BIW '98 Secretary
c/o Suzanne Barrett
SSRL, SLAC MS 99
P.O. Box 4349
Stanford, CA 94309-0210
Phone: (650) 926-3191
FAX: (650) 926-3600

BIW98@slac.stanford.edu

R.B. Shurter, J. D Gilpatrick, J. Ledford, J. O’Hara, J. Power Lawrence Livermore National Laboratory (LLNL)

An automated and highly accurate system for "mapping" 5 cm diameter beam position monitors (BPM’s) used in the Low Energy Demonstrator Accelerator (LEDA) at Los Alamos is described. Two-dimensional data is accumulated from the four micro-stri pline pickups in the probe by sweeping an antenna driven at the LEDA bunching frequency of 350 MHz in discrete steps across the aperture. These data are then used to determine the centroid, first and 3rd order sensitivities of the BPM. These probe response coefficients are then embedded in the LEDA control system database to provide normalized beam position information to t he operators. A short summary of previous systems we have fielded is given, along with their attributes and deficiencies which had a bearing on this latest design. Lessons learned from this system will, in turn, be used on the next mappers that are currently being designed for 15 cm and 2.5 cm BPMs.

500 MHz Narrowband Beam Position Monitor Electronics

I.Mohos and J.Dietrich Forschungszentrum Jülich/IKP

Beam position monitor electronics were developed in the Forschungszentrum Jülich/IKP for the orbit measurement equipment at the electron synchrotron ELSA (University Bonn). The monitor electronics, consisting of RF signal processing module and data acquisition a nd control module, measures and processes the monitor signals and delivers via serial network calculated horizontal and vertical beam position data with 1 ms time and <10 µm position resolution. In the paper the electronics and test measurements are described.

The Calibration of BEPC Beam Position Monitors

K. Ye , L. Ma, H. Hung BEPC, China

Basic requirement for beam position monitor is the beam orbit measurement of 0.1 mm precision at near the colliding point . We measured the cross section view cylindrical position monitor, before it located between beam ducts.

All of their calibration maps are tested on a test bench. A high frequency coaxial switches are used choosing buttons.

A microcomputer controlled antenna moving, data analysis and hardware control. We believe that the low frequency measurement can yield the same information as the real beam.

A constant low frequency inputed antenna , then acquired this frequency signal from four button. A spectr um analyzer was used to read data. The signal is clear. This calibration is satisfactory in BEPC operation.

Calibration of BPM Button Sensitivity and Coefficients in Narrow Beam Chambers

S. Kim Advanced Photon Source (APS)

In order to find the optimum sensitivity and beam position coefficients for a four-button beam position monitor (BPM) system, charges induced on buttons in a beam chamber of narrow rectangular cross section (width/height >>1) are calculated as a 2-D electrostatic problem of image charges. Over 90% of the induced charges are distributed within a distance of one chamber height from the charged beam position in the direction of the chamber width. Therefore, a four-button system with a button diameter of one chamber height located within this distance is the most efficient. Button sensitivities and coefficients of the BPMs installed in the 8-mm and 5-mm chambers in the Advanced Photon Source have been calculated.

Advanced Photon Source RF Beam Position Monitor Front-End Upgrade

R. Lill, G. Decker Advanced Photon S ource (APS)

This paper will describe and analyze the rf beam position monitor (RFBPM) front-end upgrade for the Advanced Photon Source (APS) storage ring. This system is based on amplitude to phase (AM/PM) conversion monopulse receivers. The design and performance of the existing RFBPM front end will be considered as the baseline desig n for the continuous effort to improve and upgrade the APS beam diagnostics. The upgrade involves redesigning the in-tunnel filter comparator units to improve insertion loss, return loss, and bandpass filter matching that presently limit the different fill patters used at APS.

