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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


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
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

Measurements of the betatron functions and phases in RHIC

Description: The Relativistic Heavy Ion Collider (RHIC) consists of two rings with six fold symmetry. The six interaction regions (IR)s are connected with twelve FODO cells. RHIC quadrupoles in the interaction regions have independent tuning capability. The betatron functions will be measured by a three methods. First, tunable IR quadrupoles will be adjusted to measure betatron functions at those locations through the change in tune. Second, sinusoidal coherent dipole oscillations will be used to measure the betatron phases and functions (as performed in LEP). Third, a correction dipole kick technique will be used (as at Fermilab). special attention will be given to the betatron squeeze procedure by which the two large experiments PHENIX and STAR will achieve minimum betatron functions between 1 and 2 m.
Date: August 1, 1998
Creator: Trbojevic, D.; Kewisch, J.; Peggs, S.; Satogata, T.; Tepikian, S. & Goddere, G.
Partner: UNT Libraries Government Documents Department

Results from betatron phase measurements in RHIC during the sextant test

Description: The Sextant Test of the Relativistic Heavy Ion Collider (RHIC) was an important step towards its completion. One sixth of the two RHIC accelerators was fully commissioned. gold ion beam was injected and transported through one sextant of one of the two rings. The betatron phase advance per cell was measured by recording differences in the horizontal and vertical positions of the beam at the end of the sextant due to a sequence of correction dipole kicks along the beam line. Measurement results show excellent agreement with predicted values, confirming that production measurements of the integral functions of the quadrupoles were very accurate, and that the polarity of all elements (correction dipoles, quadrupoles, dipoles etc.) was correct.
Date: August 1, 1998
Creator: Trbojevic, D.; Connolly, R. & Fischer, W.
Partner: UNT Libraries Government Documents Department


Description: Resonance driving terms can be derived from the frequency analysis of turn-by-turn betatron oscillation data. This paper demonstrates that the same information can also be drawn from the spectral analysis of a driven oscillation adiabatically excited by an rf dipole. The advantage of this method is that a large betatron oscillation amplitude can be sustained without loosing the coherence signal. The frequency spectrum of the driven oscillation is composed of multiples of the rf dipole modulation frequency which can be interpreted as resonance driving terms. This analysis has been applied to the data taken at the Brookhaven AGS. The adiabatically excited coherent oscillation is also very useful in measuring the betatron tune parasitically. The data taken during the AGS high intensity proton program is also presented.
Date: June 18, 2001
Partner: UNT Libraries Government Documents Department

Fast transverse instability in the NSNS Accumulator Ring

Description: This paper reports on the results of investigation of possible fast transverse instabilities in the NSNS Accumulator Ring. The instability may be caused by the presence of stripline devices like kicker magnets, the active damper system, and by the RF cavities, and the sharp steps of the vacuum pipe. The instability can be overcome by adopting aluminum as the material of the vacuum pipe.Still the growth time of the instability remains short especially for the mode in proximity of the betatron tune.
Date: August 1997
Creator: Ruggiero, A. G. & Blaskiewicz, M.
Partner: UNT Libraries Government Documents Department

Betatron motion with coupling of horizontal and vertical degrees of freedom

Description: The Courant-Snyder parameterization of one-dimensional linear betatron motion is generalized to two-dimensional coupled linear motion. To represent the 4 x 4 symplectic transfer matrix the following ten parameters were chosen: four beta-function, four alpha-functions and two betatron phase advances. The beta-functions have a meaning similar to the Courant-Snyder parameterization, and the definition of alpha-functions coincides with the standard one at regions with zero longitudinal magnetic field, where they are equal to negative half-derivatives of the beta-functions. Such a parameterization can be useful for analysis of coupled betatron motion in circular machines and transfer lines.
Date: October 1, 1999
Creator: Lebedev, V.A. & Bogacz, S.A.
Partner: UNT Libraries Government Documents Department

Emittance growth due to noise and its suppression with the Feedback system in large hadron colliders

Description: The problem of emittance growth due to random fluctuation of the magnetic field in hadron colliders is considered. Based on a simple one-dimensional linear model, a formula for an emittance growth rate as a function of the noise spectrum is derived. Different sources of the noise are analyzed and their role is estimated for the Superconducting Super Collider (SSC). A theory of feedback suppression of the emittance growth is developed which predicts the residual growth of the emittance in the accelerator with a feedback system.
Date: March 1, 1993
Creator: Lebedev, V.; Parkhomchuk, V.; Shiltsev, V. & Stupakov, G.
Partner: UNT Libraries Government Documents Department

