Session 9P - Beam Injection, Extraction, Transport and Targetry W, Insertion Devices, Other Subsystems, Beam Instrumentation (BPMs), Computer Codes X.
POSTER session, Friday morning, May 16
Pacific Ballroom,

[9P.01] The IPNS Accelerator 50 MeV and 500 MeV Transfer Lines

The Intense Pulsed Neutron Source (IPNS) accelerator delivers, with high reliability, an intense, short-pulse 450 MeV proton beam onto a uranium target for the production of neutrons. The 50 MeV and 500 MeV transfer lines carry protons from the Drift Tube Linac (DTL) to the Rapid Cycling Synchrotron (RCS) and from the RCS to the Neutron Generating Source (NGS) target, respectively. Through fifteen years of operation, IPNS operators have discovered tunes for various parts of the DTL/RCS accelerator allowing for continual improvement in average current delivered to the target; however, in numerous cases this has been achieved by moving significantly away from the original design parameters. A new attempt is being made to analyze the lines and develop computer models that can be used to alleviate some of the undesirable features of the present "best tune." In the 500 MeV line, higher order elements will be included in the modeling with the goal of providing a uniform power density profile at the NGS target. This paper describes features of the present lines, and progress-to-date in analyzing and improving them.

[9P.02] H^- Charge Exchange Injection into the NSNS Accumulator,

A scheme for efficient H^- injection into a tilted acceptance phase ellipse at the stripper foil in the FODO cell of the National Spallation Neutron Source (NSNS) accumulator ring is discussed. A 400 \mug/cm^2 carbon foil is chosen for the stripper for a high stripping efficiency and for heating of the foil consideration. Additional schemes to reduce losses due to nuclear and Coulomb scattering at the foil are discussed. Subsequent loss from magnetic field ionization of the residual H^o component is estimated and found to be small compared to nuclear loss. A method for sweeping and collecting the stripped electrons from the foil is presented.

[9P.03] The NSNS High Energy Beam Transport Line

In the NSNS design, a 160 meter long transport line connects the 1 GeV linac to an accumulator ring and provides the desired foot-print. The linac beam has a current of 56 mA and pulse length of about 1 ms. This line consists of forteen 90^\circ FODO cells, and accommodates a 60^\circ achromatic bend, an energy compressor, part of the injection system, and enough diagnostic devices to measure the beam quality before injection. To reduce the uncontrolled beam losses this line has four beam halo scrapers and very tight tolerances of both transverse and longitudinal beam dynamics under space charge conditions. The design of this line will be presented together with input beam parameters and acceptance criteria of the beam at the accumulator.

[9P.04] First Observation of the Deflection of a 33 TeV Pb Ion Beam in a Bent Silicon Crystal

The deflection of an ultra-relativistic, fully stripped Pb(82+) ion beam in a bent silicon crystal has been observed for the first time. The ions were provided by the CERN-SPS in the H4 beam at a momentum of 400 GeV/c/Z. A 60 mm long silicon crystal, bent over 50 mm to give a 4 mrad deflection angle, was used in this experiment. The measured Pb ion deflection efficiencies are comparable to the ones obtained with protons at an equivalent ratio p/Z, and are found to be about 15% for a beam with a divergence of 50 microradians (FWHM). The interaction rate observed in a background counter is reduced by about the same 15% when the crystal is well aligned with the beam. This corroborates further the channeling model, which predicts that channeled ions are steered away from regions of high electron densities as well as from the nuclei in the crystal.

[9P.05] Energy Dependence of Crystal Assisted Extraction at the CERN SPS

The feasibility of extracting particles from a halo of a circulating proton beam has been successfully demonstrated experimentally at the SPS. Although most measurements were obtained at an intermediate energy of 120 GeV, more recently we had the unique opportunity to extract protons from a coasting beam at 14 GeV and 270 GeV, thus exploiting the full available energy range of the SPS. In this report we present a comparison of the measurements at the three energies and a qualitative comparison with the predictions.

[9P.06] Extraction of 22 TeV/c Lead Ions from the CERN SPS using a Bent Silicon Crystal

The extraction of protons from the halo of a circulating beam has been repeatedly demonstrated at the SPS. In a recent experiment a coasting lead ion beam was available at a momentum of 270 GeV/c/Z corresponding to a total momentum of 22 TeV/c per ion and the possibility to extract ultrarelativistic lead ions with a bent crystal could be demonstrated for the first time. We present the experimental challenges, the measurements performed during this experiment and the first results.

[9P.07] Gabor Plasma Lens focossing for LEBT systems

Low energy beam transport (LEBT) of high perveance ion beams suffers from high space charge forces. Space charge compensation reduces the neccesary focussing force and the filling factor of the lenses and therefrom the emittance growth due to aberrations and inner fields. The use of electrostatic lenses is restricted due to decompensation by the electric fields. On the other side magnetic lenses suffer, for high mass ions, from the necessary high magnetic fields and the resulting technical problems. A different approach for a LEBT system is a lens using a static non neutral plasma confined in a magnetic and electrostatic field configuration allowing strong electrostatic focussing together with partial conservation of space charge compensation. Modelling of the plasma in a way that lens aberrations are small is very difficult and the underlying theory is not fully understood. New measurements at low residual gas pressure as well as theoretical work and the results of numerical simulations will be discussed.

[9P.08] An Idea for Selection of Short-Lived Particles by a Focusing Crystal.

An experimental technique for selection of the short-lived particles by means of a focusing crystal is proposed. A target (to produce short-lived's) and a focusing crystal [Baranov et al, NIM B95, 449 (1995)] are to be arranged in such a way that the crystal traps into channeling mode the particles emerging from the region downstream of the target only. The particles emerging from the target directly, cannot be trapped into channeling mode in the crystal. In this way one can trap the decay products of short-lived particles to carry them out of the background; the trapped beam can be bent, e.g., onto the experimental set up. The technique can handle the particles with decay length c\tau down to few micron. The capabilities of the technique, resolution, and efficiency are analyzed.

[9P.09] An Idea for Studying a Multipass Crystal Extraction by the Energy Loss Detector.

We consider a proton extraction from accelerator by a crystal equipped with an energy loss detector. The idea is proposed that the energy loss dE/dz deposited in the crystal by a channeled proton may indicate, whether this proton was extracted in the first pass, or in the subsequent passes; this is a key question in the crystal extraction. In a diffusion mode of extraction, the first passage of protons through the crystal is very close to its surface, at a depth <1\mum. Then an escape of \delta-electrons (knocked out by a channeled proton) from the crystal does essentially modify the dE/dz deposition in the crystal, thus making it to depend on a depth (impact parameter). Hence one may hope to resolve the first and multi passes by observing the dE/dz deposition of the extracted protons in a crystal (the technique is widely known). We present the estimates and simulations for this idea.

[9P.10] Expected Characteristics of the Nuclotron Beams for Experimental Setups

Carring out the experiments planned on external beams of the Nuclotron, a superconducting heavy ion synchrotron, requires the knowledge of their characteristics, such as energy range, particle energy spectrum, kinds of ions, envelope, time structure and others. The presented characteristics are based on the measured parameters of the accelerated beam and the data of the designed extraction system. A possible stretching of the beam extraction energy from the injection to the total one, 6 GeV/amu, as well as one of the main problems of obtaining a smooth-in-time beam on the external target over the range from parts to several seconds, are considered. To transport the extracted beam to the experimental hall, the most part of the existing Synchrophasotron channels should be adapted.

[9P.11] Beam Injection into the Nuclotron

A system for the single-turn injection of 5 MeV/u heavy ions into the Nuclotron is described. The system comprises a superconducting septum-magnet, kick electric plates, beam diagnostic apparatus and magnet correctors. The septum magnet has an iron yoke. The coil and septum made of a hollow superconductor, are cooled with a two-phase helium flow. The magnetic field is 1 T. The electric field and its fall time in the fast kicker are 7 kV/cm and about 100 ns respectively. The beam diagnostics is composed of Faraday cups and multi-wire collector chambers for current and profile measurements over a wide range of intensities. The magnetic correctors in the beam line and Nuclotron ring are used for injection adjustment. The system has been operating since 1992. The experimental results are presented.

[9P.12] Carbon Stripper Foils Used in the Los Alamos PSR

Carbon stripper foils produced by the modified controlled ACDC arc discharge method (mCADAD) at the Institute for Nuclear Study by Dr. Isao Sugai have been tested and used for high current 800-MeV beam production in the Proton Storage Ring (PSR) since 1993. Two approximately 110 \mug/cm2 foils are sandwiched together to produce an equivalent 220 \mug/cm^2 foil. The combined foil is supported by 4-5 \mum diameter carbon fibers attached to an aluminum frame. These foils have survived as long as five months during PSR normal beam production of near 70 \muA on target average current. Typical life-times of other foils vary from seven to fourteen days with lower on-target average current. Beam loss data also indicate that Sugais foils have slower shrinkage rates than other foils. Equipment has been assembled and used to produce foils by the mCADAD method at Los Alamos. These foils will be tested during 1997 operation.

[9P.13] LANSCE Short-Pulse Spallation Source Target Upgrade

A project to upgrade the short-pulse spallation target at LANSCE is in progress. This upgrade will reduce the target change out time from about a year to about three weeks and permit the current to be raised to 200 mA. The project includes a new target-moderator-reflector system, improved auxiliary systems, remote handling capability, and a new service building. The project has also supported calculations and experiments for target neutronics, rod-target thermohydraulics, and corrosion-related measurements in a proton beam. Results and progress to date will be presented.

[9P.14] Overview of the Bump-Magnet System at the Los Alamos Proton Storage Ring

An upgrade program for increasing the stored beam current in the Proton Storage Ring is presently under way. A part of the upgrade is the design and installation of a four-magnet beam-bumping system used for phase-space painting and minimizing interaction of the stored beam with the injection stripper foil. This paper describes the bump-magnet system including the relevant beam requirements, magnet specifications, power-cable specifications, pulsed-modulator requirements, and beam-tube eddy-current effects. The magnets are ferrite window-frame magnets with saddle windings. The series-pass pulsed modulators are programmable both in rise and fall time as well as amplitude. The peak current can be varied between 50 and 300 A. The pulsed-current rise-time is fixed at 1 ms, and the linear fall-time during which beam is injected into the ring can be varied between 0.5 and 1.5 ms.

[9P.15] Design and Simulation Studies of a One-tenth Scale Final Focus System for Heavy Ion Fussion

A scaled test of a final focus lattice for Heavy Ion Fusion (HIF) is planned at LBNL. The test parameters were set by scaling the length dimensions of the envelope equation by one tenth while maintaining the generalized perveance. The values to be scaled were taken in large part to be those of the HIBALL-II final focus system.(H. Wollnik, KfK-3840, Kernforschungszentrum Karlsruhe, 1985) The planned experimental system will focus a 120 keV Cs^+ beam to a scaled radial spot size of 0.25 mm. Tracking studies of the tenth-scale system have been performed at NSCL using a version of COSY INIFINITY(M. Berz, MSUCL-977, Michigan State University, 1995) modified to include a linear space charge force. A description of the planned experimental system, the beam parameters, and simulation results will be presented.

