High-power electrostatic free-electron maser as a future source for fusion plasma heating: Experiments in the short-pulse regime

A high-power,frequency-tunable electrostatic free-electron maser, being developed at the FOM Institute for Plasma Physics "Rijnhuizen," shows lasing at various frequencies. An output power of 730 kW at 206 GHz is generated by a 7.2-A, 1.77-MeV electron beam, and 380 kW at 165 GHz is generated by a 7.4-A, 1.65-MeV electron beam. In the present experimental setup, without recovery of the spent electron beam power, the pulse length is limited to 12 mu s. Nevertheless, the main issues, such as the possibility of high-power, single-mode operation and frequency tuning, have been confirmed. The experimental results and the dynamics of the laser process are well in accordance with simulations. [S1063-651X(99)03905-7]

A 130-260-Ghz, 1-Mw Free-Electron Maser for Fusion

We report on design work and testing of several main components of the FOM-Fusion-FEM project. Measurements on the electron gun are presented, showing a uniform beam current profile and a low halo current. A time-dependent simulation study of the interaction between the electron beam and the mm-waves shows that, for proper undulator tapering, longitudinal mode competition results in a quasi single-mode regime. Further, some high power and detailed low power measurements on mock-ups of the waveguide system are presented, showing that the reflection and outcoupling systems perform well