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Linear optics correction in the CEBAF accelerator

Description: During commissioning of the CEBAF accelerator, correcting dispersion, momentum compaction and betatron beam envelopes was essential for robust operation. To speed the diagnostic process we developed a method which allows one to track and correct the machine optics on-line. The method is based on measuring the propagation of 30 Hz modulated betatron oscillations. The beam optics of the accelerator was altered to decrease lattice sensitivity at critical points and to simplify control of the betatron function match. The calculation of the Courant-Snyder invariant from signals of each pair of beam position monitors was used for a correction of the betatron functions. The experience of optics correction and the study of long and short term machine reproducibility obtained during 1996 and early 1997 are also discussed. With minor modifications this method can also be used for on-line optics measurement and correction in circular accelerators.
Date: June 1, 1997
Creator: Lebedev, V.A.; Bickley, M. & Bisognano, J.
Partner: UNT Libraries Government Documents Department

Direct focusing error correction with ring-wide TBT beam position data

Description: Turn-By-Turn (TBT) betatron oscillation data is a very powerful tool in studying machine optics. Hundreds and thousands of turns of free oscillations are taken in just few tens of milliseconds. With beam covering all positions and angles at every location TBT data can be used to diagnose focusing errors almost instantly. This paper describes a new approach that observes focusing error collectively over all available TBT data to find the optimized quadrupole strength, one location at a time. Example will be shown and other issues will be discussed. The procedure presented clearly has helped to reduce overall deviations significantly, with relative ease. Sextupoles, being a permanent feature of the ring, will need to be incorporated into the model. While cumulative effect from all sextupoles around the ring may be negligible on turn-to-turn basis it is not so in this transfer line analysis. It should be noted that this procedure is not limited to looking for quadrupole errors. By modifying the target of minimization it could in principle be used to look for skew quadrupole errors and sextupole errors as well.
Date: March 1, 2011
Creator: Yang, M.J.
Partner: UNT Libraries Government Documents Department

Ambient beam motion and its excitation by ghost lines in the Tevatron

Description: Transverse betatron motion of the Tevatron proton beam is measured and analyzed. It is shown that the motion is coherent and excited by external sources of unknown origins. Observations of the time-varying 'ghost lines' in the betatron spectrum are reported. The direct measurement of the rms betatron oscillations amplitude estimates it at about 110 nm at {beta}{sub y} {approx} 900 m. Correspondingly, at the amplitudes at the average beta function location with {beta}{sub y} {approx} 50 m is about 25 nm. Given that such direct measurements with clearly observable betatron peak were not repeatedly reproducible, one can conclude that well know 'ghost lines' are the reason for that - as they are come and go without any obvious regularity. Our analysis of these 'ghost lines' shows that (a) besides slow motion across frequencies, they also exhibit oscillatory movements with period varying from 15-20 min to few hours; (b) for the stores analysed, the lines add about factor of 2 to average - over colliding store duration - Schottky power in the betatron bands. The latter allows to estimate that they contribute about half to the previously determined the rms normalized emittance growth rate of some 0.06 {pi} mm mrad/hr. The Tevatron 'ghost lines' look very similar to infamous 'humps' recently observed in the LHC. Those 'humps' are unwanted oscillations seen repeatedly in the LHC beams (mostly in the vertical plane) and also believed to be caused by external excitations.
Date: March 1, 2011
Creator: Shiltsev, V.
Partner: UNT Libraries Government Documents Department

TRANSVERSE COHERENT RESISTIVE INSTABILITIES OF AZIMUTHALLY BUNCHED BEAMS IN PARTICLE ACCELERATORS

Description: The transverse electromagnetic coupling of bunches of particles with each other is investigated theoretically, and shown to incorporate the possibility (due to the effect of nonperfectly conducting vacuum chamber walls) of coherent instability even when the longitudinal distance between bunches is much larger than the transverse dimensions of the vacuum tank. The modes of oscillation in which the bunches move rigidly are investigated; criteria for stability, and expressions for the small amplitude growth rates under unstable conditions are presented. The case of a single bunch is considered in detail and demonstrated to be stable (even in the absence of landau damping) provided {nu} lies between an integer and the next higher half-integer, where {nu} is the number of transverse free betatron oscillations occurring in one revolution; for many bunches which are sensibly different in intensity (a criterion for this is presented), all modes are stable provided {nu} satisfies the same restriction. For equally spaced bunches of equal numbers of particles, approximately half the modes are unstable without Landau damping. Numerical examples are presented covering some intermediate situations.
Date: April 1, 1966
Creator: Courant, Ernest D. & Sessler, Andrew M.
Partner: UNT Libraries Government Documents Department

Ion bunch length effects on the beam-beam interaction and its compensation in a high-luminosity ring-ring electron-ion collider