Calibration of an Advanced Photon Source Linac Beam Position Monitor Used for Pos itron Position Measurement of a Beam Containing Both Positrons and Electrons

N. Sereno Advanced Photon Source (APS)

The Advanced Photon Source (APS) linac beam position monitors can be used to monitor the position of a positron beam also containing electrons. To accomplish this task, both the signal at the bunching frequency of 2856 MHz and the signal at 2 x 2856 MHz are acquired and processed for each stripline. The positron beam positiion is obtained by forming a linear combination of both 2856 and 5712 MHz signals for each stripline and then performing the standard difference over sum computation. The required linear combination of the 2856- and 5712-MHz signals depends on the electrical calibration of each stripline/cable combination. In this paper, the calibration constants for both 2856- and 5712-MHz signals for each stripline are determined using a pure beam of electrons. The calibration constants are obtained by measuring the 2856- and 5712-MHz stripline signals at various electron beam currents and positions. Finally, the calibration constants measured using electrons are used to determine positron beam position for the mixed beam case.

Beam Position Monitors for the Fermilab Recycler Ring

E. Barsotti , S. Lackey, C. McClure et al. Fermi National Accelerator Laboratory (FNAL)

Fermilab’s new Recycler Ring will recover and cool "used" antiprotons at the end of a Tevatron store and also accumulate "new" antiprotons from the Antiproton Source. A wideband RF system based on barrier buckets will result in unbunched beam, grouped in one to three separate batches throughout the ring. A new Beam Position Monitor system will measure position of any one batch at a time, using low frequency signals from beam distribution edges. A signal path including an elliptical split-plate detector, radiation-resistant tunnel preamplifiers, and logarithmic amplifiers will result in a held output voltage nearly proportional to position. The results will be digitized using

Industry Pack technology and a Motorola MVME162 processor board. The data acquisition subsystem including digit ization and timing for 80 position channels will occupy two VME slots.

Beam Position Monitor System for the KEKB Injector Linac

T. Suwada, N. Kamikubota, H.Kobayashi KEK

About ninety stripline-type beam-position monitors (BPMs) has been newly installed in the KEKB injector linac. The monitors reinforces easi ly handling an orbit of a high current single bunch electron beams (~10 nC/pulse) generating positron beams supplied for the KEKB ring. The design value of the beam-position resolution is expected to be less than 0.1mm. A new data-acquisition system was newly developed in order to control the monitors. It comprises a host computer (UNIX), eighteen data-acquisition (DAQ) sta tions, which are located along the linac klystron gallery at almost regular interval. The DAQ station comprises a VME/OS-9 computer and a fast digital sampling oscilloscope and signal combiners. The pick-up signals from the five BPMs in average are sent to the one DAQ station where the signals are combined by using the signal combiners. Each combined signal is fed to the os cilloscope controlled by the VME computer through GPIB. In this report, the basic design and preliminary beam-test results of the new BPM system are presented.

The DELTA Beam Based BPM Calibration System

A. Jankowiak, T. Weis, K. Wille DELTA, Dortmund

A 3rd generation synchrotron radiation source like DELTA needs a measuring system which allows to determine the beam position with high resolution and great accuracy with respect to the centre of the quadrupole magnets. During the commissioning the closed orbit measuring system reaches the design value (10um) for the relative accuracy but the bpm offsets with respect to the magnetic centre of the quadrupole magnets are not exact ascertainable. The uncertainty in the determination of these offsets are for some bpms in the order of several 100 um. To overcome with this problem we installed an extra cabling for each quadrupole during the last shutdown which allows together with a relays cascade to change the focussing strength of each quadrupole individually. By steering the beam in the quadrupole magnets and minimising the orbit distortion induced by the change of the k-value it is possible to determine the magnetic centre of the quadrupole magnets and to get a absolute calibration of the closed orbit measuring system. Furthermore this system provides the possibilty to measure the local beta function in each quadrupole magnet.

In this paper the present installation and first results of calibration measurements will be presented.

Beam Jitter and Quadrupole Motion in the Stanford Linear Collider

R. Stege, Jr., J. Turner Stanford Linear Accelerator Center (SLAC)

Spectral analysis of beam jitter in the SLC has shown that some beam motion is confined to narrow frequency bands. Vibration analysis of Linac quadrupoles using high resolution accelerometers yield spectra of a similar footprint. Motion at 59 Hertz was found to be driven by a pressure oscillation in the accelerator structure cooling water, while other frequencies were found to be vibrational modes of the structure itself. This paper presents motivating beam data, describes instrumentation used for vibration measurements, presents vibration related data and summarizes the solutions used to reduce quadrupole motion.

