FIRST MICROWAVE GENERATION IN THE FOM FREE-ELECTRON MASER

A free-electron maser (FEM) has been built as a pilot experiment for a millimetre-wave source for applications on future fusion research dev ices such as ITER, the International Tokamak Experimental Reactor. A u nique feature of the Dutch fusion FEM is the possibility to tune the f requency over the entire range from 130 to 260 GHz at an output power exceeding 1 MW. In the first phase of the project, the so-called inver se set-up is used. The electron gun is mounted inside the high-voltage terminal. The entire beam line was tested successfully with extremely low loss current, lower than 0.05%. The first generation of millimetr e waves was achieved in October 1997. The highest peak power measured so far is 700 kW at 200 GHz. This was achieved with a beam current of 8 A and an acceleration voltage of 1.77 MV. The output power, start-up time and frequency correspond well with the simulation results. The p arameter scans for the longitudinal undulator gap. acceleration voltag e and reflection coefficient have given a wide range of interesting da ta of which a few highlights are given.