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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

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

Sensitivity and offset calibration for the beam position monitors at the Advanced Photon Source

Description: The beam position monitors (BPMs) play a critically important role in commissioning and operation of accelerators. Accurate determination of the offsets relative to the magnetic axis and sensitivities of individual BPMs is thus needed. We will describe in this paper the schemes for calibrating all of the 360 BPMs for sensitivity and offset in the 7-GeV Advanced Photon Source (APS) storage ring and the results. For the sensitivity calibration, a 2-dimensional map of the BPM response in the aluminum vacuum chamber is obtained theoretically, which is combined with the measured nonlinear response of the BPM electronics. A set of 2-dimensional polynomial coefficients is then obtained to approximate the result analytically. The offset calibration of the BPMs is done relative to the magnetic axis of the quadrupoles using the beam. This avoids the problem arising from various mechanical sources as well as the offset in the processing electronics. The measurement results for the resolution and long-term drift of the BPM electronics shows 0.06-{mu}m/{radical}Hz resolution and 2-{mu}m/hr drift over a period of 1.5 hrs.
Date: July 1, 1995
Creator: Chung, Y.; Barr, D.; Decker, G.; Evans, K. Jr. & Kahana, E.
Partner: UNT Libraries Government Documents Department

Alignment and survey of the elements in RHIC

Description: The Relativistic Heavy Ion Collider (RHIC) consists of two rings with cryogenic magnets at a 4.5K operating temperature. Control of positions of the dipole and quadrupole cold masses (iron laminations) and the beam position monitors (BPM`s) during production and installation is presented. The roll of the dipoles is controlled by a combination of rotating coil measurements with the surveying measurements. The center of the quadrupole magnetic field is obtained by direct measurement of the field shape within a colloidal cell placed inside the quadrupoles. Special attention is given to the triplet quadrupole alignment and determination of the field center position.
Date: May 1, 1995
Creator: Trbojevic, D.; Cameron, P. & Ganetis, G.L.
Partner: UNT Libraries Government Documents Department

The APS booster synchrotron: Commissioning and operational experience

Description: The Advanced Photon Source (APS) at Argonne National Laboratory (ANL) was constructed to provide a large user community with intense and high brightness synchrotron radiation at x-ray wavelengths. A 7-GeV positron beam is used to generate this light. Acceleration of the beam from 450 MeV to 7 GeV is accomplished at a 2-Hz repetition rate by the booster synchrotron. Commissioning of the booster began in the second quarter of 1994 and continued on into early 1995. The booster is now routinely used to provide beam for the commissioning of the APS storage ring. Reported here are our commissioning and operational experiences with the booster synchrotron.
Date: July 1, 1995
Creator: Milton, S.V.
Partner: UNT Libraries Government Documents Department

Toward more precise beam position measurements

Description: For the past year or so we have been examining the properties and limitations of the beam bugs in use in the ETA program at LLNL with a view toward improving the accuracy of beam position and current measurements. When considering measurements of beam position, it is very important to distinguish between relative and absolute position measurements. A relative position measurement determines only the amplitude and direction of the motion of the beam within the transport tube. If one knew where the beam was, one could determine its new position. A relative measurement is essentially independent of errors in mechanical fabrication or electrical components. The minimum measurable displacement is only limited by the strength of the electrical signals or the signal to noise ratio of the position signal. An absolute position measurement is much more challenging. All inaccuracies in mechanical components and fabrication, electrical components, installation and assembly errors must be considered and controlled along with the issues common to relative position measurements. However, if the object is to strike a small specific point on a target or pass the beam through a small hole, absolute beam position measurements are required. The following is a summary of our progress including conclusions and recommendations for developments and improvements. This is, of course, only a step in beam bug development and there is plenty of room for others to contribute.
Date: May 12, 1999
Creator: Clark, J C; Fessenden, T J & Holmes, C
Partner: UNT Libraries Government Documents Department

Operational aspects of experimental accelerator physics

Description: During the normal course of high energy storage ring operations, it is customary for blocks of time to be allotted to something called ``machine studies,`` or more simply, just ``studies.`` It is during these periods of time that observations and measurement of accelerator behavior are actually performed. Almost invariably these studies are performed in support of normal machine operations. The machine physicist is either attempting to improve machine performance, or more often trying to recover previously attained ``good`` operation, for example after an extended machine down period. For the latter activity, a good portion of machine studies time is usually devoted to ``beam tuning`` activities: those standard measurements and adjustments required to recover good operations. Before continuing, please note that this paper is not intended to be comprehensive. It is intended solely to reflect one accelerator physicist`s impressions as to what goes on in an accelerator control room. Many topics are discussed, some in more detail than others, and it is not the intention that the techniques described herein be applied verbatim to any existing accelerator. It is hoped,, however, that by reading through the various sections, scientists, including accelerator physicists, engineers, and accelerator beam users, will come to appreciate the types of operations that are required to make an accelerator work.
Date: July 1, 1995
Creator: Decker, G.A.
Partner: UNT Libraries Government Documents Department

