Gamma ray sources based on resonant backscattering of laser beams with relativistic heavy ion beams

Resonant backscattering of a high-power laser beam with non-fully stripped, ultra-relativistic ion beams in storage rings is studied as a source for γ-ray beams for elementary particle physics experiments. The laser frequency is chosen to be resonant with one of the transition frequencies of the moving ions, and the bandwidth is chosen to cover the full Doppler broadening of the ions in the beam. Due to the resonance, the scattering cross section is enhanced by a large factor compared to the Thomson cross section, of the order 10⁸ for some examples considered here. The performance of the LHC as a possible γ-generator or a γ-γ collider is estimated. We study the case where hydrogen-like Pb ions with 2.8 TeV per nucleon are scattered by a train of 1100 Å, 20 mJ laser pulses with the same pulse time format as the ion beam. A free electron laser can be designed satisfying the requirements. It is estimated that γ-rays of maximum quantum energy of 0.4 GeV at an average rate of 0.67 10¹⁸ are generated in this scheme. The luminosity of the corresponding γ-γ collider will be about 0.9 10³³ cm^-2 s^-1