LOW-LOSS ELECTRON-BEAM TRANSPORT IN A HIGH-POWER, ELECTROSTATIC FREE-ELECTRON MASER

At the FOM Institute for Plasma Physics ''Rijnhuizen'', The Netherland s, the commissioning of a high-power, electrostatic free-electron mase r is in progress. The design target is the generation of 1 MW microwav e power in the frequency range 130-260 GHz. The foreseen application o f this kind of device is as a power source for electron cyclotron appl ications on magnetically confined plasmas. The device is driven by a h igh-power electron beam. For long-pulse operation a low loss current i s essential. A 3-A electron beam has been accelerated to energies rang ing from 1.35 to 1.7 MeV and transported through the undulator at curr ent losses below 0.02%. Further, it was shown that the beam line accep ts an electron energy variation of 5% with fixed beam optics. This is essential for rapid tuning of the microwave frequency, over 10%. Elect ron beam simulations have shown to be remarkably accurate both for the prediction of the lens settings and for the intercepted current. The operational settings of the beam line which give the highest current t ransmission are within a few percent of the simulated values.