Optimization of the Compact Gamma-ray Source Based on Inverse Compton Scattering Design

Recently a MeV quasi-monochromatic compact gamma-ray source with high peak spectral density based on the inverse Compton scattering (ICS) has been proposed in the Department of Engineering Physics, Tsinghua University. This type compact gamma-ray source will be used for advanced X/gamma-ray imaging application based on the nuclear resonance Fluorescence (NRF) [1]. The machine size and the peak spectral density of scattered photons are the most important parameters for such applications. In order to make the source compact enough, a compact commercial narrow bandwidth Nd: Yag laser system with ~50 fs FWHM duration and ~1.5 J maximum energy per pulse is selected as the scattering laser, and the linac is proposed to combine a photo-injector and an X-band main linac to obtain high quality 250 MeV maximum energy electron beam with high charge (~ 200 pC) and low transverse and longitudinal emittance. In ICS, the properties of the generated photons are determined by the parameters of the incident laser and electron beam, and also their interaction geometry. In this paper, we will present the optimization of the linac design. We systematically simulate and optimize the linac design with Matlab, Astra [2] and Cain [3]. In the simulations and optimizations, we use differential evolution algorithm for simultaneous optimization of multiple parameters. Three possible types of photo-injector, S-band photocathode RF(radio frequency) gun with S-band booster, C-band photocathode RF gun with C-band booster, X-band photocathode RF gun with X-band booster, are systematically optimized and compared. We also analyzed wakefield effect on the electron beam quality.