[9P.16] Tracking Studies and Performance Simulations of the NSCL A1900 Fragment Separator

At the NSCL, secondary beams of often short lived radioative nuclei are produced by the technique of projectile fragmentation where a primary beam impinges on a thin target to produce a broad spectrum of isotopes with near-beam velocity. As a major element of a recently funded upgrade of the NSCL facility, an increased capacity fragment separator used to select a particular isotope will be constructed. The key features of the new fragment separator include high rigidity with a K value of 1900 and large acceptance with a solid angle of 8 msr, momentum acceptance of \pm3% and an energy resolution of 0.1%. Tracking studies and machine simulations have been performed using MOTER, DIMAD, and COSY INIFINITY to verify the optical stability and performance of the lattice. The results of these studies, including simulations of magnet misalignment and magnetic field errors, are presented in this paper.

[9P.17] Measurements on Injection Property in HIMAC Synchrotron

The beam intensity stacked by the multiturn injection method and the life time in HIMAC synchrotron were considerably decreased above 600 micro-amp of injection current of alpha ions with 6 MeV/n of the energy, mainly due to the space charge effect. In order to obtain higher beam intensity, therefore, the injection property has been investigated at various injection currents as follows. Total and partial efficiency of the multiturn injection. (2) Tune shift and spread in coasting and bunched beams. (3) Tune dependence of stacked intensity and life time. The paper will report the experimental results.

[9P.18] Predicted Foil Temperatures in the Brookhaven NSNS Accumulator Ring

An investigation has been carried out into the peak equilibrium stripping foil temperatures that could be expected in the 1 GeV NSNS Accumulator Ring proposed by Brookhaven National Laboratory. A Graphite foil is assumed. Computed foil temperature distributions on the foil's surface would be presented, as well as the predicted relationships between foil temperature and quantities such as the average number of recirculated proton hits, linac current, and foil mass per unit area used.

[9P.19] An Electromagnetic Micro-Undulator with Millimeter-Size Period

Microfabrication technology using the LIGA (a German acronym for Lithography, Electroforming, and Molding) process offers an attractive alternative for fabricating percision devices with micron-sized features. One such device is a mm-sized micro-undulator with potential applications in a table-top synchrotron light source for medical and other industrial uses. The undulator consists of a silver conductor embedded in poles and substrate of nickle-iron. Electromagnetic modeling of the undulator is done using the eddy-current code ELEKTRA. The silver and nickle-iron are treated as different vector-potential regions and the surrounding ``air" is treated as a combination of vector-potential and magnetic scalar-potential regions. Computations predict a field pattern of appropriate strength and quality if the current can be prevented from being shunted from silver by the nickle-iron poles either through insulation or through slotted poles. The design of the undulator along with the! computational results are discussed.

[9P.20] A Superconducting Wiggler Magnet for the NSLS X-Ray Ring.

The superconducting 5 pole, 5 Tesla wiggler which has been operating in the X-17 straight section of the x-ray storage ring at the National Synchrotron Light Source (NSLS) since 1989 will soon be replaced by a new wiggler being built by Oxford Instruments with lower operating costs, higher reliability, and greater performance. The new wiggler has three modes of operation: the full wiggler with 11 poles producing 3.3 T, the partial wiggler with 5 poles at 4.7 T, and the wavelength shifter with a single pole producing 5.5 T. The full wiggler, optimized for the digital subtraction radiography program, will produce the same x-ray flux at the 33 KeV iodine K-edge as the existing wiggler operating at 4.7 T but will reduce the higher energy harmonics delivered to the target. The partial wiggler will deliver the same flux for solid state physics experiments as the existing wiggler, and the wavelength shifter will provide an elliptically polarized x-ray beam that is not now available.

[9P.21] Magnetic Measurements on an In-Vacuum Undulator for the NSLS X-Ray Ring

Magnetic measurements have been performed on the In-Vacuum Undulator (IVUN)(P.M. Stefan et al., this Conference), built jointly by BNL, SPring-8 and Sumitomo for the NSLS X-Ray Ring. The IVUN magnet has a Halbach-type, pure-permanent magnet structure with a very short period of 11 mm and a minimum gap of only 3 mm. Results of magnetic measurements utilizing Hall probe and pulsed wire techniques will be presented and compared.

[9P.22] Siberian Snakes for Electron Storage Rings

Applying a Siberian snake to obtain longitudinally polarized electron beam is discussed. Depolarization effects are analysed and spin matching conditions to decrease the depolarization are derived. Snake schemes which provide minimal depolarization rate are proposed.

[9P.23] The Magnetic Design of a High Field Permanent Magnet Multipole Wiggler for the SRS.

Two new insertion devices will be installed as part of the Daresbury SRS upgrade project. The devices are multipole wiggler magnets with a peak field of 2 T. This paper describes the complete magnetic design of these permanent magnet devices which has been carried out in both 2 and 3 dimensions. The design has been optimised to generate the highest fields with the shortest possible period to fully utilise the limited space available in the SRS.

[9P.24] Resorting the NIST Undulator using Simulated Annealing for Field Error Reduction

We have used a simulated annealing algorithm to sort the magnets in the NIST undulator in order to optimize the spectrum of light emitted. This algorithm sorted the order of the magnets in order to minimize the magnetic field error at each pole, and to minimize the net angular deflection of the electrons passing through the undulator. In the original order, the RMS magnetic field error was more than 2.5%, and there was a maximum angular deflection of more than 400 microradians. After the sorting, the RMS magnetic field error was less than 0.25%, and there was a maximum angular deflection of less than 10 microradians. We show both the expected spectrum emitted from the undulator in its original order, and also the improved spectrum from the undulator after optimization.

[9P.25] NIST Undulator Magnetic Field Characterization

A 3.64 m undulator was constructed by the Brobeck Division of Maxwell Laboratories for FEL experiments at NIST in Washington, DC. The Duke University FEL Lab has since acquired the undulator for use as a soft x-ray source. We report on our effort to transform the undulator into a high performance soft x-ray insertion device through careful characterization of the existing magnet blocks, sorting and trimming.

[9P.26] Recent developments of Insertion Devices at ESRF

The ESRF is presently operating 41 segments of Insertion Devices. 75 (25producing variable polarization between 0.5 and 10 keV and 3 assymetric wigglers optimized for circurlarly polarized radiation between 20 keV and 500 keV. Almost all devices are made of permanent magnets. They have been designed using an internally developed 3D magnetostatic code. The field correction is made by using iron shims placed at the surface of the blocks, whch eliminates the integrated multipole and ensures maximum brilliance on all harmonics. Undulators are assembled in 1.6 m module phased with respect to each other with a newly developed magnetic structure. As a result, a record brilliance in the 1E20 Photons/sec/.1

[9P.27] Computing 3D Magnetic Fields from Insertion Devices

A 3D magnetostatics computer code optimized for Undulators and Wigglers is described. The code uses a boundary integral method and makes extensive use of analytical expressions for the field and especially field integrals along a straight line. Magnetic field boundary conditions are treated by the mirror approach. The code outperforms currently available finite element packages in the area of simple data input, cpu time of the solver and accuracy reached for the estimation of field integrals. It is written in C++ and takes advantage of object-oriented programming. The code is interfaced to Mathematica (Mathematica is a registered trademark of WolframResearch, Inc.). Pre- and post-processing of the field data is done in the Mathematica Language. These features make the code an effective tool for the development of permanent-magnet, hybrid and electro-magnet undulators and wigglers for use in synchrotron radiation sources and free-electron lasers, as well as for solving other relevant problems of magnetostatics. The code has been extensively benchmarked with respect to a commercial finite element code. All ESRF Insertion Devices built during the last 4 years have been designed using this code or an older version.

[9P.28] Development of an In-Vacuum Minipole Undulator

An in-vacuum minipole insertion device is currently being developed in collaboration between SPring-8 Insertion Device Group and the National Synchrotron Light Source (NSLS). The magnetic array is constructed by SPring-8 and it will be installed in a chamber with mechanical parts in the X-ray ring (E=2.584 GeV) at the NSLS. The device is made of permanent magnets with 31 periods and the length of the period is 11mm. It is to produce the fundamental radiation at 4.6 KeV which will be mainly used for X-ray photo-correlation spectroscopy (XPCS), and modest value of deflection parameter (K=0.7@3.3mm gap) enables higher harmonics to be used for a variety of experiments. We describe technical difficulties of constructing this type of device as well as the outline of our collaboration.

[9P.29] Spontaneous Emission Properties of a Novel Short-Period Twisted Undulator

A novel short-period undulator scheme is developed. The geometry looks like helical transformation applied to original linear undulator structure and provides a combination of fast and slow oscillations of the electron beam. Undulator design, magnetostatic fields and spontaneous emission radiation are analysed. The following unusual properties of the radiation are considered: i) reduction of relative content of higher odd harmonics as the "slow" helical field increases; ii) radiation enhancement as the number of helical turns increases; iii) spectral line splitting and intensity adjustability along with circular polarisation of the radiation for the short-period twisted structure.

[9P.30] Design of an Elliptical Undulator and X-ray Beam Line at DSR of RIKEN RI Beam Factory Project

According to the requirement of the X ray - RI collision experiment at DSR, which is proposed in the RIKEN RI beam factory project, an elliptical undulator is designed. It has 200-periods of permanent magnets and the total length of 6 m. In a period, four magnets are laid in three rows for both side to make vertical and horizontal magnetic field. Parameters K_x, K_y and the polarization are changed by adjusting the gap width and the phase between rows. The tuning range of both K values is 0.3 - 2.0 and any polarization is chosen between -1.0 and 1.0. Obtained X-ray energy is about 30 - 1000 eV for the first harmonic radiation with the electron beam energy of 0.3 - 2.5 GeV in the DSR. The X ray extracted from the undulator is tranported to an X-ray beam line and then it is injected again into another ring of the DSR to make collision with RI beams. The X-ray beam line consists of an X-ray spectrometer and the mirror system. The spectrometer is also designed so as to get high resolution and high transmission efficiency.

[9P.31] Operation of Insertion Devices in ELETTRA and Plans for Future Devices

ELETTRA is presently operating with 5 insertion devices (IDs), comprising 4 undulators and 1 multipole wiggler. The operational performance is summarised, highlighting recent work on minimizing closed orbit distortions due to the undulators by means of correction coils which are set automatically as a function of gap setting. The algorithm used to calibrate the coil currents is described, as well as its implementation and the results achieved. The practical limits to the orbit correction, and the implications for ID users are also assessed. Future devices presently under study include an in-vacuum mini-gap undulator and several devices capable of generating both linear and circularly polarized radiation. The predicted performance of these devices is discussed and the present status is summarised.

[9P.32] Design of an Electromagnetic Elliptical Wiggler for ELETTRA

An electromagnetic elliptical wiggler has been designed and is presently under construction to provide a source of circularly polarized VUV/Soft X-ray radiation with variable helicity for the ELETTRA facility. A novel feature of the design is that it employs electromagnets to generate both horizontal and vertical fields, thus allowing a wide range of field strengths and hence both undulator and wiggler operating modes. A second feature is that the structure is completely open in the horizontal plane for ease of access for magnetic measurements, and for installation in the storage ring. The vertical field is d.c. powered while a flexible power supply permits the horizontal field to be powered in either of 3 modes : d.c., trapezoidal from 0.1 to 1 Hz, and sinusoidal from 10 to 100 Hz for helicity switching. In this paper we summarize the main design aspects, including the 3D magnetic field modelling and mechanical design of the magnet, as well as the main features of the power supply and the control system. The separate system for dynamic correction of residual field integral errors is also considered.

