Beam Loss Monitoring and Machine Protection at the ELBE CW Accelerator

The superconducting CW linac of the ELBE facility produces an electron beam up to 40 MeV and 1 mA average current. The beam is used to drive two IR FELs and target stations for production of bremsstrahlung, neutrons, and positrons. An upgrade of the ELBE facility is ongoing which includes an increase of beam current as well as new experimental opportunities such as the production of broadband THz radiation and the interaction of electrons with high power laser beams. The high beam power requires a fast and safe machine protection system. It was found that a continuous beam loss of about 10 µA or a total beam loss for longer than 2 ms produce damage. The beam loss at ELBE is monitored by two systems: beam loss monitors measuring the radiation in cable-like ionization chambers along the beamline, and beam current difference measurement system based on stripe line beam position monitors.