Bunch Patterns and Pressure Rise in RHIC

Abstract

After the upgrade of the RHIC injection system, the bunch number can be increased from currently 56 to 112. However, with large bunch numbers and high-intensity bunches a significant pressure rise can be observed in several warm locations. This affects the experimental background and beam lifetime. We discuss the optimal distribution of bunches along the circumference for bunch numbers between 56 and 112.

Optimized bunch patterns for d-Au in RHIC Run-8

“…Under these circumstances, the average electron cloud density could be minimized, and the luminosity maximized, by distributing any given total intensity in as few bunches as possible, uniformly distributed along the circumference. This was found in simulations and supported by observations in experiments and operation [2][3][4][5][6].…”

“…This pattern has 2 long gaps in addition to the abort gap, preserving the 3-fold symmetry that is necessary to obtain approximately the same number of collisions at both PHENIX and STAR. The used bunch pattern is, however, different from the pattern expected to minimize the average electron cloud density, which was found in previous simulations [3,4]. This other pattern is shown in the upper part of Fig.…”

Observations on background in PHOBOS and related electron cloud simulations

“…When RHIC is operated with 45, most bunches are separated by 6 buckets and some by 9 buckets. The bunches are still distributed as uniformly as possible to minimize electron cloud effects, and have a 3-fold symmetry to provide approximately an equal amount of bunchbunch collisions for all of the four experiments [Fischer03]. For 45 bunches per ring more intensity per bunch is required in order to maintain the luminosity as with 56 bunches.…”

Reduction of secondary electron yield for E-cloud mitigation by laser ablation surface engineering

“…In high intensity particle accelerators with positively charged beams such as the LHC [1,2,3], KEKB [4], DAFNE [5], RHIC [6], PEP=II [7], etc., the beam induced electron multipacting (BIEM) and electron cloud (e-cloud) effects can significantly affect the quality of the beam and machine operation [8,9]. E-cloud was first observed on the proton/antiproton collider VAPP in the Budker Institute of Nuclear Physics in 1965 [10,11].…”