). At low aspect ratio, the theoretical mode coupling to the stabilizing plates becomes stronger as beta increases. This is supported by the experiment, as the beta limit is not a strong function of the plasma – plate distance at high beta, and the limiting modes are internal in this regime. Understanding the behavior and physics of the toroidal rotation damping, key to RWM stabilization, is examined as a function of plasma parameters. ^*Work supported by U.S. DOE Contracts DE-FG02-99ER54524 and DE-AC0276CH03073.

[GP1.107] Design of the RWM Feedback Control System for NSTX

The National Spherical Torus Experiment ( NSTX ) has been designed to investigate the physics of global mode stabilization at low aspect ratio. Present experiments are now probing performance limits determined by machine configuration and passive stabilization. For example, the ideal no-wall normalized beta limit has already been exceeded by greater than 20stabilized by a nearby perfectly conducting wall are observed to grow at a rate determined by nearby resistive structure. Sustained performance improvements may be obtained by using active feedback to suppress such long wavelength pressure driven instabilities, known as resistive wall modes (RWM). We report on the performance of several design options for an NSTX - RWM feedback control system. The VALEN feedback analysis code has been used to evaluate the performance of these configurations. We explicitly model the vacuum vessel, center stack casing, the 48 copper passive plates, their mounts, active feedback coils and sensor arrays. The highest performance system has both control coils and sensors inside the vacuum vessel. In this case it is possible to reach 94beta limit.

[GP1.108] An Alfven Mode Similarity Experiment between NSTX and DIII-D

The major radius dependence of Alfvén mode stability is studied by creating plasmas with similar minor radius, shape, magnetic field (0.5~T), density (n_e\simeq4\times10^19~m^-3), electron temperature (1.0~keV) and beam-ion population (near-tangential 80 keV deuterium injection) on both NSTX and DIII-D. The major radius of NSTX is half the major radius of DIII-D. The super-Alfvénic beam ions that drive the modes have nearly identical values of v/v_A in the two devices. The plasma current was varied to match either the edge q or the beam-ion banana width. Observed beam-driven instabilities include toroidicity-induced Alfvén eigenmodes (TAE) and compressional Alfvén eigenmodes (CAE). Preliminary analysis indicates that the stability threshold for the TAE is similar in the two devices but the most unstable toroidal mode number n increases with major radius.

[GP1.109] Bounce frequency fishbone analysis

Large amplitude bursting modes are observed on NSTX, which are identified as bounce frequency fishbone modes(PDX Group, Princeton Plasma Physics Lab, Phys Rev. Lett) 50, 891 (1983)^,(L. Chen, R. B. White, and M. N. Rosenbluth Phys Rev. Lett) 52, 1122 (1984). The identification is carried out using numerical equilibria obtained from TRANSP( R. V. Budny, M. G. Bell A. C. Janos et al), Nucl Fusion 35, 1497 (1995) and the numerical guiding center code ORBIT( R.B. White, Phys. Fluids B 2)(4), 845 (1990). These modes are important for high energy particle distributions which have large average bounce angle, such as the nearly tangentially injected beam ions in NSTX and isotropic alpha particle distributions. They are particularly important in high q low shear advanced plasma scenarios. Different ignited plasma scenarios are investigated with these modes in view.

[GP1.110] Numerical Study of Instabilities Driven by the Energetic Neutral Beam Ions in NSTX

Recent experimental observations from NSTX suggest that many modes in a sub-cyclotron frequency range are excited during neutral beam injection. Some of these modes have been identified as Compressional Alfven Eigenmodes (CAEs), which are driven unstable through the Doppler shifted cyclotron resonance with the beam ions. We have performed 3D hybrid simulations to study the excitation of instabilities by energetic ions in NSTX. In the numerical model, beam ions are treated using delta-f particle simulations, while the one-fluid resistive MHD description is used to represent the background plasma. Self-consistent equilibria have been calculated. It is shown that for large injection velocities of beam ions, V_0 > 3V_A, and strong anisotropy in the pitch-angle distribution, many Alfven modes can be excited. The most unstable modes for low toroidal mode numbers, n \sim 4, have a character of Global shear Alfven Eigenmodes (GAEs), whereas for larger n, localized modes with large compressional component are excited.

[GP1.111] Sub-cyclotron Alfvén Instablility in Spherical Tokamak and its stochastic damping.^1

Recent\footnotetext[1]This work is supported by US DoE contract DE-AC02-76CH03073. observations of sub-cyclotron frequency modes suggested these modes to be an Alfvén eigenmodes unstable in the presence of 80 keV NBI. Possible candidates for the instability are the Compressional Alfvén Eigenmodes (CAE) or Global shear Alfvén Eigenmodes (GAE) excited by superalfvenic beam ions. We compare the dispersions of CAEs and GAEs with experimental measurements. With many CAEs and/or GAEs we show that low amplitude modes with \( \delta B/B\simeq \left( 0.5-1\right) \times 10^-3 \) can result in stochastic damping of these modes on thermal plasma ions. This may provide channel for the energy transfer from the beam particles to the modes and to the background plasma ions.

[GP1.112] Characterization of the plasma edge in the National Spherical Torus Experiment

Using a set of existing and recently installed edge diagnostics, an examination of the characteristics of the edge plasma in NSTX has begun. The three more recent instruments, a four-channel divertor bolometer, a fast-reciprocating edge Langmuir probe, and a fast 2D camera imaging helium puffed at the edge join an IR divertor camera, fast neutral pressure gauges,a high resolution camera D_\alpha divertor camera, and divertor tile Langmuir probes. So far, the plasma edge conditions in a Ip = 900 kA, BT = 4 kG, lower single-null diverted discharge were varied by 1) increasing NBI heating power from 2 to 6 MW and 2) comparing with L-mode discharges. The data analysis is concentrating on: 1) using edge profiles from the reciprocating probe for 2-D modeling using UEDGE to calculate edge (SOL) perpendicular and parallel heat and particle transport 2) comparing the power lost through the SOL to the net input power and bulk plasma radiated power 3) comparing power lost in the SOL to the total heat flux to the divertor plates 4) calculating the divertor radiated power fraction 5) calculating the particle balance from the D_\alpha emission and divertor Langmuir probes 6) comparing the fluctuation spectra from edge probe and GPI camera.

[GP1.113] Heat Flux Scaling in the National Spherical Torus Experiment

We report results from heat flux scaling experiments in NSTX. An Indigo ALPHA infrared camera (7-13 micron range, 30 Hz framing rate, 25ms time constant, 12-bit digital image) was used to measure the tile temperature in the lower divertor in NSTX, from which heat fluxes were derived with a 1-D conduction model. The peak heat flux reached 10 MW/m^2 in an ELM-free H-mode for an input power of 4.5 MW in lower-single null configuration. The full-width at half-max. of the profile was as narrow as 2cm. The heat flux profile in L-mode plasmas was broader than in the ELM-free H-mode. The dependence of the heat flux peak and profile on input power and plasma density will be presented, as will comparisons with the UEDGE edge plasma transport code.

