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Understanding the nonlinear beam dynamics of the Advanced Light Source

Description: Frequency map analysis is used to study the single particle transverse beam dynamics in ALS. The maps, which provide details about the diffusion of orbits and limits on long term stability, are generated by a postprocessor attached to a tracking code. This paper describes the method and shows how the map is changed when the 12- fold symmetry of the linear lattice is perturbed by including measured magnetic field imperfections. Also the long term stability of orbits that reside in regions of large diffusion is studied.
Date: September 18, 1996
Creator: Robin, D. & Laskar, J.
Partner: UNT Libraries Government Documents Department

Orbit dynamics for unstable linear motion

Description: A treatment is given of the orbit dynamics for linear unstable motion that allows for the zeros in the beta function and makes no assumptions about the realness of the betatron and phase functions. The phase shift per turn is shown to be related to the beta function and the number of zeros the beta function goes through per turn. The solutions of the equations of motion are found in terms of the beta function.
Date: July 1997
Creator: Parzen, G.
Partner: UNT Libraries Government Documents Department

Particle motion in the stable region near the edge of a linear sum resonance stopband

Description: This paper studies the particle motion when the tune is in the stable region close to the edge of linear sum resonance stopband. Results are found for the tune and the beta functions. Results are also found for the two solutions of the equations of motion. The results found are shown to be also valid for small accelerators where the large accelerator approximation may not be used.
Date: December 1, 1995
Creator: Parzen, G.
Partner: UNT Libraries Government Documents Department

Quadrupole shunt experiments at SPEAR

Description: As part of a program to align and stabilize the SPEAR storage ring, a switchable shunt resistor was installed on each quadrupole to bypass a small percentage of the magnet current. The impact of a quadrupole shunt is to move the electron beam orbit in proportion to the off-axis beam position at the quadrupole, and to shift the betatron tune. Initially, quadrupole shunts in SPEAR were used to position the electron beam in the center of the quadrupoles. This provided readback offsets for nearby beam position monitors, and helped to steer the photon beams with low-amplitude corrector currents. The shunt-induced tune shift measurements were then processed in MAD to derive a lattice model.
Date: May 1, 1996
Creator: Corbett, W.J.; Hettel, R.O. & Nuhn, H.-D.
Partner: UNT Libraries Government Documents Department

Performance optimization of synchrotron light sources

Description: This paper will present work done at the NSLS to tailor the electron beam properties so as to maximize the performance of the photon beamlines. The electron beam properties of most importance to photon users are the total stored current, emittance, lifetime, and transverse stability. Recent and planned improvements in each of these properties will be discussed as well as the ultimate limits for each. The discussion of transverse stability will include high frequency motion, which can reduce the effective brightness, as well as slow drift during a fill and fill-to-fill reproducibility.
Date: Summer 1996
Creator: Safranek, J
Partner: UNT Libraries Government Documents Department

Orbit stability of the ALS storage ring

Description: The Advanced Light Source (ALS) storage ring, a synchrotron light source of the third generation, is specified to maintain its electron orbit stable within one tenth of the rms beam size. In the absence of a dedicated orbit feed-back system, several orbit-distorting effects were investigated, aided by a new interactive simulation tool, the code TRACY V. The effort has led to a better understanding of the behavior of a variety of accelerator subsystems and in consequence produced a substantial improvement in day-to-day orbit stability.
Date: May 1, 1997
Creator: Keller, R.; Nishimura, H. & Biocca, A.
Partner: UNT Libraries Government Documents Department

Advances in orbit drift correction in the advanced photon source storage ring

Description: The Advanced Photon Source storage ring is required to provide X-ray beams of high positional stability, specified as 17 {mu}m rms in the horizontal plane and 4.4 {mu}m rms in the vertical plane. The author reports on the difficult task of stabilizing the slow drift component of the orbit motion down to a few microns rms using workstation-based orbit correction. There are two aspects to consider separately the correction algorithm and the configuration of the beam position monitors (BPMs) and correctors. Three notable features of the correction algorithm are: low-pass digital filtering of BPM readbacks; {open_quotes}despiking{close_quotes} of the filtered orbit to desensitize the orbit correction to spurious BPM readbacks without having to change the correction matrix; and BPM intensity-dependent offset compensation. The BPM/corrector configuration includes all of the working BPMs but only a small set of correctors distributed around the ring. Thus only those orbit modes that are most likely to be representative of real beam drift are handled by the correction algorithm.
Date: June 1, 1997
Creator: Emery, L. & Borland, M.
Partner: UNT Libraries Government Documents Department

