Session 6P - Superconducting Magnets 2, Control Systems X, Feedback Systems (including Beam) 2.
POSTER session, Wednesday afternoon, May 14
Pacific Ballroom,

[6P.01] Quench Protection of SC Quadrupole Magnets

The energy stored in a superconducting accelerator magnet is dissipated after a quench in the coil normal zones, heating the coil and generating a turn to turn and coil to ground voltage drop. Quench heaters are used to protect the superconducting magnet by greatly increasing the coil normal zone thus allowing the energy to be dissipated over a larger conductor volume. Such heaters will be required for the Fermilab/LBNL design of the high gradient quads (HGQ) designed for the LHC interaction regions. As a first step, heaters were installed and tested in several Tevatron low-\beta superconducting quadrupoles. Experimental studies in normal and superfluid helium are presented which show the heater-induced quench response as a function of magnet excitation current, magnet temperature and peak heater energy density.

[6P.02] Design and operation of an experimental double-C ``transmission line'' magnet for the Pipetron.

An experimental version of a warm iron, two-in-one superconducting magnet for a low cost multi-TeV hadron collider was built. The magnet consists of a 50-70 kA superconducting power transmission line encircled by an iron yoke with a gap on each side. Each of the two gaps contains one of the circulating proton beams for a p-p collider. Beam focusing is provided by a modest alternating gradient of approximately 10 T/m and therefore the structure need not be interrupted for quadrupoles. The five meter long experimental apparatus contains a one meter long solid iron yoke assembly excited by the shorted secondary of a superdconducting current transformer. Operating experience and plans for future development are discussed.

[6P.03] A New Facility to Test Superconducting Accelerator Magnets in Superfluid Helium

Future high energy accelerators such as the Large Hadron Collider require magnets with the highest possible fields. For NbTi conductor magnets, this means operating at superfluid helium temperatures in the range of 1.8-1.9K. As part of Fermilab's superconducting magnet Ramp;D program, we have built a facility to test magnets in a vertical dewar of superfluid liquid helium. The dewar is designed for magnets up to 4 m length and 600 mm diameter, with a temperature range of 1.8K to 4.4 K and 1.2 atmosphere helium. The power system consists of 10 kA and 8 kA power supplies operating in parallel, with bus work and an extraction circuit that can accommodate up to 20 kA excitation current. A complete description of the facility as well as operational experience from the first magnet tests are presented.

[6P.04] Magnetic Design of a High Gradient Quadrupole for the LHC Low-\beta Insertions.

In order to achieve a luminosity in excess of 10^34 cm^-2s^-1 at the LHC, special quadrupole magnets are required for the final focusing triplet. These magnets must provide a high field gradient of 235 T/m over a 70 mm aperture, with a good margin in order to safely withstand the heavy radiation load due to secondary particles from beam-beam collisions. At the same time, due to large and rapidly varying values of the \beta-function, a high field quality is also required. To meet these severe constraints, a design based on a 2-layer coil geometry has been proposed. The magnet uses SSC-type NbTi superconducting strands and operates in superfluid helium. In this paper a description of the magnetic design is given, including short sample performance limits, sources and expected values of systematic and random field errors, and possible strategies for field quality correction.

[6P.05] Magnetic-Optics Design Concepts for Proton Radiography

In proton radiography, high-performance magnetic quadrupole lenses are required for point-to-point imaging of the proton-illuminated object on to the detector plane. In order to reduce chromatic aberrations, the length of the imaging system must be minimized. This requirement, along with the large field of view needed, leads to use of large-bore, relatively high-field superconducting quadrupole magnets. Performance requirements and design concepts for these magnets, along with magnetic-field models for interfacing with particle-tracking and map-generating codes are described.

[6P.06] A Mu Mu Collider Capture Solenoid System for Pions from a Tilted Target

In order to generate intense muon beams for a muon collider, pions produced in a stationary target must be captured before they can go through phase rotation and decay into muons. A 20 T solenoid with a clear bore of 150 mm can capture particles with a transverse momentum of 225 MeV/c or less. As captured particles leave the capture solenoid, the magnetic induction is decreased to 5 T while the beam pipe diameter increases to 300 mm. Phase rotation and decay of the pions will occur at 5 T. The capture solenoid and the solenoids just downstream from the capture solenoid are subject to high heat loads (up to 3.0 MW). The conventional inner solenoid of the 20 T hybrid magnet system and the water cooled absorber will absorb most of the beam power from the protons thus protecting the superconducting solenoid system from heating. Tilting the target and the incoming beam about 150 milliradians with respect to the solenoid axis appears to increase the net pion capture by about sixty percent. This paper describes approaches for capturing muons from a tilted target while getting rid of the spent proton beam.

[6P.07] Tutorial on Superconducting Accelerator Magnets

A multimedia CD-ROM tutorial on the physics and engineering concepts of superconducting magnets for particle accelerators is being developed under a U.S. Dept. of Energy SBIR grant. The tutorial, scheduled for distribution this summer, is targeted to undergraduate junior or senior level science students. However, its unified presentation of the broad range of issues involved in the design of superconducting magnets for accelerators and the extensive detail about the construction process (including animations and video clips) will also be of value to staff of research institutes and industrial concerns with an interest in applied superconductivity or magnet development. The source material, which is based on the world-wide R and D programs to develop superconducting accelerator magnets, is organized in five units with the following themes: Introduction to magnets and accelerators; (2) Superconductors for accelerator magnets; (3) Magnetic design methods for accelerator magnets; (4) Electrical, mechanical, and cryogenic considerations for the final magnet package; (5) Performance characteristics and measurement methods. A detailed outline and examples will be shown.