[GP1.114] Fueling NSTX Deuterium Discharges with Trimethylboron for Conditioning Plasma Wetted Surfaces and Establishing a Low-Z Mantle

- The application of HeGDC Boronization during maintenance periods using a mixture of 90% He and 10% deuterated trimethylboron (TMB) has significantly improved NSTX plasma performance and allowed routine access to H-modes. HeGDC/TMB has been applied on 16 separate occasions, or about every 300-400 discharges. NSTX has investigated the re-boronization of plasma eroded surfaces by direct injection of TMB into the edge of normal discharges. In the first experiment, injecting the 10% TMB mixture led to better performance in ohmically heated deuterium plasmas. Following this, pure TMB was injected into NBI heated deuterium discharges. While the wall conditions were not optimal at the time, it is noteworthy that there was sufficient improvement in edge conditions that one of the highest central electron temperatures (Te(0) ~1.6 keV) to date was observed in an NBI-heated discharge following one of these TMB fueling sequences.

[GP1.115] Gas puff imaging of edge turbulence in NSTX

The gas puff imaging (GPI) diagnostic of NSTX can be used to study the edge turbulence present in this spherical torus experiment. The turbulence seen with this diagnostic can be characterized as a combination of waves and "blobs" (intermittent density concentrations) with notable differences observed between plasmas in L-mode and H-mode confinement regimes. The space and time structure of this turbulent features is being studied with the use of fast-gated digital cameras and discrete fast chords. The results obtained by GPI will be compared with those from other diagnostics, namely, a fast reciprocating Langmuir probe and reflectometry, and the interpretation of the observed emission fluctuations in terms of density and temperature fluctuations will be discussed based on results from DEGAS 2 simulations. In addition, the experimental results will be compared with those from edge turbulence simulations using the BOUT code.

[GP1.116] Structure and Motion of Edge Turbulence in NSTX

Images of the edge turbulence in the National Spherical Torus Experiment (NSTX) are taken with the Princeton Scientific Instruments PSI-4 fast-framing camera. A series of 28 images is taken for each shot, with each frame typically having an exposure time of 10 \mu s. The two main types of structure seen in the edge turbulence are waves and blobs that move through the imaging area within the timeframe of the image series. In this study, we are analyzing these features and their motion using various methods. For example, we track the motion of the blobs in order to determine their direction and speed. Similarly, the position and motion of the wave-like structures are tracked and compared with the blobs. We also use the Gyrokinetic Visualization (GKV) code, written by William M. Nevins, to analyze the images.

[GP1.117] Simulation of the Boundary Plasma in NSTX

The boundary plasma in NSTX is simulated with the UEDGE two-dimensional fluid code and the BOUT 3-d edge plasma turbulence code. Adjustable input parameters for the UEDGE simulations include the core plasma density, total power flow from the core to the scrape-off layer, particle recycling coefficients at the walls and divertor plates, impurity content or sputtering rates, and anomalous radial transport coefficients. The model is calibrated or benchmarked against measured plasma profiles as the data becomes available. Conversely, the benchmarked code is used to predict plasma behavior at extrapolated higher power levels or with various forms of particle pumping. The BOUT code calculates edge plasma turbulence characteristics and computes the strength of the radial transport in a plasma background taken either from UEDGE or from experimental plasma profiles. The radial transport coefficients from BOUT can be used in the UEDGE simulations or compared with the UEDGE calibration values. We will present NSTX simulation results relevant to benchmarking in single-null and double-null configurations, high power operation and particle pumping.

[GP1.118] Neutral Transport Simulations of Gas Puff Imaging Experiments on NSTX

Experiments using visible imaging of D_2 and He gas puffs to characterize edge plasma turbulence have been carried out in the NSTX device. Modeling of these experiments with the DEGAS 2 Monte Carlo neutral transport code provides insight into the relationship between the observed light emission and the underlying plasma turbulence. Specifically, wavenumber spectra computed from the simulated light emission can be compared with those obtained from the plasma profiles input to DEGAS 2. Attempts to directly infer local plasma temperatures and densities by viewing multiple He emission lines might be hampered by the presence of the metastable 2^1S and 2^3S states. By treating them as separately transported species in DEGAS 2, their impact on the problem can be quantitatively evaluated. Another issue for the gas puff imaging diagnostic is the degradation of radial resolution by the finite toroidal extent of the emission cloud. Three-dimensional DEGAS 2 simulations incorporating the actual camera views allow the magnitude of this effect to be estimated.

[GP1.119] Turbulence, Magnetic Field Strength, and Profile Measurements on NSTX Using Millimeter-Wave Reflectometry

UCLA operates a suite of millimeter-wave/microwave reflectometers on NSTX for routine measurements of the electron density profile and fluctuations. The combined frequency coverage of 12 to 50 GHz (O-mode cutoff range of 0.18-3.1\times10^13 cm^-3) provides connection between measurements in the core and scrape-off layer. Profile evolution and fluctuation characteristics during L- to H-mode transitions and ELMs have been documented. Recently, three fixed-frequency quadrature reflectometer channels at 18, 28 and 50 GHz were used to look at H-mode precursors, and compressional Alfvén eigenmodes during NBI. In addition, experiments were performed to test dual-mode correlation reflectometry as an edge magnetic field strength diagnostic. Results from these and other experiments will be presented.

[GP1.120] Reflectometer Measurements in the Plasma Edge Region in Front of the HHFW Antenna on NSTX

A swept-frequency microwave reflectometer with access through the HHFW antenna is used to measure time-dependent edge density profiles during HHFW heating experiments. Utilizing x-mode polarization, a 6-26 GHz reflectometer probes the density range from 0.1-6.0 x10^18 m^-3. Typically, density fluctuations in the scrape-off layer are very large, but are suppressed during H-mode conditions. It is observed that density fluctuations are also influenced by other circumstances. For example, during HHFW current drive experiments in He discharges, density fluctuations are significantly reduced during co-current drive phasing, relative to counter-current phasing. Also, when the outermost flux surface contacts the HHFW antenna, the edge density profile steepens and in some instances fluctuations are suppressed.

[GP1.121] Phased-Array Operation With High Harmonic Fast Waves on NSTX

Phased-array experiments were performed with the 30 MHz, 12-element HHFW antenna array on NSTX at low densities (ne(0)\sim1-2e19 m-3) and low current (Ip \sim 0.3-0.5 MA) for rf powers in the 1-3 MW range. Relative phase shift of the array was scanned from 30^o to 90^o to create spectral peaks (n between 5 and 13) in both the co- and counter-current directions; it was also possible to switch from 90^o to 45^o phasing during a shot. Electron heating was observed even at the highest wave phase velocities, reaching 1.3 keV with 2.2 MW at -30^o phasing and 2.7 keV with 2.9 MW at -60^o. Definitive measurement of non-inductive current drive awaits the imminent installation of the MSE diagnostic, but \sim30% changes in the loop voltage between co- and counter-CD phasing gives encouraging indication of HHFW CD.

