Multipole error data analysis for RHIC low-energy operations

Abstract

In FY10, RHIC operated with gold beams at three different energies below its regular injection energy, namely at $\sqrt{s}$ = 5 GeV, 7.7 GeV, and 11.5 GeV. While beam lifetimes of about 10 minutes were achieved at 11.5 GeV and 7.7 GeV, leading to stable collider operation, beam lifetimes during tests at $\sqrt{s}$ = 5 GeV were only of the order of several seconds. Though space charge effects are a major concern in low energy operations due to the $1/\gamma^2$ scaling of the space charge force, these can effectively be ruled out as the main cause of this abysmal performance because of the tiny bunch intensities of approximately $10^8$ Au/bunch, compared to $10^9$ Au/bunch at the two higher energies. During these 5 GeV tests, large betatron tune spreads were observed, but the extremely short beam lifetime prevented chromaticity measurements. Instead, chromaticities were scanned over a range of 40 units, but to no effect. It was therefore suspected at that time that the large tune spread was caused by higher-order multipole errors in the RHIC magnets.