[6P.08] Superconducting Solenoids for the Polarized Electron Spin Control System of the MIT-Bates South Hall Ring (SHR)

A scientific collaboration between MIT and the Budker Institute of Nuclear Physics (BINP) has produced a design for a magnetic insertion (Siberian Snake) into the SHR lattice, which allows for spin control of 0.3 to 1.0\thinspace GeV polarized electron beams for planned internal and external target physics. This report describes the design, construction, and tests performed at BINP facilities and final tests performed at MIT-Bates on two superconducting shielded solenoids, each having the following specifications: 7.0\thinspace cm warm bore, OAL of 104\thinspace cm, Bz (max) of 7.3\thinspace T at 290\thinspace A, and integrated field strength of 5.75\thinspace T-m at 290\thinspace A. The magnetic insertion (4.8\thinspace m), consisting of two pairs of skew quadrupoles (0.3\thinspace m), one central quadrupole (0.5\thinspace m) and the two superconducting solenoids, will be installed and commissioned in the SHR later in 1997.

[6P.09] Measurement of Young Modulus and Shim Calculation for LHC Prototype Dipole Magnets

Since 1991 the company Noell-KRC Energie- und Umwelttechnik GmbH, Wuerzburg, Germany is developing superconducting dipole magnets for the Large Hadron Collider at CERN in cooperation with CERN. The design of the dipole magnets is presented e.g. in the Conceptual Design of the LHC study group. The superconducting coils wound from a Nb-Ti cable of the Rutherford type are assembled in an aluminum clamping structure, the so-called collars. The coils have to be prestressed in order to avoid movements of the superconductor during operation, which may cause quenches. The exact value of the prestress and the uniformity of the prestress over the length of the magnet are adjusted by the thickness of the inserted shims. The basis for prestressing the dipole coils is the precise measurement of the size and the Young modulus of the winding. Based on the measurements shims are calculated ensuring the correct prestress of the coil. During shim calculation several corrections of the shim thickness have to be taken into account e.g. corrections due to the deformation of the collars. The measurement of the Young modulus and the shim calculation will be presented.

[6P.10] Progress in the design, manufacture and testing of the KLOE solenoid for the DA\PhiNE ring at Frascati

Oxford Instruments took over the manufacture of the 5.7 m outer diameter 4.5 m long 0.6 T Solenoid for the KLOE detector on the DA\PhiNE ring when the Austrian company ELIN closed its magnet manufacturing plant. The paper begins by briefly discussing the magnet design before describing the approach Oxford Instruments has taken to the completion of the magnet. The results of system testing at Oxford Instruments will be described along with the proposed installation schedule.

[6P.11] Maxwellian Field Expansion of Helical Magnet

Superconducting helical diple magnets will be used in RHIC as Siberian snakes and rotators. Beam trajectory and spin motion in snakes are numerically calculated when the magnetic field map is given along the beam path. However, calculated or measured magnetic field maps may not always satisfy Maxwell's equations. This causes errors in the numerical calculations of orbit and spin matrices. The field is made more Maxwellian by reading from the map only one or two field components and by deriving the others by using appropriate expansion coefficients. In this paper, this method is applied to analyze three dimensional (3D) magnetic field calculated by TOSCA including the fringing field region of a helical dipole magnet.

[6P.12] Design of the Sector Magnets for the RIKEN Superconducting Ring Cyclotron

The RIKEN superconducting ring cyclotrons, SRC-4 and SRC-6, are the main components for the RIKEN RI Beam Factory. This paper describes the design of the sector magnets for the SRC-6. The SRC-6 consists mainly of six superconducting sector magnets, three RF cavities, and beam injection/extraction systems. The main parameters of the sector magnets are as follows: the maximum magnetic field in the beam orbit is 4.3 T; the coil ampere-turns 6 x 6 MA; the stored magnetic energy 450 MJ; the total weight of the cold mass 350 tons and the total weight including iron return yokes 4000 tons. LHe bath cooling and cryogenic stabilizing method are adopted for both of the superconducting main coils and the superconducting trim coils. The special feature is the cold-pole arrangement that is adopted to support the main coils against the huge magnetic force and to reduce the coil ampere-turns.

[6P.13] Trim Coil System for the RIKEN Superconducting Ring Cyclotron

The superconducting ring cyclotron (SRC-6), proposed as a booster of the present RIKEN Ring Cyclotron (RRC), is composed of six superconducting sector magnets, and each sector magnet uses pole pieces at 4 K to enhance the field strength and to reduce the electromagnetic forces on the coil support structure. The field trimming system suitable for cyclotron such as the SRC-6 is thought to be a combination of superconducting and normal trim coils. Optimization of the trimming system to isochronize the magnetic fields for various ions has been carried out using numerical methods, considering the properties of two different kinds of trim coils. In addition, a scheme to compensate for the fringe fields of the injection and extraction magnets using trim coils will be discussed.

[6P.14] A Superconducting Solenoid for Heavy Ion Beam Focusing

A superconducting solenoid has been constructed to use as a final focusing element at the entrance of the projectile fragment separator RIPS (T. Kubo et al, Nucl. Instr. amp; Meth. B70 (1992) 309) at RIKEN. The design field on axis is 6 tesla, the average current density being 9,600 A/cm^2. The overall coil length is 1.1 meter, and the coil is divided into three sections of equal length to ease winding and possibly to distribute the stored energy. A major feature of the magnet is that cooling is conductive without LHe involved, using a cryocooler directly attached onto the coil. The solenoid is currently being tested, and the test results will be presented. After magnet testing, the solenoid will be installed in the beamline. The results of beam experiment will also be presented, along with calculation results with TRANSPORT.

[6P.15] Design of a Model Sector Magnet for the RIKEN Superconducting Ring Cyclotron

In the RIKEN RI Beam Factory project, it is planned to build two superconducting ring cyclotrons, SRC-4 and SRC-6, as post accelerators of the existing cyclotron. This paper reports on a model sector magnet for the second cyclotron, SRC-6.

The SRC-6 has been designed to consist of six superconducting sector magnets. Its main features are as follows: the mean injection and extraction radii are 3.56 m and 5.36 m, respectively; the sector angle is 25 degrees; the maximum magnetic field is 4.3 T; the total stored energy is 450 MJ; the maximum ampere-turn of mail coil is 6 MA for each magnet; the main coil is cooled by the liquid-He bath cooling method and designed to be cryogenically stable. The sector magnet is characterized by adopting the cold-pole method, in which the electromagnetic force on the coil is supported by the pole piece.

