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| TUAX02 | Coherent Instabilities at the Fermilab Booster | impedance, dipole, booster, injection | 69 | ||
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Fermilab booster is a fast cycling synchrotron operating on 15 Hz. To exclude problem of eddy currents excited in the vacuum chamber by fast changing magnetic field Booster does not have a conventional vacuum chamber. Instead, the vacuum chamber is formed by poles of the laminated combined function magnets. The exposed magnet laminations result in large transverse and longitudinal impedances affecting both the transverse and longitudinal stability of the beam. Presently, the transverse instability is suppressed by large chromaticity negatively affecting the dynamic aperture and the beam lifetime. Earlier attempts to stabilize the instability by transverse feedback system were unsuccessful. Recently we performed experimental studies to find out the reason. We observed that at reduced chromaticity at injection the most unstable mode is the multibunch high order head-tail mode with growth time of about 12 turns. It develops at synchro-betatron tune with very small fractional part where the transverse impedance is at a maximum. Analytical calculations and numerical simulations verify the observations and allowed us to compute the value of transverse impedance. Another persistent probl
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Work supported by the Universities Research Assos., Inc., under contract DE-AC02-76CH03000 with the U. S. Dept. of Energy. |
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| TUAX06 | Electron cloud and single-bunch instabilities in the Relativistic Heavy Ion Collider | electron, beam-losses, emittance, ion | 117 | ||
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Electron cloud is one of the leading mechanisms that limit the performance of high intensity circular accelerators and colliders. Electron cloud in RHIC is in an intermediate regime sharing features of both the long-bunch (PSR) and short-bunch (photon factories) machines. Vacuum-pressure rises, transverse tune shifts, and electron flux are observed at injection, upon transition crossing, and at top energy. Transverse emittance growth, fast instabilities, and beam loss also occur upon transition crossing. Mitigation measures are implemented both to reduce the production of electron cloud and to control the beam stability. This paper summarizes the observation and initial analysis of the electron-cloud effects at RHIC.
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| TUAZ06 | Development of hybrid typoe carbon stripper foils with high durability against 1800K for RCS of J-PARC | injection, linac, laser, ion | 122 | ||
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We have successfully made long-lived and hybrid , thick, boron mixed carbon stripper foils for high energy and high intensity accelerators. The foils were made by the controlled DC arc-discharge method, and the thickness is wide range from 50 to 600 ug/cm2. The lifetime of the foils was tested with use of 3.2 MeV Ne+DC beams of 2.5 uA, in which a significant of energy was deposited in the foils and thus we could simulate the condition by high power accelerator. The lifetime in maximum was shown to be extremely long, 102 and 410 times longer those of diamond and commercially available best carbon foils, respectively.
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| WEAY06 | Experimental Strategy for Realization of 3-D Beam Ordering with Use of Tapered Cooling at S-LSR | laser, ion, coupling, proton | 231 | ||
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At ICR, Kyoto University, an ion storage/cooler ring, S-LSR has been operated since the October, 2005. S-LSR has capability of dispersion free mode* throughout the whole circumference in order to avoid the shear heating** due to momentum dispersion of ion beam orbits. With such a mode, we need a special devise to develop necessary coupling between the longitudinal and transverse degrees of freedom for 3-dimensional laser cooling.*** A Wien Filter, in which the magnetic and electric fields overlap with strengths compensating each other for ions with a certain velocity, is to be utilized in the straight section where the usual laser cooling is applied. Due to the potential difference caused by the electric field in the Wien Filter, the difference in horizontal position of the circulating ion creates the difference of the equillibrium energy after laser cooling, which realizes "Tapered Cooling"****. In the present paper, a possible strategy of experimental approach at S-LSR toward 3-dimensional crystalline ion beams with use of the Wien Filter is to be presented.
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* M. Ikegami et al., PR-STAB,7, 120101(2004). |
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| WEAZ04 | Beam-Induced Damage to the Tevatron Components and What Has Been Done About It | controls, kicker, proton, dipole | 205 | ||
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The Tevatron collimators and magnets were damaged and two thirds of the superconducting ring were quenched on December 5, 2003, induced by a failure in the CDF Roman Pot detector positioning at the end of a 2-TeV proton-antiproton colliding beam store. Analysis of a failure in the abort kicker AC distribution, and detailed modeling of a misbehaved beam dynamics, induced energy deposition and ablation process in the collimator material, have provided a good understanding of the event. The improvements to the detectors, Tevatron quench protection and beam loss monitor systems to avoid such an accident in the future are described.
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| WEAZ06 | Transfer line damage during high intensity proton beam extraction from the SPS in 2004 | extraction, power-supply, simulation, septum | 228 | ||
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During extraction of a high intensity beam from the SPS in 2004 an incident occurred in which the vacuum chamber of a transfer line quadrupole magnet was badly damaged. The beam was a 450 GeV full LHC injection batch of 3.4·1013 p+ in 288 bunches, and was extracted with the wrong trajectory. The incident causes have been identified, with details reconstructed from the logged data and the damage to the vacuum chamber. The remedial measures which were taken are explained, and further recommendations made concerning the interlocking system performance and tests, as well as the operational procedures which must be adopted when commissioning with high intensities. The specific issues of how the incident happened, why the existing protection system was not sufficient and what can/has been done about it are addressed.
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| THBW02 | Electron-Cloud Benchmarking & CARE-HHH Codes | simulation, electron, emittance, single-bunch | 350 | ||
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The state-of-the-art in code benchmarking for various types of electron-cloud simulations is reviewed. In particular, we recall possible meanings of benchmarking, summarize past and more recent code comparisons, present examples of code verifications against machine experiments, describe some remaining uncertainties, and formulate a few goals for the future. The code-benchmarking effort is supported by the CARE-HHH initiative on accelerator physics simulation codes, whose other objectives include a common web repository and the practical extension of simulation codes.
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