[9P.33] Linear Beam Dynamics Effects of Three Dimensional Static Magnetic Fields of Insertion Devices at SRRC

To understand the effects of the insertion devices on beam dynamics, Hamiltonian equations of charged particles in the presence of the insertion devices have been studied. Fields with insertion devices are considered to be periodic in the longitudinal direction with period length \lambda_s. The magnetic fields of the different types of magnet structure, namely AGID, APID and EPU, are derived and discussed. The linear beam dynamics effects for different kinds of insertion devices can be obtained directly from the canonical equations of the Hamiltonian mechanics.

[9P.34] Magnet Sorting Algorithms for a Prototype of EPU for SRRC

The Synchrotron Radiation Research Center (SRRC) is constructing a prototype of Sasaki-type elliptically polarizing undulator (EPU) characterized by its four longitudinal movable magnetic arrays, whose shifting determines the polarization of synchrotron radiation. A total of 280 pure NdFeB blocks with square cross-section of 40 mm x 40 mm and thickness of 14 mm will be magnetically energized into two types identified by the main field direction. To minimize field errors, the blocks are sorted and assigned appropriate locations on the arrays. Due to the special symmetry of the blocks, for instance the 40 mm x 40 mm square face, and arrays structure, the orientation and locations of one type of blocks can be assigned freely. However the cutting on one pair of opposite angles on each square face for rigid clamping reduces the freedom of permutation. Moreover, the perturbation of the field from the shifting of arrays must be taken into account. The authors would like to present the sorting algorithm and its contribution to field performance.

[9P.35] Insertion Devices Control Development at SRRC

Insertion devices are the most important gadget of the third generation Taiwan Light Source at SRRC. These insertion devices include the turn-key system and in-house developed system. The corresponding control configurations are different due to historical reason. However precision, fastness, simplicity, and uniformity in insertion devices control are the most desirable from practical viewpoint. The proposed uniform control systems are first applied successfully to undulator U10 and experimental one meter long adjustable polarizing undulator. The new system provides several features which are not avaliable in existed insertion device control system. The residual field compensation can be done with 100 times per second. The compensation table is updated from the server of the control system. The software design supports the beamline users to adjust gap after granting permission from the control room operator. The detailed descriptions about the features and performances will be presented in this report.

[9P.36] Design and Construction of a 1-MW, 352-MHz RF Test Load

A 1-MW, 352-MHz rf load was built at Argonne National Laboratory for performance testing the klystrons used as final rf amplifiers at the Advanced Photon Source. The load utilizes four CERN-type 300-kW coaxial water loads which are fed from a single WR2300 wave-guide using a four-way power splitter consisting of a magic-t and two WR2300 waveguide-to-dual-6\frac18" coaxial transitions. The load system is cooled utilizing deionized water at a nominal flow rate of 160 GPM. The entire load system is mounted on a wheeled carriage which allows for rapid relocation to specific areas of the APS klystron gallery. The metering and interlock system will be described. The load has logged approximately 250 hours of use and has demonstrated accuracy in flow and temperature measurement sufficient to allow calorimetric rf power measurement.

[9P.37] Design and Construction of the Advanced Photon Source 352-MHz RF System Switching Control

An rf system switching control system has been designed and built at Argonne National Laboratory to provide the capability of rapidly switching individual Advanced Photon Source rf systems off-line in the event of a failure, or to perform necessary repairs and preventive maintenance. Twelve possible modes of operation are possible, which allow for complete redundancy of the booster synchrotron rf system with up to two storage ring rf systems to be completely off-line or one used as a power source for an rf test stand. A programmable controller is used to send commands to intermediate control panels which interface to waveguide switches and phase shifters, rf cavity interlock and low-level rf distribution systems, and klystron power supply control for rapid reconfiguration of the rf systems in response to a mode selection command. Mode selection is made locally by a keyswitch system. The programmable controller also monitors for hardware malfunction and guards against ``h! ot-switching'' the rf systems. The rf switching control system is monitored via the EPICS control system status check.

[9P.38] Supports and Installation System of the RHIC Superconducting Magnets

The Relativistic Heavy-Ion Collider that is currently under construction at Brookhaven National Laboratory is composed of hundreds of superconducting magnets. A careful study was done in order to support and install these magnets inside the RHIC tunnel systematically and efficiently. A basic systems-approach was pursued and primary consideration was given to develop a system that would not be only both economical and efficient but also well-suited to a fast-paced production environment. This report will present a description of the design of the magnet stands, and the magnet transport and installation system, the procurement and the fabrication phase, and then finally, the experience gained in implementing the system. In summary, the system turned out to be very efficient and cost-effective far beyond our expectations.

[9P.39] Proposed Systems Layout of the Low-\beta Insertions for the LHC Experiments

The final focus in the LHC experimental insertions is achieved with an inner triplet together with a tuning section of superconducting quadrupoles. Besides providing high gradients in a sufficiently wide aperture to accommodate large beam size, the superconducting low-\beta quadrupoles must sustain considerable heat loads from secondary particles, generated in particular in the high luminosity ATLAS and CMS experiments. In these insertions, the triplets are located in heavily shielded areas with difficult access. In the other two experiments, ALICE and LHC-B, the triplets and the tuning sections share the available space with the injection equipment. In the low-\beta triplets the counter rotating beams travel in a single beam tube, so that conditions of beam separation must be respected both at injection and collision. In this report we present the proposed systems layout of the experimental insertions for the LHC, and review the requirements for the superconducting magnets.

[9P.40] Higher Order Modes Power Loss in the Vertical Separators at CESR

At CESR the two 2.7 meter long vertical separators are used to separate the two beams vertically at the symmetric point in the north and are also used for luminosity tuning. Each separator provides a 1 mrad kick for a 100KV differential voltage between the electrodes. There is a gap of 1.4 inches between the high voltage electrodes ends and the ends plates of the outer tank to avoid high voltage breakdown. The vertical separation of 55 mm between the electrodes is 4 times smaller then the electrodes width and is only 10% wider then the normal CESR beam pipe vertical dimension. Therefore, as the beam passes through the separators, the 1.4 inches gap between the electrodes ends and the ends plates, is the main cause of the higher order modes power loss. An accurate calorimetric system has been built to measure the total power dissipated in the separator. Using this system, which is able to measure the power to whitin \pm3%, we were able to measure the loss factor k and study the power distribution to each component of the separator.

[9P.41] Photocurrents in Electrostatic Separators at CESR

At CESR a pair of vertical separators is used to separate the two beams verticaly at the symmetry point, in the north, of the interaction point in the south. They are 2.7 meter long and each one is providing a 1.0 mrad kick for a differential voltage of 100KV between the electrodes. One side of the separators is exposed to the high flux of synchrotron radiation from a soft bend, 140 meter radius, magnet and a hard bend, 34.8 meter radius, magnet. The radiation generates large amount of photoelectrons which are converted to a large photocurrent by being drawn to the positive voltage electrode. The photocurrent is 1.2-1.5 ma DC which is 1 percent of the electron or the positron currents. It triggered, few times a day, a partial high voltage drop which caused a vertical beam blow up and beam loss. In addition the photocurrent increased the heat load of the positive electrode by 25 percent. In the paper we will show how we were able to suppress the photocurrent almost to zero. As a result we have seen an increase in the life time of the beams and as well an increase in the luminosity.

[9P.42] REC Quadrupole's Beam Pipe Temperature Control at CESR

In CESR the clearance between the beam pipe and the REC magnet is only 1mm. The 160 cm beam pipe in this section is sloped and has steps to mask the detector from radiaton. During high energy operation the beam pipe temperature increses due to synchrotron radiation and higher order modes power loss and effects the temperature of the REC magnet via convective and radiative heat transfer. The temperature change is proportional to the beam current. This causes an irregular time dependent change in the REC magnetic field strength, resulting in an irregular betatron tune shift of about \Delta Q=0.011/^\circC for each quadraupole. To prevent the temperature changes of the beam pipe in this section, a sensitive temperature control cooling system was developed. The temperature of the beam pipe is stabilized within \pm 0.1^\circC. The loss parameter of the sloped pipe and power dissipated by synchrotron radiation was calculated from temperature measuremants and used to estimate performance at higher current.

[9P.43] Improved Measurement of Electric Field Uniformity in Horizontal Electrostatic Separators

An improved technique for measuring the uniformity of the electric field between the plates of a electrostatic separator was developed and applied to the measurement of a horizontal separator at CESR. The effect of stray charge on the previous measurements was found to be limiting the accuracy. Appropriate shielding has eliminated the problem.

[9P.44] Commissioning and Performance of Low Impedance Electrostatic Separators for High Luminosity at CESR

Installation and commissioning of new horizontal electrostatic separators, designed for high current, high luminosity e^+ e^-beams at CESR, was completed in late 1996. To obtain higher luminosity CESR is increasing the stored beam current to a total 1 ampere. The new separators were designed to minimize the impedance seen by the beam, accommodate `pretzeled' orbits, have lower spark rate and generally better reliability than the previous separators. In this paper we describe the measured beam power absorbed by the separators, spark rate, photocurrents, and other performance data.

[9P.45] Industrial controls for DESY utilities using PLCs and EPICS

The infrastructure of large particle accelerators requires utilities including power, water cooling and air conditioning. The utilities run continuisly in the background but problems in critical systems may cause long interuption in the operation of the accelerators and of the HEP detectors. Utilities require continuous supervision with data logging and an automatic alarm system. DESY started an upgrade project using industrial controls based on PLCs. The first system targeted was the water cooling system of HERA, a storage ring of 6.3 km circumference for protons and electrons. The aim was improve the running conditions for HERA and to reduce the start-up time after breakdowns of the water cooling system. The first step was to integrate PLCs into the switchboard plants and to cross-link them. The second step was to add a supervisory control system. The control program EPICS was chosen. Data archiving, the display server and the alarm server are done in EPICS. The terminals are cross-linked by the DESY ETHERNET network. This control system has been running for nearly two years with good performance. DESY is now expanding the system to include the 10 kV substations and the air conditioning plants.

[9P.46] Transverse and Longitudinal Impedance Measurements for the RKTBA Induction Accelerating Gap

An induction accelerating gap design is being studied for Relativistic Klystron Two Beam Accelerator (RKTBA). The accelerating gap has to satisfy the following major requirements: hold-off of the applied 100 kV accelerating voltage pulse, low transverse impedance for beam break up minimization, low longitudinal impedance at the beam modulation frequency to minimize power absorption. To optimize the gap design various gap geometries, materials and novel insulating techniques will be explored. We shall report on the experimental effort to evaluate the RF properties of the accelerating gaps in a simple pillbox cavity structure. The experimental cavity setup was designed using the AMOS, MAFIA and URMEL numerical codes. We shall present results of the gap cavity transverse impedance measurements using the two wire measuring system. This will include also longitudinal impedance above beam tube cut off frequency using a single wire measuring system.