Description: One of the luminosity limits in a ring-ring electron-ion collider is the beam-beam effect on the electrons. In the limit of short ion bunches, simulation studies have shown that this limit can be significantly increased by head-on beam-beam compensation with an electron lens. However, with an ion bunch length comparable to the beta-function at the IP in conjunction with a large beam-beam parameter, the electrons perform a sizeable fraction of a betatron oscillation period inside the long ion bunches. We present recent simulation results on the compensation of this beam-beam interaction with multiple electron lenses.
Date: May 20, 2012
Creator: C., Montag; Oeftiger, A. & Fischer, W.
Partner: UNT Libraries Government Documents Department

Benchmarking / Crosschecking DFS in the ILC Main Linac

Description: In an effort to compare beam dynamics and create a ''benchmark'' for Dispersion Free Steering (DFS) a comparison was made between different ILC simulation programs while performing DFS. This study consisted of three parts. First, a simple betatron oscillation was tracked through each code. Secondly, a set of component misalignments and corrector settings generated from one program was read into the others to confirm similar emittance dilution. Thirdly, given the same set of component misalignments DFS was performed independently in each program and the resulting emittance dilution was compared. Performance was found to agree exceptionally well in all three studies.
Date: January 8, 2007
Creator: Smith, Jeffrey C.; /Cornell U., LEPP; Eliasson, Peder; Latina, Andrea; Schulte, Daniel; /CERN et al.
Partner: UNT Libraries Government Documents Department

Nonlinear Spin Acceptance in Electron Storage Rings

Description: It is shown that the degree of polarization of a beam in electron storage rings can be limited by nonlinear effects. The strength of a nonlinear effect depends on theamplitude of the particles. Particles performing synchrotron and betatron oscillations with high amplitudes can contribute over proportionally to depolarization. As aresult, the emittance of a beam is not allowed to exceed certain boundaries, otherwise the beam will become more and more depolarized. This limit is called nonlinearspin acceptance.
Date: July 1, 1988
Creator: Kewisch, Jorg & Rossmanith, Robert
Partner: UNT Libraries Government Documents Department

Determination of linear optics functions from TBT data

Description: A method for evaluation of coupled optics functions, detection of strong perturbing elements, determination of BPM calibration errors and tilts using turn-by-turn (TBT) data is presented as well as the new version of the Hamiltonian perturbation theory of betatron oscillations the method is based upon. An example of application of the considered method to the Tevatron is given.
Date: May 1, 2006
Creator: Alexahin, Y. & Gianfelice-Wendt, E.
Partner: UNT Libraries Government Documents Department

The correction of linear lattice gradient errors using an AC dipole

Description: Precise measurement of optics from coherent betatron oscillations driven by ac dipoles have been demonstrated at RHIC and the Tevatron. For RHIC, the observed rms beta-beat is about 10%. Reduction of beta-beating is an essential component of performance optimization at high energy colliders. A scheme of optics correction was developed and tested in the RHIC 2008 run, using ac dipole optics for measurement and a few adjustable trim quadruples for correction. In this scheme, we first calculate the phase response matrix from the. measured phase advance, and then apply singular value decomposition (SVD) algorithm to the phase response matrix to find correction quadruple strengths. We present both simulation and some preliminary experimental results of this correction.
Date: May 4, 2009
Creator: Wang,G.; Bai, M.; Litvinenko, V.N. & Satogata, T.
Partner: UNT Libraries Government Documents Department

Wake field produced by a particle in the presence of conductive plates: a vehicle for the excitation of the coupled betatron-synchrotron instabilities

Description: Beam instabilities observed in ADONE were studied. The interaction of a single particle betatron oscillation with conductive plates was analyzed. First, Fourier analysis of the field source was performed, then the usual approach to determine the plate response was used by treating the plates as transmission lines. Finally, with a process of anti-transformation the total response to the oscillation of a single particle was constructed. The wake field decays over a distance which is of the order of magnitude of the length of the plates themselves. Nevertheless, the shape of the wake field depends on the terminating independence. Several cases, for instance matched, open and shorted plates are considered. (auth)
Date: May 22, 1973
Creator: Ruggiero, A.G.
Partner: UNT Libraries Government Documents Department

Stability of bunched beams against high order nonlinear resonances

Description: For a given tune, beams can be made stable against the effects of isolated high order resonances. However, in a system whose betatron tune is changing, there exists a mechanism for beam loss. This mechanism is discussed and applied to the case of bunched beams, where the synchrotron motion introduces a time variation of tune. A stability criterion for a system with varying tune is presented, together with a set of suggested parameter values. The basic constraint is that the linear tune spread in the bunches (arising through the chromaticity) be smaller than the nonlinear tune spread (arising from the nonlinearities of magnetic field as well as the beam-beam interaction). This can be achieved with a small chromaticity and a relatively large nonlinear term causing a tune spread with betatron amplitude. Specific values for chromaticity and nonlinearity are suggested. A limit on the resonance excitation strength is also given. Since the beam-beam interaction introduces a tune spread with amplitude, then in some range it is found to have a stabilizing influence insofar as isolated high order nonlinear resonances are concerned. This point is discussed together with a brief discussion on the onset of stochastic phenomena, which are due to the interaction of many resonances. It is concluded that with the given set of parameters, bunched beams stable against high order nonlinear resonances can be achieved. (auth)
Date: December 1, 1973
Creator: Month, M.
Partner: UNT Libraries Government Documents Department

