An efficient tabulated collisional radiative equilibrium radiation transport model suitable for multidimensional hydrodynamics calculations

Abstract

A computationally efficient method for transporting radiation in multidimensional 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 multidimensional 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 nonlocal 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 tabulated as a function of plasma internal energy, ion density, and the line probability of escape from a uniform plasma, and then used in multidimensional calculations. Given the internal energy and ion density, and by calculating the line probability of escape from a zone of the multidimensional plasma, the equation of state, including emissivities and absorption coefficients, of the zone is 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 plasma radiating imploding source model code [F. L. Cochran et al., Phys. Plasmas 2, 2765 (1995)] to determine the influence of radiation transport in argon Z-pinch experiments performed on the Z machine [R. B. Spielman et al., Phys. Plasmas 5, 2105 (1998)] at Sandia National Laboratories.

Two-dimensional radiation MHD modeling assessment of designs for argon gas puff distributions for future experiments on the refurbished Z machine

“…This model couples a non-LTE kinetics and non-local radiation transport model (TCRE) [10] to a two-dimensional MHD code (Mach2) [9]. Calculations were performed for three measured initial gas puff distributions emanating from a newly developed AASC multi-shell gas nozzle, one of which is likely to be fielded in the initial experiments to be performed on ZR.…”

“…It is called the tabular collisional radiative equilibrium (TCRE) model [10]. The TCRE model is a computationally efficient and reasonably accurate method for modeling the ionization dynamics and radiation transport of K-shell emitting multi-dimensional Z-pinch plasmas.…”

A non-LTE kinetic model for quick analysis of K-shell spectra from Z-pinch plasmas

“…In ZSPEC, the atomic data used to compute the rates of these atomic processes are all calculated by the integrated software package FAC [9] . As has been discussed [8] that for z-pinch K-shell sources the time scale for the atomic collisional and radiative processes is small compared to the time scale for plasma motion, the population kinetics of Eq. (1) in ZSPEC is usually solved in the steady state.…”

“…Many non-LTE models, codes and calculation results have been developed and published to add to the understanding of the behavior of z-pinch plasmas [5]- [7] . Some of them have already been coupled to complex MHD models to better describe the real physical processes [8] . However, in practice for the purpose of quickly analysis of K-shell spectra and understanding of basic ionization and radiation processes, simple and computationally efficient K-shell non-LTE models which only take limited atomic levels into consideration and neglect some of the unimportant atomic processes, are also very useful.…”

Benchmarking multilevel, 2-D cylindrical radiation transport in a high energy density plasma environment

“…Accordingly, a variety of approximate methods for numerical radiation transport have been developed to cope with such situations while retaining reasonable computational run times and capturing the important physics. Some approximations that have been adopted are: use of a diffusion approximation [4e7], photon escape probabilities [8e13], and the employment of precalculated, tabulated NLTE source functions [14]. Sometimes, the radiation transport approximations are made possible by related simplifications of the MHD or atomic physics.…”