[9P.47] Stack Insulator Induction Gaps

Stack insulators, with alternating layers of insulating material and conducting film, have been shown to support high gradient electrical field gradients. We are investigating the application of the Stack Insulator to the design of the Relativistic-Klystron Two-Beam Accelerator program. The rf properties of accelerator gaps using stack insulators, particularly the impedance at frequencies above the beam pipe cutoff frequency, are being investigated. Having low impedance is critical for the Relativistic-Klystron Two-Beam Accelerator applications where a high current, bunched beam is transported through many accelerating gaps. Properties of Stack Insulators and the gap designs will be presented.

[9P.48] Permanent Magnet Assembly Tooling for the 8 GeV Transfer Line and Recycler Ring at Fermilab

The beam transfer line between the Fermilab Booster and Main Injector and the Recycler antiproton storage ring are constructed using permanent magnet ferrite bricks surrounding a steel pole and housed inside a steel flux return shell. The transfer line consists of 51 dipoles, 67 gradient magnets, and 8 quadrupoles. The Recycler ring consists of approximately 350 gradient magnets and 60 quadrupoles. Positioning and handling large steel plates lined with magnetized ferrite bricks pose several challenges to the design of assembly tooling. Large attractive forces between mating magnet sub-assemblies must be controlled in order to minimize personnel hazards. Position of sub-assemblies must be precise to allow insertion of mechanical fasteners and to maintain consistent magnetic performance in all similar magnets and provisions must be made for magnet disassembly in the event that repairs or adjustments are indicated by magnetic measurements. This paper describes and illustrates the assembly tooling designed and fabricated to facilitate construction of all of the nearly 500 dipole and gradient magnet assemblies in the 8 GeV transfer line and Recycler ring.

[9P.49] A Distributed Monitoring and Control System

A monitoring and control system designed and implemented at Fermilab's magnet test facility is presented. The system consists of a set of configurable communicating distributed objects. It includes graphical user interfaces, archivers, a data acquisition subsystem, and direct control components. The system is open and its functionality can be altered by: a) selecting modules that plug into an event-based software bus, b) developing new modules with help of the existing APIs to access system resources, and c) modifying system configuration data. The article presents the system architecture, discusses its unique features, and describes applications of the system to control cold tests of superconducting accelerator magnets.

[9P.50] Pulsed Magnetic Field Measurement System

Methods for measuring magnetic fields in a pulsed magnet typically employ induction methods or the Hall effect. The interpretation of these measurements becomes difficult for frequencies above audio frequencies. Also these methods have problems if the field is not uniform, for example when the fringe fields of the magnets are important. An alternative measurement method, developed for the next generation of fast kickers at FNAL makes use of interferometer techniques. The measurement system is a phase bridge circuit operating at X band in which one arm of the bridge is a ferrite waveguide passing through the field region of the kicker. The kicker field changes the mu of the ferrite, resulting in a measurable phase delay in that arm of the bridge. This method gives a simple single measurement of the integrated field without involved corrections e.g. correcting for reflections and transit time effects in the pickup coil. The measurement of pulsed fields with this method have resulted in 1% accuracy and time resolution of 50 nsec over a 3000 nsec pulse.

[9P.51] Resonant Ring For Testing of Accelerator RF Windows

A klystron-driven resonant ring has been designed and assembled at the Los Alamos National Laboratory for use in the Accelerator Production of Tritium Project (APT). The ring was built to test RF windows for the 700 MHz section of the APT accelerator. The ring has been designed to apply an effective power of approximately 1 MW on test windows. Details of ring design, operation and performance will be presented.

[9P.52] Beam Expansion with Specified Final Distributions

The formation of nearly uniformly distributed beams has been accomplished by the use of multipole magnets. Multipole fields, however, are an inappropriate basis for creating precise distributions, particularly since substantial departures from uniformity are produced with a finite number of multipole elements. A more appropriate formalism that allows precise formation of a desired distribution is presented. Design of nonlinear magnets for uniform-beam production and the optics of an accompanying expansion system are presented.

[9P.53] Development of a Fast Traveling-Wave Beam Chopper for National Spallation Neutron Source.

High current and severe restrictions on beam losses, below 1 nA/m, in the designed linac for the NSNS require clean and fast (with the rise time from 2% to 98% less than 2.5 ns to accommodate a 402.5 MHz beam structure) beam chopping in its front end, at beam energy 2.5 MeV. The present Ramp;D program includes both modification of the existing LANSCE coax-plate chopper to reduce parasitic coupling between adjacent plates, and development of new traveling-wave deflecting structures, in particular, based on a meander line. Using analytical methods and three-dimensional time-domain computer simulations we study transient effects in such structures to choose an optimal chopper design.

[9P.54] Design of Quasi-Travelling Wave Pinger Magnet for Beam Diagnostics on the Advanced Light Source

A beam diagnostic tool to modify single bunch orbits in all four quadrants is proposed for measuring various machine physics parameters at the Advanced Light Source (ALS). Quasi-Travelling Wave Pinger magnets were chosen to provide programmable bipolar horizontal and vertical kicks of sufficient duration while providing negligible deflection on subsequent beam revolutions in the storage ring. This magnet technology, originally investigated at the SSC(D. Anderson and L. Schneider, "Design and Preliminary Testing of the LEB Extraction Kicker Magnet at the SSC", Proceedings of 1993 Particle Accelerator Conference, May 1993, pp. 1354-6.), provides a cost-effective method of achieving the moderately fast pulse requirements of the pinger application. The design of the pinger magnet and associated pulsed power drive unit will be presented. Electrical response results of initial pinger magnet prototypes and ceramic beampipe coatings will also be given.

[9P.55] TiN Coating of Accelerator Beamline Chambers

One of the problems encountered in many high-power rf systems is multipactoring inside vacuum cavities. The potential for multipactoring occurs whenever the secondary electron emission (SEM) coefficient of the surface exceeds unity. The secondary electtron emission coefficient of titanium-nitride is always less than unity. Therefore, a TiN coating can reduce multipactoring and also reduce photoemission electron from beam-pipe surfaces. The TiN film is very stable. A new technique is being explored at LBNL that will allow an efficient way to coat differently shaped surfaces. In this technique, rf-induction discharge with an exposed Ti induction antenna is used. Tests are being performed using argon, nitrogen, and a mixture of argon/nitrogen gases. Results of this testing will be presented.

[9P.56] Breakdown Studies for Induction Accelerators Gaps under Burst Mode Operation

As part of a feasibility study of accelerators that would enhance radiographic imaging we are looking at rapid burst capability of induction accelerators. The voltage hold off capability for the insulators used in the induction gaps under these conditions is not known. If the pulse separation is under a few microseconds we are concerned that plasma generated by the early pulses will effect the standoff for later pulses. We have started tests that study these effects, and will report on the results. We will also report on vacuum breakdown levels for the electrodes under these conditions. Early tests indicate that the level for a four-pulse train of short pulses with 0.5 microseconds separation is close to that for a single pulse.

[9P.57] Ramping Efficiency Studies in the LNLS Synchrotron Light Source

The 1.37 GeV LNLS UVX electron storage ring is injected from a 120 MeV LINAC. In order to minimise current loss, orbit and tune corrections have been implemented along the energy ramp. In this report, we present a description of the energy ramping operational scheme, performce, orbit and tune corrections and efficiency optimisation.

[9P.58] Power Factor Correction at MIT-Bates Linear Accelerator Center with Pulsed Loads of up to 180\thinspace MW Peak (2.7\thinspace MW Average)

Recent changes in electrical loads at MIT-Bates have increased power levels and energy usage while adversely affecting the overall power factor of the facility. The latest contract for power and energy calls for MIT-Bates to pay for power factors lower than 0.9 lagging. A study revealed that power factor correction equipment could reduce our energy costs by about 10\thinspace %. Due to the fact that MIT-Bates has 12 pulsed klystron loads that operate at varied repetition rates and pulse widths, it was determined that the power factor correction would be best done at the 23\thinspace kV level of the incoming line rather than at the 480\thinspace V level. Additional design concerns required that a study of operating conditions at the 23\thinspace kV level be performed to verify that the harmonics developed as a result of the pulsed nature of the MIT-Bates transmitter loads were reasonable. This report describes the measurements taken and the resulting power factor correction system design. The pay back time of the designed, constructed, and installed equipment is calculated to be less than 9 months under normal operating levels. The equipment will be installed in 1997.

[9P.59] Harmonic Resonance Analysis for PEP II Power Factor Control Upgrades

Recent upgrades to the high voltage utility distribution network at the Stanford Linear Accelerator Center have been accompanied by the installation of a large number of power supplies associated with the PEP-II B Factory project. These power supplies include a diverse assortment of single and three phase units, in two, six and twelve pulse configurations, with chopped, pulsed and continuous loading. Viewed as harmonic power sources in a range from a hundred to several kilohertz, they have the potential to be in resonance with the utility system network, a condition to be avoided. This paper analyzes and evaluates these resonance conditions with a view toward adding electric power factor correction upgrades to achieve substantial cost savings associated with power factor penalty avoidance. Similar studies and upgrades at SLAC in the past have reduced electric power costs over time by several hundred thousand dollars, thus providing the incentive to evaluate the recent upgrades to the PEP-II utility network.

[9P.60] A Dynamic Local Bump System for Producing Synchrotron Radiation with an Alternate Elliptical Polarization

To facilitate high sensitivity soft-X-ray magnetic circular dichroism experiments, we have developed a dynamical local bump system at the SRRC storage ring. This system was devised to vary dynamically the vertical slope of electron beam in a bend magnet, producing, in the electron orbit plane, soft-X-rays with an alternate ellipitical polarization. The local bump was created by using two pairs of vertical correctors located on each side of the bend magnet. Bump strength coefficient was obtained from both calculated estimation and measured beam response matrix. Control electronics for proper bump strength settings was designed to incorporate the existed orbit corrector function. Corresponding graphic user interface was implemented so that bump amplitude can be easily adjusted. Performance of this system is presented. Disturbance on the stored electron beam orbit was observed while flipping of corrector polarity during EPBM operation. A local feedback loop developed to eliminate such disturbance on other beamlines is also described.

[9P.61] Statistical Analysis of Cavity RF Faults

During commissioning of the CEBAF accelerator, it was found that cavities could not be operated reliably at the gradients achieved for short periods during individual cavity commissioning. The principal hypothesis for the cause of the faults seen is charging of the cold ceramic RF window, which is 7.6 cm off the beam axis. Beginning in February 1995, most RF systems faults were automatically logged. Simple statistical analysis of the accumulated fault data was first applied in July 1995, with a substantial drop in fault rate recorded. The intent of the analysis was to predict the gradient for each cavity at which it would fault once every ten days, leading to a fault rate for the machine of about 33/day (330 cavities). This analysis method was pursued through July 1996, with substantial benefit. Cavity gradients were increased for the following six months to check the limits set, and fault rate increased. The methods used for the analysis of the faults recorded between February 1995 and December 1996 will be presented. Results of the analysis fall into a few categories, and typical cavity results will be presented for each.

