Abstract
To compensate the beam-beam tune spread and beam-beam resonance driving terms in the polarized proton operation in the Relativistic Heavy Ion Collider (RHIC), we will introduce a low energy DC electron beam into each ring to collide head-on with the opposing proton beam. The device to provide the electron beam is called an electron lens. In this article, using a 6D weak-strong beam-beam interaction simulation model, we will investigate the effects of head-on beam-beam compensation with electron lenses on the proton beam dynamics for the RHIC 250 GeV polarized proton operation. Frequency maps, dynamic apertures, and proton beam loss rates are calculated for this study. Key beam parameters involved in this scheme are varied to search for the optimum compensation condition. The sensitivities of head-on beam-beam compensation to beam imperfections and beam offsets are also studied.
Highlights
The working point in the polarized proton operation in the Relativistic Heavy Ion Collider (RHIC) is chosen to provide a good beam-beam lifetime and to maintain the proton polarization during the energy acceleration and at the physics store
The current working point is constrained between 2=3 and 7=10 [1,2]. 2=3 is a strong third order betatron resonance. 7=10 is a 10th order betatron resonance and a depolarization resonance [3]
For each proton bunch intensity, we compare the relative proton beam losses in 2 Â 106 turns without beam-beam compensation, with half beam-beam compensation, with the optimized betatron phase advances ð9; 11Þ between IP8 and the e-lens, and with the global second order chromaticity correction
Summary
The working point in the polarized proton operation in the Relativistic Heavy Ion Collider (RHIC) is chosen to provide a good beam-beam lifetime and to maintain the proton polarization during the energy acceleration and at the physics store. To further increase the luminosity in the polarized proton operation in RHIC, it is planned to increase the proton bunch intensity from currently 1:65 Â 1011 up to 3:0 Â 1011 with an upgraded polarized proton source [4] With such a high proton bunch intensity, the linear incoherent beam-beam tune shift and the amplitude dependent beam-beam tune spread will be about 0.03. Head-on beam-beam compensation in proton colliders with electron beams was first proposed and studied by Tsyganov in 1993 [8,9]. The idea is to introduce a low energy electron beam to collide head-on with the opposing proton beam to compensate the beam-beam nonlinear effects. In our current design for the RHIC head-on beam-beam compensation [14], two e-lenses are needed. The sensitivity of headon beam-beam compensation to beam imperfections and beam offsets are studied
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