Radiation Transport In Plasmas Research Articles

Multi‐level model of radiation transport in inhomogeneous plasma

Radiation transport in plasma can be important for a number of problems, for example, first wall‐shielding effects or influence of hydrogen isotope radiation on tokamak edge plasma. Existing calculations in the field employ many simplifying assumptions. For example, the model of radiation transport in one of the most used codes, SOLPS, suggests that photoexcitation can be ignored for all transitions, not including the ground level. We develop a collisional radiative model of radiation transport in a multi‐level system, fully accounting for all transitions between levels. The role of the Stark effect in line shape is taken into account. The validity of some of the approximations made in SOLPS is analysed for detached divertor plasma in DIII‐D‐like tokamak geometry. It is shown that total radiation flux is directed away from the divertor target due to nonuniform plasma temperature and density.

High accuracy radiative data for plasma opacities1This article is part of a Special Issue on the 10th International Colloquium on Atomic Spectra and Oscillator Strengths for Astrophysical and Laboratory Plasmas.

Opacity, which gives the measure of the radiation transport in plasmas, is caused by the repeated absorption and emission of the propagating radiation by the constituent plasma elements. Microscopically, opacity (κ) depends mainly on two radiative processes: (i) photo-excitation (bound-bound transition) and (ii) photo-ionization (bound-free transition) in addition to electron-photon scattering. The monochromatic opacity κ(ν) at photon frequency ν is determined by the atomic parameters, oscillator strengths (f), and photo-ionization cross sections (σPI). However, total monochromatic opacity is obtained from summed contributions of all possible transitions from all ionization stages of all elements in the source. The calculation of accurate parameters for such a large number of transitions has been the main problem for obtaining accurate opacities. The overall mean opacity, such as the Rosseland mean opacity (κR), depends also on the physical conditions, such as temperature, density, elemental abundances, and equation of state. The necessity for high-precision calculations for opacities may be exemplified by the existing problems, such as the determination of solar elemental abundances. With new computational developments under the Iron Project, we are able to calculate more accurate atomic parameters, such as oscillator strengths for large number of transitions using the relativistic Breit–Pauli R-matrix (BPRM) method. We are finding new features in photo-ionization, such as the existence of extensive and dominant resonant structures in the high-energy region not studied before. These new data should provide more accurate opacities in high-temperature plasmas and can be used to investigate the well-known solar abundance problem.

Fractional Boltzmann equation for multiple scattering of resonance radiation in low-temperature plasma

The fractional Boltzmann equation for resonance radiation transport in plasma is proposed. We start with the standard Boltzmann equation; averaging over photon frequencies leads to the appearance of a fractional derivative. This fact is in accordance with the conception of latent variables leading to hereditary and non-local dynamics (in particular, fractional dynamics). The presence of a fractional material derivative in the equation is concordant with heavy tailed distribution of photon path lengths and with spatiotemporal coupling peculiar to the process. We discuss some methods of solving the obtained equation and demonstrate numerical results in some simple cases.

Integral and Lagrangian simulations of particle and radiation transport in plasma

Accurate integral and Lagrangian models of transport in plasmas, in which the models reflect the actual physical behaviour as closely as possible, are presented. These methods are applied to the behaviour of particles and photons in plasmas. First, to show how these types of models arise in a wide range of plasma physics applications, an application to radiation transport in a lighting discharge is given. The radiation transport is solved self-consistently with a model of the discharge to provide what are believed to be very accurate 1D simulations of fluorescent lamps. To extend these integral methods to higher dimensions is computationally very costly. The wide utility of ‘treecodes’ in solving massive integral problems in plasma physics is discussed, and illustrated in modelling vortex formation in a Penning trap, where a remarkably detailed simulation of vortex formation in the trap is obtained. Extension of treecode methods to other integral problems such as radiation transport is under consideration.

Calculation of plasma radiation transport for description of propellant ignition and simulation of interior ballistics in ETC guns

The energy transport by radiation is one of the most important effects in an electrothermal-chemical (ETC) accelerator. At the beginning of the ETC round, after the initiation of the plasma e.g. by an exploding wire, the plasma radiation is responsible for the ignition of the propellant and the observed enhancement of mass production. This could be validated by different closed vessel tests e.g. at TZN and ICT. Therefore the radiation energy reaching the propellant has to be known for the description and understanding of the plasma-propellant interaction. Furthermore radiation energy leaving the hot plasma core enhances the temperature of the colder plasma boundary layer and the surrounding powder gases. For this reason the calculation of radiation transport is necessary to simulate the temperature and pressure development during the interior ballistics processes of an ETC round. A simulation program is described, which can be used for studying the plasma-propellant interaction and which can be used directly in gasdynamic codes, like the 2D code IBECA, for solution of the energy balance equation.

Resonance radiation transport in plasma display panels

In fluid models of the gas discharges in plasma display panels, the trapping of resonance radiation is usually accounted for by a trapping factor. In this work, we present a Monte Carlo model for resonance photons, which gives a much more accurate description. First, we compare the results of this Monte Carlo model with the results of the fluid model trapping factor approach. Although the trapping factor approach does not yield the same spatial distribution for the density of the resonant state atoms, the spatially integrated density is in good agreement with the results of the Monte Carlo model. Next, we compare the results of the Monte Carlo model with measured spectra of emitted resonance radiation. The agreement is very good. Thus we provide, via the Monte Carlo model, experimental support for the widely used trapping factor approach.

Plasma induced energy deposition and radiation transport effects in ion beam heated plane metal targets and analytic solutions of the non-linear radiation conduction equation

The effects of microscopic energy deposition in hot, dense plasmas and radiation transport in plasmas, on the interaction of ion beams with plane metal targets are investigated in this paper. In order to do this we analyze the plasma dynamics of ablatively accelerated plane metal foils. The physical analysis of these results is achieved by the derivation of solutions of the non-linear radiation conduction equation with boundary temperatures which increase in time. We illustrate, by means of numerical simulations, how range shortening due to plasma effects such as increased energy loss to excited electrons and an increased effective charge due to a reduction in the recombination rate, may be compensated for by radiation transport. The effect of radiation transport and detailed microscopic energy deposition on ion beam implosions, including hydrodynamic instability, is discussed.