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 applications on future fusion research devices such as the International Tokamak Experimental Reactor (ITER). A unique feature of the Dutch FEM is the possibility to tune the frequency over the entire range from 130 to 260 GHz at an 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%. The first generation of mm waves was achieved in October 1997. Up to now a peak power exceeding 730 kW was measured at 200 GHz and 350 kW at 167 GHz. Output power, start-up time and frequency correspond well with simulation results. Parameter scans for the longitudinal undulator gap, accelerator voltage, and reflection coefficient have given a wide range of interesting data of which a few highlights are given.