Measurements for the energy and flux of laser Compton scattering γ-ray photons generated in an electron storage ring: NewSUBARU

The maximum energy and flux of laser Compton scattering gamma ray photons generated in the electron storage ring NewSUBARU by CO2 (∼10.6 μm) and Nd (1.064 μm, 0.532 μm) laser beams were measured with a Ge detector calibrated by gamma rays from radioisotopes and a GSO detector, respectively. The electron beam energy derived from the measured maximum gamma ray energy agreed fairly well with the electron beam energy derived from the physical parameters for bending electromagnets in NewSUBARU. The maximum normalized flux for gamma ray photons was found to be 6.0×103 (±5%) photons W−1 mA−1 s−1 at the beam hatch. For a stored current of 200 mA and a Nd laser output of 4.2 W, the photon flux was measured to be 5.0×106 photons s−1. These values were well reproduced through theoretical calculations. Calculations for the laser alignment accuracies showed that the separation between the electron and laser beam axes and the beam cross angle between them are required to be less than 0.2 mm and 0.2 mrad, respectively, to suppress the reduction of the maximum photon flux in less than 10%.