Digital signal processing for the APS transverse and longitudinal damping system

Description: The Advanced Photon Source (APS) at Argonne National Laboratory will be a 7-GeV machine. It is anticipated that for beam operations beyond the baseline design of 100 mA stored beam current, a transverse and longitudinal damping system is needed to damp instabilities. A key part of this digital damping system is digital signal processing. This digital system will be used to process samples taken from the beam and determine appropriate correction values to be applied to the beam. The processing will take the form of a transversal digital filter with adaptable filter weights. Sampling will be done at 176 MHz with a possible correction bandwidth of 88 MHz. This paper concentrates on the digital processing involved in this system, and especially on the adaptive algorithms used for determining the digital filter weights.
Date: July 1, 1995
Creator: Barr, D. & Sellyey, W.
Partner: UNT Libraries Government Documents Department

A low-cost non-intercepting beam current and phase monitor for heavy ions

Description: A low cost ion beam measurement system has been developed for use at ATLAS. The system provides nondestructive phase and intensity measurement of passing ion beam bunches by sensing their electric fields. Bunches traverse a short tubular electrode thereby inducing displacement currents. These currents are brought outside the vacuum jacket where a lumped inductance resonates electrode capacitance at one of the bunching harmonic frequencies. This configuration yields a basic sensitivity of a few hundred millivolts signal per microampere of beam current. Beam induced radiofrequency signals are summed against an offset frequency generated by the master oscillator. The resulting difference frequency conveys beam intensity and bunch phase information which is sent to separate processing channels. One channel utilizes a phase locked loop to stabilize phase readings during microsecond beam drop outs. The other channel uses a linear full-wave active rectifier circuit which converts sine wave signal amplitude to a DC voltage representing beam current. Plans are in progress to install this new diagnostic at several locations in ATLAS which should help shorten the tuning cycle of new ion species.
Date: July 1, 1995
Creator: Bogaty, J.M. & Clifft, B.E.
Partner: UNT Libraries Government Documents Department

The development of beam current monitors in the APS

Description: The Advanced Photon Source (APS) is a third-generation 7-GeV synchrotron radiation source. The precision measurement of beam current is a challenging task in high energy accelerators, such as the APS, with a wide range of beam parameters and complicated noise, radiation, and thermal environments. The beam pulses in the APS injector and storage ring have charge ranging from 50pC to 25nC with pulse durations varying from 30ps to 30ns. A total of nine non- intercepting beam current monitors have been installed in the APS facility (excluding those in the linac) for general current measurement. In addition, several independent current monitors with specially designed redundant interlock electronics are installed for personnel safety and machine protection. This paper documents the design and development of current monitors in the APS,. discusses the commissioning experience in the past year, and presents the results of recent operations.
Date: July 1, 1995
Creator: Wang, X.; Lenkszus, F. & Rotela, E.
Partner: UNT Libraries Government Documents Department

High precision electron beam diagnostic system for high current long pulse beams

Description: As part of the effort to develop a multi-axis electron beam transport system using stripline kicker technology for DARHT II apploications, it is necessary to precisely determine the position and extent of long high energy beams (6-40 MeV, 1-4 kA, 2 microseconds) for accurate position control. The kicker positioning system utilizes shot-to-shot adjustments for reduction of relatively slow (<20 MHz) motion of the beam centroid. The electron beams passing through the diagnostic systems have the potential for large halo effects that tend to corrupt measurements performed using capacitive pickoff probes. Likewise, transmission line traveling wave probes have problems with multi-bounce effects due to these longer pulse widths. Finally, the high energy densities experienced in these applications distort typical foil beam position measurements.
Date: March 24, 1999
Creator: Nelson, S D; Fessenden, T; Chen, Y J; Holmes, C & Selchow, N
Partner: UNT Libraries Government Documents Department

Performance of a beam monitor in the Fermilab Tevatron using synchrotron light

Description: Synclite, the beam monitor in the Fermilab Tevatron using synchrotron light is described. The calibration, monitoring and performance of the system is discussed. Observation of some effects of long range beam-beam interactions seen in the beam monitor will be presented as well as a measurement of DC beam in the Tevatron.
Date: June 4, 2003
Creator: Cheung, Harry W.K.; Hahn, Alan & Xiao, Aimin
Partner: UNT Libraries Government Documents Department

On the Choice of Method to Cancel 60 Hz Disturbances in Beam Position and Energy

Description: Because the voltage applied to magnets in accelerators is likely to be rectified, there can be 60 Hz related fluctuations in beam position and energy. Correcting such errors as well as other less repeatable errors can be done with combinations of feedback, feedforward, real time repetitive control, and batch update repetitive control. This paper studies how to mix these approaches for optimized performance. It is shown that use of feedback control can be counterproductive because of the waterbed effect operating on errors such as BPM noise. Also, it is seen that iterative repetitive control updates can produce significantly better error levels than pure feedforward control. Making corrections of errors for harmonics of 60 Hz that are above the Nyquist frequency can be accomplished, and this can save the expense and integration effort to produce fast beam sampling.
Date: June 1, 2001
Creator: Akogyeram, R.A.; Longman, R.W.; Hutton, Andrew & Juang, J.-N.
Partner: UNT Libraries Government Documents Department