Characterising the Surface Resistance of Laser-Treated LHC Beam Screens with the Shielded Pair Method

TL;DR

This paper investigates how laser treatment of LHC beam screens affects their surface resistance and microwave response, balancing electron cloud mitigation benefits against potential impacts on beam stability and heating.

Contribution

It introduces a novel assessment of laser-induced surface roughening on beam screen impedance and microwave response for the LHC upgrade.

Findings

Laser treatment reduces secondary electron emission.

Surface roughening alters surface impedance.

Impact on beam stability and heating analyzed.

Abstract

The presence of strong electron clouds in the quadrupole magnetic field regions of the Large Hadron Collider (LHC) leads to considerable heating that poses challenges for the cryogenic cooling system, and under certain conditions to proton beam quality deterioration. Research is being conducted on laser-treated inner beam screen surfaces for the upgraded High-Luminosity LHC to mitigate this issue. Laser-induced surface structuring, a technique that effectively roughens surfaces, has been shown to reduce secondary electron emission; an essential factor in controlling electron cloud formation. Conversely, the resulting surface roughening also alters the material's surface impedance, potentially impacting beam stability and increasing beam-induced resistive wall heating. Different laser treatment patterns have been applied to LHC beam screens to estimate this potential impact and assessed for their microwave responses.