The general particle tracer code applied to the fusion free-electron maser

The fusion Free-Electron Maser (FEM) is the prototype of a high power, electrostatic mm-wave source, tunable in the range 130-260 GHz. In order to achieve a high overall efficiency, the charge and energy of the spent electron beam, i.e. the beam which leaves the undulator after interaction with the EM-wave, has to be recovered. A 50% overall efficiency is achieved, even for the maximum energy spread of 320 keV generated in the undulator, using a collection system consisting of a decelerator and a depressed collector. The General Particle Tracer code (GPT) is being used as the major design tool for the whole fusion FEM beam line: from the accelerator to the depressed collector. The high accuracy, ability to include FEL interaction and full 3D treatment make GPT the ideal choice for such a project. An overview of the separate sections and the use of GPT for each part of the FEM is presented. GPT is currently being applied to the design of the energy recovery system of the fusion FEM, The first simulation results, including a 3D off-axis bending scheme and scattered incident electrons, are shown. (C) 1998 Elsevier Science B.V.