Electron cloud observations and cures in RHIC

Abstract

OBSERVATIONSSince 2081 M I C has experienced electron cloud effects, which have Iimited the beam intensity. These include dynamic pressure rises -including pressure instabilities, tune shifts: electrons, a reduction of the stability threshold for bunches crossing the transition energy, and possibly slow emittance growth. We summarize the main observations in operation and dedicated experiments, as well as countermeasures including baking, NEG coated warm beam pipes, solenoids, bunch patterns, anti-grazing rings, pre-pumped cold beam pipes, and scrubbing. This article is a condensed version of Ref. El].Dynamic pressure rise from electron-impact desorption after an electron cloud has been formed was the first, and still is the most common electron cloud observation in RHIC [2,4,5]. It is also the operationally most relevant electron cloud effect in RHIC. This pressure rise is particularly pronounced at transition crossing when the ion bunches are short [6,73. In some cases the electron cloud switched off spontaneously, like in a second order phase transition [S], which can be explained if the both and electron and ion cloud is assumed 195.

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].…”

“…Initially, large dynamic pressure rises were observed at a few locations that could not be baked at high temperature. This could be remedied by 2 hours of scrubbing at injection with the highest available beam intensities, and further beam conditioning throughout the run [6].…”

Summary of the rhic performance during the FY07 heavy ion run

“…In order to increase the number of bunches per ring beyond the previously achieved 45 bunches we spent about 2 hours on scrubbing [7]. Fig.…”

Influence of Film Coating Thickness on Secondary Electron Emission Characteristics of Non-Evaporable Getter Ti-Hf-V-Zr Coated Open-Cell Copper Foam Substrates

“…Low-energy electrons generated and accumulated in accelerators interact with circulating beam, leading to the formation of EC, accompanied with other detrimental effects, such as the increase in vacuum pressure [ 1 ], additional heat loads on the cryogenic vacuum system [ 2 ], and adverse impact on the stability of accelerated beam [ 3 , 4 ], etc. Beyond a certain electron density threshold, the EC can seriously affect the actual beam quality, and inducing beam instability and even disruption, as well as the degradation of the vacuum [ 5 , 6 ].…”