Mitigation of the electron-cloud effect in the psr and sns proton storage rings by tailoring the bunch profile

Pivi, M.; Furman, M.A.

doi:10.1109/pac.2003.1289868

Cited by 2 publications

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References 2 publications

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“…The electron cloud saturates typically within a few bunch passages. During the gap between bunches, electrons dissipate and the remaining slow electrons that remain in the chamber are trapped by the head of the next bunch [27][28][29]. Fig.…”

Section: Long-bunch Casementioning

confidence: 99%

Electron-cloud build-up in hadron machines

Furman¹

2004

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The first observations of electron-proton coupling effect for coasting beams and for long-bunch beams were made at the earliest proton storage rings at the Budker Institute of Nuclear Physics (BINP) in the mid-60's [1]. The effect was mainly a form of the two-stream instability. This phenomenon reappeared at the CERN ISR in the early 70's, where it was accompanied by an intense vacuum pressure rise. When the ISR was operated in bunched-beam mode while testing aluminum vacuum chambers, a resonant effect was observed in which the electron traversal time across the chamber was comparable to the bunch spacing [2]. This effect ("beam-induced multipacting"), being resonant in nature, is a dramatic manifestation of an electron cloud sharing the vacuum chamber with a positively-charged beam. An electron-cloud-induced instability has been observed since the mid-80's at the PSR (LANL) [3]; in this case, there is a strong transverse instability accompanied by fast beam losses when the beam current exceeds a certain threshold. The effect was observed for the first time for a positron beam in the early 90's at the Photon Factory (PF) at KEK, where the most prominent manifestation was a coupled-bunch instability that was absent when the machine was operated with an electron beam under otherwise identical conditions [4]. Since then, with the advent of ever more intense positron and hadron beams, and the development and deployment of specialized electron detectors [5][6][7][8][9], the effect has been observed directly or indirectly, and sometimes studied systematically, at most lepton and hadron machines when operated with sufficiently intense beams. The effect is expected in various forms and to various degrees in accelerators under design or construction.The electron-cloud effect (ECE) has been the subject of various meetings [10][11][12][13][14][15]. Two excellent reviews, covering the phenomenology, measurements, simulations and historical development, have been recently given by Frank Zimmermann [16,17]. In this article we focus on the mechanisms of electron-cloud buildup and dissipation for hadronic beams, particularly those with very long, intense, bunches. Primary sources of electrons and secondary electron emissionDepending upon the type of machine, the EC is seeded by primary electrons from three main sources: photoelectrons, ionization of residual gas, and electrons generated when stray beam particles hit the chamber walls. In addition, for HIF drivers, an important expected source of electrons is a combination of two of the above, namely: gas will be desorbed by stray ions striking the chamber walls which will subsequently be ionized by the beam. These electrons get kicked by successive bunches mostly in the * Published as Sec. 2.9 of the ICFA Beam Dynamics Newsletter No. 33, July 2004, p. 70. 2 direction perpendicular to the beam; as they strike the walls of the chamber, they generate secondary electrons which add to the existing electron population.Of all hadron machines presently existing or under construction...

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Section: Long-bunch Casementioning

confidence: 99%

Electron-cloud build-up in hadron machines

Furman¹

2004

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“…Recently we carried out a numerical investigation of the effect of the bunch profile on trailing-edge multipacting at the PSR by simulating the ECE with bunches with truncated tails keeping the bunch population constant [31]. The idea that truncating the tail breaks the resonance condition that causes multipacting was clearly supported by the simulations.…”

Section: Sensitivity To the Bunch Profilementioning

confidence: 89%

A preliminary comparative study of the electron-cloud effect for the PSR, ISIS, and the ESS

Furman¹,

Pivi²

2003

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We present preliminary electron-cloud simulation results for the Proton Storage Ring (PSR) at LANL, the ISIS synchrotron at RAL, and the European Spallation Source (ESS). For each machine, we simulate the build-up and dissipation of the electron cloud (EC) in a representative field-free section of the vacuum chamber. For all three cases, we choose the same residual gas temperature, secondary emission yield (SEY), and secondary emission spectrum. Other variables such as proton loss rate, bunch profile, intensity and energy, residual gas pressure and chamber geometry, are set at the corresponding values for each machine. Under these assumptions, we conclude that, of the three machines, the PSR is the most severely affected by the electron cloud effect (ECE), followed by the ESS, with ISIS in third place. We illustrate a strong sensitivity of the ECE to the longitudinal bunch profile by choosing two different shapes for the case of the PSR, and a weak sensitivity to residual gas pressure and proton loss rate. This preliminary study does not address the ECE in other regions of the machine, nor the beam instability that might arise from the EC.

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Mitigation of the electron-cloud effect in the psr and sns proton storage rings by tailoring the bunch profile

Cited by 2 publications

References 2 publications

Electron-cloud build-up in hadron machines

Electron-cloud build-up in hadron machines

A preliminary comparative study of the electron-cloud effect for the PSR, ISIS, and the ESS

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