Skew chromaticity in large accelerators

Description: The 2-D ``skew chromaticity`` vector k is introduced when the standard on-momentum description of linear coupling is extended to include off-momentum particles. A lattice that is well decoupled on-momentum may be badly decoupled off-momentum, inside the natural momentum spread of the beam. There are two general areas of concern: (1) the free space in the tune plane is decreased; (2) collective phenomena may be destabilized. Two strong new criteria for head-tail stability in the presence of off-momentum coupling are derived, which are consistent with experimental and operational observations at the Tevatron, and with tracking data from RHIC.
Date: May 1, 1995
Creator: Peggs, S. & Dell, G.F.
Partner: UNT Libraries Government Documents Department

Design and implementation of a slow orbit control package at Thomas Jefferson National Accelerator Facility

Description: The authors describe the design and implementation of a C++ client/server based slow orbit and energy control package based on the CDEV software control bus. Several client applications are described and operational experience is given.
Date: June 1, 1997
Creator: Zeijts, J. van; Witherspoon, S. & Watson, W.A.
Partner: UNT Libraries Government Documents Department

Stability and halo formation in axisymmetric intense beams

Description: Beam stability and halo formation in high-intensity axisymmetric 2D beams in a uniform focusing channel are analyzed using particle-in-cell simulations. The tune depression-mismatch space is explored for the uniform (KV) distribution of the particle transverse-phase-space density, as well as for more realistic ones (in particular, the water-bag distribution), to determine the stability limits and halo parameters. The numerical results show an agreement with predictions of the analytical model for halo formation.
Date: October 1, 1997
Creator: Gluckstern, R.L. & Kurennoy, S.S.
Partner: UNT Libraries Government Documents Department

Survey, alignment, and beam stability at the Advanced Light Source

Description: This paper describes survey and alignment at the Lawrence Berkeley Laboratories Advanced Light Source (ALS) accelerators from 1993 to 1997. The ALS is a third generation light source requiring magnet alignment to within 150 microns. To accomplish this, a network of monuments was established and maintained. Monthly elevation surveys show the movement of the floor over time. Inclinometers have recently been employed to give real time information about magnet, vacuum tank and magnet girder motion in the ALS storage ring.
Date: October 1, 1997
Creator: Krebs, G.F.
Partner: UNT Libraries Government Documents Department

Orbit correction using virtual monitors at Jefferson Lab

Description: An orbit correction algorithm is developed to achieve the following goals for the CEBAF accelerator at Jefferson Lab.: (1) Pre-processing of orbit input to account for estimated misalignment and monitor errors. (2) Automatic elimination of blind spots caused by response matrix degeneracy. (3) Transparency of exception handling to interchangeable generic steering engines. (4) CEBAF-specific demands on control of injection angle, path length, orbit effects on optics, simultaneous multiple pass steering, and orbit control at un-monitored locations. All of the above can be accomplished by the introduction of virtual monitors into the processed input orbit, whose theoretical basis is to be discussed in this report. Implementation of all or part of these features and operational experience during the CEBAF variable energy runs will also be discussed.
Date: August 1, 1997
Creator: Chao, Yu-Chiu; Bowling, B.; Witherspoon, S.; Zeijts, J. van & Watson, W.A. III
Partner: UNT Libraries Government Documents Department

Analysis of ultra-relativistic charged particle beam and stretched wire measurement interactions with cylindrically symmetric structures

