Comparison of the current LHC Collimators and the SLAC Phase 2 Collimator Impedances

TL;DR

This paper compares the beam coupling impedance of current LHC secondary collimators with proposed SLAC Phase 2 designs, highlighting implications for beam stability and system upgrades.

Contribution

It provides a simulation-based comparison of various collimator designs, introducing new options for the LHC phase II upgrade to improve beam stability.

Findings

SLAC Phase 2 collimator designs show different impedance characteristics.

Comparison highlights potential improvements over existing LHC collimators.

Results inform choices for future collimator materials and designs.

Abstract

One of the key sources of transverse impedance in the LHC has been the secondary graphite collimators that sit close to the beam at all energies. This limits the stable bunch intensity due to transverse coupled-bunch instabilities and transverse mode coupling instability. To counteract this, new secondary collimators have been proposed for the phase II upgrade of the LHC collimation system. A number of designs based on different jaw materials and mechanical designs have been proposed. A comparison of the beam coupling impedance of these different designs derived from simulations are presented, with reference to the existing phase I secondary collimator design.