Operation of a fast diamond γ-ray detector at the HIγS facility

Operations of a diamond sensor placed in a high average-intensity beam of photons with energies of a few MeV are reported. Data was taken at the HIγS facility of TUNL in parasitic mode while nuclear-physics experiments were taking place. The energies of the photons during data taking were 2, 3 and 7 MeV with circular and linear polarisations of the photon beam. The collected charge appears to be constant at these energies, which is consistent with simulations. A dedicated run with bunches of photons separated by 16 ns shows that they are unambiguously distinguished. This is possible thanks to a FWHM of the pulses measured to be about 6 ns. The results indicate that the tested apparatus fulfils the requirements for a fast monitoring detector for the ELI-NP source currently under construction, which motivates this work, and demonstrates for the first time the capabilities of such detectors in high average-intensity photon beams.