Temporal dynamics of Fusion-FEM oscillations: comparison of experiment and simulations

At the first stage of the Fusion-FEM experiment, a high-power electrostatic free-electron laser operating in the mm-wave regime was tested without the energy recovery system. In this situation, a slow temporal drop of the acceleration voltage complicated significantly the dynamics of the FEM operation. In this paper, experimental results are compared to simulations. It is demonstrated that the decrease of the frequency of the output radiation, caused by the voltage drop, has a stepped character: the value of this step is as large as the width of the amplification band. (C) 1999 Elsevier Science B.V. All rights reserved.