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Determination of coupled-lattice properties using turn-by-turn data

Description: A formalism for extracting coupled betatron parameters from multiturn, shock excited, beam position monitor data is described. The most important results are nonperturbative in that they do not rely on the underlying ideal lattice model. Except for damping, which is assumed to be exponential and small enough to be removed empirically, the description is symplectic. As well as simplifying the description, this leads to self-consistency checks that are applied to the data. The most important of these is a {open_quotes}magic ratio{close_quotes} of Fourier coefficients that is required to be a lattice invariant, the same at every beam position monitor. All formulas are applied to both real and simulated data. The real data was acquired June, 1992 at LEP as part of decoupling studies, using the LEP beam orbit measurement system. Simulated data, obtained by numerical tracking (TEAPOT) in the same (except for unknown errors) lattice, agrees well with real data when subjected to identical analysis. For both datasets, deviations between extracted and design parameters and deviations from self-consistency can be accounted for by noise and signal processing limitations. This investigation demonstrates that the LEP beam position system yields reliable local coupling measurements. It can be conservatively assumed that systems of similar design at the SSC and LHC will provide the measurements needed for local decoupling.
Date: December 1, 1992
Creator: Bourianoff, G.; Hunt, S. & Mathieson, D.
Partner: UNT Libraries Government Documents Department

Calibration of an Advanced Photon Source linac beam position monitor used for positron position measurement of a beam containing both positrons and electrons.

Description: 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 position 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-MHz 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.
Date: May 19, 1998
Creator: Sereno, N. S.
Partner: UNT Libraries Government Documents Department

Computation of Nonlinear One-Turn Maps from Measurement with Model-Independent Analysis

Description: It is desirable to determine the nonlinear transformation maps, especially the one-turn map, of a storage ring from measured BPM data for nonlinear analysis in order to improve the machine performance. However, the accuracy of detecting the weak signals from nonlinear effects is often limited by the available BPM resolution. With the recent development of Model-Independent Analysis methods, which can significantly reduce BPM random noise via statistical analysis, it is possible to more accurately determine the nonlinear maps from measured data by using a large number of BPMs. Computational techniques and some simulation results for PEP-II will be presented.
Date: April 12, 1999
Creator: Wang, Chunxi
Partner: UNT Libraries Government Documents Department

Automated beam based alignment of the ALS quadrupoles

Description: Knowing the electrical offset of the storage ring beam position monitors (BPM) to an adjacent quadrupole magnetic center is important in order to correct the orbit in the ring. The authors describe a simple, fast and reliable technique to measure the BPM electrical centers relative to the quadrupole magnetic centers. By varying individual quadrupole magnets and observing the effects on the orbit they were able to measure the BPM offsets in half the horizontal and vertical BPMs (48) in the ALS. These offsets were measured to an accuracy of better than 50{mu}m. The technique is completely automated and takes less than 3 hours for the whole ring.
Date: April 1995
Creator: Portmann, G.; Robin, D. & Schachinger, L.
Partner: UNT Libraries Government Documents Department

Electron beam bunch length characterizations using incoherent and coherent radiation on the APS SASE FEL project.

Description: The Advanced Photon Source (APS) injector linac has been reconfigured with a low-emittance rf thermionic gun and a photocathode (PC) rf gun to support self-amplified spontaneous emission (SASE) free-electron laser (FEL) experiments. One of the most critical parameters for optimizing SASE performance (gain length) is the electron beam peak current, which requires a charge measurement and a bunch length measurement capability. We report here initial measurements of the latter using both incoherent optical transition radiation (OTR) and coherent transition radiation (CTR), A visible light Hamarnatsu C5680 synchroscan streak camera was used to measure the thermionic rf gun beam's bunch length ({sigma} {approximately}2 to 3ps) via OTR generated by the beam at 220 MeV and 200 mA macropulse average current. In addition, a CTR monitor (Michelson Interferometer) based on a Golay cell as the far infrared (FIR) detector has been installed at the 40-MeV station in the beamline. Initial observation s of CTR signal strength variation with gun a-magnet current and interferograms have been obtained. Progress in characterizing the beam at these locations and a comparison to other bunch length determinations will be presented.
Date: August 28, 1999
Creator: Berg, W. J.; Happek, U.; Lewellen, J. W.; Lumpkin, A. H.; Sereno, N. S. & Yang, B. X.
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


