Electronics for lcls-ii beam containment system loss monitors*

LCLS-II is a new FEL facility which is under construction at SLAC National Accelerator Laboratory. Its super-conducting electron linac is able to produce up to 1.2 MW of beam power. In the event of electron beam loss, radiation can exceed allowed levels outside the thin shielding originally built for the lower power LCLS linac. Beam Containment System (BCS) loss monitors are employed to detect the beam loss and shut off the beam within 200 μs, limiting the radiation dose in occupied areas and minimizing damage to equipment associated with personal safety. Single-crystal (sCVD) diamond particle detectors are used as Point Beam Loss Monitors (PBLM) to detect losses locally. Long Beam Loss Monitors (LBLMs) measure losses throughout the beam path, from electron gun to beam dump, using optical fibers up to 200 m long. A PMT at the downstream end of each fiber detects light produced by Cherenkov radiation along the length of the fiber. A unified electronics design integrates the charge from the PMT or diamond detector, compares the loss with a predefined threshold and generates a fault if the limit is breached. Continuous self-checking is implemented for both types of sensors.