FIRST HIGH-POWER EXPERIMENTS WITH THE DUTCH FREE-ELECTRON MASER

A free electron maser (FEM) has been built as a mm-wave source for app lications on future fusion research devices such as ITER, the internat ional tokamak experimental reactor [M. A. Makowski, F. Elio, and D. Lo eser, April 97, Proc. 10th Workshop on ECE and ECRH, EC10, 549-559. Wo rld Scientific (1998)]. A unique feature of the Dutch fusion-FEM is th e possibility to tune the frequency over the entire range from 130 to 260 GHz at an output power exceeding 1 MW. In the first phase of the p roject, a so-called inverse setup is used. The electron gun is mounted inside the high-voltage terminal. The entire beam line was tested suc cessfully with extremely low loss current, lower than 0.05%. This incl uded the accelerating structure up to 2 MV level and the transport thr ough the undulator. First generation of mm-waves was achieved in Octob er 1997. With an electron beam current around 8 A and an accelerator v oltage of 1.76 IMV the mm-wave pulse starts after 3 mu s and lasts for 3 mu s, reaching a maximum saturated peak power level of more than 50 0 kW at a frequency of 200 GHz. Output power, start-up time, and frequ ency correspond well with simulation results. (C) 1998 American Instit ute of Physics.