Effect of a large Oth harmonic octupole on stable betatron oscillations

Description: S>The effect of a 0th harmonic octupole (that is, constant in dependence on azimuth) on stable betatron oscillations is treated in smooth approximation. In this approximation, an exact invariant is obtained. Bounded motion results, except when the octupole component is very large. A condition for stability- is obtained and, in the case of bounded motion, an expression for the amplitude variation is given. Some comments are made regarding the method of phase averaging. (auth)
Date: September 20, 1973
Creator: Month, M.
Partner: UNT Libraries Government Documents Department

Quasi-3D space charge simulation

Description: The longitudinal space charge effect is simulated by binning the longitudinal beam profile in order to calculate the force on the bins using the binned particle distribution via FFT, and applying momentum kick based upon this space charge force to macro-particles. Usually, the longitudinal space charge kick is calculated once per turn since the longitudinal profile doesn't change much in a single turn. Besides, the longitudinal profile is used as a weighting factor for the transverse space charge force. The transverse space charge effect is simulated by projecting the 3-D beam to a 2-D Gaussian distribution in order to use the complex error function to compute the transverse space charge force, and applying this space charge force to macro-particles. One transverse space charge calculation per scale length of the beam shape variation requires at least ten transverse space charge force calculations per betatron oscillation.
Date: April 1, 2007
Creator: Yang, Xi
Partner: UNT Libraries Government Documents Department

RHIC VERTICAL AC DIPOLE COMMISSIONING.

Description: The RHIC vertical ac dipole was installed in the summer of 2001. The magnet is located in the interaction region between sector 3 and sector 4 common to both beams. The resonant frequency of the ac dipole was first configured to be around half of the beam revolution frequency to act as a spin flipper. At the end of the RHIC 2002 run, the ac dipole frequency was reconfigured for linear optics studies. A 0.35 mm driven betatron oscillation was excited with the vertical ac dipole and the vertical betatron functions and phase advances at each beam position monitor (BPM) around the RHIC yellow ring were measured using the excited coherence. We also recorded horizontal turn-by-turn beam positions at each BPM location to investigate coupling effects. Analysis algorithms and measurement results are presented.
Date: June 2, 2002
Creator: BAI,M.; DELONG,J.; HOFF,L.; PAI,C.; PEGGS,S.; PIACENTINO,J. et al.
Partner: UNT Libraries Government Documents Department

Measurements of the longitudinal and transverse beam loss at the Tevatron

Description: Measurements of the transverse and longitudinal beam losses during a Tevatron store will be presented. The measurements utilize scintillation counters to monitor the nuclear interactions of the 1 TeV halo particles with a scraper that is located near the beam. If the particles are in time with the primary bunches, they are assumed to come from transverse perturbations inducing large betatron oscillations. Particles lost longitudinally drift around the ring due to synchrotron radiation and become asynchronous with respect to the bunches. A pulsed electron lens is then used to induce large betatron oscillations that extract these particles onto the scraper. The resulting nuclear interactions in the scraper are recorded by a gated scintillating counter system. The counting rates from the two channels provide an online measurement of the two types of beam loss. Known beam loss due to interactions at the IP and to nuclear collisions in the residual gas can be subtracted which then exposes the underlying losses from longitudinal and transverse instabilities.
Date: June 2, 2003
Creator: al., Alvin V. Tollestrup et
Partner: UNT Libraries Government Documents Department

Spectral analysis of reltivistic bunched beams

Description: Particles in a storage ring are oscillating in the longitudinal and transverse dimensions, and therefore, the frequency domain is natural for analyzing many beam generated signals. Information ranging from oscillation frequencies to beam phase space distributions can be extracted from the spectral content of these signals. The spectrum of a single particle is like a Green`s function, and it is the key to understanding the spectrum produced by a beam. Three separate cases are consider in an order of increasing complexity: (1) constant revolution frequency, (2) Frequency Modulation introduced by synchrotron oscillations, and (3) Amplitude Modulation introduced by betatron oscillations.
Date: May 1, 1996
Creator: Siemann, R.H.
Partner: UNT Libraries Government Documents Department

