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Improvement of the noise figure of the CEBAF switched electrode electronics BPM system

Description: The Continuous Electron Beam Accelerator Facility (CEBAF) is a high-intensity continuous wave electron accelerator for nuclear physics located at Thomas Jefferson National Accelerator Facility. A beam energy of 4 GeV is achieved by recirculating the electron beam five times through two anti-parallel 400 MeV linacs. In the linacs, where there is recirculated beam, the BPM specifications must be met for beam intensities between 1 and 1,000 {micro}A. To avoid a complete redesign of existing electronics, they investigated ways to improve the noise figure of the linac BPM switched electrode electronics (SEE) so that they could be used in the transport lines. This paper will focus on the source of the excessive out-of-band noise and how it was reduced. The development, commissioning and operational results of this low-noise variant of the linac style SEE BPMs as well as techniques for determining the noise figure of the RF chain will also be presented.
Date: May 1, 1998
Creator: Powers, Tom
Partner: UNT Libraries Government Documents Department

Preliminary results of RMS emittance measurements performed on the sub-picosecond accelerator using beam position monitors

Description: The Sub-picosecond Accelerator at Los Alamos National Laboratory is a 1300 MHz, 8 MeV photoinjector. Concerned mainly with the exploration of bunched electron beams, the Sub-picosecond Accelerator facility is also used for a variety of other research. One ongoing task is the exploitation of the second moment properties of beam position monitor signals to measure the rms emittance. The unique properties of photoinjector beams make Gaussian assumptions about their distribution inaccurate and traditional methods of measuring the rms emittance fail. Using beam position monitors to measure the emittance, however, requires no beam distribution assumptions. Presented here are the first emittance measurements with this method on the Sub-picosecond Accelerator.
Date: August 1, 1997
Creator: Russell, S.J.
Partner: UNT Libraries Government Documents Department

Calibration of the beam-position monitor system for the SLAC PEP-II B factory

Description: 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 onboard calibrator. Results for these portions of the calibration are presented.
Date: June 1, 1997
Creator: Johnson, R.; Smith, S. & Kurita, N.
Partner: UNT Libraries Government Documents Department

Multivideo image processing for beam profile monitoring system

Description: Some experiments at Jefferson Lab demand tight beam size ({approx} 100 {mu}m) and very low energy spread (< 5 x 10{sup {minus}5}). These experiments also require simultaneous and continuous monitoring of these quantities. This paper focuses on the development of the image processing aspects of the beam profile monitoring system. A pipelined image processor, Datacube's MaxVideo MV200, calculates beam sizes and positions from two beam profile monitors simultaneously at 10 Hz rate. Multiplexing software in the EPICS environment allows a single digitizer to process several input channels at high speed. This system makes the profile monitors usable for tuning the accelerator, as well as delivering critical information to the end stations. This paper discusses the issues related to the daily operational use of the system. The availability and reliability of the monitoring system became acceptable only after the implementation of programs that automatically setup and periodically check the monitors and digitizer. The system permits additional video channels without significant additional hardware cost.
Date: May 1, 2000
Creator: Hardy, D.; Chevstov, P.; Denard, J-C. & Dickson, R.
Partner: UNT Libraries Government Documents Department

Damping spurious harmonic resonances in the APS storage ring beam chamber.

Description: The APS storage ring beam chamber has been storing the beam up to 100 mA successfully. However, in some beam chambers, spurious signals corrupted the BPM outputs. The cause of the unwanted signals was investigated, and it was found that transverse electric (TE) longitudinal harmonic resonances of the beam chamber were responsible. The beam chambers have small height in the area between the ovid beam chamber and the antechamber. The structure behaves like a ridge waveguide so that the cut-off frequency of the waveguide mode becomes lower. The pass-band then includes the frequency around 350 MHz that is important to the beam position monitors (BPMs). The spurious harmonic resonances are damped with two types of dampers to restore the useful signals of the BPMs; coaxial loop dampers and lossy ceramic slab loading are used.
Date: April 20, 1999
Creator: Kang, Y.
Partner: UNT Libraries Government Documents Department

Four-button BPM coefficients in cylindrical and elliptic beam chambers.

