Status of the Rehovot EN tandem accelerator free electron laser

The EN tandem electrostatic accelerator at the Weizmann Institute of Science has been converted into an electron accelerator with a source intensity of 2 A and with beam current recovery. The tandem FEL configuration, in which the wiggler is located in the high voltage terminal, allows for stable, long pulse operation. Two wire-mesh diagnostic systems for monitoring of the beam shape have been installed; one between the electron gun and the entrance to the accelerating tube, the other between the exit from the decelerating tube and the beam collector. We believe to be able to operate our machine with pulse lengths of the order of 1 ms without terminal voltage droop during such a pulse. At present, when operating with 5 μs pulses, only after 10-20 ms there is a noticeable terminal voltage droop. A beam current of 0.8-1.0 A enters the acceleration tube and 75% of it can be presently recovered at the collector. We expect to improve on this figure considerably. The long pulse operation mode, for which we are striving, offers interesting possibilities for the operation of free electron lasers, in particular demonstrating high coherence, single mode operation. A three year FEL experimental study program based on the tandem accelerator was recently proposed. (orig.)