Distributed Beam Loss Monitor Based on the Cherenkov Effect in Optical Fiber

A distributed beam loss monitor based on the Cherenkov effect in optical fiber has been implemented for the VEPP­5 electron and positron linacs and the 510 MeV damping ring at the Budker INP. The monitor operation is based on detection of the Cherenkov radiation generated in optical fiber by means of relativistic particles created in electromagnetic shower after highly relativistic beam particles (electrons or positrons) hit the vacuum pipe. The main advantage of the distributed monitor compared to local ones is that a long optical fiber section can be used instead of a large number of local beam loss monitors. In our experiments the Cherenkov light was detected by photomultiplier tube (PMT). Timing of PMT signal gives the location of the beam loss. In the experiment with 20 m long optical fiber we achieved 3 m spatial resolution. To improve spatial resolution optimization and selection process of optical fiber and PMT are needed and according to our theoretical estimations 0.5 m spatial resolution can be achieved. We also suggest similar techniques for detection of electron (or positron) losses due to Touschek effect in storage rings.