Study and optimization of power output and electron beam energy spread in a Free Electron Laser oscillator

(MO-4-07)

A. Abramovich, Y. Pinhasi, A. Yahalom, D. Bar-Lev, S. Efimov, A. Gover  

Department of Electrical and Electronic Engineering, The College of Judea and Samaria and the Department of Electrical Engineering, Physical Electronics, Tel-Aviv University.

Design of a multi-stage depressed collector for efficient operation of a Free Electron Laser (FEL) oscillator requires detailed knowledge of the electron beam energy distribution. This knowledge is necessary for determination of the voltages of the depressed collector stages so that the collection efficiency of the electrons after the interaction and the overall energy conversion efficiency of the FEL will be maximized. The energy spread of the electron beam is generated inside the wiggler due to the different saturation dynamics of electrons entering the interaction region at different phases relative to the EM Wave. This can be fully simulated by our three dimensional simulation code FEL3D.

The main adjustable parameters that determine the electron beam energy spread after interaction are the initial beam energy and current and the quality factor of the resonator. Using FEL3D, we study the influence of these parameters on the generated power and the electron beam distribution at the undulator exit. Simulations performed with an assumption of I=1.5A, E=1.4MeV, L=18% (Internal loss factor) led to the conclusion that highest power output and smallest energy spread are attained for output coupler transmission coefficient TM = 39%.