M. Tecimer, S. Efimov, M. Canter, J. Sokolowski, A. Gover
Dept. of Electrical Engineering, Physical Electronics, Tel-Aviv University
A three stage asymmetric type depressed collector has been designed for the Israeli mm-wave FEL that is driven by a 1.4 MeV, 1.5 A electron beam. After leaving the interaction section the spent beam has an energy spread of 120 keV and 22 pi mm-mrad transverse beam emittance. Simulations of the beam transport system from the undulator exit through decelerator tube into the collector have been carried out using EGUN and GPT codes. The latter has also been employed to study trajectories of the primary and scattered particles within the collector, optimizing the asymmetrical collector geometry and the electrode potentials at the presence of a deflecting magnetic field. The estimated overall efficiency reaches up to 55% and backstreaming is limited to 0.1% to attain the targeted milliseconds long pulse operation and 1 - 10 kW average power.
Simulation results are implemented in a mechanical design that leads to a simple, cost efficient assembly eliminating ceramic insulator rings between collector stages and the associated brazing in the manufacturing process. Instead, each copper plate is supported by insulating posts and freely displaceable within the vacuum chamber.
We will report on the simulation results of the beam transport and recovery systems and on the mechanical and electrical aspects of the multistage collector design. Experimental results obtained from a preceeding two stage collector model providing measured data about the beam energy spectrum will be presented as well.
