Three-beam instability in the LHC

TL;DR

This paper investigates the three-beam instability observed in the LHC at 4TeV, proposing that an electron cloud generated by proton beams causes the instability, with analysis based on observed oscillations and beam conditions.

Contribution

It introduces the hypothesis that an electron cloud acts as a third beam causing the observed transverse instability in the LHC.

Findings

Evidence of instability occurring when beams are separated by about ten transverse rms sizes.

Observation that only one beam oscillates during the instability.

The proposed electron cloud hypothesis explains all observed phenomena.

Abstract

In the LHC, a transverse instability is regularly observed at 4TeV right after the beta-squeeze, when the beams are separated by about their ten transverse rms sizes [1-3], and only one of the two beams is seen as oscillating. So far only a single hypothesis is consistent with all the observations and basic concepts, one about a third beam - an electron cloud, generated by the two proton beams in the high-beta areas of the interaction regions.