Description: Beam position monitor (BPM) coefficients are calculated from induced charges on four-button BPMs in circular and elliptic beam chambers for {gamma} >>1. Since the beam chamber cross-section for the APS storage ring is different from an exact elliptic geometry, numerical values of the BPM coefficients and their inversions are computed from two-dimensional electrostatic field distributions inside an exact geometry of the beam chamber. Utilizing Green's reciprocation theorem, a potential value is applied to the buttons rather than changing the beam position, and potential distributions corresponding to the beam positions are then computed.
Date: April 8, 1999
Creator: Kim, S. H.
Partner: UNT Libraries Government Documents Department

Coherent sychrotron radiation detector for a non-invasive subpicosecond bunch length monitor

Description: This CSR detector was developed to monitor nondestructively the length of a subpicosecond bunch with high sensitivity. The monitor uses a state of the art GaAs Schottky whisker diode which is operated at room temperature at a wavelength of a few hundred microns. The detector is capable of detecting radiation power as low as 10 nW, depending on wavelength. This paper describes design specifications, parameter ranges, and monitor features and also reports its performance and comparison between measurement and calculation. The measurement results are cross-compared with an independent bunch length measurement using phase modulation. It was found that the output power varies with bunch length and that detectors at shorter wavelengths are preferred.
Date: December 31, 1995
Creator: Krafft, G.A.; Wang, D.; Price, E.; Feldl, E.; Porterfield, D.; Wood, P. et al.
Partner: UNT Libraries Government Documents Department

Transverse feedback systems for the PEP-II B-factory

Description: Growth rates of coherent beam oscillations are faster than the natural damping mechanisms for the parameters of the PEP-II B-factory storage rings at nominal currents, even with damping of cavity higher order modes (HOM`s). With 165 8 bunches separated by 4.2 ns, and a large current of up to 3A (2.14 A nominal in the low energy ring), many coupled-bunch modes are excited by the resistive wall impedance and cavity higher order mode impedance. Fastest growth times of transverse rigid-bunch modes of approximately 300 ps are expected, two orders of magnitude faster than the radiation damping time. We will provide broadband, bunch-by-bunch feedback to suppress this coherent motion of the beam. Experience gained with a prototype system, installed and successfully operating at the LBNL Advanced Light Source (ALS), has been used extensively in developing the design of the PEP-II systems.
Date: October 1, 1995
Creator: Corlett, J.N.; Barry, W.; Byrd, J.M.; Lambertson, G.; Johnson, J. & Fahmie, M.
Partner: UNT Libraries Government Documents Department

High current CW beam profile monitors using transisiton radiation at CEBAF

Description: One way of measuring the profile of CEBAF`s low emittance and high power beam is to use the Optical Transition Radiation (OTR) emitted from a thin foil surface when the electron beam passes through it. We present the design of a monitor using the forward OTR emitted from a 0.25 {mu}m carbon foil. We believe that the monitor will resolve three main issues: (i) whether the max temperature of the foil stays below the melting point, (ii) whether the beam loss remains below 0. 5%, in order not to trigger the machine protection system, and (iii) whether the monitor resolution (unlike that of synchrotron radiation monitors) is better than the product {lambda}{gamma}. It seems that the most serious limitation for CEBAF is the beam loss due to beam scattering. We present results from Keil`s theory and simulations from the computer code GEANT as well as measurements with Al foils with a 45 MeV electron beam. We also present a measurement of a 3.2 GeV beam profile that is much smaller than {lambda}{gamma}, supporting Rule & Fiorito`s calculations of the OTR resolution limit due to diffraction.
Date: July 1, 1996
Creator: Piot, P.; Denard, J.C.; Adderley, P; Capek, K. & Feldl, E.
Partner: UNT Libraries Government Documents Department

A Novel Wire Scanner for High Intensity Pulsed Beams

Description: A novel wire scanner has been developed with applications at linear accelerators where small beam spots or high intensities would otherwise destroy wires. A pattern of wires is supported on a thin membrane and remains in place even when punctured by the beam. Many scans can be made before the material needs to be replaced. Tests of the principle have been carried out at the Final Focus Test Beam at SLAC.
Date: February 19, 1999
Partner: UNT Libraries Government Documents Department

Performance of the beam position monitor for the Advanced Photon Source

Description: Performance measurement and analysis of the Advanced Photon Source (APS) beam position monitor (BPM) electronics are reported. The results indicate a BPM resolution of 0.16 {mu}m{center_dot}mA/{radical}Hz in terms of the single-bunch current and BPM bandwidth. For the miniature insertion device (ID) BPM, the result was 0.1 {mu}m{center_dot}mA/{radical}Hz. The improvement is due to the 3.6 times higher position sensitivity (in the vertical plane), which is partially canceled by the lower button signal by a factor of 2.3. The minimum single-bunch current required was roughly 0.03 mA. The long-term drift of the BPM electronics independent of the actual beam motion was measured at 2 {mu}m/hr, which settled after approximately 1.5 hours. This drift can be attributed mainly to the temperature effect. Implications of the BPM resolution limit on the global and local orbit feedback systems for the APS storage ring will also be discussed.
Date: October 19, 1995
Creator: Chung, Y. & Kahana, E.
Partner: UNT Libraries Government Documents Department

The Holifield Radioactive Ion Beams Facility (HRIBF) -- getting ready to do experiments