Polarized proton experiment in the AGS with a partial snake

Description: In three polarized proton runs at the AGS it was recently shown that the imperfection depolarizing resonances in the AGS can be overcome with a 5% partial snake and the intrinsic depolarizing resonances could be jumped with the pulsed tune-jump quadrupoles even in the presence of the partial snake. For the first time polarized proton beam was accelerated up to the required RHIC injection energy of 25 GeV. No polarization was lost due to the imperfection resonances and the depolarization from most intrinsic resonances was avoided with the tune-jump quadrupoles. However, significant amount of polarization was lost at 0+{nu}{sub y}, 12+{nu}{sub y} and 36+{nu}{sub y}, which is believed to be partially due to coupling resonances. A novel energy-jump method and other new schemes to overcome the coupling and intrinsic resonances are discussed.
Date: December 1, 1996
Creator: Huang, H.; Ahrens, L. & Alessi, J.G.
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

Controlling the vertical mode coupling instability with feedback in the ALS

Description: The authors present the results of experiments to control the mode coupling instability in the vertical direction using a feedback system. Presently, they can raise the instability threshold from {approximately} 20 mA to 35 mA. The maximum current threshold is reached when the feedback is operated in a resistive mode.
Date: January 1, 1997
Creator: Byrd, J. & Barry, W.
Partner: UNT Libraries Government Documents Department

Revised lattice for the APS storage ring

Description: As a result of more detailed engineering studies of vacuum chamber components and related accelerator physics studies, the circumference of the APS storage ring is increased by 44 m to a value of 1104 m. The increase is 1.1 m for each of the 40 sectors. The insertion region straight section is lengthened by 0.52 m to 6.72 m. This allows full 20-cm vacuum chamber transition sections leading into and out of the 5.2-m insertion devices. Computer studies using TBCI and MAFIA-T3 have indicated that 20-cm-long transition regions reduce the transverse coupling impedance to an Acceptable low value. The results for 10-cm transition length were marginal.
Date: August 1, 1989
Creator: Crosbie, E.A.
Partner: UNT Libraries Government Documents Department

Ion effects in the SLC electron damping ring

Description: The authors report on the ion-related beam behavior in the electron damping ring during unusually poor vacuum conditions in the weeks that followed a catastrophic kicker chamber failure that contaminated the ring vacuum system. The vacuum gradually improved over several months of beam operation, during which time the vertical emittance remained blown up by a factor of 2. The emittance blowup was accompanied by a transverse instability that produced jitter in the extracted beam size. Both the characteristic spectrum of self-excited betatron sidebands and the emittance blowup exhibited a threshold behavior with beam current and vacuum pressure. This behavior depended strongly on the betatron tune and it was found that the ion effects could be minimized by operating just below the 1/2 integer resonance.
Date: May 1, 1997
Creator: Krejcik, P.; Pritzkau, D.; Raubenheimer, T.; Ross, M. & Zimmermann, F.
Partner: UNT Libraries Government Documents Department

Spectral function calculation of angle wakes, wake moments, and misalignment wakes for the SLAC Damped Detuned Structures (DDS)

Description: Transverse wake functions so far reported for the SLAC DDS have been limited to those caused by uniform offset of the drive beam in a straight perfectly aligned structure. The complete description of the betatron oscillations of wake coupled bunches requires an array of wake functions, referred to as moments. Modifications of these arrays induced by structure misalignments are also of interest. In this paper we express the array elements in terms of a spectral function array. Examples are given based upon DDS1.
Date: May 1, 1997
Creator: Jones, R.M.; Miller, R.H. & Kroll, N.M.
Partner: UNT Libraries Government Documents Department

On possibility to increase the TMCI threshold by RF quadrupole

Description: Transverse mode coupling instability is one of the major limitations of a single bunch current in storage rings. Up to now it appeared in large electron-positron machines, while its presence in proton colliders is under question. This paper is devoted to a theoretical analysis of the effect of longitudinal variation of the betatron tune (induced by RF quad) on transverse mode coupling instability threshold. It is shown, that it is possible to significantly enhance the threshold, introducing the difference of betatron tunes for the head and the tail of a bunch (due to RF quad) comparable with the synchrotron tune.
Date: November 1, 1997
Creator: Danilov, V.V.
Partner: UNT Libraries Government Documents Department

Beam motions near separatrix

Description: Experimental data on particle motion near the separatrix of the one dimensional (1-D) fourth-integer islands are an-alyzed. When the beam bunch is initially kicked to the separatrix orbit, we observed a strong decoherence in the coherent betatron motion. We find that, through intensive particle tracking simulation analysis, the decoherence has resulted from the beam being split into beamlets in the beta-tron phase space. However, we also observe an unexpected recoherence of coherence signal, which may result form a modulated closed orbit or the homoclinic structure near the separatrix.
Date: May 4, 1999
Creator: al., M. Ball et
Partner: UNT Libraries Government Documents Department