Synchronous Phase Shift at LHC

TL;DR

This paper investigates how electron clouds in the LHC cause energy loss in the beam, showing how this effect varies with beam intensity, bunch spacing, and scrubbing, and providing insights into electron cloud build-up.

Contribution

It presents detailed measurements of the electron cloud effects on beam energy loss and phase shift in the LHC, including the impact of scrubbing and bunch-by-bunch analysis.

Findings

Energy loss depends on total beam intensity.

Scrubbing reduces electron cloud build-up.

Bunch-by-bunch phase measurements reveal cloud dynamics.

Abstract

The electron cloud in vacuum pipes of accelerators of positively charged particle beams causes a beam energy loss which could be estimated from the synchronous phase. Measurements done with beams of 75 ns, 50 ns, and 25 ns bunch spacing in the LHC for some fills in 2010 and 2011 show that the average energy loss depends on the total beam intensity in the ring. Later measurements during the scrubbing run with 50 ns beams show the reduction of the electron cloud due to scrubbing. Finally, measurements of the individual bunch phase give us information about the electron cloud build-up inside the batch and from batch to batch.