Description: The beam impedance and wakefield are quantities which describe the stability of charged particles in their trajectory within an accelerator. The stretched wire measurement technique is a method which estimates the beam impedance and wakefield. Definitions for the beam impedance, the wakefield, and the stretched wire measurement are presented. A pillbox resonator with circular beampipes is studied for its relatively simple profile and mode structure. Theoretical predictions and measurement data are presented for the interaction of various charged particle beams and center conductor geometries between the cavity and beampipe. Time domain predictions for the stretched wire measurement and wakefield are presented and are shown to be a linear interaction.
Date: December 31, 1996
Creator: Deibele, C.E.
Partner: UNT Libraries Government Documents Department

The advanced photon source

Description: The Advanced Photon Source (APS) is a 7-GeV third-generation synchrotron radiation storage ring and full-energy positron injector. Construction project funding began in 1989, and ground breaking took place on 5 May 1990. Construction of all accelerator facilities was completed in January 1995 and storage ring commissioning is underway. First observation of x-rays from a bending magnet source took place on 26 March 1995. Nearly all performance specifications of the injector have been reached, and first observations indicate that the reliability, dynamic aperture, emittance, and orbit stability in the storage ring are satisfactory. Observation of radiation from the first of 20 insertion device beamlines is scheduled for October 1995. Start of regular operations is expected to take place well before the APS Project target date of December 1996.
Date: July 1, 1995
Creator: Galayda, J.N.
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

Particle motion inside and near a linear half-integer stopband

Description: This paper studies the motion of a particle whose tune is inside and near a linear half-integer stopband. Results are found for the tune and beta functions in the stable region close to an edge of the stopband. Results are found for the growth rates and for the exponentially growing particle motion inside the stopband. It is shown that the eigenvalues and the eigenfunctions of the transfer matrix are real inside the stopband. All the results found are also valid for small accelerators where the large accelerator approximation is not used.
Date: July 1, 1995
Creator: Parzen, G.
Partner: UNT Libraries Government Documents Department

Linearized error analysis for an accelerator and application to the APS injector synchrotron

Description: This paper presents a tolerance budget for accelerators dictated by the linear transverse dynamics of particle motion. The linearized equations satisfied by the particle motion when errors in the lattice are present are given along with the solution to these equations. The forms of these errors giving rise to the linearized equation are stated. These results are used to derive a tolerance budget for the Advanced Photon Source (APS) injector synchrotron.
Date: July 1, 1995
Creator: Koul, R.K. & Mills, F.E.
Partner: UNT Libraries Government Documents Department

On the feasibility of tracking with differential-algebra maps in long-term stability studies for large hadron colliders

Description: A time-saving alternative to conventional element-by-element tracking in long-term stability studies is the use of truncated Taylor maps. This report discusses how the non-symplecticity of a moderately high-order truncated Taylor map affects its reliability when the map is used for tracking over several thousand turns. Various machines and two different map-constructing programs are compared. It is found that the discrepancies between the Taylor map results and those obtained by direct tracking grow with amplitude. Thus, such maps are not guaranteed to be sufficient for long-term tracking over millions of turns without suitable symplectification.
Date: January 1, 1992
Creator: Kleiss, R.; Schmidt, F. & Yan, Y.
Partner: UNT Libraries Government Documents Department

Orbit control at the ALS based on sensitivity matrices

Description: A third-generation synchrotron-light source storage ring requires accurate orbit correction because its lattice is very sensitive to magnet imperfections and misalignments. If model-based control is used, calibration of this model is required in advance. Therefore, it is preferable to prepare some kind of model-free orbit control scheme that is complementary to model-based control. A sensitivity matrix (S matrix) works effectively as the kernel of a model-free orbit control system for a given optics of a lattice. This paper describes recent efforts in this respect at Advanced Light Source (ALS).
Date: April 1, 1995
Creator: Nishimura, H.; Schachinger, L. & Ohgaki, H.
Partner: UNT Libraries Government Documents Department

CHAMBER MOTION MEASUREMENTS AT THE NSLS X-RAY RING.

