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Zhang, S. Y.

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TUPAS106 Observation of Experimental Background in RHIC Polarized Proton Run 2006 1883
  • S. Y. Zhang, D. Trbojevic
    BNL, Upton, Long Island, New York
  Funding: * Work supported by U. S. DOE under contract No DE-AC02-98CH1-886

There are three main sources of the experimental background at RHIC. The beam-gas induced background is associated with the vacuum pressure, the beam-chamber-interaction induced background can be improved by collimations, and the beam-beam induced background is somewhat inherent, and probably harmless for the experimental data taking. The zero degree calorimeter (ZDC) is an essential luminosity detector for heavy ion operations in RHIC. It is shown that, however, the ratio of ZDC singles (background) and coincident rate is also useful in proton runs for background evaluations. In this article, the experimental background problem in RHIC polarized proton runs is reported.

TUPAS107 Proton Beam Emittance Growth at RHIC 1886
  • S. Y. Zhang, V. Ptitsyn
    BNL, Upton, Long Island, New York
  Funding: Work supported by U. S. DOE under contract No DE-AC02-98CH1-886

The beam emittance growth in RHIC polarized proton runs has a dependence on the dynamic pressure rise, which is caused by the electron cloud and peaked at the end of the beam injection and the early energy acceleration. This emittance growth is usually presented without beam instability, and it is slower than the ones above the instability threshold. The effect on the machine luminosity, nevertheless, is significant, and it is currently a limiting factor in machine performance. The electron cloud is substantially reduced at the store, the emittance growth there has no dependence on the bunch spacing and instead it has a clear dependence on the beam-beam parameter. The results of the machine operation and beam studies will be reported.

TUOCKI02 Summary of the RHIC Performance during the FY07 Heavy Ion Run 722
  • K. A. Drees, L. Ahrens, J. G. Alessi, M. Bai, D. S. Barton, J. Beebe-Wang, M. Blaskiewicz, J. M. Brennan, K. A. Brown, D. Bruno, J. J. Butler, R. Calaga, P. Cameron, R. Connolly, T. D'Ottavio, W. Fischer, W. Fu, G. Ganetis, J. W. Glenn, M. Harvey, T. Hayes, H.-C. Hseuh, H. Huang, J. Kewisch, R. C. Lee, V. Litvinenko, Y. Luo, W. W. MacKay, G. J. Marr, A. Marusic, R. J. Michnoff, C. Montag, J. Morris, B. Oerter, F. C. Pilat, V. Ptitsyn, T. Roser, J. Sandberg, T. Satogata, C. Schultheiss, F. Severino, K. Smith, S. Tepikian, D. Trbojevic, N. Tsoupas, J. E. Tuozzolo, A. Zaltsman, S. Y. Zhang
    BNL, Upton, Long Island, New York
  Funding: Work performed under Contract Number DE-AC02-98CH10886 under the auspices of the US Department of Energy.

After the last successful RHIC Au-Au run in 2004 (Run-4), RHIC experiments now require significantly enhanced luminosity to study very rare events in heavy ion collisions. RHIC has demonstrated its capability to operate routinely above its design average luminosity per store of 2x1026 cm-2 s-1. In Run-4 we already achieved 2.5 times the design luminosity in RHIC. This luminosity was achieved with only 40% of bunches filled, and with β* = 1 m. However, the goal is to reach 4 times the design luminosity, 8x1026 cm-2 s-1, by reducing the beta* value and increasing the number of bunches to the accelerator maximum of 111. In addition, the average time in store should be increased by a factor of 1.1 to about 60% of calendar time. We present an overview of the changes that increased the instantaneous luminosity and luminosity lifetime, raised the reliability, and improved the operational efficiency of RHIC Au-Au operations during Run-7.

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TUODKI04 Accelerating Polarized Protons to 250 GeV 745
  • M. Bai, L. Ahrens, I. G. Alekseev, J. G. Alessi, J. Beebe-Wang, M. Blaskiewicz, A. Bravar, J. M. Brennan, K. A. Brown, D. Bruno, G. Bunce, J. J. Butler, P. Cameron, R. Connolly, T. D'Ottavio, J. DeLong, K. A. Drees, W. Fischer, G. Ganetis, C. J. Gardner, J. W. Glenn, T. Hayes, H.-C. Hseuh, H. Huang, P. F. Ingrassia, J. S. Laster, R. C. Lee, A. U. Luccio, Y. Luo, W. W. MacKay, Y. Makdisi, G. J. Marr, A. Marusic, G. T. McIntyre, R. J. Michnoff, C. Montag, J. Morris, P. Oddo, B. Oerter, J. Piacentino, F. C. Pilat, V. Ptitsyn, T. Roser, T. Satogata, K. Smith, S. Tepikian, D. Trbojevic, N. Tsoupas, J. E. Tuozzolo, M. Wilinski, A. Zaltsman, A. Zelenski, K. Zeno, S. Y. Zhang
    BNL, Upton, Long Island, New York
  • D. Svirida
    ITEP, Moscow
  Funding: The work was performed under the US Department of Energy Contract No. DE-AC02-98CH1-886, and with support of RIKEN(Japan) and Renaissance Technologies Corp.(USA)

The Relativistic Heavy Ion Collider~(RHIC) as the first high energy polarized proton collider was designed to provide polarized proton collisions at a maximum beam energy of 250GeV. It has been providing collisions at a beam energy of 100GeV since 2001. Equipped with two full Siberian snakes in each ring, polarization is preserved during the acceleration from injection to 100GeV with careful control of the betatron tunes and the vertical orbit distortions. However, the intrinsic spin resonances beyond 100GeV are about a factor of two stronger than those below 100GeV making it important to examine the impact of these strong intrinsic spin resonances on polarization survival and the tolerance for vertical orbit distortions. Polarized protons were accelerated to the record energy of 250GeV in RHIC with a polarization of 45\% measured at top energy in 2006. The polarization measurement as a function of beam energy also shows some polarization loss around 136GeV, the first strong intrinsic resonance above 100GeV. This paper presents the results and discusses the sensitivity of the polarization survival to orbit distortions.

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TUXAB02 E-cloud experiments and cures at RHIC 759
  • W. Fischer, M. Blaskiewicz, J. M. Brennan, H.-C. Hseuh, H. Huang, V. Ptitsyn, T. Roser, P. Thieberger, D. Trbojevic, J. Wei, S. Y. Zhang
    BNL, Upton, Long Island, New York
  • U. Iriso
    ALBA, Bellaterra (Cerdanyola del Valles)
  Funding: Work supported by U. S. DOE under contract No DE-AC02-98CH1-886.

Since 2001 RHIC has experienced electron cloud effects, which have limited the beam intensity. These include dynamic pressure rises – including pressure instabilities, a reduction of the stability threshold for bunches crossing the transition energy, and possibly slow emittance growth. We report on the main observations in operation and dedicated experiments, as well as the effect of various countermeasures including baking, NEG coated warm pipes, pre-pumped cold pipes, bunch patterns, scrubbing, and anti-grazing rings.

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