RHIC performance with 56 MHz RF and gold ion beams pre-cooled at lower energy

Abstract

Presently there is an R&D ERL under construction at Collider-Accelerator Department (CAD) at BNL with its commissioning scheduled for FY09-10 [1]. The use of this full energy 21 MeV ERL in RHIC tunnel was recently proposed for a Proof-of-Principle demonstration of Coherent Electron Cooling of gold ions at 40 GeV/nucleon [2]. The purpose of this Note is to summarize numerical studies aimed at understanding the potential improvement of RHIC luminosity by using this R&D ERL for pre-cooling of Au ion beams with conventional electron cooling system at 40 GeV/nucleon. The constraints were such that electron beam parameters should be close to those expected from R&D ERL. Additionally, the cooling section in RHIC should not require major RHIC modification. As a result of these studies it was found that pre-cooling of gold ion at about 40 GeV/nucleon approximately doubles the average store luminosity of RHIC at top energy of 100 GeV/nucleon compared to the expected luminosity improvement with 56MHz RF upgrade [3, 4]. Significant luminosity improvement may be also gained on top of future expected luminosity performance with combined upgrades of 56MHz RF and all-plane stochastic cooling system with present beam parameters [5]. The electron beam parameters needed for such pre-coolingmore » (see Table 1) are close to those expected from the R&D ERL which is presently under construction at BNL. With electron beam parameters from Table 1 it takes about 20 minutes to cool the transverse emittance of gold ions by a factor of two at 40 GeV/nucleon. Similar studies were done for protons as well. However, it was found that the electron beam parameters needed for pre-cooling of protons would require a significant upgrade of the present injector of the R&D ERL. Thus, discussion about protons is omitted from the present Note.« less