[GP1.122] Power and voltage limits in the NSTX Ion Cyclotron System*

The high-harmonic-fast-wave ion cyclotron system on NSTX was used extensively in the recent operational period. Heating and current drive experiments were carried out under a wide variety of plasma conditions. The amount of power that could be delivered to the plasma was usually limited to about 3 MW, caused by rf arcs in the antenna or vacuum transmission lines. This presentation will look at the behavior of the power limit as a function of plasma parameters, antenna voltages, neutral gas pressure, and other variables to see if a systematic trend can be identified that may indicate the major factors that are causing the limitation.

[GP1.123] Modeling of HHFW heating and current drive experiments in NSTX

Plasma heating and noninductive current drive via applied fast magnetosonic waves at high harmonics of the ion cyclotron frequency are being explored on the NSTX device. Unlike icrf heating in conventional tokamaks, the dominant heating mechanisms in a high beta ST plasma are predicted to be TTMP damping on electrons and ion damping at high harmonics of the ion cyclotron frequency. Experiments on NSTX have been performed in a number of different regimes, including moderate temperature plasmas in which TTMP damping is predicted to dominate, beam-heated plasmas in which significant ion absorption is predicted, and current drive experiments in which the driven currents depend on the launched wave spectrum. Power partitioning between the ions and electrons in these discharges will be analyzed using a variety of rf modeling codes, including both ray tracing and full wave models.

[GP1.124] Modeling of HHFW Current Drive Discharges on NSTX Using CURRAY and TRANSP

Recent HHFW current drive experiments on NSTX have measured loop voltage differences, \DeltaV, between pairs of similar plasma discharges where the antenna phasing reversed from co- to counter-CD (\pm60^o, \pm45^o, \pm30^o). This result indicates that current drive may have been observed, even though direct verification awaits future installation of MSE diagnostics. In this paper, steady-state HHFW CD calculations from the CURRAY ray optics code for some of these discharges are presented and compared with estimates from measured \DeltaV. The calculated full antenna spectrum is modeled using up to 100 rays with different N_\phi, N_\theta, and launch locations. The presence of a DC electric field will be accounted for by invoking a modified conductivity, while other approaches are being explored. Presently, CURRAY is being implemented as an NTCC (National Transport Code Collaboration) module for interfacing to the TRANSP analysis code. The combined package will be used to analyze time-dependent HHFW CD discharges, where the calculated driven current is treated as a source term in the current diffusion equation. Progress and results on this will be reported.

[GP1.125] Current Drive by Electron Bernstein Waves

Electron Bernstein waves (EBW) can be excited at the edge of NSTX and MAST type plasmas by mode conversion of the slow X mode. The EBWs propagate into the overdense plasma and damp on electrons at the Doppler-shifted electron cyclotron resonance (or its harmonics). Depending on the poloidal location of EBW excitation, the magnitude of the parallel wavenumber can be either less than one (for equatorial excitation) or greater than one (for excitation away from the equatorial plane). Furthermore, the spatial region of wave damping depends on the poloidal angle of launch of the EBWs. In the weakly relativistic limit, suitable for present plasmas, we are studying the effect of plasma parameters, frequency, and parallel wavenumbers on EBW current drive. This formulation, necessitated by EBWs, is for arbitrary values of k_\perp \rho_e. A description of the model and of analytical estimates for current drive efficiency will be presented. Comparisons with results from a Fokker-Planck code will be included.

Work supported by DoE and Euratom/UK-OST.

[GP1.126] Coaxial Helicity Injection for plasma start-up in NSTX*

To minimize the aspect ratio of toroidal plasmas, elimination of the central solenoid is a consideration for future ST designs. CHI is a promising candidate for initial plasma generation and for edge current drive during the sustained phase. Experiments on NSTX thus far have succeeded in attaining 390kA of CHI generated toroidal current using about 28kA of injector current in 330ms long pulse discharges. Recent measurements of the divertor and vessel neutral pressure shows a temporal increase of the upper divertor pressure early in the discharge but a gradual decrease after 100ms with possible implications of SOL flows providing the needed charge carriers during the high current portion. The ESC equilibrium code and the TSC simulation code are being used to study these discharges. Preliminary results from these simulations and the near term program plan will be presented. * Work supported by US. DOE Contract No. DE-AC02-76CH03073 and DE-AC0276CH03073.

[GP1.127] Transient CHI plasma for secondary current drive

Non-inductive startup of a spherical torus (ST) such as NSTX is necessary for ST concept due to the limited volt-second from the small central solenoid. Co-axial helicity injection (CHI) is an attractive candidate to prepare initial plasma and field configuration which can be handed over to secondary current drives for profile optimization and sustainment. The secondary drive can be transformer-based (inductive), or utilizes particle beams or radio-frequency waves (non-inductive). These methods rely on good confinement properties of the startup plasma to operate effectively. The minimum requirement is to have a plasma core with closed poloidal flux, on which the secondary current drive can target. Although steady state CHI plasma with good core confinement remains an issue of debate, transient CHI plasma can easily satisfy the requirements. The most straightforward approach forces axisymmetric (2D) magnetic reconnection by either pinching off the injector poloidal flux or modulating the electro-static drive. Large axisymmetric plasmoid arises through the 2D reconnection. One undesirable feature of the 2D MHD scheme is that the closed poloidal flux of the axisymmetric plasmoid is distributed in an opposite way from the eventual ST profile. The q is typically very high in the center and large fraction of the plasmoid has little rotational transform. This adds burden to the secondary current drive. An alternative approach is to drive the CHI sufficiently hard that the 3D instabilities redistribute the axisymmetric current. Simulation shows the saturated n=0 MHD component can have substantial closed poloidal flux with considerably lower q. When subjected to relaxation, for example, by modulating the electro-static drive, the transient CHI plasma favors the n=0 component and can yield a better-conditioned MHD target for secondary current drive.

[GP1.128] Design and Installation of New Insulator for NSTX CHI Experiments

Coaxial Helicity Injection (CHI), a non-inductive method to initiate plasma and provide plasma current, is being investigated in the National Spherical Torus Experiment. In NSTX the center stack and outer vacuum vessel are separated with insulated gaps at the top and bottom so that high voltage (<2 kV) can be applied between them to initiate a helical arc discharge. This has been successful in providing up to 25 kA of injector current from the center stack to the outer vacuum vessel and up to 390 kA of toroidal current. The investigation of CHI has been limited because arcs across the insulator at the top of the machine (absorber), which terminate the desired discharge. During the shutdown in 2002, the absorber region is being modified to improve the ability to avoid these arcs. The new design provides a simpler geometry, a new ceramic insulator on the high field side of the absorber region, and two new coils near the absorber to minimize the field connecting the center stack and outer vacuum vessel.

