Characterization of bremsstrahlung X-ray emission as a reason for optics degradation at rep-rate e-beam-pumped KrF laser driver in IFE application

摘要

Time-resolved scintillation technique and absolutely calibrated thermo-luminescence dosimeters have been applied to characterize bremsstrahlung X-ray emission from a large-aperture GARPUN KrF laser module pumped in a transverse geometry by double-sided e-beams stabilized by pulsed magnetic field of 0.1 T. It was produced by electrons with ～300 keV kinetic energy, 50 A/cm ~2 current density, and 100 ns pulse duration when they passed from vacuum diodes through foil windows into laser chamber and were decelerated in a working gas. Regularization algorithm was developed to reconstruct the bremsstrahlung spectra using experimental data on X-ray transmission through different absorbers. The energy fluence of ionizing radiation escaped onto laser windows has been measured. It was shown that a long-term degradation of optical transmission due to bremsstrahlung X-ray irradiation should be taken into account for KrF laser application in Inertial Fusion Energy.