Electron cloud effects in the CERN PS

Abstract

The beam-induced electron cloud build-up is one of the major concerns for the SPS and the design of the future LHC. Recently, this effect has been observed also in the PS with the nominal LHC-type beam, consisting of a batch of 72 bunches of 1.110 11 p/b spaced by 25 ns. The electron cloud induces baseline distortion in electrostatic pick-up signals that is observed, both in the last turns of the PS when the full bunch length is reduced to less than 4 ns, and in the transfer line between the PS and the SPS rings. Experimental observations are presented and compared to simulation results and predictions from theory. Furthermore, possible cures, such as variation of the bunch spacing, inserting gaps in the bunch train and applying weak solenoidal fields, are also discussed.

High-Density and High-Intensity Beams at the CERN PS

“…The experiments require a beam of the highest possible intensity, together with rms bunch length σ b shorter than 7 ns, to allow for high precision time-of-flight measurements. In practice, typical beam parameters are: N b ≈ 7×10 12 p/b and σ b about 6 ns at extraction (occurring at 20 GeV/c) [6].…”

Coherent motion with linear coupling

“…This point is missed in Refs. [2,3], where denominators of dispersion integrals are based on the uncoupled incoherent tunes. And second, an amplitude of the coherent shift / Z x 1x Z y 1y is a function of coupling as well.…”

“…[2,3]. According to these papers, a localized skew-quad entangles coasting beam modes with different longitudinal numbers.…”

“…The second disagreement between (12) and Refs. [2,3] is that denominators in dispersive integrals [e.g. Eq.…”

“…This problem was considered in Refs. [1][2][3], and discussed in [4]. Here, we suggest our view of the problem, and come to a solution, which is general and simple at the same time.…”