Fibre Monitoring System for the Beam Permit Loops at the LHC and Future Evolution of the Beam Interlock System

TL;DR

This paper proposes a real-time, out-of-band fibre monitoring system for CERN's LHC beam permit loops, enhancing reliability by detecting fibre attenuation issues caused by radiation and other events, using commercial components.

Contribution

It introduces a novel fibre monitoring system that operates in parallel with existing beam permit loops, enabling online diagnostics with off-the-shelf components for the LHC upgrade.

Findings

Improved detection of fibre attenuation issues.

Enhanced system reliability and availability.

Use of commercial components reduces complexity.

Abstract

The optical fibres that transmit the beam permit loop signals at the CERN accelerator complex are deployed along radiation areas. This may result in increased attenuation of the fibres, which reduces the power margin of the links. In addition, other events may cause the links to not function properly and result in false dumps, reducing the availability of the accelerator chain and affecting physics data taking. In order to evaluate the state of the fibres, an out-of-band fibre monitoring system is proposed, working in parallel to the actual beam permit loops. The future beam interlock system to be deployed during LHC long shutdown 2 will implement online, real-time monitoring of the fibres, a feature the current system lacks. Commercial off-the-shelf components to implement the optical transceivers are proposed whenever possible instead of ad-hoc designs.