[9P.62] Comparison of Cavity Input Q Measurements via Power Balance

Cavity input Q has been measured on each of the 330 cavities in the accelerator using three methods. Time decay measurements were taken during cryomodule commissioning, as were bandwidth Q measurements. Bandwidth Q measurements were repeated during July 1995. The third determination is made as part of an automated tuning program.(M. Chowdhary et al., Proceedings of the 1995 PAC, 2268.) The last often gives results which are substantially different from the first three values. Comparisons of the four sets of data will be shown. These comparisons led to a decision to cut the autotune data set at +/-30% of the time decay data. The means of the resulting autotune data and the time decay data are then used to calculate RF power demands due to beam loading, and these results compared with measurements made with the highest power levels obtained to date, 500 kW as of this writing. To date, the correlation between calculated and measured values is not significantly different---not too surprising given the data cut cited. Analysis continues so as to minimize RF setup time with changing energy and beam current requirements, constrained by the need for high availability and minimum power bill.

[9P.63] Interactive Troubleshooting Guide for Accelerators

Modern accelerators face the challenge of supporting increased machine complexity and higher levels of utilization while relying on downsized maintenance and support groups. To improve system availability, reduce reliance on system experts and provide a systematic approach to problem solving, an interactive troubleshooting system has been implemented for the CEBAF injector at Jefferson Lab. The guide uses a tree structure with hypertext links to trace problems from a set of symptoms through a series of diagnostic tests to a specific corrective action. This guide is used in conjunction with an active parameter monitoring system, which is part of the EPICS control system tool kit, which generates operator alarms when injector rf or magnet parameters fall outside pre-set windows. In this way, operators are given immediate feedback when injector components vary from their standard values and a systematic guide is provided on how to correct the problem.

[9P.64] A Method of Producing Surface Conduction on Ceramic Accelerator Components Using Metal Ion Implantation

An important technique used for the suppression of surface flashover on high voltage DC ceramic insulators as well as for RF windows is that of providing some surface conduction to bleed off accumulated surface charge. We have used metal ion implantation to modify the surface of high voltage ceramic vacuum insulators to provide a uniform surface resistivity on the order of 10^10 ohms per square. A vacuum arc ion source based implanter was used to implant Pt in ceramic surfaces at about 130 keV using doses of up to more than 5 \times 10^16 ions/cm^2. Tests were performed both on small ceramic test coupons and on the inside surface of a ceramic accelerator column 25 cm I.D. by 28 cm long. Here we describe the experimental setup used to do the ion implantation, and summarize the results of our exploratory work on implantation into test coupons as well as the implantation of the ceramic column.

[9P.65] Runtime Accelerator Configuration Tools at Jefferson Laboratory

RF and magnet system configuration tools and associated monitoring processes have been recently implemented at Jefferson Lab to improve system reliability as well as operating costs. These tools are prototype components of the overall Momentum Management System currently under development. The RF systems are of special interest because they affect the energy spread and the positional stability of the beam, and because of the immediate financial impact of trimming unnecessary headroom capability by managing the klystron DC supply voltage. The magnets require special attention to enhance the overall reproducibility of machine optics and because of the need to reduce the time required for configuration changes. We describe monitoring and archiving of on-crest accelerating phase, cavity frequency detuning (important for the narrow-band superconducting cavities), and the procedures used to minimize line power consumption. We also discuss special cases for magnet system handling in the beam switchyard for experimental hall routing.

[9P.66] High Power Electron Beam Dumps at CEBAF

The CEBAF accelerator produces a very small emittance CW electron beam of up to 200 \muA average current. The resulting beam power, up to 1 MW at 5 GeV, and the very high beam power density, pose challenging problems for beam dump design. Two styles of high power dumps have been developed. The first, rated for 100+ kW, is used for beam tuneup and accelerator commissioning. The beam power is entirely contained in metal in these dumps, minimizing the problems associated with radioactive water handling. Full power 1 MW dumps are used with the experimental halls. In these dumps, one third of the beam power is absorbed in water. Both dump designs require the beam to be rastered when the smallest beam sizes are used. Design details for each of these dump designs will be presented.

[9P.67] Non-intrusive Diagnosis of Individual Cell Frequencies in a Coupled Cavity Chain

When tuning an accelerating cavity chain, the cell frequency must be measured cell by cell by inserting probes into the cavity. This process takes a very long time for long multicell or non-uniform chains. Moreover, the frequencies within a sealed cavity or a superconducting cavity in a liquid helium bath can not be diagnosed by inserting a probe. A method has been developed to estimate the frequency of each cell and neighbor couplings without introducing a probe into the cavity chain. This methold is based on the information obtained from an RF network analyzer. The data analysis program combines the Newton and Simplex methods;therefore, the program can accept a wide range of initial data, converges quickly.This program has been tested by experimental results and can be used as substitution for the measurements of accelerating cavity chain.

[9P.68] A New Measurement Method of the Delay Line Length in the X-band Delay Line Distribution System(DLDS)

In order to control the driving RF phase at the input of the accelerating structure of X-band linear collider main linacs, it is necessary to measure the length of the long TE01 mode delay lines of 40-80m. A new measurement scheme by using the low frequency resonant mode of the TE01mode delay line was proposed. The delay lines have the tapered guide on its both ends, thus the low frequency resonant mode around 2GHz can be the measure of the delay line dimensions. The operational principle and the elementary characteristics of this measurement method such as, sensitivity, S/N ratio and other basic design parameters are presented.

[9P.69] Performance of the Upgraded NSLS Beam Position Monitors

The NSLS beam position monitor (BPM) was developed by J. Bittner and R. Biscardi in 1989. This device, sometimes called the "rf receiver", processes rf signals from a set of four pick-up electrodes (PUEs) using a time division multiplexing-demultiplexing scheme and sum over difference normalization. A total of 92 BPMs were installed in the X-ray and VUV storage rings for orbit monitoring and feedback stabilization. The original design had a dynamic signal range of approximately 32 dB with a low limit corresponding to about 2 mA of stored beam current. As for most systems at the NSLS, the BPMs have been continuously upgraded to improve their performance. In particular, the signal sensitivity has been improved, the dynamic range has been increased to over 60 dB and the front end has been modified to prevent saturation during high current single bunch runs. In addition, the detector operating point was changed to optimize signal linearity and the gain calibration was equalized in both planes to simplify record keeping and trouble-shooting. Most of the receivers in both NSLS rings have now been upgraded. This paper describes the modifications, summarizes BPM performance and reports on recent beam position measurements. -------------------------------------------------------------

[9P.70]

This abstract was not submitted electronically.

[9P.71] A Compact Beam Position Monitor for the Fermilab Main Injector

The Main Injector will use Beam Position Monitors (BPM) located inside the downstream end of every quadrupole magnet. These magnets are reused (or derivatives of) the Main Ring quads with existing beam tube still in place. The limited space available, and desire to maintain the beam pipe aperture, required an unusual shaped BPM with innovative design and production techniques. Information on the various stages of the design, assembly, testing, calibration, and installation of the BPMs is presented.

[9P.72] Upgrade of the BPM System for the BEPC Storage Ring

The Beijing Electron Positron Collider (BEPC) is a machine with a designing energy up to 2.8 GeV. Thirty-two button-type beam position monitors (BPM) are used for the position measurement of the colliding e+ e- beams in the storage ring. In order to improve the measurement resolution and reduce the measurement time, the hardware and software of the BPM system have been partially modified and have been tested with beams at last year. The BPM processing electronics and the measurement behaviors can be fully controlled by a personal computer (PC) in the local control room. The measured beam position data are stored in memories on another PC, which serves as a communication server. These data can be accessed by the main computer in the central control room through network. The short-term reproducibility of the measurement is better than 10 microns. The measurement time for scanning all 32 BPMs is about 11 seconds. The reliability of the measurement is assured by the self-consistency check. The dynamic rang of the system is over 81 dB and the minimum measurable beam intensity is less than 0.5 mA. This paper will describe the hardware and software of our new BPM system.

[9P.73] Bunch Shape Monitors For The Desy H-Minus Linac

In order to tune and control the longitudinal bunch shape and energy spread in the DESY Proton linac (LINAC III), three Bunch Shape Monitors (BSM) have been developed and installed. The mechanical layout has been optimised in order to fit the extremely narrow space between the DTL tanks. One of the BSMs, as an additional feature, can measure the absolute energy of the beam and is installed downstream of three Alvarez tanks. Using of thin wire as a source of secondary electrons, these devices can be used as a non-destructive beam diagnostic tool during Linac operation. The performance of the BSMs as well as the results of the Linac III studies using the new devices will be presented.

[9P.74] Design and Commissioning of Beam Position Monitors for the IUCF Cooler Injector Synchrotron

IUCF is completing construction of the cooler injector synchrotron (CIS). Two beam position monitor systems (BPM) have been built to facilitate and enable commissioning and operation. In the 7 MeV injection beamline, high input impedance front-end amplifiers are used to detect the signal from the 4-quadrant, electrostatic pickups. The beam in this area will average 300 uA peak intensity, with pulse widths of 100 - 200 us. and repetition rate of 1s. In the CIS ring, elliptically shaped electrostatic pickups are used for impedance matching to the beamline. An electric field modeling program was used to determine the parameters of the plates in the 4-quadrant pickup. Logarithmic amplifiers are used to detect the beam in the CIS ring, providing a linear output and an extended range.

[9P.75] Measurement of Injection Orbit using a Single Pass BPM System at the PF Ring

A single-pass beam-position monitor system to measure the injection-beam positions in the storage ring was developed. The purpose of this system is the correction of the injection orbit error in advance of the beam storage during the commissioning period after the large reconstruction of the PF ring to install a lower emittance lattice. The signal processing method was reported previously. Bipolar bunch signals extracted through button electrodes were recorded in real time using a high-speed waveform digitizer, and the beam positions were determined from the ratio of the four-button signals. For the single-pass measurement, 16 BPMs were selected and the signals from the BPMs were processed at the same time using RF power combiners and two 4-channel waveform digitizers. The injection orbit during the 1st turn to the 4th turn could be measured by one injection pulse. The resolution of the measurement was estimated at about 0.2 mm for the typical electron pulse of 0.2 nC with 2 ns duration. Some results of the injection-orbit correction based on this measurement will be reported.

[9P.76] Calibration for KEKB Beam Position Monitors

Beam parameters are very sensitive to COD of rings having strong sextupole magnets, for example, in KEKB. Stabilization of COD is essential, and requires that the beam position measurement has to be done with respect to a fixed reference point. Position measurement is usually done with respect to the electronic BPM center, which is, however, likely to move due to long-term drifts of components inserted between the BPM and the detector. Authors have already proposed a method for finding a geometrical BPM center with beams, the center which is defined by ideal position response functions of the BPM, and never moves. This paper reports that the same method can be applied to BPM calibration in order to measure the absolute beam position. By the calibration with an antenna, the geometrical center is measured with respect to the BPM reference point, with which the BPM block is to be aligned to the adjacent quadrupole magnet.

