First mm-wave generation in the FOM free electron maser

A free electron maser (FEM) has been built as a pilot mm-wave source for ap plications on future fusion research devices such as international tokamak experimental reactor (ITER), A unique feature of the Dutch FEM is the possi bility to tune the frequency over the entire range from 130 to 260 GHz at a n output power exceeding one MW, In the first phase of the project, the so- called inverse setup is used, where the electron gun is mounted inside the high-voltage terminal. The entire beam line was tested successfully with an extremely low loss current, lower than 0.05 %, First generation of mm wave s was achieved in October 1997, Up to now a peak power exceeding 730 kW was measured at 200 GHz and 350 kW at 167 GNz, Output power, start-up time and frequency correspond well with simulation results, Parameter scans for the longitudinal undulator gap, accelerator voltage, and reflection coefficien t have given a wide range of interesting data of which a few highlights are given.