[GP1.129] Comparison of the Electron Temperature Results from a High-Resolution X-Ray Crystal Spectrometer and Thomson Scattering on NSTX

An effort was made during the last experimental campaign at the National Spherical Torus Experiment (NSTX) to explain the discrepancies between the electron temperature results from Thomson scattering and a high-resolution X-ray crystal spectrometer, which records spectra of 1s^2 ^1S_0 - 1s2p ^1P_1 resonance line of helium-like argon, ArXVII, and the associated 1s^2nl - 1s2l'nl" dielectronic satellites in the wavelength range from 3.94 to 4.0 ÅIn the course of this work, a calibration error of the Thomson scattering system was found and corrected; and an inaccuracy in the theoretical predictions for the line strengths of the n \ge 3 dielectronic satellites, which led to an overestimate of the electron temperature, was eliminated in new atomic physics calculations, so that the electron temperature values which are derived from the n = 2 and n \ge 3 satellites are now consistent and in agreement with the data from the newly calibrated Thomson scattering system. The paper will present these experimental and theoretical results, which may also be important for the interpretation of astrophysical spectra.

[GP1.130] Analysis of Charge Exchange Recombination Spectra on NSTX

Ion temperature and toroidal plasma velocity profiles on NSTX are measured using charge exchange recombination spectroscopy (CHERS). The intersection of three neutral beam sources with an array of sightlines provides local measurements. The charge exchange spectrum of C VI at 529 nm is complicated by non-local emission, predominantly from electron-impact ionization at the plasma edge, which can have comparable intensity. A background array of sightlines, not viewing the neutral beams, provides an independent measure of the intrinsic emission in the plasma Careful cross calibrations of photometric sensitivity, intsrumental lineshape, wavelength, and tangency radius between the two viewing arrays are essential for the proper characterization of the background emission. Systematic variations in background measurements, such as reflections for different toroidal views, also affect the analysis. Modeling of the background emission for each sightline using temperature and velocity measurements from exterior CHERS sightlines along with independent electron density measurements may further improve the analysis.

[GP1.131] An Edge Rotation Diagnostic on NSTX

A new diagnostic for the National Spherical Torus Experiment (NSTX) is described whose function is to measure the rotation of the plasma edge. The diagnostic is sensitive to C III and C IV ambient emission, covering (with down to ~1 cm spacing) a radial region of 15 cm at the extreme edge of the outboard midplane. Thirteen chords are distributed between toroidal and poloidal views, allowing the toroidal and poloidal rotation of the plasma edge to be characterized with 10 ms resolution. This measurement complements the toroidal rotation and carbon impurity temperature profiles, which will be measured by the NSTX Charge-Exchange Recombination Spectroscopy (CHERS) diagnostic. Combined with the local pressure gradient and EFIT reconstructed magnetic field profile, the edge flow will give a measure of the local radial electric field. The edge rotation diagnostic and CHERS have similar hardware, and were installed during the current outage. Unlike CHERS, the edge rotation diagnostic does not require a neutral beam, and hence can provide measurements during a wider array of plasma conditions.

[GP1.132] The Motional Stark Effect (MSE) Diagnostic for the National Spherical Torus Experiment (NSTX)

The adoption of the motional Stark effect (MSE) polarimetry is due to its very good temporal and spatial resolution of the q-profile, combined with its exceedingly good accuracy. This has resulted in many important scientific contributions towards our understanding of stability and transport. Despite the success of MSE on mid to large size devices, with magnetic fields above 1 Tesla, it has not been implemented on low field or small experiments. This is due to the large expense of a neutral beam and/or the inability of the technique to work at magnetic fields below 0.75 Tesla. Two approaches are being developed to remedy this; (1)MSE-LIF using laser-induced fluorescence (LIF), with a small diagnostic neutral beam, and (2)MSE-CIF using collsionally induced fluorescence (CIF) to allow the MSE technique to function at significantly lower magnetic fields than previously demonstrated. This work describes the implementation of the MSE-CIF diagnostic on NSTX which views the heating beam with 8 inch collection optics, imaged onto a fiber array. The optical system is configured to maximize the polarization fraction by reducing the Doppler broadening from the heating beam. In addition, a spectral filter with high throughput and high resolution is required to achieve the necessary signal-to-noise. This can be achieved with a wide field Lyot filter. This will permit MSE data to be obtained at magnetic fields >0.3 Tesla. A wide field tunable birefringent filter has been designed and tested that has the required throughput with a bandwidth of \sim 0.07 nm.

[GP1.133] Upgrade plan of the NSTX FIReTIP system

Two channel measurement of line density using the multichannel Far Infrared Tangential Interferometer/Polarimeter (FIReTIP) system on the National Spherical Tokamak Experiment (NSTX) and a test of the polarimetry capability are completed. A Stark-tuned optically pumped far infrared CH3OH laser serving as a local oscillator (LO) source together with two additional FIR lasers at 119 mm have been successfully implemented for the first time. During the last run period, extensive work has been performed to perfect the density measurement which suffered from mechanical vibrations and an extensive test of polarimetry system was conducted. Demonstration of the two channel system and the polarimetry test results warrant a full system expansion. The upgrade design of the full seven channel system and fabrication of parts have been completed. Partial installation is planned during this opening (2002) and design characteristics and upgrade plan are described in detail in this presentation.

*This work is supported by the U.S. Department of Energy under contract Nos. DE-AC02-76CH03073 and DE-FG03-95ER54295

[GP1.134] A Stark-tuned Laser Application for Interferometry and Polarimetry on NSTX

Application of a Stark tuned FIR laser allows higher IF frequency for fast time resolution together with stable operation of the interferometer/polarimeter systems. The low IF frequency of the previous generation has been mainly due to the intrinsic narrow gain profile of the lasers. A Stark-tuned optically pumped far infrared CH3OH laser serving as a local oscillator (LO) source together with two additional FIR lasers at 119 mm has been successfully implemented in the Far Infrared Tangential Interferometer/Polarimeter (FIReTIP) system which has provided temporally and radially resolved 2-D electron density profile [ne(r,t)] and toroidal field profile [BT(r,t)] data for the National Spherical Tokamak Experiment (NSTX). The characteristic frequencies of the IF system are ~3, ~4 and ~7 MHz and a phase lock system was utilized for tracking the drift of the IF frequencies. In this presentation, the characteristics and operation of the Stark-tuned laser are described in detail. The measured electron density and Faraday rotation for various physics operational regimes are compared to the line integral of Thomson scattering measurement and EFIT results, respectively.