The coil vessel is fixed to the pole piece, which is separated from a yoke and cooled down together with the main coil.

A full scale model is to be built to make sure the design of sector magnet.

Its detailed structure such as the coil vessel, the cold pole and the coil winding will be presented.

[6P.16] Three Dimensional Field Analysis of Helical Magnet for RHIC Siberian Snake

The Siberian Snake that consists of four helical dipole magnets will be installed in Relativistic Heavy Ion Collider (RHIC) to preserve the polarization of the proton beam. To promote this project we are collaborating with Brookhaven national Laboratory (BNL) in studying helical magnet designs. At present, two types of helical magnets are being developed. One is being designed by the BNL magnet group, and the other by Advanced Magnet Technology (AML). These magnets use the same superconducting cable but have different shapes especially in the end regions. We are evaluating the performance of both magnet designs using three dimensional magnetic field analysis code TOSCA. In particular, saturation effect, field strength, multipole component and magnet quenching features will be quantified. Also the impact on the spin dynamics and beam motion will be addressed.

[6P.17] Multipole Expansion for a Single Helical Current Conductor

The purpose of this paper is to give the expression of the multipole expansion for a single helical current conductor. This analytical expression will be useful for the electromagnetic analysis of various helical coils such as helical dipoles, multifilamentary superconductors and superconducting strands. The present treatment of the multipole expansion for a single helical current conductor is derived as the extension of the case for a single straight current conductor. In addition, the comparison between the analytical and numerical calculations is presented for a single helical current conductor. As a result, the agreement between the analytical and numerical calculations is quite good, except the region near the radius of a single helical current conductor. Then, for the sum of the multipole expansion for a single helical current conductor, the Cesaro's method of summation are adopted.

[6P.18] Analytical Field Calculation of Helical Dipole Magnets for RHIC Snake

The purpose of this paper is to give the analytical expression for the magnetic field of helical dipole magnets, deriving the multipole coefficients. The helical multipole coefficients are defined so that the non-twist helical multipole coefficients is equal to the conventional 2-dimensional multipole coefficients, and the twist dependence of helical multipole coefficients is studied. The expression of the multipoles for the helical coil will be useful for the helical field analysis. The comparison between the analytical and numerical calculations is presented for the simple helical dipole coils. First of all, it is confirmed that the helical multipole coefficients derived from the numerically calculated field are consistent with those calculated analytically, for a infinitely long helical dipole. Secondly, the comparison between the analytical and numerical calculations for a helical dipole with the finite length is made, and the length dependence of helical dipole field is analyzed. In addition, it is also confirmed that the numerical calculation with OPERA-3d/TOSCA is consistent with this analytical calculation.

[6P.19] Design Study of the Injection and Extraction Elements for the RIKEN Superconducting Ring Cyclotron

The injection system for the RIKEN six-sector superconducting ring cyclotron (SRC-6) consists of four bending magnets, three magnetic inflection channels and an electrostatic inflection channel. The four bending magnets and one of the three magnetic channels are superconducting. It is required that the disturbance due to the bending magnets in the acceleration region should be less than 100 G. Two types of bending magnets - with an iron yoke or a shield coil - have been studied. It was found that the iron yoke is ineffective due to the stray fields of up to 0.6 T from the sector magnets. As a result, the bending magnets of an active shield type have been adopted for those close to the sector magnets. The magnetic inflection channels are also designed to be coils of an active shield type. The extraction elements are similar to the injection elements. In this paper, the status of the design study of the injection and extraction elements will be reported.

[6P.20] Applications Toolkit for Accelerator Control and Analysis

The Advanced Photon Source (APS) has taken a unique approach to creating high-level software applications for accelerator control and analysis. The approach is based on self-describing data, modular program toolkits, and scripts. Self-describing data provides a communication standard that aids the creation of modular program toolkits by allowing compliant programs to be used in essentially arbitrary combinations. These modular programs can be used as part of an arbitrary number of high-level applications. At APS, a group of about 60 data analysis, manipulation, and display tools is used in concert with about 20 control-system-specific tools to implement applications for commissioning and operations. High-level applications are created using scripts, which are relatively simple interpreted programs. The Tcl/Tk script language is used, allowing creation of graphical user interfaces (GUIs) and a library of algorithms that are separate from the interface. This allows greater automation of control by making it easy to take the human out of the loop. Applications of this methodology to accelerator commissioning and operation such as orbit correction, and data archiving and review will be discussed.

[6P.21] A Bunch Clock for the Advanced Photon Source

A bunch clock timing module has been developed for use by Advanced Photon Source beamlines. The module provides bunch pattern and timing information that can be used to trigger beamline data collection equipment. The module is fully integrated into the control system software (EPICS) and is automatically loaded with the storage ring fill pattern at injection time. Fast timing outputs (~ 1 ns FWHM) are generated for each stored bunch by using the storage ring low level rf and revolution clock as input references. Fiber optic based transmitters and receivers are used to transmit the 352MHz rf reference to distributed bunch clocks. The bunch clock module occupies a single width VME module and may be installed in a VME crate located near beamline instrumentation. A prototype has been in use on the SRI CAT beamline for several months. The design and integration into the control system timing software along with measured performance results will be presented.

[6P.22] Embedded Controllers, Field Bus and a Modular IO Concept: Central elements of BESSY\,II Controls

Wherever applicable IO nodes connected by a field bus (FB) have apparent advantages: Simple and flexible installation and cabling, easy signal conditioning as well as data filtering and process security provided by intelligent actuators and sensors. The cost of a complex 3rd control system layer may be a high development effort. At BESSY several design principles of this layer control the risk: A few multi purpose IO cards form a modular set. Multiple IO bus connectivity provides high installation flexibility. `Controller Area Network' (CAN) is the FB connected to the VME system of the standard model control system. Communication is provided by a small set of software modules designed to be easily adapted to hardware changes. Communication protocol with BESSY IO modules is a small and efficient subset of the `CAN Application Layer' (CAL) standard. That protocol minimizes the effort to integrate commercial modules from vendors following the CANopen standard. At BESSY II the CAN based FB layer will satisfy more than 80% of the IO demands.