The BOAT Beam Position Monitor Prototype Test Results

E. Medvedko, S. Smith, A. Fisher Stanford Linear Accelerator Center (SLAC)

Loss of stored bea m in an uncontrolled manner can cause damage to the PEP-II machine.

We describe here a device which detects large beam position excursions, or unexpected beam loss and triggers the beam abort system to extract the stored beam safely.The bad orbit abort trigger beam position monitor (BOAT BPM) purpose is to generate a trigger pulse when the beam orbit is far off the center (>20 mm), or rapid beam current loss (dI/dT) is detected. The BOAT BPM shall average the input signal over 1 turn (136 kHz).

AM demodulation technique is used to convert high input frequency signal (476 MHz) to baseband voltage. Detected signal goes to filter section (for revolution frequency sup pression), then feeds amplifiers, dividers, and comparators for position / current measurements and triggering. The derived current signal goes to a special filter, designed to perform dI/dT monitoring at fast, medium and slow current loss rates. The BOAT BPM prototype test results confirm the design ideas.

BPM Testing, Analysis, and Correction

J . A. Fitzgerald, J. L. Crisp, E. S. McCory, G. Vogel Fermi National Accelerator Laboratory (FNAL)

A general purpose stretched wire test station has been developed and used for mapping Beam Position Monitors (BPM). A computer running LabView software controlling a network analyzer and X-Y positioning tables operates the station and generates data files.

The data is analyzed in Excel and can be used to generate correction tables. Test results from a variety of BPMs used for the Fermi Main Injector and elsewhere will be presented.

Beam Position Monitor System of DAFNE

A. Stella, A. Drago, A. Ghigo, C. Milardi, F. Sannibale, M. Serio, C. Vaccarezza, INFN, Frascati

The F-Factory DAFNE is a high current multibunch e+e- double ring collider, presently under commissioning at INFN-LNF. The beam position monitor (BPM) system of DAFNE consists of 150 monitors installed all along the machine. Because of the various requirements of each part of DAFNE, due to the different beam characteristics or to the vacu um chamber geometry, several different pickup devices and monitor configurations were designed and installed in the Transfer-lines, Accumulator and Main Rings. They include short circuited strip-lines, matched strip-lines, button electrodes pickup and special monitor for use in the interaction regions. We describe design issues, calibration procedures, numerical simulations, experimental results and performance of the BPM realized. The closed orbit in the Main Rings is extracted from the BPM signals through narrowband receivers (realized by Bergoz Precision Beam Instrumentation for DAFNE), then acquired and processed by a real-time task in four VME crates, located in different areas of the machine.

The data acquisition system is integrated in the DAFNE control system and measures five complete orbits in a second: implementation criteria, measurements and results are reported.

Two Bunch Beam Position Monitor Commissioning Results

R. Traller, E. Medvedko, S. Smith Stanford Linear Accelerator Center (SLAC), R. Aiello Interv al Research Corporation

New beam position processing electronics for the Linear Accelerator allow faster feedback and processing of both positron and electron bunch positions in a single machine pulse. More than 30 Electron-positron Beam Position Monitors (epBPMs) have been installed at SLAC in various applications and have met all design requirements. The SLC production electron bunch follows the positron bunch down the Linac separated by 58.8 nS.

The epBPM provides accurate sampling of both bunches with an accuracy of better than 5 µm at nominal operating intensities. For SLC the epBPMs have measured the position of bunches consisting of from 1 to 8E10 particles per bunch. In PEPII epBPMs have used larger electrodes and measured the position of pulses of as little as 2E9 particles per pulse. To meet the demands of SLC and PEPII injection the epBPM has been designed with three triggering modes: 1) as a self triggering detector it can trigger off the beam and hold the peak signal until read out by the control program; 2) it can use external timing signals to g ate the beam trigger; 3) it can use the external timing signals offset by internal vernier delays to precisely catch peak signals in noisy environments. In this last mode the epBPM operates like a digital oscilloscope. Finally, the epBPM also has built-in timing verniers capable of nulling errors in cable set fabrication and differences in channel-to-channel signal delay. Software has made all this functionality available through the SLC control system.

