A Fast Beam Protection System

The MEA 500 MeV high duty factor electron linac has been designed to accelerate electrons eventually on a pulse-to-pulse base. Each beam pulse may have a different current and/or energy and may serve one or several experimental beam lines. The usual beam protection sprstems impose limitations on this multiuser scheme. Due to good emittance of the electron beam, a very fine beam spot may be focussed accidentally on an unwanted place, causing damage within 50 microsec. Therefore a system has been developped which provides reliable beam shut-off within less than 10 microsec. Copper protection collimators positioned at crucial places will intercept a faulty beam. The gamma rays produced will then induce current in a special downstream compton battery, which is part of the emergency injector stop-line. More than 50 units have been installed to protect beam lines, vacuum valves, beam monitors, etc.