[6P.23] RHIC Beam Permit and Quench Detection Communications System

A beam permit module has been developed to concentrate RHIC ( Relativistic Heavy Ion Collider) subsystem sensor outputs, permit beam, and initiate emergency shutdown. Modules accept inputs from the vacuum, cryogenic, power supply, beam loss, and superconducting magnet quench detection systems. Modules are located at equipment locations around the RHIC ring. The modules are connected by three fiberoptic communications links; a beam permit link, and two magnet power supply interlock links. During operation, carrier presence allows beam. If a RHIC subsystem detects a fault, the beam permit carrier terminates - initiating a beam dump. If the fault was a superconducting magnet quench, a power supply interlock carrier terminates - initiating an emergency magnet power dump. In addition, the master module triggers an event to cause remote sensors to log and hold data at the time-of-failure.

[6P.24] RHIC Real Time Data Link System

The RHIC Real Time Data Link (RTDL) System distributes to all locations around the RHIC ring machine parameters of general interest to accelerator systems and users. The system, along with the supporting host interface, is centrally located. The RTDL System is comprised of two module types: the Encoder Module and the Input Module. There is only one Encoder Module, but many (up to 128) Input Modules. The RTDL System provides multiple buffered outputs to be used locally or to drive fiber optic transmitters for optical transmission to other RHIC equipment locations. Machine parameters are generated directly from the Waveform Generator Module or from machine hardware and coupled directly through a fiber optic serial link to one of two channels on the Input Module.

[6P.25] Evaluation of IEEE 1394 Serial Bus for Distributed Data Acquisition

One trend in accelerator instrumentation is the digitization of signals further upstream in the signal processing chain. In some systems, this leads to distributed data sources that must be interconnected in a standard way. IEEE 1394 Serial Bus provides a possible interconnection standard for these systems. With Serial Bus, data acquisition is implemented via memory to memory transfers within a distributed 64 bit address space. Because this functionality is provided in silicon, software overhead is significantly reduced. This technology is under evaluation for use in the RHIC position monitor system. Using this example system, the suitability of IEEE 1394 for the accelerator environment will be described. Also, the results from recent electromagnetic interference tests of a system spanning over 100 meters will be presented.

[6P.26] Precision Timing Control System

Operation of the CESR storage ring with complex bunch patterns has made necessary more flexible timing controls. Multiple trains of bunches based on a fundamental spacing of 14 ns are used in both the injector and the storage ring. Hence, a generally programmable trigger pattern is needed for electron gun pulsing, beam detection, and beam feedback gating. To achieve this, an upgrade of the previous CESR timing system(R. E. Meller, IEEE Trans. Nucl. Sci., Vol. NS-26, No. 3, p. 4152 (June 1979)) using small-feature CMOS logic has been built. Complex trigger patterns are obtained by using a dual-port RAM which is loaded from a control computer and unloaded by the 14 ns real-time clock. Time delay adjustment with 10 ps resolution is obtained with a phase-locked loop circuit which uses a precision linear phase detector balanced against a 12 bit DAC. The phase detector uses commercial CMOS logic and has RMS noise of less than 15 ps and maximum deviation from linearity of 45 ps. An optimized CMOS integrated circuit version of the phase detector is under development.

[6P.27] Implementation of a New RF Monitoring System for the SRS Using = LabVIEW.

The SRS Computer Control System is undergoing a programme of upgrade from a system of Concurrent Computer Corporation mini computers to a network of PCs (Planned Upgrades to the SRS Control System, B.G.Martlew, M.J.Pugh, W.R. Rawlinson, Proceedings of the 4th European Particle Accel. Conf. London 1994, pp 1788-90). The old RF monitoring system, based on CAMAC hardware, has been replaced with two Industrial PC front end computers running Windows 95 and controlling Hewlett Packard instrumentation and Eurotherm Temperature Controllers. Measurements on the new system are now performed using the data acquisition software LabVIEW=D2 combined with standard PC cards for GPIB and serial communication. This paper describes the hardware and software used in this project, and also how it has been interfaced onto the existing SRS ISOLDE PC control system.

[6P.28] A Bunching Process Control in the Test Linac (S-band) DES

The structure of the control object of the S-band test linac - the electron gun, the focusing systems, two bunchers with RF transmitters and the autonomous systems for regulation of the amplitude, the phase and the resonans frequency of the cavities is presented. The mathematikal model is described with using of the automatic control theory methods for the bunching process and the practical results are presented. The control system of the S-band test linac is described.

[6P.29] Commissioning of SPring-8 Linac Control System

The SPring-8 Linac was completed at end of July 1996, and the beam commissioning has begun since 1st August 1996. On 8th August 1996, we achieved the purpose energy(1GeV). Until the beam commissioning, the computer-aided automatical RF aging system was developed and successfully operated. So that, it took only 550 hours to reach the full power operation, 80MW-60pps-4\musec, of whole klystrons. In the beam commissioning, it is difficult to search the best parameter for getting optium performance on the electron beam. In this scheme, we have designed the automatical parameter searching system. In this paper, we report the status of Linac and the concept of the future automatical control plan.

[6P.30] Improvements to the LANSCE Accelerator Timing System

The Los Alamos Neutron Science Center (LANSCE) 800 MeV proton linear accelerator (linac) operates at a maximum repetition rate of twice the AC power line frequency, i.e. 120 Hz. The start of each machine cycle occurs a fixed delay after each zero-crossing of the AC line voltage. Fluctuations in the AC line frequency and phase are therefore present on all linac timing signals. Proper beam acceleration along the linac requires that the timing signals remain well synchronized to the AC line. For neutron chopper spectrometers, e.g. PHAROS at the Manuel Lujan Jr. Neutron Scattering Center (MLNSC), accurate neutron energy selection requires that precise synchronization be maintained between the beam-on-target arrival time and the neutron chopper rotor position. This is most easily accomplished when the chopper is synchronized to a stable, fixed frequency signal. A new zero-crossing circuit which employs a Phase-Locked Loop (PLL) has been developed to increase the phase and frequency stability of the linac timing signals and thereby improve neutron chopper performance while simultaneously maintaining proper linac operation. Results of timing signal data analysis and modeling and a description of the PLL circuit will be presented.

