Radiation hydrodynamics of x-ray driven targets

Abstract

A multigroup radiation transport algorithm is implemented in planar and spherical geometry and coupled to a one-dimensional Lagrangian hydrodynamic code. The radiative transfer equations are derived under the assumptions of local thermodynamic equilibrium (LTE), no scattering, the neglect of Doppler shifts and the neglect of the time derivative. A second-order form of the transfer equation which reproduces the correct result at high and small optical depths is used. The curvature in spherical geometry is dealt with using a ray trace scheme that is particularly suited to very anisotropic incident x-ray sources and the study of preheat at the centre of spherical targets. Preliminary simulations of an indirectly driven National Ignition Facility (NIF) design target using an approximate equation of state, show the performance is degraded because of radiative heating of the shell from the central hot spot just before the time of peak compression. This reduces the maximum density achieved. The maximum temperature is limited by the radiative cooling of the central hot fuel.