*This work is supported by the U.S. Department of Energy under contract Nos. DE-AC02-76CH03073 and DE-FG03-95ER54295

[GP1.135] Advanced Fluctuation Diagnostics for ITG and ETG modes on NSTX*

Recent progress in Microwave Imaging Reflectometry clearly demonstrated that the conventional reflectometry operating in the diffraction limit, which has been widely used for ITG modes (k_\bot \rho_i \sim 0.2) in toroidal devices, has severe constraints in real applications. Imaging Reflectometry for long wavelength ITG modes can remedy these shortcoming on NSTX although the high magnetic shear and low magnetic field of NSTX may add more complexity to the system compared to that of the conventional tokamak (e.g. TEXTOR). The electron thermal transport has been cited in recent years as one of the major scientific transport challenges in fusion research. Recent numerical simulations have shown that extremely small amplitude (\sim0.1 %) and short-scale (k_\bot \rho_e \sim 0.2) turbulent fluctuations driven by the ETG mode could significantly affect the transport of electrons in NSTX. The high magnetic shear in the ST provides an excellent spatial resolution for coherent scattering which is ideal for the search for ETG modes. On NSTX, advance diagnostic systems such as MIR system and high-resolution scattering system with the excellent spatial and k resolution for both ITG and ETG turbulence studies, are essential for understanding the transport physics of the Spherical Torus.

[GP1.136] Next Step Spherical Torus Experiment (NSST)

The progress on the on-going Proof-of-Principle and Concept Exploration spherical torus research has been quite productive and rapid in the recent years. In view of these encouraging results, we examine here a possible next step ST (NSST) facility as a successor to the present PoP level experiments such as NSTX. A logical next-step spherical torus (NSST) device is a “performance extension” (PE) stage ST with Ip A = 8 MA (for non-inductively sustained long pulse) and Ip A = 16 MA (for inductively sustained high performance) discharges. These values are similar in Ip A to the PE tokamak devices such as JET. As a PE-class-ST facility, NSST aims to contribute to a timely and cost effective ST and fusion energy development path. One of the important missions of NSST is to support the physics design and construction of a Component Test Facility (CTF) by developing non-inductively start-up and current maintenance operations. One can also envision operations of NSST as a test bed for CTF operational scenario development once the CTF facility becomes operational, and is fully devoted to its component testing mission. The NSST facility can also explore more advanced ST regimes relevant for DEMO and a power plant such as ARIES-ST. To make timely progress toward this goal, the design philosophy of NSST is to give high priority for physics flexibility including ample diagnostic access.

[GP1.137] Implication of Recent Spherical Torus (ST) Results for a Component Test Facility

Recent progress in ST research at the level of IpA = 1-2 MA such as NSTX, has been encouraging toward the physics basis for a Component Test Facility (CTF). The CTF requires a sustained burning-plasma-produced volumetric neutron environment, and adequate device materials and technology components, to enable testing to high accumulated neutron dose. Analysis and extrapolation of the physics results so far indicate a relevant parameter range of beta-N = 4-7, beta-p/A = 0.8-1.2, bootstrap current fraction = 0.5-0.9, and H(98H) = 1.5-2.0 in plasmas with qMHD = 7-14, kappa = 2.5-3.1, and IpA = 15-30 MA. This parameter range spans the basic to the advanced ST plasma properties and delivers a range of performance from basic testing to possible production of net electricity. Key CTF physics issues, which include solenoid-free startup and sustainment, will require testing at the level of IpA = 8-15 MA using a “Performance Extension” level Next Step ST experiment, NSST.

Work supported by DoE Contract Nos. DE-AC02-76CH03073 and DE-AC05-96OR22464.

[GP1.138] Divertors, Edge Physics and Fueling

[GP1.139] Plasma Boundary Conditions in Ignitor

In a burning plasma, impurity production and penetration need be limited, while maintaining good confinement and adequate high density for fusion reactivity. For a compact, high density experiment like Ignitor, these objectives can be attained more efficiently by an all metal (Mo) first wall acting as an extended limiter rather than a classic divertor. The first advantage derived by the high core plasma density is the corresponding high density, low temperature at the edge (n_a \simeq 2-3 \times 10^20 m^-3, T_a \simeq 35-60 eV). In this conditions, a high level of ionization takes place in the Scrape Off Layer (SOL), the impurities are screened from the core plasma, and the high density of neutrals is effective in reducing and redistributing the energy of ions flowing onto the first wall. The magnetic field topology of a limited plasma is another important factor in determing low thermal loads on the wall (peaks \leq 1.8 MW/m^2, 0.7 MW/m^2 on average), in particular on the inner wall, where the field lines are essentially tangent to the surface. Provisions for precise alignement and edge smoothing of the first wall tiles have been made. Work supported in part by ENEA of Italy and by the US DOE.

[GP1.140] Improvements and Benchmarking of the TEP Neutral Transport Code GTNEUT

The GTNEUT neutral transport code is based on the Transmission and Escape Probabilities (TEP) method(W.M. Stacey, J. Mandrekas, Nucl. Fusion 34) (1994) 1385. and has been benchmarked extensively against Monte Carlo and experiment(W.M. Stacey, J. Mandrekas, R. Rubilar, Fusion Sci. amp; Technol. 40) (2001) 66., (R. Rubilar, W.M. Stacey, J. Mandrekas, Nucl. Fusion 41) (2001) 1003.. We present several recent upgrades to the code and methodology including the implementation of a realistic wall reflection model, a two energy group calculation and an improved treatment of the angular neutral distribution at the interfaces. This upgrade was made possible by replacing our original assumption of an isotropic neutral distribution at the half-space interfaces (equivalent to a double P_0 approximation) with double P_1 and higher approximations. Comparisons of the updated code with Monte Carlo and DIII-D experiments are presented.

[GP1.141] Poloidally Varying Neutral Fueling Effects on the Tokamak Edge

The presence of neutral atoms in the tokamak edge affects the radial electric field and toroidal plasma flow velocity through charge exchange interactions. The radial localization of the atoms to within a neutral penetration depth of the separatrix introduces shear in the electric field and flow. Since the toroidal flow is not a flux function, poloidal localization of the neutral fueling provides an adjustable brake on the flow by altering the radial electric field. The effect depends sensitively on the poloidal location of the fueling just inside the separatrix, especially in a spherical tokamak. In particular, it is found that the radial electric field and toroidal flow velocity on the outboard side of a collisional edge plasma tend to be larger if the atoms are concentrated on the inboard side rather than on the outboard side. This effect may suppress turbulence with a strong ballooning character and offer an explanation for recent observations on MAST and COMPASS-D indicating easier H-mode access when gas is puffed from the inboard side of the tokamak. The results suggest an external means for controlling the toroidal flow and radial electric field and their shearing rates, and have motivated further measurements on MAST which appear to support the predictions.

