A non-LTE radiation transport model suitable for multi-dimensional hydrodynamic calculations

Abstract

Summary form only given. A computationally efficient method for transporting radiation in multi-dimensional plasmas has been developed and evaluated. The basis of this method is a uniform plasma approximation that allows one to utilize existing escape probability techniques that are successfully used in one-dimensional (1D) calculations to approximately solve the multi-dimensional radiation transport problem. This method is superior to diffusion methods because, (1) the probability of escape technique insures that the plasma goes to the correct optically thin and thick limits, (2) the effects of line absorption due to photoexcitations are modeled, and (3) this method uses source functions that are based on a self-consistent non-local thermodynamic equilibrium calculation, not an ad hoc assumption that the source functions are Planckian. This method is highly efficient because equation of state information from 1D calculations is first tabulated as a function of plasma internal energy, ion density, and the line probability of escape from a uniform plasma, and then used in multi-dimensional calculations. Given the internal energy, ion density, and the line probability of escape from a zone of the multi-dimensional plasma, the local equation of state, including emissivities and absorption coefficients, is then determined from the table. Total radiative power, K-shell radiative power, total radiative yield, K-shell radiative yield, and plasma density and temperature profiles obtained from 1D Z-pinch calculations employing this method are in good agreement with the same powers, yields, and profiles calculated using a full radiation transport model. This method has been implemented in the 2D PRISM code to study how Rayleigh-Taylor instability growth influences radiation yields in Z-pinch experiments and is applied to the analysis of several Al:Mg shots on the long risetime Saturn generator.