Position Resolution of Optical Fibre-based Beam Loss Monitors Using Long Electron Pulses

Beam loss monitoring systems based on optical fibres (oBLM), have been under consideration for future colliders for several years. To distinguish losses between consecutive quadrupoles, the position resolution of detected losses is required to be less than 1 m. A resolution of better than 0.5 m has been achieved in machines with single, short pulses of the order of a nanosecond. In the case of longer beam pulses with 150 ns duration, as they would be in the Compact LInear Collider (CLIC), the longitudinal length of signals in the fibre is close to the duration of the beam pulse which makes loss reconstruction very challenging. In this contribution results from experiments into the position resolution of an oBLM system based on long beam pulses are presented. These measurements have been performed at the CLIC Test Facility (CTF3) at CERN and the Australian Synchrotron Light Source (ASLS). In the former, controlled beam losses were created in a 22.5 m long decelerating Test Beam Line (TBL) LINAC. In the latter, loss localization was studied by comparing that from single bunches with those from longer bunch trains. In both cases the losses were detected using a 200 μm core pure silica fibre coupled to a Silicon Photomultiplier (SiPM) photon detector.