Description: The conversion of the HHIRF facility to a Radioactive Ion Beam facility started in 1994. In this ISOL type facility the Cyclotron has been re-fitted as a driver providing high intensity proton beams which react with the target from which the radioactive products are extracted and then accelerated in the Tandem Electrostatic Accelerator to the desired energy for nuclear science studies. Facilities for nuclear physics experiments are at different stages of development: A Recoil Mass Spectrometer (RMS) with a complement of detectors at the focal plane and around the target is used primarily for nuclear structure studies. A large recoil separator combining velocity and momentum selection, with its complement of focal plane detectors, will be dedicated to measurements relevant to nuclear astrophysics. The Enge Split Pole spectrograph is being re-fitted for operation in a gas filled mode, making it a more versatile tool for nuclear reaction studies. With the new experimental equipment being commissioned and the prospects of running experiments with low intensity radioactive beams a significant effort to develop equipment for beam diagnostics is underway. Some of the efforts and results in developing beam diagnostic tools will be described.
Date: February 26, 1998
Creator: Shapira, D. & Lewis, T.A.
Partner: UNT Libraries Government Documents Department

Instrumentation concepts for the very large hadron collider (VLHC)

Description: Instrumentation concepts for the Very Large Hadron Collider (VLHC) are discussed. Different design concepts for the VLHC result in substantially different instrumentation layouts. High field, cold bore magnets have instrumentation requirements very similar to the SSC and LHC. In contrast, the low field warm bore transmission line magnets have very sparse instrumentation and the long magnet length allows the cable plant to be preinstalled on the magnets. Specialized beam instrumentation concepts including permanently sealed semi-rigid coax BLM's and distributed coupled-bunch damping systems are discussed.
Date: August 28, 2000
Creator: Foster, George William
Partner: UNT Libraries Government Documents Department

HOTLink rack monitor

Description: A remote data acquisition chassis, called a HOTLink Rack Monitor, HRM, has been developed for use in the Fermilab control system. This chassis provides for 64 analog input channels, 8 analog output channels, and 8 bytes of digital I/O. The interface to the host VMEbus crate is by way of a 320 MHz HOTLink serial connection to a PMC mezzanine module. With no processor intervention, all data sources in the remote chassis are read at 100 sec intervals, time stamped, and stored in a 2 MB circular buffer on the PMC module. In operation, the memory always contains the most recent 16 k samples of 10 kHz data from all 64 analog input channels. An expansion module that resides in the HRM chassis records snapshot data for 8 analog channels, each channel consisting of up to 16 k readings, digitized at rates up to 10 MHz. Snapshot data is also returned and stored in buffers on the PMC module. Because the HRM presents a memory-mapped interface to the host, it is independent of the operating system and may be used in any system that supports PMC mezzanine modules.
Date: December 3, 2001
Creator: al., Al R Franck et
Partner: UNT Libraries Government Documents Department


Description: A movable Beam Position Monitor (BPM) using shorted stripline Pick-Up Electrode (NE) elements has been resonated using matching stub techniques to achieve a relatively high Q resonance at about 230MHz. This PUE has been used in a feasibility study of phase-locked-loop tune measurement [1], using a lock-in amplifier and variable frequency generator to continuously track betatron tune in RHIC, as well as to observe Schottky signals of the Gold beam. The approach to providing a high Q PUE for difference mode signals, simulation studies, and the results of initial tests will be presented.
Date: June 18, 2001
Partner: UNT Libraries Government Documents Department


Description: In the Relativistic Heavy ion Collider (RHIC) much larger background signals were occurring at BRAMS, one of the four experiments. This was especially pronounced at the time when vacuum conditions deteriorated due to the beam ionization profile monitor replacements. Recording the beam intensities during the store provided the beam lifetime. Predictions from the beam gas interactions to the above measured values are compared The ionization gauges simultaneously recorded the vacuum pressure data.
Date: June 18, 2001
Partner: UNT Libraries Government Documents Department

Signals from Microwave Unstable Beams in the SLC Damping Rings

Description: The longitudinal microwave instability is present in the SLC damping rings during routine operations. Experimental studies of the instability at nominal conditions have been reported previously. To complement those studies and better understand the properties of the instability a series of dedicated experiments were performed under a broad range of operating parameters. These experiments included spectral measurements of BPM signals as well as time domain diagnostics using a custom detecting circuit. This paper describes the techniques, the results and discusses possible interpretations of these measurements.
Date: April 5, 1999
Creator: Podobedev, Boris
Partner: UNT Libraries Government Documents Department

Optimization of four-button BPM configuration for small-gap beam chambers.

