Demonstration of low-loss electron beam transport and mm-wave experiments of the fusion-FEM

Abstract In the Fusion-FEM electrostatic Free Electron Maser, an electron beam loss current of less than 0.2% is essential for long-pulse operation. At reduced beam current, 3 A instead of the nominal 12 A, we have demonstrated electron beam acceleration and transport through the undulator at current losses less than 0.02%. This paper summarizes the results of beam transport experiments and outlines the simple yet effective beam diagnostics system. The status of the mm-wave cavity and low-power measurements are given. It is shown that cavity characteristics, such as losses, bandwidth, frequency-tuning and feedback coefficient, can be checked in situ via the output window, by injecting a low power test-signal into the mm-wave system and analyzing the reflected signal.