Luminosity issues in 2009 100 GeV polarized proton run

Zhang,S.Y.

关键词: CLOUDS;    ELECTRONS;    INSTABILITY;    LIFETIME;    LUMINOSITY;    POLARIZATION;    PROTONS controls;    relational databases;    relativistic heavy ion collider;   

DOI  :  10.2172/970518
RP-ID  :  BNL--90497-2009-IR
PID  :  OSTI ID: 970518
Others  :  R&D Project: KBCH139
Others  :  Other: KB0202011
Others  :  TRN: US1000955

学科分类：物理（综合）

美国|英语

来源: SciTech Connect

【 摘 要 】

Several luminosity issues are reviewed. Questions remain, which are stated for further investigation. Some suggestions are made for possible luminosity improvement. There are several factors affecting the luminosity in 2009 100 GeV polarized proton run: (1) The highest bunch intensity at RHIC early store (1.5 hour after accramp in this note) in 2009 is 1.25 x 10{sup 11} protons. In 2008 run, it was 1.42 x 10{sup 11} protons, which gives rise to 30% higher luminosity if other conditions are the same. Yellow ramp efficiency is identified as one of the main problem. Meanwhile, the beam-beam induced loss in about 1 hour into collision accounts actually no less than the ramp. (2) The typical transverse emittance at early store is 13 {pi}{micro}m for bunch intensity of 10{sup 11} protons, but it is 17 {pi}{micro} for 1.25 x 10{sup 11} protons. The increase of the emittance implies a 30% difference in luminosity if other conditions are the same. The emittance growth with electron cloud below instability threshold may be partially responsible. Meanwhile, the Booster scraping may also be relevant. (3) The luminosity lifetime in 2009 run is significantly lower than that in 2005, 2006, and 2008 runs. At the beam-beam parameter of 0.01, the typical average luminosity lifetime in early store is 10 hours in 2009, and it is 15 hours in previous runs. Given 8 hours of store time, this implies more than 20% of the difference in integrated luminosity. The 0.7 m betastar adopted in 2009 might be relevant, but the evidence is not fully convincing. On the other hand, the continuing RF voltage ramp in store may be of concern. (4) In the last month of the run, the polarization at RHIC early store is declined from 60% to 55%, a 30% reduction in p{sup 4} factor. It is noted that the Booster scraping is reduced in order to increase bunch intensity at RHIC, and the source polarization is also declined at the same time. Questions regarding these issues are discussed, and some suggestions are made.