Journal of Quantitative Spectroscopy & Radiative Transfer 67 (2000) 273}291 Radiative transport in a two-dimensional axisymmetric thermal plasma using the S}N discrete ordinates method on a line-by-line basis J. Menart Department of Mechanical and Materials Engineering, Wright State University, Dayton, OH 45435, USA Received 19 July 1999 Abstract A theoretically rigorous method for handling the transport of radiant energy in a two-dimensional, axisymmetric, thermal plasma is presented. A S}N discrete ordinates method is used to solve the radiative equation of transfer on a line-by-line basis. A line-by-line solution of the radiative equation of transfer is an exact method of handling the spectral characteristics of thermal radiation. Plasmas are highly non-gray emitters and absorbers of radiant energy, making proper handling of the spectral characteristics extremely important. To demonstrate this method a few results are presented for a 200 A, free-burning, argon arc.  2000 Elsevier Science Ltd. All rights reserved. 1. Introduction Since radiation is a signi"cant mechanism of energy transport in a plasma, it is important to have accurate techniques to model this phenomenon. At the present time many approximations are made in regards to the spectral characteristics of the radiant energy. In this paper the spectral characteristics are handled using a line-by-line technique. Theoretically, the line-by-line technique is an exact method of modeling spectral characteristics. Practically, calculations are done over a small enough spectral interval such that the absorption coe$cient can be taken as a constant over this interval. In the limit of very small intervals an exact solution is obtained. Accurately modeling the spectral characteristics of radiative transport in a plasma is important due to the large amount of line emission. Menart et al. [1] have shown that line emission is more than nine times as strong as the continuum emission in an atmospheric, argon plasma. For this work radiant energy is tracked on a spectral basis as it passes through an emitting, absorbing plasma that is in local thermodynamic equilibrium (LTE). This tracking is done by a numerical technique called the S}N discrete ordinates method [2,3]. The S}N method was 0022-4073/00/$ - see front matter  2000 Elsevier Science Ltd. All rights reserved. PII: S 0 0 2 2 - 4 0 7 3 ( 9 9 ) 0 0 2 3 7 - X