[9P.77] The LEDA Beam Position Measurement System

This paper describes the electronics portion of the beam position measurement system being developed for the LEDA and APT projects at Los Alamos National Laboratory. The system consists of the cabling, down-converter modules, position/intensity modules, an on-line calibration system, and the necessary control system interfaces. The modules are built on the VXI-interface standard and are capable of duplex data transfer with the control system. Some of the key, system parameters are position measurement bandwidth of 180 kHz, the ability to measure beam intensity, a beam centroid measurement accuracy of \pm0.125 mm which is about one percent of the bore diameter, a beam-current dynamic range of 46 dB, a total system dynamic range in excess of 75 dB, and built-in on-line digital system error correction. Additionally, the paper will discuss the sub-system interface requirements, specifications, and how the on-line error correction is performed.

[9P.78] Orbit Measurement and Correction in the LNLS Synchrotron Light Source

The orbit measurement and correction system of the LNLS synchrotron light source is presented. Measurements of long term orbit stability, fast orbit fluctuations as well as the orbit reproducibility are presented and discussed.

[9P.79] Real Time Dispersion Measurements at the MIT-Bates Linac

The MIT-Bates Linear Accelerator Center comprises a 1\thinspace Ge\kern-.31mm V linac/recirculator system, beam lines to two main experimental halls, and a pulse stretcher/storage ring. Proper tuning of the beam requires the transverse dispersion to be zero, or some specified non-zero value, at all locations along the beam line. Dispersion measurements are made by correlating beam positions measured by BPMs, with energy measurements made using a BPM in a region of known non-zero dispersion. Data are acquired continuously from the BPMs and displayed on a graphical user interface in real time. This allows the accelerator operators to set dispersion quadrupoles and sextupoles so that the first and second order position and angle dispersions have their correct values at all points along the beam line. Details of the system design and operation will be presented.

[9P.80] Beam Size Effects on Beam Position Measurements in Proton Synchrotron

Beam size effects on beam position measurements have been calculated using three dimensional boundary element methods. We have confirmed that a highly distorted oval-shaped beam leads to beam position errors. The calculated results were compared with experimental data, indicating the validity of the simulation.

[9P.81] Two Frequencies Cavities for Beam Position Monitor.

Use of the symmetrical SBLC section coupler as well as one of the section cell for beam position monitor was studied. The requirements in both cases consisted of the high order mode (HOM) power withdrowing without changing frequencies at operational and high order modes. In case of symmetric coupler two HOM polarizations were withdrawn using protrusions inside the cavity. In case of 15-th cell of SBLC structure four cutoff waveguides at operating frequency with mismatched loads were used for that purpose. These loads dissipated RF energy and could be used for the change of hybrid mode own frequency for the 15-th cell. Caculations and measurements with 1 meter disk loaded waveguide of SBLC are presented.

[9P.82] Beam-Based Offset Calibration of the PLS BPM,

The PLS is a dedicated third generation synchrotron light source with nominal beam energy 2-GeV. Total 108 beam position monitors (BPMs) are used for the orbit measurement and the closed-orbit correction. As the BPM pick-up electrodes are assembled directly on the 10-m long vacuum chamber, the calibration of the electrical center of BPMs with the external transmission-reflection method is not accurate enough. Reading the orbit deviation after the closed orbit correction is no better than 500-\mum. To improve the accuracy of the absolute position reading, we are developing the beam-based calibration method for the BPMs. The first experiment has shown BPM offsets better than 10-\mum. In this paper, we describe the modulation of the quadrupole magnet currents and the control system of the beam-based offset calibration system for BPMs as well as the basic algorithm.

[9P.83] Calibration of the Beam-Position Monitor System for the SLAC PEP-II B Factory.

The Beam-Position Monitors (BPM) for the PEP-II B Factory consist of four 1.5-cm diameter button-style pickups mounted on the diagonals of the quadrupole vacuum chambers. Before installation of the vacuum chambers in the quadrupole assemblies, the electrical center of the BPMs is measured with respect to the mechanical center in a calibration test stand. In this paper the calibration test stand is described and the precision and accuracy of the calibrations are presented. After installation of the quadrupole assemblies in the PEP-II tunnel, the passive attenuation for each channel of the system is measured to preserve the accuracy of the calibration. Finally, the active electronics includes an on-board calibrator. Results for these portions of the calibration are presented.

[9P.84] A Two-Bunch Beam Position Monitor.

A new beam position monitor digitizer module has been designed, tested and tuned up at the SLAC. This module, the electron-positron beam position monitor (or epBPM), measures position of single electron and positron bunches for the SLC LINAC and PEP-II injection lines and final focus. The required dynamic range is fron 5 \cdot 10^8 to 10^11 particles per bunch (46~dB). The pulse-to-pulse resolution is less than 2~\mum for 5 \cdot 10^10 particles per bunch for the 12~cm long striplines, covering 30^\circ at 9~mm radius. The epBPM module has been made in CAMAC standard, single width slot. Four epBPM inputs are split for eight signal processing channels to catch two bunches, first -- the positron, then the electron bunch in one cycle of measurements. The signal processing channels bandwidth is 40~MHz. Minimum electron and positron bunch is 60~ns. The epBPM has internal and external trigger modes of operations. The internal mode has two options -- with or without external timing, catching only first bunch in the untimed mode. The epBPM has on-board calibration circuit for measuring gain of the signal processing channels and for timing scan of on board digital delays to synchronize the trigger and the signal's peak. There is a mode for pedestal measurements. The epBPM has 3.6~\mus conversion time.

[9P.85] Effect of TE Mode Power on the PEP-II LER BPM System.

The beam chamber of the PEP-II B-Factory Low Energy Ring (LER) arc sections is connected to an antechamber for the absorption of synchrotron radiation on discrete photon stops. The presence of the antechamber substantially reduces the cutoff frequency of the vacuum chamber and, in particular, allows the propagation of higher-order-mode (HOM) TE power generated by beamline components at the BPM signal processing frequency. Calculations of the transmission properties of the TE mode in different sections of the vacuum chamber show that the power is trapped between widely separated bellows in the arc sections. Because of the narrow signal bandwidth and weak coupling of the TE mode to the BPM buttons, the noise contributed by the HOM TE power will not produce a noticeable effect on the BPM position signal voltage.

[9P.86] Detection of Beam Induced Dipole-Mode Signals in the SLC S-Band Structures

Beam emittance dilution caused by wakefield effects is one of the important issues in the SLC linac. The detection of beam induced dipole mode signals in the C-band range could provide a direct measure of the strength of transverse wakefield kicks the beam experiences in the accelerating structures. We investigate the applicability of these microwave signals for beam steering purposes. The existing RF distribution system in the linac sectors 2, 6 and 29 has been equipped with a simple experimental setup to observe the beam induced dipole mode signals. The paper discusses the setup, the mode-structure of the observed signals as well as experimental results from beam steering scans, obtained in the SLC runs 95/96.

[9P.87] Beam Position Monitor System for PEP-II

We describe the beam position monitor system built for PEP-II, SLAC's B-Factory. The system reports beam position for bunches of between 5x10^8 and 8x10^10 electron charges either singly or as continuous streams of bunches every 4.2 ns. Beam pickups are 1.5 cm diameter buttons in beam ducts with radii from 3.3 cm to 4.5 cm. Resolution at full charge is to be better than 10 microns in a single turn. Higher resolution is available via on-board multi-turn averaging. The position signal is processed in a 20 MHz bandwidth around 952 MHz. This bandwidth, rather broader than that typical of RF position monitors, allows good resolution for low charge single bunches. Additional novel features include stringent control of return losses in order to minimize cross-talk between nearby bunches which may contain very different charges. The digitizing electronics is multiplexed between the two PEP-II storage rings. Design, construction, and installation experience, as well as first results with beam (expected in March 1997) are presented.

[9P.88] Optical Measurement Resolution and BPM Errors

We study the impact of BPM resolution on optics measurements at various levels of complexity: Formula linking a given distribution of BPM resolutions to the degree of precision to which any beam trajectory can be determined based on these BPM's. (2) Formula for the precision achievable in a generalized experimental scheme measuring transfer matrices in the presence of (potentially coupled) orbit errors. (3) Formula constructed from results of (1) and (2) to relate the precision of the transfer matrix measurement to the signal-to-noise ratio of the BPM system. (4) Criterion defined to summarize how well the overall optical behavior of a large modular beam transport system can be quantified. The results from (1), (2) and (3) are used to arrive at the final analytical expression providing a generic criterion on BPM resolution for such systems. Realistic examples are discussed.

[9P.89] 1 nA Beam Position Monitoring System

A system has been developed at Jefferson Lab for measuring transverse position of very low current beams delivered to the Experimental Hall B of the Continuous Electron Beam Accelerator Facility (CEBAF). At the heart of the system is a position sensitive cavity operating at 1497 MHz. The cavity utilizes a unique design which achieves a high sensitivity to beam position at a relatively low cavity Q. The cavity output RF signal is processed using a down-converter and a commercial lock-in amplifier operating at 100 kHz. The system interfaces with a VME based EPICS contol system using the IEEE 488 bus. The main features of the system are simple and robust design, and wide dynamic range capable of handling beam currents from 1 nA to 1000 nA with an expected resolution better than 100 \mum. This paper outlines the design and presents first operational experience with the system.

[9P.90] First Operating Experiences of Beam Position Monitors in the TESLA Test Facility Linac

Different types of monitors where installed in the TESLA Test Facility Linac to measure the beam position. At each superconducting quadrupole, the transverse beam position will be measured with a resolution of better than 10~\mu\mboxm, using a cylindrical cavity excited in the \mboxTM_110-mode by an off-center beam. In addition, two 'warm' cavities working at room temperature were built for the Injector I and the Bunch Compressor. The amplitude of the \mboxTM_110-mode and its phase are measured in a homodyne receiver. For the experimental area, stripline monitors having a resolution of better than 100~\mu\mboxm were built, tested and installed. The averaged position of the whole bunch train of Injector I is measured in a narrowband receiver using the amplitude-to-phase conversion. This paper summarizes the designs, cold tests and first operating experiences of both monitor types.

[9P.91] Beam Position Monitors inside the FEL-Undulator at the TESLA Test Facility Linac

The beam-based alignment procedure is essential for the operation of a SASE-FEL at the TESLA Test Facility Linac. It requires the transverse beam position to be measured at several points inside and between the undulator modules with a resolution of better than 5~\mu\mboxm. Between the undulator modules resonant monitors will be used. In a cylindrical cavity the \mboxTM_110-mode will be excited by an off-center beam. The amplitude of this mode is detected in a homodyne receiver by mixing the cavity output and a 12~\mboxGHz reference signal down to DC. Inside the undulator modules, new beam position monitors are under development. They consist of four rectangular waveguides oppositely arranged around the chamber. The averaged position of a single bunch train will be measured in a narrowband X-band receiver. As an alternative, button-type monitors using very small feedthroughs as an electrode where desigend in parallel. The fabrication and test of prototypes is under way. This paper summarizes the designs and some preliminar results for all types of monitors.