Development Of Nanometer Resolution C-Band Radio Frequency Beam Position Monitors In The Final Focus Test Beam

G. Mazaheri, T. Slaton Stanford Linear Accelerator Center (SLAC), T. Shintake (KEK)

Using a 47 GeV electron beam, the Final Focus Test Beam (FFTB) produces vertical spot sizes around 70 nm [1]. These small beam sizes introduce an excellent opportunity to develop and test high resolution Radio Frequency Beam Position Monitors (RF-BPMs). These BPMs are designed to measure pulse to pulse beam motion (jitter) at a theoretical resolution of approximately 1 nm [2]. The beam induces a TM ₁₁₀ mode with an amplitude linearly proportional to its charge and displacement from the BPM's (cylindrical cavity) axis. The C-band (5712 MHz) TM₁₁₀ signal is processed and converted into beam position for use by the Stanford Linear Collider (SLC) control system. Presented are the experimental procedures, acquisition, and analysis of data demonstratin g resolution of jitter near 25 nm. With the design of future e⁺e^- linear colliders requiring spot sizes close to 3 nm [3], understanding and developing RF-BPMs will be essential in resolving and controlling jitter.

Performance of the Beam-Position Monitor System for the SLAC PEP-II B-Factory

R. Johnson, S. Smith Stanford Lin ear Accelerator (SLAC), G. Aiello (Interval Research Corporation)

The Beam-Position Monitor (BPM) System for the SLAC PEP-II B-Factory was designed to measure the positions of single-bunch single-turn to multi-bunch multi-turn beams in both rings of the facility. Each BPM is based on four button-style pickups. At most locations the but tons are connected to provide single-axis information (x only or y only). Operating at a harmonic (952 MHz) of the bunch spacing, the BPM System combines broadband and narrow-band capabilities and provides data at a high rate. The active electronics is multiplexed for signals from the High-Energy Ring (HER) and Low-Energy Ring (LER). The system will be briefly described; ho wever, the main purpose of the present paper is to present operational results. The BPM system operated successfully during commissioning of the HER (primarily) and the LER over the past year. Results to be presented include on-line calibration, single-bunch single-turn resolution (<100 um), and multi-bunch multi-turn resolution (<3 um), multiplexing, and absolute cal ibration. Thus far the system has met or exceeded all the requirements that have been tested. The remaining requirements will be tested when both rings are completed and commissioned this summer. In addition, typical results of beam physics studies relying on the BPM system will be presented.

1 nA Beam Position Monitor

M. Piller, R. Flood, L. Ham mer, M. Parks, E. Strong, L. Turlington, R. Ursic, Thomas Jefferson National Accelerator Facility (TJNAF)

A new BPM system, based on resonant cavities, has been developed for measuring the transverse position of very low intensity electron beams delivered to Experimental Hall B at the Continuous Electron Beam Accelerator Facility (CEBAF) in Newport News, VA. The system requirements called for measuring down to 1 nA with a 100 m m resolution. The actual system is much better: it can measure down to 100 pA at the 100 m m required resolution. A 100 pA beam yields about 1 electron per bunch. Each 1 nA BPM utili zes three resonant RF cavities to determine the position of the beam: one cavity sensitive to X position, a second cavity sensitive to Y position, and a third cavity which measures intensity. The position cavities operate at room temperature in a dipole type mode at 1497 MHz and contain internal field perturbing rods in an arrangement similar to that of the CEBAF RF Separat or cavities. The position cavities are electron beam welded assemblies made of copper plated stainless steel. The RF output signal from each cavity is processed using a down-converter and a DSP based commercial lock-in amplifier operating at 100 kHz. The lock-in amplifiers connect to the EPICS control system via an IEEE 488 bus. System features under development include int ensity and position modulation measurement capabilities. This paper provides measured performance results and an updated overview of the installed and operational 1 nA BPM system.