[6P.31] A Components Database Design and Implementation for Accelerators and Detectors.

Many accelerator and detector systems being fabricated for the PEP-II Accelerator and BaBar Detector needed configuration control and calibration measurements tracked for their components. Instead of building a database for each distinct system, a Components Database was designed and implemented that can encompass any type of component and any type of measurement. In this paper we describe this database design which is especially suited for the engineering and fabrication processes of the accelerator and detector environments where there are thousands of unique component types. We give examples of information stored in the Components Database, which includes accelerator configuration, calibration measurements, fabrication history, design specifications, inventory, etc. The World Wide Web interface is used to access the data, and templates are available for international collaborations to collect data off-line.

[6P.32] The Use of Programmed Logic Controllers (PLC) in High Power RF Control Systems

High power and critical equipment safety system have traditionally been implemented using hard wired relay logic based on the assumption that these systems are more reliable under a high power fault condition. The extensive use of PLC's in industry has shown this assumption in no longer true. The NLCTA RF protection and klystron modulator make use of PLC's for both equipment interlocks and more complex operational controls. This paper describes the control system and the first results of its operation.

[6P.33] PEP-II Injection Timing Control

New hardware and software have been developed for the SLC control system to control injection of beam pulses from the accelerator into the PEP-II storage rings. Hardware includes a camac module to delay the machine timing fiducial in order that a beam pulse extracted from a damping ring will be injected into a selected group of four 476 MHz buckets in a PEP-II ring. Further timing control is accomplished by shifting the phase of the bunches stored in the damping rings before extraction while leaving the phase of the PEP-II stored beam unchanged. The software which drives timing devices on a pulse-to-pulse basis relies on a dedicated communication link on which a scheduling microprocessor broadcasts a 128-bit message to all distributed control microprocessors at 360 Hz. PEP-II injection will be driven according to lists specifying bucket numbers in arbitrary order while at the same time trying to maximize the useful beam delivered to other experiments. These lists will be generated by a microprocessor monitoring the current stored per bucket in each of the PEP-II rings. Diagnostic injection lists may also be sent from the operator consoles to the scheduling microprocessor.

[6P.34] Automated Optimization Tuning Package for the SLC

A linear collider requires precision optimization of multiple parameters to achieve peak performance. Of particular importance are emittance reduction throughout the accelerator and final tuning of the transverse beam size at the interaction point (IP). To facilitate this optimization at the SLC, a semi-automated software package was implemented. Emittance is measured non-invasively with sets of wire scanners at different phases which are located at several positions in the Linac or in the Final Focus. Beam size at the IP is measured by beam-beam deflection scans or indirectly by a luminosity monitor. Typically, the control to be optimized is an orthogonal, closed bump in the beam orbit used for global cancellation of wakefield tails. The SLC feedback system is utilized to implement and to close the bump. The control variable is automatically stepped through a range of values while measuring the resulting beam emittance or other signal. A parabolic fit to the data is performed and the optimal setting for the bump can then be implemented. History plots are available to track the corrections, fit parameters and other quantities of interest over long time periods. The system is database-driven for easy expansion and is layered on top of the Correlation Plot software.

[6P.35] Ground Fault Diagnosctic System for PEP-II

This paper describes a diagnostic system designed into the String Magnet Power Conversion System that localizes magnet or cable ground faults in the PEP-II rings. This system provides online diagnostics that allow the operator/maintenance personnel to identify the magnet string that has the ground fault and the region in the ring where the ground fault exists. Furthermore, it is our goal to identify within 2 adjacent magnets where this fault exists.

The system utilizes the existing PEP-II control system with transient digitizers, ADCs to monitor voltages and currents from the DC/DC converters and the voltage across the soft ground resistor at each bulk power supply. Also, the magnet string voltages are monitored in six locations around the ring to provide an adaptive model of the voltage distribution for each for each magnet string. These signals are utilized in a ground fault location algorithm that identifies and displays the magnet string and specific magnet candidate with the ground fault, on the operators console. Wave forms taken during the fault event are also available for examination at the operators console.

[6P.36] Arc Detection and Interlock Module for the PEP-II Low Level RF System

A new arc detection and interlock generating module for the SLAC PEP-II low-level RF VXI-based system has been developed. The system is required to turn off the RF high voltage power supply in the event of arcing in the cavity windows, klystron window, and circulator. Infrared photodiodes receive arc signals through radiation resistant optical fibers. Optical emitters are paired with the detectors to allow continuity and attenuation monitoring of the optical fiber cable. Gain and bandwidth are selectable for each channel to allow tailoring response. The module also responds to interlock requests from other modules in the VXI system and communicates with the industrial controller responsible for much of the low-level RF system's interlock functionality.

[6P.37] Automatic Lattice Parameters Measurement Tools at SRRC

In order to acquire necessary machine parameters information within reasonable time for machine physicists, supporting tools for automatic lattice parameters measurement were implemented at SRRC. Hardware components include devices for signal waveform detection, spectrum analysis, and control circuits. Developed software package consists of tools for instrument control, data acquisition, analysis, and visualization of measured parameters. Typical applications of the tool package were tune identification, resonance diagram for working point evolution, measured lattice function display, and filling pattern of the stored electron bunches in the ring. Real-time displaying absolute orbit and difference orbit with persistence display option have shown to be a powerful tool for orbit study. These tool boxes can be activated with simple pop-up operation on workstation. Detailed functions and its status will be presented in this report.

[6P.38] An Orbit Correction Algorithm for General Beam Lines

An algorithm is developed for orbit correction in beam lines where the corrector and BPM configuration can take on a wide range of possibilities. Corrector strength minimizaton is effected in the process. Performance analysis and limitations of the algorithm are discussed. Application to the CEBAF arcs will also be demonstrated.

