Coherent beam-beam experiments and implications for head-on compensation

TL;DR

This paper investigates how coherent beam-beam modes in RHIC affect proton beam stability, especially with head-on compensation using electron lenses, through experiments and simulations.

Contribution

It provides new insights into the stability of polarized proton beams under head-on compensation and the role of coherent modes in beam dynamics.

Findings

Coherent modes can become unstable with external excitation.

Head-on compensation reduces tune spread and Landau damping.

Experiments and simulations reveal impacts on beam stability.

Abstract

In polarized proton operation in the Relativistic Heavy Ion Collider (RHIC) coherent beam-beam modes are routinely observed with beam transfer function measurements. These modes can become unstable under external excitation or in the presence of impedance. This becomes even more relevant in the presence of head-on compensation, which reduces the beam-beam tune spread and hence Landau damping. We report on experiments and simulations carried out to understand the impact of coherent modes on operation with electron lenses.