Plasma Radiation Transport

Abstract

Radiative energy transfer is one of the principal properties of gases under plasma conditions. It is a direct consequence of the excitation to higher energy states of the elementary particles in a plasma and their return to lower energy states, or the ground state, by emission of radiation over a wide range of the spectrum. In this chapter, following a general definition of general concepts of blackbody and gaseous radiation, a review is presented of the radiation emission and absorption in plasmas. This includes line and continuum radiation, total effective radiation of plasmas, and thermal plasma radiation modeling. Examples are given of the contribution of line and continuum emission to the total volumetric emission of argon and nitrogen at atmospheric pressure as function of temperature. This is followed by an introduction to the concept of effective or net emission coefficient (NEC) as a means of taking into account self-absorption in plasmas. This is followed by a discussion of mixing rules for complex plasma gas mixtures. Examples are given of the total volumetric emission coefficients of gases such as argon, nitrogen, hydrogen, helium, air, water vapor, and their mixtures at atmospheric pressure over the temperature range from 5000 to 25,000 K. The effect of the presence of metal vapors such as copper and iron in the plasma gases is discussed. Data are provided for different metal vapor concentrations ranging from a few percentage points up to pure metal vapor plasmas. A brief discussion is presented of blackbody radiation of high temperature, of high-pressure plasmas, and of two-temperature nonequilibrium plasmas.