Description: The Cooler Synchrotrons and storage ring COSY at the Forschungszentrum Juelich accelerates protons to momenta between 600 MeV/c and 3300 MeV/c [2]. At present the beam is used at four internal and three external target places. In addition, a polarized beam can be produced and accelerated at COSY. A colliding beams source, developed by a collaboration of the universities of Bonn, Erlangen, and Cologne is in operation [3]. The polarized H{sup {minus}} beam delivered by this source is pre-accelerated in a cyclotron to 295 MeV/c and injected via stripping injection into the COSY ring. The polarization of the circulating proton beam in COSY is measured continuously during acceleration with the internal EDDA detector [4]. In this paper the methods to overcome depolarizing resonances in COSY are discussed and the progress to preserve polarization during acceleration is presented.
Date: May 20, 1999
Creator: LEHRACH,A.
Partner: UNT Libraries Government Documents Department

Beam instrumentation for an ISOL test stand

Description: TRIUMF is constructing a test bed for the first stages of the proposed TISAC accelerated radioactive beam facility. The authors will present the requirements for the diagnostic system for this test stand and describe the design and development work underway. Scintillators, beamstops and a Faraday Cup have been tested using stable, mass analyzed, 12 keV beams of ions from mass 14 to 132. The design of a linear drive, with 10 {micro}m resolution, for scanning wires and slits has begun.
Date: September 1, 1995
Creator: Mackenzie, G.H.; Dombsky, M.; Rawnsley, W.; Stanford, G.; Yin, Y. & Novikov, A.
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

Design of the digitizing beam position limit detector.

Description: The Digitizing Beam Position Limit Detector (DBPLD) is designed to identify and react to beam missteering conditions in the Advanced Photon Source (APS) storage ring. The high power of the insertion devices requires these missteering conditions to result in a beam abort in less than 2 milliseconds. Commercially available beam position monitors provide a voltage proportional to beam position immediately upstream and downstream of insertion devices. The DBPLD is a custom VME board that digitizes these voltages and interrupts the heartbeat of the APS machine protection system when the beam position exceeds its trip limits.
Date: May 27, 1998
Creator: Merl, R.
Partner: UNT Libraries Government Documents Department

First multi-GeV particle-beam measurements using a synchroscan and dual-sweep x-ray streak camera.

Description: Particle-beam characterizations of a multi (7)-GeV storage ring beam have been done for the first time using a synchroscan and dual-sweep x-ray streak camera at the Advanced Photon Source (APS). The hard x-rays (2-20 keV) from a bending magnet source were imaged using an adjustable pinhole aperture, and both the horizontal size, {sigma}{sub x} {approximately} 190 {micro}m, and bunch length, {sigma}{sub t} {approximately} 28 ps, were measured simultaneously. The Au photocathode provides sensitivity from 10 eV to 10 keV covering the three orders of magnitude in wavelength from the UV to hard x-rays.
Date: May 27, 1998
Creator: Lumpkin, A. H.
Partner: UNT Libraries Government Documents Department

Measurement of Small Electron Beam Spots

Description: Measurements of transverse beam size are tremendously important to the performance of e{sup +}e{sup {minus}} linear colliders. In this paper we review the traditional technologies used to make such measurements, such as profile monitors and wire scanners, and the limitations on same. We then introduce a new tool for electron beam size measurement: Compton-scattered laser light, which may be used as an unbreakable ''wire'' or in the form of an interferometer beam size monitor. We describe the use of such an interferometer BSM, noting both the general issues related to its design and operation and the specific experiences with such an interferometer at the Final Focus Test Beam (FFTB) at SLAC. We conclude by considering the ultimate limits of the laser-interferometer BSM.
Date: February 3, 1999
Creator: Tenenbaum, Peter G
Partner: UNT Libraries Government Documents Department


Description: We have built monitors for use as beam diagnostics in the narrow gap of an undulator for an FEL experiment. They utilize an intercepting screen of doped YAG scintillating crystal to make light that is imaged through a periscope by conventional video equipment. The absolute position can be ascertained by comparing the electron beam position with the position of a He:Ne laser that is observed by this pop-in monitor. The optical properties of the periscope and the mechanical arrangement of the system mean that beam can be spatially determined to the resolution of the camera, in this case approximately 10 micrometers. Our experience with these monitors suggests improvements for successor designs, which we also describe.
Date: May 7, 1998
Creator: JOHNSON,E.D.
Partner: UNT Libraries Government Documents Department

Advanced Photon Source monopulse RF beam position monitor front-end upgrade.

Description: 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 BPM front-end will be considered as the baseline design 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 patterns used at APS.
Date: May 27, 1998
Creator: Lill, R. M.
Partner: UNT Libraries Government Documents Department

Time-resolved imaging for the APS linac beams.