Emittance growth for the LHC beams due to head-on beam-beam interaction and ground motion

Description: The influence of ground motion on the LHC beam is estimated applying the existing theories of particle diffusion due to a weak-strong beam-beam collision with random offset at the interaction point. Noise at odd harmonics of the betatron frequency contributes significantly to particle diffusion. The spectrum of the random offset, as obtained from the ground motion spectrum at the LHC site, shows a fast fall-off with frequency and the amplitude is very small even at the first harmonic. They find that the head-on beam-beam force in the weak-strong approximation and ground motion by themselves do not induce significant diffusion over the lifetime of the beam.
Date: April 18, 2000
Creator: Sen, Mari Paz Zorzano and Tanaji
Partner: UNT Libraries Government Documents Department

Skew chromaticity

Description: The on-momentum description of linear coupling between horizontal and vertical betatron motion is extended to include off-momentum particles, introducing a vector quantity called the ``skew chromaticity``. This vector tends to be long in large superconducting storage rings, where it restricts the available working space in the tune plane, and modifies collective effect stability criteria. Skew chromaticity measurements at the Cornell Electron Storage Ring (CESR) and at the Fermilab Tevatron are reported, as well as tracking results from the Relativistic Heavy Ion Collider (RHIC). The observation of anomalous head-tail beam Iowa new the tune diagonal in the Tevatron are explained in terms of the extended theory, including modified criteria for headtail stability. These results are confirmed in head-tail simulations. Sources of skew chromaticity are investigated.
Date: December 31, 1994
Creator: Peggs, S. & Dell, G.F.
Partner: UNT Libraries Government Documents Department

Is the momentum space optimally used with the FODO lattices?

Description: The available momentum space of a FODO lattice is determined by the maximum value of the dispersion function ({delta}x = D{sub x} {partial_derivative}p/p). In a regular FODO lattice the dispersion function oscillates between its maximum and minimum values, which are always positive. The maximum value of the dispersion function in a FODO cell of a fixed length depends on the cell phase difference. An example of a new lattice, in which the dispersion function is lowered to half its value in the same FODO cell, is presented. ne available momentum space in the new lattice is raised to twice that in the FODO lattice by allowing the dispersion function to oscillate between the same positive and negative values. The maxima of the dispersion function in the new lattice have half the value of those within the regular 900 cells.
Date: July 1, 1993
Creator: Trbojevic, D.; Ng, K.Y. & Lee, S.Y.
Partner: UNT Libraries Government Documents Department

A simple way to characterize linear coupling in a storage ring

Description: The techniques of normal form analysis, well known in the literature, can be used to provide a straightforward characterization of linear betatron dynamics in a coupled lattice. Here, we consider both the beam distribution and the betatron oscillations in a storage ring, assuming that the beam emittances and betatron actions respectively are provided as parameters. We find that the beta functions for uncoupled motion generalize in a simple way to the coupled case. Defined in the way that we propose, the beta functions remain well behaved (positive and finite) under all circumstances, and have essentially the same physical significance for the beam size and betatron oscillations as in the uncoupled case. We discuss a technique for making direct measurements of the ratio of the coupled lattice functions at different points in the lattice.
Date: March 24, 2004
Creator: Wolski, Andrzej
Partner: UNT Libraries Government Documents Department

Analysis of optical stochastic cooling including transverse effects

Description: The phase space area plays an important role in determining the performance of optical stochastic cooling. Specifically, the number of samples in the beam consists of three factors corresponding to three dimensions, the factor in each dimension being given by the ratio of the total phase space area in that dimension to the radiation wavelength.
Date: May 1, 1995
Creator: Kim, K.J. & Zege, A.V.
Partner: UNT Libraries Government Documents Department

Normal form analysis of linear beam dynamics in a coupled storagering

Description: The techniques of normal form analysis, well known in the literature, can be used to provide a straightforward characterization of linear betatron dynamics in a coupled lattice. Here, we consider both the beam distribution and the betatron oscillations in a storage ring. We find that the beta functions for uncoupled motion generalize in a simple way to the coupled case. Defined in the way that we propose, the beta functions remain well behaved (positive and finite) under all circumstances, and have essentially the same physical significance for the beam size and betatron oscillation amplitude as in the uncoupled case. Application of this analysis to the online modeling of the PEP-II rings is also discussed.
Date: June 30, 2004
Creator: Wolski, Andrzej & Woodley, Mark D.
Partner: UNT Libraries Government Documents Department