Study on energy variable laser-compton gamma-ray with a fixed energy electron beam

The electron beam in medium scale (1-2 GeV) synchrotron radiation ring is attractive to generate an intense and narrow energy spread of laser-Compton gamma-ray beam in an MeV-region. Since the storage ring is operated with fixed electron energy for synchrotron radiation (SR) users, methods for changing the gamma-ray energy should be investigated. Three methods, 1) using a tunable laser, 2) changing the collision angle between the laser and the electron beam, and 3) selecting the scattering angle of the laser-Compton gamma-ray by using a collimator and an absorber, are studied by analytical calculation and simulation which takes into account the electron beam size and effective length of laser-electron interaction. Since a tunable laser has no enough power in the infrared wavelength region, an intense gamma-ray beam can not be generated by using a tunable laser at present stage. The collimator-absorber method generates enough amounts of gamma-rays, but simulation shows a broad energy spread, -7%, of the gamma-ray. An acceptable gamma-ray beam can be obtained by changing the incident angle of the laser beam whose pulse width and timing are synchronized with the electron beam pulse.