Description: The particle-beam imaging diagnostics for the Advanced Photon Source (APS) injector lime have been enhanced by the installation of optical transition radiation (OTR) screens and the use of Ce-doped YAG crystals as beam profile monitors. Both converters have improved spatial resolution and time responses compared to the standard Chromox (Al{sub 2}O{sub 3}:Cr) screens used elsewhere in the linac. These enhancements allow us to address the smaller beam sizes (< 100 {micro}m) and the critical micropulse bunch length of higher brightness gun sources For the Linac macropulse of 30-ns duration composed of 86 micropulses at S-band frequency intervals, only the OTR mechanism is prompt enough to separate individual micropulses and to allow streak camera measurements of the micropulse averaged bunch length. Tests have been performed at 400 to 625 MeV using the gated DC thermionic gun source. Beam sizes less than {sigma}{sub x} = 30 {micro}m have been observed with a micropulse bunch length of {sigma} = 2-3 ps using OTR. First results on the lower-emittance rf thermionic gun are briefly discussed.
Date: September 29, 1998
Creator: Lumpkin, A. H.
Partner: UNT Libraries Government Documents Department

Design and Development of the LEDA Slow Wire Scanner Profile Measurement

Description: The Low Energy Demonstration Accelerator (LEDA) [1, 2] is being developed at Los Alamos National Laboratory as part of the Accelerator Production of Tritium (APT) project. One of the diagnostics being developed to commission LEDA [3] is a slow wire scanner beam profile measurement. Initial profile measurements will be made at 6.7 MeV beam energy and 100 mA beam current. The wire scanner is an interceptive device that will move two silicon carbide coated graphite mono-filament fibers (wires) through the beam, in order to obtain the profile. Some of the design considerations discussed are; Mechanical design, wire temperature analysis, secondary electron detection, signal processing, and system control.
Date: August 31, 1998
Creator: O'Hara, J.F.; Power, J.F.; Ledford, J.; Gilpatrick, J. D.; Stettler, M. & Sage, J.
Partner: UNT Libraries Government Documents Department

Construction and measurement techniques for the APS LEUTL project RF beam position monitors.

Description: The design, construction, and assembly procedure of 24 rf beam position monitors used in the Advanced Photon Source low-energy undulator test line and linear accelerator (linac) are described. Beam stability as well as beam positioning capabilities are essential to the LEUTL project. A design objective of the LEUTL facility is to achieve better than 1-{micro}m resolution. The highest care was used in the mechanical fabrication and assembly of the BPM units. The latest experimental results using these BPMs are presented.
Date: April 20, 1999
Creator: Gorski, A.
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

An Apparatus for the Direct Measurement of Collimator Transverse Wakefields

Description: The design of the NLC Beam Delivery System requires a firmer understanding of the effects of collimators on short, intense bunches than is presently available. We describe an experiment to directly measure these effects through use of a dedicated apparatus located at the 1.19 GeV point in the SLAC Linac. The apparatus consists of an outer vacuum vessel and an interchangeable insertion containing up to 5 distinct collimator apertures. The insertion is capable of remote-controlled translation, allowing the collimator apertures to be misaligned relative to the electron beam without changing the incoming beam orbit; the wakefield deflection is then measured by observing the change in the outgoing orbit on 32 beam position monitors. The parameters of the apertures have been selected to allow confirmation of the scaling laws for collimator wakefields, and to strongly enhance either the geometric or resistive wall contribution of each aperture. Details of the apparatus design, the aperture parameters, and the experimental program are discussed.
Date: April 23, 1999
Creator: Tenenbaum, Peter G
Partner: UNT Libraries Government Documents Department

Design and performance of the ALS diagnostic beamline

Description: Synchrotron light sources have evolved from accelerators which produced this radiation as a by-product to dedicated, third generation storage rings such as the Advanced Light Source (ALS). Optimization of beam line designs to take advantage of these new sources requires information on electron beam parameters and their stability. A real-time, image of the electron beam is useful to accelerator physicists in helping their understanding of beam dynamics, monitoring of accelerator operation, and providing a means of diagnosing problems as they arise. A diagnostic beam line for these purposes has been built at the ALS to image the electron beam by focusing bend magnet radiation. Measurement of beam parameters, electron-bunch time structure and beam dynamics can now be routinely made. The image of the electron beam can be continuously monitored via standard video equipment and the size and location of the beam redundantly measured via a second detection system utilizing a slit scanned in front of a photocathode. Longitudinal electron bunch lengths can be measured with a port providing visible light to an optical platform on which a fast photodiode or a streak camera can be mounted. An additional set of diagnostic tools built into the beam line allows determination of the acceptance of the beam line and the locations of the vertical and horizontal focal planes of the system. The system also provides a discrete method of attenuating the photon flux for equalizing the signal on the video system over the wide range of expected accelerator operating conditions.
Date: September 1, 1995
Creator: Renner, T.; Padmore, H.A. & Keller, R.
Partner: UNT Libraries Government Documents Department

