Precise alignment of laser and electron beams in a periodic focusing system for multiple Compton backscattering

Abstract

In the present paper, methods of precise alignment of laser and electron beams in a periodic focusing system for generating intense γ-rays by multiple Compton backscattering are discussed. In the system, a CO 2 laser beam and a 5.8 GeV electron beam are focused by a series of optical lenses and permanent quadrupole magnets, respectively. Since the beam sizes are as small as 20– 50 μm at 120 collision points, a precise alignment within about 3 μm is required. The electron beam can be aligned by the energy-scanned beam-based method, but this method is not appropriate for the laser beam since the wavelength is not changed easily. Instead, a new method of normal reflection using Michelson interferometers is considered. Diffraction analysis shows that the misalignment of lenses can be corrected by reducing the integrated intensity of the laser beam at the detector of the interferometer, which decreases monotonically with the reduction of alignment errors.