Numerical investigation of laser radiation conversion to X rays in experiments with spherical boxes with interior coatings of different materials

The dynamics of laser and X-ray radiation fields in experiments with spherical boxes was numerically investigated in a sector approximation using the SND-LIRA numerical code. The experiments were performed on the Iskra-5 laser facility at a wavelength λ=0.657 μm (the second harmonic of iodine laser radiation). The characteristics of X-ray generation were investigated with the inner surface of a converter box coated with different-Z materials (Au, Cu, Mg). With lowering Z, the laser energy absorption coefficient k_a decreases and there occurs a lowering of the effective X-ray radiation temperature. Our calculations reveal a strong dependence of the results on the electron free-streaming flux limitation f. In particular, on lowering f from 0.1 to 0.03 for a conventional box with a gold coating, the coefficient k_a decreases from 0.83 to 0.5 and the peak X-ray radiation temperature drops from 170 to 150eV. In these calculations, the rms nonuniformity of the X-ray irradiation of a capsule with thermonuclear fuel amounted to 1%—3%.