BLM Beam Loss Monitor

Largest dynamic range | lowest cost of any BLM

K. Wittenburg was awarded the Faraday Cup in 2000 for the design of the PIN-photodiode Beam Loss Monitor and its implementation at HERA.


The Beam Loss Monitor (BLM) is a new approach to measure and localise beam losses. Its very small size and low unit cost make it possible to monitor all locations where beam loss is predicted.


BLM features:

Schema  BLM


  • Up to 10 MHz count rate
  • Dynamic range > 1E8
  • Spurious count very low (Less than 1 count in 10 seconds)
  • Recovers 100 ns after a hit
  • Choice of detector solid angle (Large or small PIN-diodes)
  • Output is a TTL compatible pulse, for easy counting
  • Withstand up to 1E8 Rads radiation
  • Vacuum distribution can be measured based on BLM count rate
  • Two PIN-photodiodes mounted face-to-face detect charged particles. Coincidence counting make it insensitive to synchrotron radiation


The charged particle crosses both PIN-diodes, which causes a coincidence. Synchrotron radiation photons, if stopped by the first PIN-diode, do not cause a coincidence.