Intense heavy-ion beam transport with electric and magnetic quadrupoles

Description: As part of the small induction recirculator development at LLNL, the authors are testing an injector and transport line that delivers 4 {micro}s beams of potassium with repetition rates up to 10 Hz at a nominal current of 2 mA. The normalized K-V equivalent emittance of the beams is near 0.02 {pi} mm-mrad and is mostly determined by the temperature of the source (0.1 eV). K{sup +} ions generated at 80 keV in a Pierce diode are matched to an alternating gradient transport line by seven electric quadrupoles. Two additional quads have been modified to serve as two-axis steerers. The matching section is followed by a transport section comprised of seven permanent magnet quadrupoles. Matching to this section is achieved by adjusting the voltages on the electric quadrupoles to voltages calculated by an envelope matching code. Measurements of beam envelope parameters are made at the matching section entrance and exit as well as at the end of the permanent magnet transport section. Beam current waveforms along the experiment are compared with results from a one-dimension longitudinal dynamics code. Initial experiments show particle loss occurring at the beam head as a result of overtaking. The apparatus is also being used for the development of non or minimally intercepting diagnostics for future recirculator experiments. These include capacitive monitors for determining beam line-charge density and position in the recirculator; flying wire scanners for beam position; and gated TV scanners for measuring beam profiles and emittance.
Date: August 1, 1995
Creator: Fessenden, T. J.; Barnard, J. J.; Cable, M. D.; Deadrick, F.J.; Eylon, S.; Nelson, M. B. et al.
Partner: UNT Libraries Government Documents Department

Numerical simulation of the PEP-II beam position monitor

Description: The authors use MAFIA to analyze the PEP-II button-type beam position monitor (BPM). Employing proper termination of the BPM into a coaxial cable, the output signal at the BPM is determined. Thus the issues of signal sensitivity and power output can be addressed quantitatively, including all transient effects and wakefields. Besides this first quantitative analysis of a true BPM 3D structure, they find that internal resonant modes are a major-source of high value narrow-band impedances. The effects of these resonances on coupled-bunch instabilities are discussed. An estimate of the power dissipation in the ceramic vacuum seal under high current operation is given.
Date: September 1, 1995
Creator: Kurita, N.; Martin, D.; Ng, C.K.; Smith, S. & Weiland, T.
Partner: UNT Libraries Government Documents Department


Description: This report examines the possibility of observing transverse beam profiles by using synchrotron light emission from the 100 GeV/nucleon heavy-ion gold beam in the Relativistic Heavy Ion Collider (RHIC). Synchrotron radiation experiences a shift towards higher photon energy when the magnetic field at the end of a dipole varies rapidly over a short distance. Synchrotron light signals from high energy (larger than 400 GeV) proton beams have already been routinely used to observe the transverse beam profiles at the SPS in CERN and at the TEVATRON at Fermilab. Because of the modest relativistic factor of the fully stripped stored gold ions in RHIC this ''push'' towards higher critical energy is not large enough to place the synchrotron light within the visible region of the spectrum. The critical wavelength remains within the infrared region. A 77K cooled infrared array detector with 160 elements, made of PbSe (Lead salt) could be used for beam profile detection. It would cover the wavelength range between 1 and 6 microns, with maximum sensitivity at a wavelength of 4.5 microns.
Date: June 26, 1998
Creator: TRBOJEVIC, D.
Partner: UNT Libraries Government Documents Department

CVD-diamond-based position sensitive photoconductive detector for high-flux x-rays and gamma rays.

Description: A position-sensitive photoconductive detector (PSPCD) using insulating-type CVD diamond as its substrate material has been developed at the Advanced Photon Source (APS). Several different configurations, including a quadrant pattern for a x-ray-transmitting beam position monitor (TBPM) and 1-D and 2-D arrays for PSPCD beam profilers, have been developed. Tests on different PSPCD devices with high-heat-flux undulator white x-ray beam, as well as with gamma-ray beams from {sup 60}Co sources have been done at the APS and National Institute of Standards and Technology (NIST). It was proven that the insulating-type CVD diamond can be used to make a hard x-ray and gamma-ray position-sensitive detector that acts as a solid-state ion chamber. These detectors are based on the photoconductivity principle. A total of eleven of these TBPMs have been installed on the APS front ends for commissioning use. The linear array PSPCD beam profiler has been routinely used for direct measurements of the undulator white beam profile. More tests with hard x-rays and gamma rays are planned for the CVD-diamond 2-D imaging PSPCD. Potential applications include a high-dose-rate beam profiler for fourth-generation synchrotrons radiation facilities, such as free-electron lasers.
Date: April 19, 1999
Creator: Shu, D.
Partner: UNT Libraries Government Documents Department