New Microwave Beam Position Monitors for the TESLA Test Facility FEL

R. Lorenz, T. Kamps DESY Zeuthen

Beam-based alignment is es sential for the operation of the SASE-FEL at the TESLA Test Facility Linac. In order to ensure the overlap of the photon beam and the electron beam, the position of the electron beam has to be measured along the undulator beamline with a resolution of some microns. Due to the severe space limitations, a new microwave concept is being considered. It is based on special ridged waveguides coupling by small slots to the magnetic field of the electron beam. The four waveguides and slots of each monitor were split into two symmetric pairs separated in beam direction. All waveguides are about 35 degrees apart in azimut from the horizontal axis and will be fabricated using electro-discharge machining (EDM). Waveguide-to-coax adaptors were designed to couple the signal of each waveguide into a coaxial cable. It is aimed to measure the averaged position of a bunch train in a narrowband receiver having a center frequency of 12 GHz. A prototype of this monitor was built and tested on a testbench, as well as at the CLIC Test Facility at CERN. The paper summarizes the concept, the design and further improvements of this wave guide monitor.

Investigation of Beam Position Monitor Technologies for the LCLS FEL Undulator

R. Hettel, R. Carr, D. Martin Stanford Synchrotron Radiation Laboratory (SSRL), C. Field Stanford Linear Accelerator Center (SLAC)

A free electron laser requires that the electron beam travel on a straight trajectory so that it is continuously bathed in the radiation it creates. In the 100 m long, 6 mm diameter vacuum chamber for the linac-driven Linear Coherent Light Source FEL undulator the beams must propagate colinearly to within ~5 microns over distances comparable to the 10 m FEL gain length in order to maintain gain.  We have co nsidered a variety of intercepting and non-intercepting position monitor technologies to establish and maintain this beam alignment.  We present a summary of our investigation of the applicability and estimated performance of monitors detecting synchrotron radiation, transition radiation, diffraction radiation, fluoresence, photoemission or bremsstrahlung from thin wir es, Compton scattering from laser wires, and image currents from the electron beam.  We conclude that non-intercepting rf cavity electron BPMs, together with a beam based alignment system, are best suited for this application.  In addition, we will employ intercepting wire BPMs for rough alignment, beam size measurements, and for simultaneous electron and photon b eam coincidence measurements, using diffraction of the photon beam and bremsstrahlung created by the electron beam.

Test Results of the LEDA Beam Position/Intensity Measurement Module

C. Rose, M. Stettler Los Alamos National Laboratory (LANL)

This paper describes to-date progress in the design and testing of the log-ratio-based beam-position/intensity measurement module being built for the Low Energy Demonstration Accelerator (LEDA) and Accelerator Production of Tritium (APT) projects at Los Alamos National Laboratory. The VXI-based module uses four, 2 MHz, IF inputs to perform two-axis position measurements and one intensity measurement. To compensate for systematic errors, r eal-time error-correction is performed on the four input signals after they are digitized and before calculating beam position and intensity. Beam intensity is computed by using the average of the four log-amplifier outputs. This method provides a better off-axis intensity response than the traditional method of summing the rf power from the four lobes. Several types of test data are presented including results of the realtime error correction technique, a working dynamic range of over 80 dB, and achievable resolution and accuracy information.

Diagnostics Used in Commissioning the IUCF Cooler Injector Synchrotron

M. Ball, D. Friesel, B. Hamilton Indiana University Cyclotron Facility (IUCF)

Sev eral new diagnostics systems were designed to aid in the commissioning of the IUCF Cooler Injection Synchrotron (CIS). Among them are a time of flight measurement system (ToF), a multi-wire profile monitor system (Harp) and a beam position monitor system (BPM). Pulsed beam from the 7 Mev linear accelerator is monitored using the ToF system. Several removable Harps are mount ed in the injection beamline and ring which are instrumental for tuning ring injection and accumulation. BPMs are placed at the entrance and exit of the four ring dipole magnets to facilitate beam centering during injection and ramping. Fast and slow BPM displays are available to the operator for these functions. These diagnostics and their uses for CIS ring commissioning w ill be discussed.

Diagnostics Development in the SRRC

K. T. Hsu, C. H. Kuo, J. Chen, C. S. Chen, K. K. Lin, C. C. Kuo, R. Sah, SRRC, Taiwan

There are several new developments in diagnostics of SRRC. These new developments include orbit feedback system, tune monitor, filling pattern monitor, time-domain coupled bunch oscillat ion observation system, and improved synchrotron radiation monitor. Global orbit feedback system as well as local orbit feedback system has been developed to eliminate orbit excursion from reference orbit that are cause by various perturbation sources. Digital receiver based tune monitor provide a fast tune reading as a complementary tool to commercial spectrum analyzer.