Heating of Low-Density Matter by Soft X-Ray Radiation and Radiation Waves

We investigate the nonlinear radiative thermal conductivity model, which is theoretically well substantiated and based on a small number of assumptions. We consider the spatial and temporal evolutions for a low-density polymer foam heated by radiation waves taking into account the dependence of the absorption coefficients on the quantum energy. The form of the radiation wavefront (its slope and speed of propagation) differs from the classical form by a low-temperature "tongue" penetrating deep into the plasma. The plasma in this segment of the wavefront is heated up to a temperature of 1-2 eV by photons in the hard part of the spectrum, with energies for which h nu/kT > 4. We simulate numerically the experiments at the PHELIX facility to heat a low-density cellulose triacetate (TAC, C12H16O8) taking into account the radiation transfer. The energy and the spectral flux of radiation that passed through the TAC layer are satisfactorily consistent with the experimental results.