[6P.39] Orbit Correction Using Virtual Monitors at Jefferson Lab

An orbit correction algorithm is developed to achieve the following goals for the CEBAF accelerator at Jefferson Lab.: 1). Pre-processing of orbit input to account for estimated misalignment and monitor errors. 2). Automatic elimination of blind spots caused by response matrix degeneracy. 3). Transparency of exception handling to interchangeable generic steering engines. 4). CEBAF-specific demands on control of injection angle, path length, orbit effects on optics, simultaneous multiple pass steering, and orbit control at un-monitored locations. All of the above can be accomplished by the introduction of virtual monitors into the processed input orbit, whose theoretical basis is to be discussed in this report. Implementation of all or part of these features and operational experience during the CEBAF variable energy runs will also be discussed.

[6P.40] Pulse Selection Control for the IR FEL Photocathode Drive Laser

The method for current control of the photocathode source is described. This device allows remote control of drive laser output pulses for resulting beam currents of less than 1 microamp to full current of 5 milliamps. The low current modes are accomplished by counting discrete micropulses and gating electro-optical cells. The higher current modes are done by varying both the photons per pulse and the frequency of the laser output pulses. Programmable Logic Devices (PLDs) provide the choice in micropulses per macropulse and the macropulse frequency. All macropulses are line locked to 60 Hz and have the ability to be slewed through a line cycle in discrete steps.

[6P.41] Experience With Vsystem in a Wide Variety of Applications

Over the past eight years, Vsystem has developed from the in-house software licensed from Los Alamos Laboratory to a product solving demanding problems in a wide variety of industrial and research applications. Steel and aluminum production, power distribution monitoring, power plant training systems, nuclear power plant monitoring, petrochemical plants, semiconductor wafer processing, flour mills, breweries, under-water weapons testing and radio transmitters are a number of our current applications outside the accelerator, tokamak and laser applications in research. This paper will review some of these applications and discuss novel usage made of Vsystem and conclude that there are many similarities between the requirements of accelerator control systems and industrial systems. More interesting are the differences in requirements and we find that these differences enhance Vsystem in ways that help all users. We will also review these areas of difference.

[6P.42] Tuning and Optimization at Brookhaven and Argonne: Results of Recent Experiments Using a Portable Intelligent Control System

Vista Control Systems Inc. is developing a portable system for intelligent accelerator control.(Supported by DOE/SBIR Grant DE-FG05-94ER81897) Our system is general purpose and has been designed to be reused at multiple accelerator facilities. This portability arises directly from the hierarchical object-oriented organization of the architecture. We briefly describe the basic features of the architecture. The control system employs a multi-level architecture in which knowledge based inferencing is used to dynamically configure a variety of powerful optimization and control algorithms. These include neural networks, genetic algorithms, and fuzzy reasoning. We then discuss results from recent beamline tuning and optimization tests at the Brookhaven National Laboratory ATF and the ATLAS facility at Argonne. We report a number of significant successes, particularly in the areas of portability, optimization, and noise handling.

[6P.43]

This abstract was not submitted electronically.

[6P.44] APT LLRF Control System Model Results

The low-level RF (LLRF) control system is an essential component of the RF= system for the Accelerator Production of Tritium (APT). Requisite for good= performance at a reasonable cost is system modeling prior to actual= hardware build. Models have been created to help establish the LLRF= control system baseline design. These Matrix_X (R) models incorporate= common signal processing functions and control functions as well as mixed= continuous and discrete-time analysis. Components include klystron= saturation curves, waveguide delays, realistic resonant cavity equivalents= and LLRF proportional, integral, and differential (PID) control transfer= functions. They predict the performance of the LLRF system in the presence= of beam noise, excitation of non-fundamental modes which occur in the= superconducting cavities and pulsed beam situations. This paper will= describe the basic model and will present results for a variety of= operating scenarios.

[6P.45] Algorithms and Implementation of APT Resonant Control System

A digital signal processor is used to control resonant frequency of the RFQ prototype in APT/LEDA. Two schemes are implemented to calculate the resonant frequency of RFQ. One uses the measurement of the forward and reflected fields. The other uses the measurement of the forward and transmitted fields. The former is sensitive and accurate when the operation frequency is relatively far from the resonant frequency. The latter gives accurate results when the operation frequency is close to the resonant frequency. Linearized algorithms are derived to calculate the resonant frequency of the RFQ efficiently using a fixed-point DSP. The control frequency range is about 100kHz for 350MHz operation frequency. A frequency agile scheme is employed using a dual direct digital synthesizer to drive the klystron at the cavitys frequency (not necessarily the required beam resonant frequency) in power-up mode. This paper will address the algorithm implementation, error analysis, as well as related hardware design issues.

[6P.46] Status of the PEP-II Transverse Feedback Systems

The feedback systems for controlling transverse coupled-bunch instabilities in both the high and low energy rings of the PEP-II collider are complete and installed on site. Presently, the high energy ring system is undergoing beam commissioning. Design specifications and the basic systems are reviewed. Selected bench-test data for various system components is presented including results from the sum-signal orbit offset cancellation electronics. Available beam commissioning data is presented and discussed.

[6P.47] Stabalization of the Bates Electron Beam through Phase and Amplitude Detection and Energy Feedback

Experiments in which high precision measurements are necessary, such as parity violation experiments, require small systematic errors associated with the beams used in those experiments. To help minimize the systematic errors associated with the polarized electron beam used at the MIT Bates Linear Accelerator, we have developed a diagnostic system which extracts the amplitude and phase of the RF power accelerating the beam, as well as a prototype feedback system which stabalizes the beam energy. Design considerations and preliminary results will be presented, as well as plans for future development of this system.

[6P.48] Beam Test of the Acceleration System with the DDS in HIMAC Synchrotron

The HIMAC acceleration system with a direct digital synthesizer (DDS) is operating stably. In this system acceleration frequency is controlled by use of the magnetic field with step width of 0.2 Gauss. In the design stage this small step width, which is required in the system with the DDS, is adopted to make the frequency jump small. To see the effect of this jump on this growth, we have accelerated the beam with the different step width of the magnetic field. In this test we have also adjusted the acceleration voltage pattern to have optimum acceleration. This optimized voltage pattern is important in the case of high beam intensity. In this paper we will present the experimental results.