[GP1.142] Effects of Poloidally Varying Neutral Density on Collisional Transport and Plasma Flow in Tokamaks

Due to their large diffusivity and strong charge exchange coupling to the ions, neutrals can strongly influence the radial transport of particles and heat, and plasma flow at the tokamak edge [1] even for a small neutral to plasma density ratio, (N_n/N_i). In particular, we consider the effect of the poloidal variation of the neutral density on fluxes and flows just inside the separatrix. We find it generates a poloidal variation of the plasma density, electron and ion temperatures, and electrostatic potential, leading to additional parallel plasma flows and convective radial fluxes which for a collisional edge are comparable to or larger than the usual Pfirsch-Schlüter values for (N_n/N_i) \sim 10^-3 in Alcator C-Mod. The additional plasma flows are strongly sheared and may therefore affect turbulent transport and the L to H transition. Even though the poloidally varying neutral driven ion heat flux can compete with the standard ion Pfirsch-Schlüter radial ion heat flux, it does not lead to significant energy loss since it is always smaller than the diffusive neutral radial heat flux. [1] P. J. Catto et. al, Phys. Plasmas 5, 3961 (1998); T. Fülöp et. al, ibid. 5 3969 (1998).

[GP1.143] Modeling of Ion Impurity Transport in Turbulent Edge Plasmas

The issue of impurity ion transport in the edge plasma is quite important but not well understood, as it is known to be anomalous i.e. dominated by plasma turbulence. Recently there has been substantial progress in simulating tokamak edge plasma turbulence with the fluid turbulence code BOUT(X.Q.Xu et al., Phys. of Plasmas, Vol.7, 1951 (2000).). BOUT results are often in good agreement with the experiment in the frequency and wavenumber spectra, as well as the rough fluctuation amplitude. Accepting that the turbulent electric field \tilde\phi produced by BOUT is correct, one should expect that the output of BOUT can be used to describe the transport of impurity ions as well, assuming that impurities have a small effect on the bulk plasma. We examine this idea by studying the transport of test impurity ion particles in the turbulent potential \tilde\phi generated by BOUT. The transport of impurity ions is modeled by solving the drift kinetic equation with a Monte Carlo procedure which includes the parallel motion, the drifts (E \times B, \nabla B, and curvature drift) and collisional scattering; thus the model includes neoclassical effects. With a large volume of spectroscopic data on impurity ions in tokamak edge, one can potentially use it for comparison of the theory with the experiments.

[GP1.144] Temporal response of edge-plasmas to ELMs

Edge plasmas in tokamaks are strongly modified by periodic profile relaxation caused by edge-localized modes (ELMs), which in turn are believed driven by MHD instabilities in the H-mode confinement regime. The ELM results in injection of substantial amounts of plasma density and energy into the scrape-off layer (SOL) region with open magnetic field-lines, where the plasma then flows to divertor plates and walls. Determination of the resulting peak heat load on material surfaces is a key issue for burning-plasma tokamak experiments because of erosion and possible melting of the surfaces. The time-dependent flow of particles, momentum, and energy in the SOL is analyzed, with particular emphasis on currents and ExB drifts. The roles of the fast electron response and the slower ion response are clarified. The thermo-electric current along the magnetic field can cause large asymmetries to the heat-flux to divertor surfaces. The spatial profile and temporal variation of the heat pulse to the divertor plate is shown using the 2D UEDGE transport code, and the modifications necessary to model kinetic effects are discussed.

[GP1.145] Temperature-dependent mechanisms of lithium erosion from lithium-based liquid metals under low-energy bombardment

Erosion from liquids under low-energy, light-particle bombardment has been studied at the Ion-surface Interaction Experiment (IIAX) facility at the University of Illinois^1. A variety of liquids are studied including lithium, tin-lithium and tin. Quartz crystal microbalance technology is used to measure lithium erosion including evaporation and sputtering under a variety of surface conditions, temperatures and incident particle energies.

In addition to these measurements, this work includes self-consistent modeling done with VFTRIM-3D ^2 and TRVMC-95. Results indicate that the near-surface deposited energy density and temperature-dependent surface binding energy are important mechanisms in understanding the erosion behavior of liquid metals as the sample temperature and incident particle energy is varied. The study includes measurements with H^+, D^+, He^+, Ne^+, Ar^+ and Li^+ bombardment at energies between 0.1-1.0 keV and 45-degree incidence.

^1J.P. Allain, D.N. Ruzic, M.R. Hendricks, J. Nucl. Mater. 290-293 (2001) 180. ^2D.N. Ruzic, Nuclear Instrum. Methods B 47 (1990) 118.

[GP1.146] Beryllium/Tungsten Mixed Material Analysis of FIRE Plasma Facing Components

An extensive computer modeling effort has been done as part of the Fusion Ignition Research Experiment (FIRE) design study, combining several independent computer codes and focusing on Be/W mixed-material erosion issues. Since the FIRE design calls for a beryllium first wall and tungsten divertor, beryllium can be sputtered from the first wall and transported to the divertor, forming a Be/W mixture on the divertor. The goal is to determine the amount of Be that ends up on the divertor surfaces and to model the sputtering and erosion/redeposition properties of the resulting mixture. Sputtering is calculated from deuterium neutral fluxes obtained from the DEGAS2 neutral transport code, together with a D ion flux from the background plasma. The sputtering of Be due to the total D flux is determined by VFTRIM-3D, a variant of the TRIM-SP binary-collision simulation code. The transport of Be to the divertor region is calculated with the WBC+ code, part of the ANL REDEP impurity transport package. Results show that the average Be sputtering yield is \sim0.039, and \sim73% of sputtered Be is transported to the divertor. The next step is to analyze the erosion properties of the Be/W mixed material with the ITMC and WBC codes.

[GP1.147] Plasma-liquid metal interaction studies in FLIRE

FLIRE (Flowing Liquid-metal Illinois Retention Experiment) is designed to study the interaction between a plasma and free-surface flowing liquid-metal streams. It uses an ion gun to bombard the liquid metal with He and D ions. Previous experiments have calculated the He diffusion coefficient to be 4.5x10^-3 \pm 2x10^-3 cm^2/s based on retention measurements. A hollow-cathode DC plasma source is added to allow FLIRE to measure retention and diffusion data for the case of exposure to a thermal plasma instead of a monoenergetic beam. The plasma density and temperature are obtained in a separate experiment by use of a Langmuir probe. The liquid-lithium stream is exposed to helium, deuterium and deuterium/helium plasmas. Measurements and modeling of the liquid-metal stream exposed to both ion beam and DC plasma are presented. The effect of beam/plasma energy, liquid-metal flow velocity and liquid-metal temperature on the retention properties will be presented and discussed, as well as the model used to calculate the diffusion coefficient from retention measurements, both for reactive (D) and inert (He) species.

