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Beam dynamics group summary

Description: This paper summarizes the activities of the beam dynamics working group of the LHC Collective Effects Workshop that was held in Montreux in 1994. It reviews the presentations that were made to the group, the discussions that ensued, and the consensuses that evolved.
Date: December 31, 1994
Creator: Peggs, S.
Partner: UNT Libraries Government Documents Department

Feedback between Accelerator Physicists and magnet builders

Description: Our task is not to record history but to change it. (K. Marx (paraphrased)) How should Accelerator Physicists set magnet error specifications? In a crude social model, they place tolerance limits on undesirable nonlinearities and errors (higher order harmonics, component alignments, etc.). The Magnet Division then goes away for a suitably lengthy period of time, and comes back with a working magnet prototype that is reproduced in industry. A better solution is to set no specifications. Accelerator Physicists begin by evaluating expected values of harmonics, generated by the Magnet Division, before and during prototype construction. Damaging harmonics are traded off against innocuous harmonics as the prototype design evolves, lagging one generation behind the evolution of expected harmonics. Finally, the real harmonics are quickly evaluated during early industrial production, allowing a final round of performance trade-offs, using contingency scenarios prepared earlier. This solution assumes a close relationship and rapid feedback between the Accelerator Physicists and the magnet builders. What follows is one perspective of the way that rapid feedback was used to `change history` (improve linear and dynamic aperture) at RHIC, to great benefit.
Date: December 31, 1995
Creator: Peggs, S.
Partner: UNT Libraries Government Documents Department

On the calibration of TEVATRON beam position and intensity monitors used in E778

Description: In the second run of E778 two sets of electronics were used to record the motion of the center of mass of the beam. The first, the standard Fermilab Beam Position Monitor (BPM) front end, gives direct horizontal, vertical and intensity signals. The second is a peak sensing circuit which gives signals from the separate plates of two horizontal and one vertical pickup. This note addresses the question of calibration of the signals from the standard Tevatron beam position (HF42 and HF44 in the case of E778) and intensity monitors (I-45). Following is the summary of this study: Calibration Constants /minus/ Position Monitors = .0083 mm/mV; Smear data = /minus/147 LSB/10/sup 10/ particles; Resonance island data = (/minus/134 +- 7) LSB/10/sup 10/ particles. 6 figs.
Date: May 1, 1988
Creator: Merminga, L.; Gerig, R. & Peggs, S.
Partner: UNT Libraries Government Documents Department

Pattern Recognition: The Importance of Dispersion in Crystal Collimation

Description: One aspect of the upcoming CRYSTAL experiment is to study the dynamics of single protons circulating the SPS in the presence of a crystal. Under some circumstances (for example under crystal channeling) a proton may hit the crystal and the neighboring silicon strip position detectors only once, before extraction from the SPS. In general (at most crystal rotation angles) it is expected that single protons will hit the crystal many times, with many accelerator turns between each hit, before escaping. Intermediate regimes are also possible (for example under volume reflection) in which a proton hits the crystal only a few times over many turns before being lost. It is crucial that the data analysis of each single proton data set be able to distinguish between these different dynamical phases, and to be able to convincingly demonstrate that the fundamental processes at play in each phase are well understood. Distinguishing between dynamical phases depends crucially on the ability to perform pattern recognition--at least visually, but preferably quantitatively--on the single proton data sets. This note shows that synchrotron oscillations significantly affect the hit pattern of a proton on the crystal. (By hit pattern we mean either the measurement vector of turn number and penetration depth, for each proton, or a vector that can be directly derived from the measurement vector, such as the vector of inferred synchrotron phase and penetration depth.) The analysis is (deliberately) as rudimentary as possible, using an elementary linear calculation which neither includes any higher order effects in the accelerator, nor any dynamical interactions between the test proton and the crystal or the silicon detectors. Single particle simulation studies need to be carried out for CRYSTAL, exploring realistic effects besides dispersion, such as multiple scattering, dead zones, energy loss, dispersion slope, and linear coupling. Only after analysis software ...
Date: September 1, 2008
Creator: Peggs,S. & Shiraishi, S.
Partner: UNT Libraries Government Documents Department

Beam-beam collisions and crossing angles in RHIC

Description: This paper evaluates the strength of head on and parasitic beam-beam collisions in RHIC when the crossing angle is zero. A non-zero crossing angle is not required in normal operation with 120 bunches, thanks to the early separation of the two beams. The RHIC lattice is shown to easily accommodate even conservatively large crossing angles, for example in beam dynamics studies, or in future operational upgrades to as many as 360 bunches per ring. A modest loss in luminosity is incurred when gold ions collide at an angle after 10 hours of storage.
Date: June 1, 1999
Creator: Peggs, S.
Partner: UNT Libraries Government Documents Department

RHIC status

Description: The design and construction status of the Relativistic Heavy Ion Collider, RHIC, which is in the seventh year of a nine year construction cycle, is discussed. Those novel performance features of a heavy ion collider that are distinct from hadron colliders in general are noted. These features are derived from the experimental requirements of operation with a variety of ion species over a wide energy range, including collisions between protons and ions, and between ions of unequal energies. Section 1 gives a brief introduction to the major parameters and overall layout of RHIC. A review of the superconducting magnet program is given in Section 2. Activities during the recent Sextant Test are briefly reviewed in Section 3. Finally, Section 4 presents the plans for RHIC commissioning in 1999.
Date: August 1, 1997
Creator: Peggs, S.
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

Simulation of the space charge effect in RHIC

Description: Space charge forces, representing the weak-strong case, are simulated by kicks from a line charge having a 2D-Gaussian transverse charge distribution. A series of particles having initial coordinates consistent with the dimensions of the injected beam are tracked sequentially, and tunes are obtained from analysis of the coordinates, x, x{prime}, y, and y{prime}, at the end of each turn. Stability is tested using 30K turn tracking runs during which the momentum error {delta} varies as {delta} = {delta}sin(2{pi}Q{sub s}t).
Date: May 1, 1995
Creator: Dell, G.F. & Peggs, S.
Partner: UNT Libraries Government Documents Department