Studies on electron Beam injector system for linac-based coherent THz source in Thailand

Abstract

Copyright © 2016 CC-BY-3.0 and by the respective authors. Main components of a linac-based THz source at the Plasma and Beam Physics Research Facility, Chiang Mai University, Thailand, are a thermionic cathode RF electron gun, an alpha magnet and a linear accelerator. The electron beam produced from this system is currently used to generate a coherent transition radiation in FIR and THz regimes. To increase the capability of the accelerator on production of the THz radiation, it will be upgraded to be a future THz free-electron laser (THz-FEL) by adding a magnetic bunch compressor, an undulator magnet and an optical oscillator. To investigate the optimal performance of the injector system, beam dynamic simulations are performed by using computer codes PARMELA and ELEGANT. The input 3D field distributions of the RF-gun for PARMELA simulations are obtained from the RF modelling program CST Microwave Studio 2012. The beam transport calculation using the program ELEGANT is performed to study behaviour of the electron beam from the RF-gun exit through all components until it reaches the undulator entrance. Energy slits inside the alpha magnet vacuum chamber are used to select electrons with desired kinetic energies. The alpha magnet compresses electron bunches with certain bunch length before the beam entering the linac to obtain minimum energy spread at the linac exit. Then, the electron bunches are further compressed by the magnetic bunch compressor to have a bunch length in order of picosecond at the undulator entrance. Preliminary results of electron beam optimization with appropriated conditions for the THz-FEL are reported and discussed in this contribution.