[GP1.148] Erosion properties of liquid phase tin due to D^+ and He^+ bombardment

The erosion properties of liquid tin at temperatures from 240 to 400 ^oC due to irradiation by 300-1000 eV D^+ and He^+ at an oblique angle have been measured using the Ion-Surface InterAction Experiment (IIAX); these properties include the temperature-dependent absolute sputtering yield, oxide effects, and secondary ion sputtered fraction. IIAX brings a velocity- and neutral- filtered ion beam onto a solid or liquid target at 45^o incidence. The absolute sputtering yield and evaporative flux are measured via a quartz-crystal microbalance (QCM). Flowing liquid tin is being examined for use as a plasma-facing component (PFC) in next-step fusion devices due to its relatively low vapor pressure and melting point. A comparison of this and previous data^1 on liquid lithium, another candidate metal, as well as VFTRIM-3D^2 modeling for both systems was performed. Also discussed is the impact on PFC design due to the erosion characteristics of liquid tin. ^1J.P. Allain, D.N. Ruzic, and M.R. Hendricks, J. Nucl. Mater. 290-293 (2001) 180. ^2D. N. Ruzic, Nuclear Instruments and Methods in Physics Research B47 (1990) 118.

[GP1.149] Fast Radial Convective Transport in Tokamak SOL Plasmas

Reduced 2D resistive MHD system of electromagnetic equations is applied to describe fast radial convective density transport[1,2] in the tokamak SOL and the divertor region. The study is concentrated on properties of single and multiple plasma blobs propagation and interaction. A formation of a stable front of the blob as well as a formation of the canonical blob shape and size is demonstrated. Existence of the density limit in the model is analyzed. Impact of the density gradient term in the vorticity equation on the fast radial blobs propagation is discussed. The ideal limit of the model is considered as well as the influence of parallel current resistive effects. The 2D results are compared and verified with 3D blob propagation simulations by the BOUT code[3], based on 5-field fluid Braginskii model. The results of the comparison will be reported. [1] S.I. Krasheninnikov, Phys. Let. A 283, 368 (2001); [2] D.A. D'Ippolito, J.R. Myra, S.I. Krasheninnikov, Phys. Plasmas 9, 222 (2002); [3] X.Q. Xu, R.H. Cohen, Contrib. Plasma phys. 36, 158 (1998),. Presented at the 44 Annual APP-DPP meeting, Orlando, FL, November 11-15, 2002

[GP1.150] Simulations of far-SOL recycling and anomalous convective cross-field transport in C-Mod, NSTX, and DIII-D tokamaks*

Recently, fast intermittent transport was observed in far SOL on C-Mod [1], NSTX, and DIII-D [2] tokamaks. This non-diffusive transport strongly increases plasma flux to the chamber wall and enhances recycling of neutral particles in the main chamber [1,3]. We use 2D fluid code UEDGE to model the effect of non-diffusive transport on edge plasma parameters. Our transport model includes time-independent anomalous cross-field convective velocity Vconv directed outward [3]. With UEDGE we simulate a series of L-mode discharges obtained on these tokamaks. Based on our modeling results that accurately match experimental data, we discuss the dominance of anomalous convection in the far SOL transport, describe similarities in characteristics of convection on these tokamaks, and highlight trends for Vconv variation with plasma radius and discharge density. [1]B. Labombard et al, Phys. Plasmas 8 (2001) 2107; [2]J. Boedo et al, Phys. Plasmas 8 (2001) 4826; [3]A. Pigarov et al, Phys. Plasmas 9 (2002)1287. *Work supported by US DoE

[GP1.151] On Cross-field Impurity Transport in Tokamak SOL Plasmas*

Usually in edge plasma modeling with 2D transport codes like UEDGE impurity cross-field transport is described by diffusion process with some ad hoc diffusion coefficient. Meanwhile based on recent findings of strongly intermittent effects in edge plasma turbulence (e. g. Ref. 1), it is obvious that diffusive model of impurity transport is, at least, incomplete. With a blob/dip paradigm of SOL plasma turbulence (e. g. Ref. 1), the picture of impurity transport in the SOL, very much different from simple diffusion, would emerge, where impurity ions entrapped into plasma density dips are convected towards core plasma [2]. In this report we present the results of our numerical study of impurity transport adopting the 2D model of the SOL plasma turbulence similar to that of Ref. 1. [1] S. I. Krasheninnikov, Phys. Letters A 283 (2001) 368; D. A. D'Ippolito, J. R. Myra, and S. I. Krasheninnikov, Phys. Plasmas 9 (2002) 222; A. Yu. Pigarov, et al., Phys. Plasma 9 (2002) 1287. S. A. Galkin et al. this meeting. [2] S. I. Krasheninnikov et al., "Blobby cross-field plasma transport in tokamak edge" 29th EPS Conference on Plasma Physics and Controlled Fusion, 17-21 June 2002, Montreux, Switzerland.

[GP1.152] Spatial structure of SOL turbulence on CASTOR tokamak

The electrostatic turbulence in the scrape-off-layer (SOL) region of CASTOR tokamak is studied using 32 Langmuir probes, embedded in a poloidal array of 32 plane electrodes [1]. This arrangement is meant to test the possibility of actively modifying the edge turbulence structure, in analogy to what has been done in the linear experiment MIRABELLE [2]. It provides for the first time the complete poloidal structure for poloidal wave numbers up to m=16. The SOL turbulence in CASTOR is composed of two branches [3]. The branch with a broad frequency spectrum and low wave number corresponds to fully developed turbulence usually observed in large tokamaks. The other branch, with larger frequency and poloidal wave number, has a well-defined periodicity in time and space. Its spatial periodicity is related to the edge safety factor and follows its dynamics. The evolution of the SOL turbulence is also studied in presence of constant and modulated biasing on the poloidal array [4]. These results are compared to the case where the biasing is applied on a single electrode located at the top of the tokamak. [1] M. Hron et al., EPS 2002, Montreux ; [2] C. Shroeder, et al., Phys. Rev. Lett., 86, 5711 (2001); [3] P. Devynck, et al., and [4] J. Stockel, et al., EPS, 2002, Montreux

[GP1.153] Measurement of H_2^+ and H_3^+ concentrations in a weakly-ionized hydrogen discharge

The hydrogen molecular ions H_2^+ and H_3^+ form readily in weakly-ionized hydrogen plasmas and are thought to play an important role in a wide variety of systems, such as planetary ionospheres, neutral beam sources, and tokamak divertors. Here, the concentrations of the hydrogen ions H^+, H_2^+ and H_3^+ are measured using an omegatron-type mass spectrometer in steady-state hydrogen discharges with electron densities N_e = 10^11 - 10^12 \: \rmcm^-3, electron temperatures T_e = 3 - 7 \: \rmeV, and neutral hydrogen densities N_H2 = 5 \times 10^13 - 10^15\: \rmcm^-3. Dominant ion concentrations are predicted within about 25% using currently available rate coefficients if the measured vibrational excitation of the ambient H_2 neutral molecules is included. The predicted molecular ion concentrations are typically 3-5 times too low if vibrational excitation is ignored, so inclusion of vibrational energy is crucial for accurate modeling of molecular ion production in these plasmas.