[6P.49] Transverse Beam Feedback System in PLS,

Since September 1995, the PLS serves as the national users facility. During two years of its operation, it is understood that the stored beam current is limited by the coupled-bunch beam instability. To suppress the beam instability, we will use the feedback systems as well as the improvements of the rf cavities. The transverse feedback system is completed and is being commissioned. There are two detectors for accurate adjustments of the phase delay between the pickup signal and the feedback signal. A correlator filter composed of two coaxial cable delay lines suppresses the revolution harmonics below -30dB. The bandwidth of the system is 100kHz to 250MHz. We describe the characteristics and the performance of the PLS transverse feedback system in this paper.

[6P.50] The Design of the ELETTRA Fast Local Feedback System

The stability of the electron beam position is one of the main issues for third generation synchrotron radiation sources. A fast local feedback system based on digital signal processing techniques has been designed and installed on ELETTRA. After a characterization of the main system components, the design choices are presented. The software environment used for system development and measurements is described.

[6P.51] First Operational Results with the ELETTRA Fast Local Feedback System

A fast local feedback system has been installed on one of the ELETTRA beamlines. The first operational results are presented and compared with the performance foreseen with a simulated model of the system.

[6P.52] Commissioning Experience with the PEP-II Low Level RF System

The low-level RF system for PEP-II is a modular design housed in a VXI environment. Remotely configurable feedback loops are used to control coupled-bunch instabilities driven by the accelerating mode of the RF cavities. A programmable DSP based feedback loop is implemented to control phase variations across the klystron due to required adjustment of the cathode voltage to limit cathode power dissipation. The DSP loop also adaptively cancels modulations caused by klystron power supply ripple at selected power line harmonics between 60 Hz and 10 kHz. An adaptive technique is used to generate the station RF reference which tracks the ion clearing gap induced cavity transients. All RF signal processing and measurements are done using inphase and quadrature (IQ) techniques. This paper presents observations and measured data from the system.

[6P.53] SLC Fast Feedback Performance Improvements at Higher Frequencies

A beam-based fast feedback system has been used to stabilize orbits, energy and other beam parameters throughout the SLC since 1991. In early implementations, the measured frequency response in the Linac was less than optimal for 120 Hz operation, partly due to hardware limitations which prevented the feedbacks from operating at the full beam rate. For the 1996 SLC run, hardware upgrades and a new operational strategy significantly improved the Linac feedback system and reduced beam jitter. Recently measured performance results now achieve the ideal response required for a future linear collider. Additionally, the beam collision feedback at the interaction point was enhanced to damp oscillations at and near the Nyquist frequency of 60 Hz. Specialized correctors support separate control of the beam collisions on alternate pulses of the accelerator, and customized software controls the beam position separately for even and odd tagged pulses. Initial performance measurements indicate that the feedback is able to damp beam noise at and around 60 Hz in addition to controlling low frequency oscillations.

[6P.54] Design and Verification of Controllers for Coupled Bunch Instabilities Using Optimal Control Theory and Numerical Simulation: Predictions for PEP-II

We present a technique for the design and verification of efficient bunch-by-bunch controllers for damping longitudinal multibunch instabilities. The controllers attempt to optimize the use of available feedback amplifier power - one of the most expensive components of a feedback system - and define the limits of the closed loop system performance. Our design technique alternates between analytic computation of single bunch optimal controllers and verification on a multibunch numerical simulator. The simulator uses PEP-II parameters and identifies unstable coupled bunch modes, their growth rates and their damping rates with feedback. The results from the simulator are shown to be in reasonable agreement with analytical calculations based on the single bunch model. The technique is then used to evaluate the performance of a variety of controllers proposed for PEP-II.

[6P.55] Numerical Simulations of the PEP-II Longitudinal Feedback Kicker.

The feedback system in PEP-II will employ a drift-tube type kicker to supplement cavity damping in suppressing longitudinal coupled-bunch instabilities. In addition to prototyping, numerical modeling has been used to verify the kicker performance and to study related design issues such as beam impedance and parasitic heating. The simulations have been carried out in the time domain using a realistic MAFIA model that includes the coaxial feedthroughs and the delay lines between the electrodes. The calculated shunt impedance and beam impedance are in good agreement with measurements performed on a prototype.

[6P.56] Gap Voltage Feed-Forward Board for PEP-II Low Level RF System

This paper describes the Gap Voltage Feed-Forward VXI module used in the PEP-II Low Level RF System. This module produces adaptively generated inphase (I) and quadrature (Q) reference signals for a single RF station based on measurements of periodic (1-turn) beam induced cavity transients caused by the presence of an ion clearing gap. In addition the module receives a fiber optically transmitted, bandlimited ``kic'' signal from the longitudinal feedback system which is used to phase modulate the RF drive. This allows the RF system to act as a ``subwoofer'' for the longitudinal feedback system for low order coupled-bunch instabilities driven by the fundamental mode of the accelerating cavities. The module includes hardware for remote measurement and adjustment of the ``kick'' transfer function.

[6P.57] VXI Based Multibunch Detector and QPSK Modulator for the PEP-II/ALS/DA\PhiNE Longitudinal Feedback System

The PEP-II/DA\PhiNE/ALS feedback systems are complex systems implemented using analog, digital and microwave circuits. The VXI hardware implementation for the front-end and back-end analog processing modules is presented. The front-end module produces a baseband beam phase signal from pickups using a microwave tone burst generator. The back-end VXI module generates an AM/QPSK modulated signal from a baseband correction signal computed in a digital signal processor. These components are implemented in a VXI package that allows a wide spectrum of system functions including a 120 MHz bandwidth rms detector, reference phase servo, woofer link to the RF control system, the standard VXI status/control, and user defined registers. The details of the design and implementation of the VXI modules including performance characteristics are presented.