[9P.92] The Closed Orbit Measurement System at the DELTA Synchrotron Radiation Facility and First Investigations Concerning the Installation of a Beam Based BPM Calibration System

For a synchrotron radiation source it is necessary to operate a monitoring system to determine the beam position with high resolution and accuracy with respect to the axis of the quadrupole magnets. In this paper the present closed orbit measurement system of the DELTA SR-Facility, concerning the hardware setup, data processing and the calibration methods, will be presented. The results of the calibration measurements and the recent operating experience will be discussed. These results show, that the system is close to the design resolution. But the BPM offsets with respect to the magnetic center of the quadrupole magnets turn out to be not acceptable. For some BPMs they are in the order of several 100\,\mu m. Therefore it was decided to install a beam based BPM calibration system in the near future . This system should allow to determine the BPM offsets relative to the center of the quadrupole magnets for all 40 BPMs. It is planned to install a system in order to change the focussing strength of each quadrupole individually either in a static or dynamic way.

[9P.93] Development of a Resistive Beam Position/Current Monitor for the UMD Electron Ring

A prototype resistive beam position/current monitor (BPM) has been developed for the electron ring at the University of Maryland. The BPM consists of 32 low-inductance resistors which are uniformly distributed around a ceramic gap between two conducting pipes. The resistors are divided into four quadrants and each quadrant has a total resistance of 0.625 Ømega. Measurement of image currents in the four quadrants provides information about beam position and total beam current. A bench test has been done for a prototype BPM (diameter=4.2 cm), yielding total beam currents with an error of 2 % and position information with errors of 0.2 mm in radial direction and 5^\circ in azimuthal direction. The rise time of the monitor was measured to be about 1 ns.

[9P.94] Performance of the Single-pass Position Monitor at SOR-RING

A third-generation VUV and soft x-ray ring, the VSX Light Source, is being designed at the University of Tokyo. For such a ring, single-pass position monitors are expected to play an important role in the efficient commissioning and easy tuning. We carried out the Ramp;D of single-pass monitor at the 500 MeV electron storage ring, SOR-RING, and at the beam transport line between the ring and the injector. The bunch signals from four button electrodes are directly fed into a 4-channel digital oscilloscope through semi-rigid cables. The digitized data are sent to a workstation and beam position is calculated there. The relative accuracy of less than 0.1 mm has been obtained. In this paper, a comparison between a few methods of data processing will be also reported.

[9P.95] Tracking Routines for General Insertion Devices

A package of FORTRAN tracking routines for general insertion devices has been developed at BESSY( Funded by the Bundesministerium für Bildung, Wissenschaft, Forschung und Technologie and by the Land Berlin) and incorporated in the tracking code BETA( L.~Farvacque, J.~L.~Laclare, A.~Ropert, BETA User's Guide, ESRF-SR/LAT-88-08). A first group of routines is based on Taylor expansions of generating functions. Another group of routines tracks the particle explicitly through a user-defined magnetic field configuration. The package includes routines to interpolate the 3D field from a field map as well as routines that calculate the magnetic field from analytical models. A comparison of tracking results and computing time for special devices is presented.

[9P.96] Tracking Tunes with Wavelets

Wavelet are useful time-frequency analysis tools and lend themselves naturally to tracking frequency changes with time. I will present results from wavelet transforms that display the horizontal and vertical tunes of the Brookhaven AGS as functions of time. I also point out the varying results that different analyzing wavelets induce, and how to resolve these discrepancies into a useful tool that displays tunes versus time.

[9P.97] Simulation of electron guns with the cathode in strong magnetic field.

New possibilities of code SuperSAM for electron guns simulation are presented. The intensive electron beams in strong magnetic field are used in various applications, for example in electron cooling systems. If the magnetic field is not normal on the cathode surface and strong enough, classical Childs-Lengmuir low is not useful and have to be modified. Model of emission in arbitrary magnetic field was developed in code SuperSAM and tested on various electron guns.

[9P.98] Simulation of Multipacting in RF cavities and waveguides.

The code for multipacting simulations in axisymmetrical RF cavities, waveguides and coaxial lines is presented. Physical model includes secondary emission simulations and particle trajectory integration in realistic RF fields. The code calculates multipactor voltage levels and discharge distribution. The paper contains simulation results for 180 MHz cavity of INP microtron-recuperator as well as measured data for this cavity demonstrating good agreement with the calculations.

[9P.99] Consideration of DC Space Charge Effects in the Modal Analysis of Aperture Coupled-Cavities

The modal analysis of aperture-coupled cavities is frequently applied to the field theoretical analysis of high-power tube cavities and accelerating structures in high energy physics. Besides the rf electromagnetic field, dc space charge effects may also be important in such applications. Because there is no magnetic field related with dc space charges a straightforward application of the modal expansion method, which makes use of matching the aperture tangential magnetic field, to the investigation of dc space charge fields is not possible. In this contribution it is therefore demonstrated that the computation of the dc spectral component of the electric field due to space charges can also be included in the modal analysis of aperture-coupled cavities if instead of the aperture tangential magnetic field the corresponding axial electric field is matched. It is shown that even in this case the solenoidal electric eigenfunctions of the cavity have to be taken into account because of the waveguide coupling. Furthermore, the validity of the method is checked by applying it to a field problem for which a solution is already well-known from another analysis.

[9P.100] A Self-Consistent Beam Loaded Travelling Wave Accelerator Model for use in TRACE-3D

An optics model of a constant gradient traveling wave (CGTW) accelerator structure has been implemented for TRACE-3D. TRACE-3D is an envelope code including space charge that is used to model bunched beams in magnetic transport systems and radio frequency (rf) accelerators when the effects of beam current might be significant. The new matrix model has been developed to allow incorporation of particle beam loading (current) effects on the accelerator gradient and the accelerator structure's beam focusing properties in a self-consistent manner. The beam loaded electric field for a CGTW accelerator structure is constant for only a particular design current (e.g., 0 current), otherwise it can be written as a function of accelerator attenuation and axial position along the structure. The variation of the electric field through the structure has been taken into account in the new model. CGTW structures differ substantially in focusing properties and beam loading properties from standing wave structures. Examples will be presented using the new TW model, propagating electron beams with different currents through the Stanford Linear Accelerator Center's 3 m structure. The results will be compared to the zero current TW structure model in TRANSPORT and the Tank model (a standing wave structure model) in TRACE-3D. A computer demonstration of the code with the new element will also be presented.

[9P.101] Monte Carlo Simulation of Nonlaminar DC Beam Transport Including the Influence of Self-Fields

We present a method to simulate the transport of a nonlaminar DC beam under the influence of self-fields. The beam profile at the position s along the reference trajectory is expressed as a distribution function with parameters \vec a(s). Initial parameters \vec a(0) are chosen to define the initial profile of the beam, and n beam particles are randomly assigned positions from the initial profile distribution. Transverse momenta are randomly assigned using the beam emittance. The beam profile distribution is used to compute the beam self-fields at the position of each particle, and the external fields are added to the self-fields. Each particle is propagated a short distance to a new position and momentum. The parameters \vec a for the new beam profile are then computed from an unbinned maximum likelihood fit to the n particle positions. The total computation required by the simulation scales linearly with n. The simulation for a neutralized electron beam with a phase space given by the Kapchinskij-Vladimirskij (KV) distribution is in good agreement with the beam profile predicted by the KV envelope equation.

[9P.102] Use of the LANA Code for the Design of a Heavy Ion Linac

The \tt LANA computer code (Linear Accelerators Numerical Analysis) has been developed in INR, Moscow during the last several years and still is in further development. This code is designated for the design and simulation of various kinds of linear accelerators. Recently the code has been extensively used for the design and study of the separated function heavy ion DTL for the ISAC project at TRIUMF. The paper describes the mathematical models used in the \tt LANA code including space charge effects and three-dimensional realistic accelerating field representation. In particular the procedure for drift tube geometry generation based on three-dimensional electromagnetic field distributions extracted from \tt MAFIA are described in detail. The \tt LANA code is also used to determine the influence of the asymmetry in the fields of the H-type structure on the beam dynamics.

[9P.103] Simulation of Fast Beam-ion Instability Based on Bassetti-Erskine Formula

Recently a new type of instability named fast beam-ion instability is suggested. This instability can have a very harmful effect on the machines such as B-factory and future linear collider. To study this kind of instability, a computer simulation code based on Bassetti-Erskine formula was developed and employed during the experimental studies in TRISTAN AR. In this paper the description of the code and some simulation results using AR machine parameters are presented, furthermore, the comparison with a strong-strong simulation code is also discussed.

[9P.104] Comparison of C++ and Fortran 90 for scientific computing

C++ and Fortran 90 are compared as object-oriented languages for use in scientific computing. C++ is a full-featured, object-oriented language that provides support for inheritance and polymorphism. Fortran 90 can mimic some object-oriented features through combinations of its TYPE and MODULE syntax elements, but it lacks inheritance and, thus, does not permit code reuse to the same extent as C++. These aspects, the features of each language missing in the other, and a comparison of speed of code compiled in each language are discussed.

[9P.105] IMPACT: An Integrated-Map amp; Particle Accelerator Tracking Code for Linac Simulation

We have developed a new rf linac simulation code to model accelerators for a variety of projects including waste transmutation, tritium production, and next-generation spallation neutron sources. The new code uses a split-operator approach to combine map-based methods of single-particle tracking with standard Particle-In-Cell simulation techniques. The code, called IMPACT, uses field data to compute transfer maps associated with accelerating cavities. It uses a 3D Particle-In-Cell algorithm based on area weighting to treat space charge. At present, the code assumes open boundary conditions transversely and either open or periodic boundary conditions longitudinally. The space charge routines have been optimized to run efficiently on parallel computers using techniques developed in the computational cosmology community. In this paper we will report on the status of IMPACT running on various machines including a Cray T3E at the National Energy Research Scientific Computing Center at LBNL and a Silicon Graphics/Cray SMP cluster at the LANL Advanced Computing Laboratory.

[9P.106] Relativistic Klystron Two-Beam Accelerator Simulation Code Development

We present recent work on the development and testing of a 3-D simu- lation code for relativistic klystron two-beam accelerators (RK-TBAs). This new code utilizes symplectic integration techniques to push macro- particles, coupled to a circuit equation framework that advances the fields in the cavities. Space charge effects are calculated using a Green's function approach, and pipe wall effects are included in the electrostatic approximation. We present simulations of the LBNL/LLNL RK-TBA device, emphasizing cavity power development and beam dynamics, including the high- and low-frequency beam break-up instabilities.

[9P.107] Measured and Theoretical Characterization of the RF Properties of Stacked, High-Gradient Insulator Material

Recent high-voltage breakdown experiments of periodic metallic-dielectric insulating structures have suggested several interesting high-gradient applications. One such area is the employment of high-gradient insulators in high-current electron beam accelerating cell modules. In this application, the understanding of the RF characteristics of the insulator plays an important role in estimating beam-cavity interactions. In this paper, we examine the RF properties of the insulator material comparing simulation results with experiment. Different insulator designs will be examined to determine RF transmission properties in gap geometries.

[9P.108] Wake Properties of a Stripline Beam Kicker

The transport of a high current relativistic electron beam in a stripline beam kicker is strongly dependent on the wake properties of the structure. The effect of beam induced fields on the steering of the beam must be determined for a prescribed trajectory within the structure. A 3-D time domain electromagnetic code is used to determine the wake fields and the resultant Lorentz force on the beam both for an ultra-relativistic electron beam moving parallel to the beamline axis as well as a beam that follows a curved trajectory through the structure. Usually in determining the wake properties of the structure, a wake impedance is found for a beam that is moving parallel to the beamline axis. However, we extend this concept to curved trajectories by calculating beam induced forces along the curved trajectory. Comparisons are made with simple transmission line models of the structure. The wake properties are used in models to transport the beam self-consistently through the structure.