Description: Work has been ongoing at the NSLS to improve the orbit stability of the X-Ray Ring by accounting for the thermal motion of the vacuum chamber, which supports the electron beam position monitors (BPMs). In-situ contact measurements of the vacuum chamber motion have been carried out using support stands that have been designed and extensively tested to reduce errors associated with thermal changes in the stands themselves. Using this chamber motion as a correction to the orbit motion measured by the BPMs, the precise location of the radiation beam can be predicted. These predictions are compared with actual radiation beam measurements on the experimental floor, and with predictions based solely on BPM measurements of the electron beam position. This paper reviews this work including stand design and performance, chamber motion measurements, predictions based on these data, and results.
Date: March 29, 1999
Creator: SOLOMON,L.; LYNCH,D.; SAFRANEK,J. & SINGH,O.
Partner: UNT Libraries Government Documents Department

Electron beam stability and beam peak to peak motion data for NSLS X-Ray storage ring

Description: In the past two years, a significant reduction in electron beam motion has been achieved at the NSLS X-Ray storage ring. The implementation of global analog orbit feedbacks, based on a harmonics correction scheme, has reduced the beam motion globally. Implementation of six local analog feedback systems has reduced the beam motion even further at the corresponding beam line straight sections. This paper presents beam motion measurements, showing the improvement due to the feedback systems. Beam motion is measured using a spectrum analyzer and data is presented at various frequencies, where peaks were observed. Finally, some of the beam motion sources are discussed.
Date: July 1, 1993
Creator: Singh, O.
Partner: UNT Libraries Government Documents Department

Commissioning results of the APS storage ring rf beam position monitors

Description: The commissioning of the 360 rf beam position monitors (BPMs) in the Advanced Photon Source (APS) storage ring (SR) is nearing completion. After using the single-turn capability of the BPM electronics in the early ring commissioning phase, resolution measurements versus current and bandwidth were successfully performed. In the standard Sr vacuum chamber geometry, the resolution was measured with beam as 0.16 {micro}mA/{radical}(Hz). For the insertion device vacuum chamber geometry, the resolution was measured to be 0.1 {micro}mA/{radical}(Hz). Since the photon beam stability requirement for the users is only 4.5 microns rms in the vertical direction, investigations of rf BPM offset versus current and bunch pattern have also been initiated. Both single bunch and multibunch beam patterns with varying intensity were used to determine offset stability for both the global and the local orbit feedback applications.
Date: July 1, 1996
Creator: Kahana, E. & Chung, Y.
Partner: UNT Libraries Government Documents Department

Impact-generated atmospheric plumes: The threat to satellites in low-earth orbit

Description: Computational simulations of the impacts of comet Shoemaker-Levy 9 (SL9) fragments on Jupiter provide a framework for interpreting the observations. A reasonably consistent picture has emerged, along with a more detailed understanding of atmospheric collisional processes. The knowledge gained from the observations and simulations of SL9 has led us to consider the threat of impact-generated plumes to satellites in low-Earth orbit (LEO). Preliminary simulations suggest that impacts of a size that recur about once per century on Earth generate plumes that rise to nearly 1000 km over an area thousands of km in diameter. Detailed modeling of such plumes is needed to quantify this threat to satellites in LEO. Careful observations of high-energy atmospheric entry events using both satellite and ground- based instruments would provide validation for these computational models.
Date: February 1, 1996
Creator: Boslough, M.B. & Crawford, D.A.
Partner: UNT Libraries Government Documents Department

Theoretical estimation of the dynamic aperture for a Chasman-Green lattice

Description: A comparison between the predicted stability region and the results of tracking for the 7-GeV Advanced Photon Source CDR lattice is given. The tracking results are obtained by searching for the limit of stability in N{sub y} for a fixed value for N{sub x}. (Negative N{sub x} is understood to mean cos {phi}{sub xo} = {minus}1.) The limits of the stable region for this lattice are caused by the chromaticity correcting sextupoles and the predominance of the integral resonance for v{sub x} = 0.88 per period.
Date: November 1, 1988
Creator: Crosbie, E.A.
Partner: UNT Libraries Government Documents Department