[6P.58]

This abstract was not submitted electronically.

[6P.59] Local Feedback Experiment in the Taiwan Light Source

A highly-effective digital global feedback system (DGFB) has been developed to control closed-orbit error in the Taiwan Light Source (TLS). However, the beam orbit in the TLS is intrinsically so stable that a digital local feedback system may be preferred for some operating conditions. Consequently, a prototype digital local feedback loop has been developed and tested for suppressing orbit disturbances at the source point of a photon beamline. This prototype consists of a local orbit bump whose strength is dynamically controlled to preserve the beam trajectory. The measured bump response is used in this feedback system, and the controller uses a PID algorithm. Digital filtering is used to reduce the noise in beam position measurements. The hardware of the local feedback system is integrated with that of the global feedback system.

[6P.60] Digital Global Orbit Feedback System Developing In SRRC

The digital global orbit feedback system for the storage ring of SRRC has been upgraded in terms of its feedback bandwidth extension by increasing its data acquisition sampling rate and compensating eddy current effect of vacuum chamber with filter. This orbit feedback system has been applied incorporate with the insertion devices operation, such as W20 wiggler and APU undulator, in order to eliminate beam orbit disturbance. Applying this system to suppress orbit drift during energy ramping has also shown to be effective. Performance of this upgraded system will be presented in this report.

[6P.61] Developement of Digital Longitudinal Damper for the TLS Storage Ring

Longitudinal coupled-bunch instabilities occurred in the stored electron beam of the SRRC/TLS storage ring are the sources of its longitudinal emittance degradation. A digital feedback system that rely on commercial parallel digital signal processing boards is designed and being built to damp the phase oscillations of the electron bunches. The designs of the feedback system and some critical hardwares such as bunch phase detector, fast A/D and D/A converters, multiplexer and demultiplexer, and longitudinal kicker will be described. And a preliminary online test will be reported.

[6P.62] Optimising Injection into CELSIUS with a Steering Feedback and Beta-Matching System

In order to provide reproducible conditions, a steering feedback system consisting of two beam position monitors and two steering magnets will be installed in the beam line immediately upstream of the injection point into CELSIUS. Moreover, a 1 mm aluminium wire placed vertically on the horizontally moving stripping foil mechanism measures the beam profile and the emittance. This allows adjusting upstream quadrupoles to optimise injection conditions. Preliminary operational experience is presented.

[6P.63] Development of Digital Feedback Systems for Beam Position and Energy at the Thomas Jefferson National Accelerator Facility

The development of beam-based digital feedback systems for the CEBAF accelerator has gone through several stages. As the accelerator moved from commissioning to operation for the nuclear physics program, the top priority was to stabilize the beam against slow energy and position drifts (< 1 Hz). These slow drifts were corrected using the existing accelerator monitors and actuators driven by software running on top of the EPICS control system. With slow drifts corrected, attention turned to quantifying the higher frequency disturbances on the beam and to designing the required feedback systems needed to achieve the CEBAF design stability requirements. Results from measurements showed the major components in position and energy to be at harmonics of the power line frequencies of 60, 120, and 180 Hz. Hardware and software was installed in two locations of the accelerator as prototypes for the faster feedback systems needed. This paper gives an overview of the measured beam disturbances and the feedback systems developed.

[6P.64] Design and Implementation of a General Slow Orbit Control Package at Jefferson Lab

During the commissioning and operation of a particle accelerator it is neccessary to have orbit control packages to control slow drifts. Here we describe a Client/Server based implementation of a general orbit control package designed to lock and steer the beam at a maximum rate of several Hz. The package is written in C++ and uses the CDEV software device control bus. As such the implementation is independent of any underlying control system. New algorithms can be added by subclassing the existing base classes and full configuration control is inherited. We describe the implementation of a standard algorithm like SVD and of a more advanced beam steering algorithm.

[6P.65] Analogues of the Robinson criteria for RF cavity resonators with delayed, voltage-proportional feedback

Robinson gave two criteria for the stability of a charged particle beam interacting with the RF cavity resonator that is responsible for accelerating that beam. A widely adopted procedure for high current beams, is to reduce the apparent cavity impedance by voltage-proportional feedback, to avoid the power-limited instability. Inevitably, the feedback is delayed; and this introduces exponential terms into the system characteristic equation. We give a general, exact, analytic procedure for determining whether there are poles/zeros in the right-half complex plane; and apply the method to find analogues of the Robinson criteria.

[6P.66] Study of Orbit Feedback Systems for the TESLA Linear Collider

In order to reduce the influence of magnet vibrations which can cause luminosity reduction in the TESLA Linear Collider, several feedback loops are foreseen to control the beam orbit and to keep the beams in collision. The complete control system for orbit correction can be divided into three different feedback systems: A slow feedback system is foreseen in the main linac to cancel perturbations in the low frequency range which are mainly due to ground motion. In the beam delivery section a fast feedback system is to be installed to compensate disturbances containing higher frequency components, mainly from pulse-to-pulse quadrupole vibrations and potentially also due to microphonics and Lorentz-force detuning in the superconducting cavities. At the interaction point a fast feedback system will keep the two beams in collision, using the beam-beam-deflection signal. This paper summarizes design studies for all three orbit correction schemes and the main components are discussed in detail.

[6P.67] SPEAR-III: A Facility Upgrade at SSRL

The 3 GeV SPEAR storage ring presently operates with a FODO lattice having 130 nm-rad natural emittance. By installing a DBA lattice with a new vacuum chamber, the emittance is reduced to below 20 nm-rad, and the lifetime exceeds 50 hr at 200mA. In this configuration, the focused photon flux for existing insertion devices increases by more than an order of magnitude, while for future undulators the brightness exceeds 10^18 in the 5 keV range. In the 20 keV range, the hardened bend magnet radiation increases by more than two orders of magnitude. This paper describes plans to implement the upgrade with minimum downtime.

*Work supported by the Department of Energy Contract DE-AC03-76SF00515 and Office of Basic Energy Sciences, Division of Chemical Sciences.

Part 6 of program listing