[GP1.154] Evaluation of wall conditioning on the HANBIT mirror device

The wall recycling effect dominantly appears in the ICRH-heated discharges in the HANBIT mirror device. The methods and evaluation of wall conditioning are described in this work. The progress of wall conditioning is monitored with neutral pressure and plasma parameters. Electron cyclotron resonance discharge cleaning(ECR-DC) is applied to improve wall conditioning, and then electron impact desorption(EID) by filament heating is utilized in order to desorb the impurities from the wall. The impurities are analyzed quantitatively by quadrupole mass spectrometer(QMA). We have also installed a new baking system by Halogen lamp radiation with 2 kW. It is observed that H-alpha emission is reduced after the lamp heating. The evolution of neutral pressure profiles has been carefully evaluated during discharge and discharge cleaning effect monitored after several hundred of radio frequency(rf) shots. It appears that the partial pressure of light impurities is much reduced after rf discharges. The line integrated density and edge density also decrease significantly after rf shots, while edge temperature increases. A similar wall-conditiniong effect is also observed after ECR-DC.

[GP1.155] Effects of line radiation on tokamak edge plasmas

Historically, tokamak edge plasma research has employed the assumption of freely escaping radiation (the optically thin approximation) without further exploration into the consequences of radiation interaction. However, in high-density low-temperature (HDLT) tokamak edge plasma regions, such as those found near the divertor target plate in detached experiments and Marfes, Hydrogen line radiation strongly interacts with the plasma (the optical depth is greater than unity) and affects edge plasma transport models. In optically thick plasmas the atomic physics model is dependent on the global radiation field; ionization, recombination and energy loss rates become non-local quantities. Since optical depth effects increase with the extent of the system, line radiation will have a more dramatic influence on plasmas in larger next generation experiments and future reactors. Therefore, to move toward a fuller understanding of the effect of line radiation on plasma transport, we are working to develop a more comprehensive physics model that is numerically implemented in one-dimension. The physics model includes the addition of magnetically broadened line profiles and plasma transport to an existing fully coupled non-local thermodynamics (NLTE) atomic kinetics and radiation transport code. Our computational model will allow the study of: 1) the role of excited state transport in partially ionized plasmas; and 2) the possibility of extending atomic data models, which currently depend on the local electron density and temperature, to include radiation effects. Thus, exploration using the physics model provides a foundation to answer the general question, ``In what manner does line radiation influence edge plasma transport?''

This work was performed under the auspices of the U.S. Department of Energy by the University of California, Lawrence Livermore National Laboratory through contract number W-7405-Eng-48.

[GP1.156] Edge Pedestal and Er-Layer Formation by X-transport

A new Monte Carlo guiding center code has been developed to study the X-transport phenomenon [1], including the plasma pedestal formation, flow development , and a self-consistent Er-layer formation in the plasma edge. We will use the new results to shed light on many of the unresolved observations in the H-mode and edge pedestal experiments. X-transport is a baseline source of strong edge Er and pedestal formation immediately inside the separatrix in a diverted tokamak, which can trigger an H-confinement. It is a non-tokamak type of collisional transport localized to the X-region, caused by a lack of poloidal magnetic field. It is intrinsically non-ambipolar and stronger than the usual neoclassical transport. We will also analyze a compact tokamak in comparison to an ordinary tokamak. [1] C.S. Chang, et al, IAEA Fusion energy Conference, Italy, 2000.

[GP1.157] Tokamak edge E_r studies by turbulence and divertor simulations

Numerical coupling of the divertor code B2(B.~J.~Braams, Next European Torus Technical Report 68 (1987).) and the turbulence code DALF(B.~D.~Scott, Phys. Fluids B 4), 2468 (1992). is pursued. Within this model, space and time dependent transport coefficients (D and \chi) respond to the dynamics of drift wave turbulence. The Braginskii transport model of the B2 code incorporates guiding-center plasma drifts self-consistently and generate E_r shear in the presence of steep pressure gradients. This Braginskii type E_r can enter the turbulence model as a background E \times B shear flow which suppresses the radial flux together with Reynolds stress induced electric fields. As an example of L-H transition, influx at the core boundary is controlled to produce steepening of the edge gradients. ( Y.Hamada et al.), in Proceedings of the 17th IAEA Fusion Energy Conference (IAEA-F1-CN-69/PD, 1998) reveals heat pulse induced L-H transitions after sawtooth events.

[GP1.158] Edge Harmonic Oscillations Produced by Toroidal Velocity Shear

It is shown that a plasma with similar edge density and parallel velocity profiles to that of DIII-D operating the in the Quiescent Double Barrier regime (QDB) is unstable to the parallel velocity shear instability. By means of three-dimensional nonlinear fluid simulations, we find that this system produces turbulence that is radially localized in the vicinity of the parallel velocity gradient and has a distinct toroidal structure. These results bear a great deal of resemblance to the Edge Harmonic Oscillations observed in DIII-D during the QDB discharge. Previously, it was thought that the EHOs were a due to a magnetic MHD mode, yet such structures have not been observed in any one-fluid theoretical models. These results indicate that EHOs may be due to this instability which can only be realized in a two-fluid model.

[GP1.159] Underlying Mode Structure of the Poloidal Spin-Up Instability

The theory of the poloidal spin-up instability^1,2, thought to play a role in the L-H transition in tokamaks, is discussed in detail in this poster. The underlying mode structure and nature of MHD forces acting on the plasma are described with a different perspective than has previously been given. We show that the instability is associated with the growth of an up-down asymmetrical toroidal magnetic field perturbation. This perturbation gives rise to an in-out asymmetrical magnetic tension force and a vertical torque in the poloidal plane. This torque tends to divert an up-down asymmetrical equilibrum toroidal flow into a poloidal flow. The instability growth rate depends on the assumed equilibrium toroidal flow speeds and not directly on the plasma beta. The possibility that the magnetic perturbation and associated ``plasma shift'' might be detected in experiments is examined.

^1 A. B. Hassam and J. Drake, Phys. Fluids B 5(11), Nov. 1993, p. 4022

^2 H. R. Strauss, Phys. Plasmas 2 (4), April 1995, p. 1229.

Part G of program listing