Stability of shock waves in high temperature plasmas

The Dyakov-Kontorovich criteria for spontaneous emission of acoustic waves behind shock fronts are investigated for high temperature aluminum and beryllium plasmas. To this end, the Dyakov and critical stability parameters are calculated from Rankine-Hugoniot curves using a more realistic equation of state (EOS). The cold and ionic contributions to the EOS are obtained via scaled binding energy and mean field theory, respectively. A screened hydrogenic model, including l-splitting, is used to calculate the bound electron contribution to the electronic EOS. The free electron EOS is obtained from Fermi-Dirac statistics. Predictions of the model for ionization curves and shock Hugoniot are found to be in excellent agreement with available experimental and theoretical data. It is observed that the electronic EOS has significant effect on the stability of the planar shock front. While the shock is stable for low temperatures and pressures, instability sets in as temperature rises. The basic reason is ionization of electronic shells and consequent increase in electronic specific heat. The temperatures and densities of the unstable region correspond to those where electronic shells get ionized. With the correct modeling of bound electrons, we find that shock instability for Al occurs at a compression ratio similar to 5.4, contrary to the value similar to 3 reported in the literature. Free electrons generated in the ionization process carry energy from the shock front, thereby giving rise to spontaneously emitted waves, which decay the shock front. (C) 2011 American Institute of Physics. [doi:10.1063/1.3653253

Radiative opacity of low-Z plasma using screened hydrogenic model including l-splitting

Radiative opacities of low-Z plasma are computed using average atom model. Screened Hydrogenic Model including l-splitting (SHML) is used as the atomic model to obtain the internal structure of ions embedded in plasma. The phenomenon of pressure ionization of levels is described by a Gaussian density dependent degeneracy function. Use of the most recent compilation of the screening constants makes it possible to include l-splitting in a direct manner. The average ionization in the plasma is obtained by self-consistently solving the non-linear set of coupled SHML equations along with the charge neutrality condition of Wigner-Seitz cell. The frequency dependent opacity of Aluminum plasma is compared with the data obtained from Los Alamos (LANL) opacity library and a reasonable agreement is seen. The computed values of Rosseland and Planck opacity of C, Al and Fe plasma are also in good agreement with the LANL opacity database value for different plasma density and temperature. (C) 2011 Elsevier Ltd. All rights reserved