[9P.109] BBU Design of Linear Induction Accelerator Cells for Radiography Application

There is an ongoing effort to develop accelerating modules for high-current electron accelerators for advanced radiography application. Accelerating modules with low beam-cavity coupling impedances along with gap designs with acceptable field stresses comprise a set of fundamental design criteria. In this paper, we examine improved cell designs which have been developed for accelerator application in several radiographic operating regimes. We will evaluate the interaction impedances, beam-breakup growth rates, and examine 3-D scattering effects in accelerating modules. We will also provide estimates of coupling through interesting insulators in accelerating gap designs.

[9P.110] RESOLVE Upgrades for On-Line Lattice Error Analysis

We have increased the speed and versatility of the orbit analysis process by adding a command file, or 'script' language, to RESOLVE. This command file feature enables us to automate data analysis procedures to detect lattice errors. We describe the RESOLVE command file and present examples of practical applications.

[9P.111] Dark Current Simulation for Linear Collider Accelerator Structures

The dynamics of field-emitted electrons in the traveling wave fields of a constant gradient (tapered) disk-loaded waveguide is followed numerically. Previous simulations have been limited to constant impedance (uniform) structures for sake of simplicity since only the fields in a unit cell is needed. Using a finite element field solver on a parallel computer, the fields in the tapered structure can now be readily generated. We will obtain the characteristics of the dark current emitted from both structure types and compare the two results with and without the effect of secondary electrons. The NLC and JLC detuned structures are considered to study if dark current may pose a problem for high gradient acceleration in the next generation of Linear Colliders.

[9P.112] Parallel Eigensolvers for Modeling Large Accelerator Structures.

A set of 2 amp; 3D finite element programs has been developed on parallel platforms to simulate large complex RF structures which otherwise are impractical to model on serial machines. These are frequency domain eigensolvers implemented with the following notable features for efficiency and accuracy. They are formulated with quadratic elements to fit curvatures more precisely. They have the capability for adaptive refinement to obtain the optimal mesh for a desired accuracy. They adopt domain decomposition to distribute computations over multiple processors using Message Passing Interface (MPI) with minimal communication overhead. Finally they are supported by a library of direct and iterative solvers that use special algorithms to accelerate convergence on a specific problem. Examples will be shown from the SLAC structure design effort to demonstrate the application of the codes.

[9P.113] A Flexible-Variable Truncated Power Series Algebra in Zlib

Zlib is a numerical library for Truncated Power Series Algebra (TPSA) and Lie Algebra for application to nonlinear analysis of single particle dynamics. The first version was developed in 1990 with the One-Step Index Pointers in Zlib nerve system that offer optimal computation and allow order grading as well as flexible initialization of the global number of variables for the TPSA. While the one-step index pointer concept is still kept for fast computation, a new feature has been added to allow flexible local number of variables in each object of the Truncated Power Series (Tps) class. This new feature along with its applications are to be discussed.

[9P.114] Aperture Calculation of AURORA-2D Compact Electron Storage Ring with Superconducting Wigglers

Apertures of AUORORA-2D compact electron storage ring with two 7 Tesla wigglers are calculated with a tracking program NABO written by Takayama. This ring has two 180 ^o normal conducting bending magnets of orbit radius 0.87 m and the maximum field 2.7 Tesla, eight quadrupole magnets, and two 3 m long straight sections. Electrons are injected at 150 MeV from a microtron and stored at 700 MeV. Two superconducting wigglers can be installed in two straight sections. Since the perturbations of the superconducting wigglers and of the fringe fields of the bending and quadrupole magnets are large for small rings, they are taken into account in the tracking program NABO on the basis of sixth order Runge-Kutta method. The magnetic field data of the bending magnets, the quadrupole magnets, and the superconducting wigglers are obtained by measurements and/or 3 dimensional calculations. As a particle loss in the tracking program is determined by the beam duct aperture, the calculated aperture is the intersection of physical and dynamical apertures. Apertures are compared with the ones calculated by a tracking program which satisfies symplectic condition to evaluate the validity of the application of the sixth order Runge-Kutta method to the multi turn tracking.

[9P.115] Numerical Simulation and RF Model Measurements of the New GSI IH-DTL

Two IH drift tube cavities will be part of the new pre-stripper LINAC being under construction at the GSI accelerator facility in Darmstadt (Germany) in order to provide higher beam intensities.

The first part of the cavity design process consisted of numerical electromagnetic simulations using MAFIA( Solution of M)axwell's equations using a Finite Integration Algorithm.

Based on these calculations the tanks are under construction and a 1:5.88 scaled RF model was built to compare the results and to determine the exact drift tube geometry as well as to find optimum positions and shapes for the tuners. To accelerate the design process, an equivalent circuit model (ECM) is under construction, which will read its input parameters from MAFIA calculations.

This paper describes the most important steps in the design process. It presents results for the MAFIA simulation, the rf model measurement the state of the ECM studies.

[9P.116] Broad-Band Impedance of LHC Shielded Bellows

To compensate for thermal expansion the LHC ring has to accommodate about 3000 bellows which together with beam position monitors are the biggest contributors to the LHC broad-band impedance budget. In order to reduce this impedance to an acceptable value the bellows have to be shielded. In this paper we compare different designs proposed for the bellows and calculate their transverse and longitudinal wake fields and impedances. Due to the 3D geometry of the bellows MAFIA was used for the wake-field calculations; when possible the MAFIA results were compared with those obtained with ABCI. The results presented in this paper indicate that two designs for the bellows in which shielding is provided by using sprung fingers which can slide along the beam screens both have acceptable impedances, but one design may be preferable to the other from mechanical considerations. Several failure modes such as missing fingers and imperfect rf contact have also been studied.

[9P.117] Calculation of Microwave Instability Threshold

Based linearized Vlasov equation,a code for studying the microwave instability with potential-well distortion is presented. This code uses action-angle variables and expands perturbation distribution \psi_1 in term of the Laguerre polynomials and sine-cosine series. The result is compared with that obtained by simulation.

[9P.118] GdfidL: A Finite Difference Program with Reduced Memory and CPU Usage

Two new field solvers based on the FDTD Algorithm are described. One solver computes resonant fields in lossfree structures, the other computes time dependent fields, scattering parameters and wake potentials in lossy or lossfree structures. The program uses linked lists instead of three dimensional arrays to model the computational volume. The main advantage of this approach is: Grid cells are only needed in regions, which are not filled with electric or magnetic conducting materials. For realistic geometries, this reduces the memory and CPU requirements by a factor of 4 to 10. The modeling via the linked lists is described in detail and some examples of calculated realistic geometries are given.

[9P.119] Expression Templates for Truncated Power Series

Truncated power series are used extensively in accelerator transport modeling for rapid tracking and analysis of nonlinearity. Such mathematical objects are naturally represented computationally as objects in C++. This is more intuitive and produces more transparent code through operator overloading. However, C++ object use often comes with a computational speed loss due, e.g., to the creation of temporaries. We have developed a subset of truncated power series expression templates(http://monet.uwaterloo.ca/blitz/). Such expression templates use the powerful template processing facility of C++ to combine complicated expressions into series operations that exectute more rapidly. We compare computational speeds with existing truncated power series libraries.

[9P.120] New Integration Methods for Longitudinal Beam-Cavity Systems

Integrating simulations of the longitudinal beam-cavity system is improved with two techniques: removal of fast time scales and symplectic integration. Both techniques rely on a single-wave model of the system. By removing the fast time scale of the particle revolution frequency, the size of the time step can be increased many orders of magnitude. Symplectic integration, extended to non-Hamiltonian systems, also allows one to use larger time steps for the same accuracy by avoiding spurious damping effects associated with traditional Runge-Kutta integrators.

[9P.121] A field-cancellation algorithm for constructing economical planar permanent magnet (PM) multipoles with large high-quality field apertures

In recent years studies have been initiated on a new class of multipole field generators consisting of cuboid planar permanent magnet (PM) pieces arranged in bi-planar arrays of 2-fold rotational symmetry(R. Tatchyn, "Planar Permanent Magnet Multipoles: for Particle Accelerator and Storage Ring Applications ," IEEE Trans. Mag. 30, 5050(1994).)(T. Cremer, R. Tatchyn, "Planar Permanent Magnet Multipoles: Measurements and Configurations," in Proceedings of the 1995 Particle Accelerator Conference, IEEE Catalog No. 95CH35843, paper FAQ-20.). These structures, first introduced for Free Electron Laser (FEL) applications(R. Tatchyn, "Selected applications of planar permanent magnet multipoles in FEL insertion device design," NIM A341, 449(1994).), are based on reducing the rotational symmetry of conventional N-pole field generators from N-fold to 2-fold. One consequence of this reduction is a large higher-multipole content in a planar PM multipole's field at distances relatively close to the structure's axis, making it generally unsuitable for applications requiring a large high-quality field aperture. In this paper we outline an economical field-cancellation algorithm that can substantially decrease the harmonic content of a planar PM's field without breaking its biplanar geometry or 2-fold rotational symmetry. This will enable planar PM multipoles to be employed in a broader range of applications than heretofore possible, in particular as distributed focusing elements installed in insertion device gaps on synchrotron storage rings. This accomplishment is expected to remove the conventional restriction of an insertion device's length to the scale of the local focusing beta, enabling short-period, small-gap undulators to be installed and operated as high-brightness sources on lower-energy storage rings(R. Tatchyn, P. Csonka, A. Toor, "Perspectives on micropole undulators in synchrotron radiation technology," Rev. Sci. Instrum. 60(7), 1796(1989).). Operation as ordinary focusing elements in storage ring magnetic lattices, as well as the performance of other high-quality multipole applications, should also becomes possible with the realization of the proposed structures.

[9P.122] Conceptual and Experimental Feasibility Study of a Superconductive Micro-Undulator

Generating synchrotron radiation from conventional undulators in the hard X-ray region requires high electron energies. In order to open this spectral region for sources with smaller electron energy such as ANKA (2.5 GeV) the period length of the undulator has to be decreased. In this paper the concept and the first successful tests towards a superconductive micro-undulator are described. The structures were built with a commercially available NbTi wire. It was possible to run about 1000 Ampere through the coil at 4 K. A full prototype of a superconductive micro-undulator is now under construction.

[9P.123] Comparison of Beam-Position-Transfer Functions using Circular Beam-Position Monitors

A typical cylindrical beam-position monitor (BPM) used in many accelerator facilities has four electrodes on which beam-image currents induce bunched-beam signals. These probe-electrode signals are geometrically configured to provide beam-position information about two orthogonal axes. An electronic processor performs a mathematical transfer function on these BPM-electrode signals to produce an output signals whose time-varying amplitude is proportional to the beam's vertical and horizontal position. The processor-output signals are digitized for use by the accelerator-control system. This paper will compare various beam-position transfer functions using both pencil and diffuse beams.

Part 9 of program listing