Optical Beam Loss Monitor for RF Cavity Characterisation

Beam Loss Monitors (BLMs) based on optical fibres have been under development for many years as an alternative solution to commonly used methods, such as ionisation chambers. Optical BLMs (oBLMs) maintain standard BLM functionality but can also be used for machine and personal protection. They can be implemented over the entire beam line providing excellent position and time resolution, while being insensitive to radiation induced damage. This contribution describes how oBLMs can also assist in the characterisation of RF cavities during commissioning and operation. It first presents the design principle of highly compact monitors and the underpinning theory for particle loss detection, before discussing data obtained in experimental tests at the electron accelerator CLARA. It then shows how a 4-channel oBLM can be applied for efficient cavity monitoring. Finally, the results are put into a broader context underlying the application potential in accelerators and light sources.