Description: Configuration of four-button beam position monitors (BPMs) employed in small-gap beam chambers is optimized from 2-D electrostatic calculation of induced charges on the button electrodes. The calculation shows that for a narrow chamber of width/height (2w/2h) >> 1, over 90% of the induced charges are distributed within a distance of 2h from the charged beam position in the direction of the chamber width. The most efficient configuration for a four-button BPM is to have a button diameter of (2-2.5) h with no button offset from the beam. The button sensitivities in this case are maximized and have good linearity with respect to the beam positions in the horizontal and vertical directions. The button sensitivities and beam coefficients are also calculated for the 8-mm and 5-mm chambers used in the insertion device straight sections of the 7-GeV Advanced Photon Source.
Date: May 27, 1998
Creator: Kim, S. H.
Partner: UNT Libraries Government Documents Department

Luminosity monitor topics for RHIC spin and AA, and pA interactions.

Description: This is a note to define topics to be studied in more depth for the Luminosity monitoring for Spin Asymmetries. My numerical examples here are to stimulate discussion and should be taken with a grain of salt. The RHIC Spin experiments will require a very high degree of coordination between the experiments and the accelerator. For example see AGS/RHIC/SN 035. In this note we list some of the issues to be considered in monitoring the relative luminosity between various beam-beam spin combinations and beam-gas combinations. We give simplified numerical examples of the problems encountered in doing the luminosity monitoring to the 10{sup {minus}4} level. It is hoped that this will provide a framework for serious study of these problems with simulations and other means. Many of the issues may also be relevant to pA and AA running where there may be sizable beam-gas backgrounds.
Date: February 17, 1998
Creator: Underwood, D.
Partner: UNT Libraries Government Documents Department

Luminosity monitor.

Description: Luminosity monitors are needed in each experiment doing spin physics at RHIC. They concentrate on the luminosity aspects here because, for example, with a 10{sup {minus}3} raw asymmetry in an experiment, an error of 10{sup {minus}4} in the luminosity is as significant as a 10% polarization error. Because luminosity is a property of how two beams overlap, the luminosity at an interaction region must be measured at that interaction region in order to be relevant to the experiment at that interaction region. The authors will have to do the physics and the luminosity measurements by using labels on the event sums according to the polarization labels on the colliding bunches. Most likely they will not have independent polarization measurement on each bunch, but only on all the filled bunches in a ring, or perhaps all the bunches that are actually used in an experiment. Most analyses can then be handled by using the nine combinations gotten from three kinds of bunches in each ring, +, {minus} and empty bunches. The empty bunches are needed to measure beam-gas background, (and some, like six in a row, are needed for the beam abort). Much of the difficulty comes from the fact that they must use a physics process to represent the luminosity. This process must have kinematic and geometric cuts both to reduce systematics such as beam-gas backgrounds, and to make it representative of the part of the interaction diamond from which the physics events come.
Date: July 16, 1998
Creator: Underwood, D. G.
Partner: UNT Libraries Government Documents Department

Wiggler insertion of the PEP-II B-Factory LER

Description: The Low Energy Ring (LER) of the PEP-II B Factory at SLAC employs two identical wiggler insertions for emittance control and extra damping with each insertion designed to absorb 400 kW of synchrotron radiation. The wiggler is a set of individual iron core dipoles designed to operate at 1.6 T. The basic variant will include nine 0.4-m length magnets and two 0.2-m length magnets. A copper vacuum chamber is used with continuous antechambers connected to both sides of the beam chamber via slots. Synchrotron radiation dump surfaces and distributed vacuum pumping are located in both antechambers. We describe the design and analysis of the vacuum chamber, dump and magnets.
Date: April 1, 1995
Creator: Heim, J.; Bertolini, L. & Dressler, J.
Partner: UNT Libraries Government Documents Department

Nanometer resolution BPM using damped slot resonator

Description: A new type of high resolution beam position monitor called the damped slot resonator rf BPM has been installed at the focal point of the FFTB. It is comprised of a cylindrical resonant cavity with a tuned choke joint at the TM{sub 110} resonances. The BPM has a large dynamic range from the nm to mm range with a minimum resolution of 1 nm. We report on the rf cavity cold tests performance, processing electronics design, and some experimental results obtained in obtained in the high energy electron beam line.
Date: May 1, 1995
Creator: Hartman, S.C.; Shintake, T. & Akasaka, N.
Partner: UNT Libraries Government Documents Department


Description: It is well known that beam position monitors (BPM) utilizing signals from pickup electrodes (PUE) provide good resolution and relative accuracy. The absolute accuracy (i.e. position of the orbit in the vacuum chamber) is not very good due to the various reasons. To overcome the limitation it was suggested to use magnetic centers of quadrupoles for the calibration of the BPM [1]. The proposed method provides accuracy better then 200 microns for centering of the beam position monitors using modulation of the whole quadrupole family.
Date: November 1, 2005
Creator: PINAYEV, I.
Partner: UNT Libraries Government Documents Department