LINE RADIATION SPECTRA OF INHOMOGENEOUS FLUCTUATING PLASMA VOLUMES

Abstract

The influence of spatial inhomogeneity and temporal fluctuations of the parameters of equilibrium plasma on the intensity and shape of the lines in the spectrum of its radiation was investigated. A closed mathematical model based on the solution of the radiation transfer equation, which describes the formation of the emission spectrum of the plasma volume with given characteristics, has been constructed. A semianalytical approximation that permits adequate description of the line radiation spectra of optically transparent plasma has been developed. The laws of formation of the line radia- tion spectra of inhomogeneous fluctuating plasma volumes and the relations relating the charac- teristics of these spectra to the emissivity and local parameters of the plasma have been found. For the presentation of the results, we have chosen atmospheric-pressure argon plasma. Introduction. Analysis of the intensity and the profiles of spectral lines in the radiation spectrum of plasma is one of the most effective methods of its diagnostics with the use of optical emission spectroscopy (OES). Plasma diagnostics by OES methods is based on the relation between the emissivity of the plasma and its local parameters, which is usually nonlinear. The OES diagnostics involves the recording of the spec- tral line profile and the intensity summed over the line and the observation period. To determine the emissiv- ity of an inhomogeneous plasma, it is necessary to solve the inverse problem. This problem is formally considered as incorrect: a small error in measured data can cause marked errors in the determination of the desired quantities (1). In the general case, it is solved by tomography methods. In so doing, the number of rays of observation and their directions are determined by the character of inhomogeneity, and their number can be very large. In the simplest case of axisymmetric inhomogeneities, the problem reduces to the inverse Abelian transform (2−4). The amount of recorded data increases significantly when the spectral line profiles obtained by scanning the radiation spectrum are used for diagnostics. The instability of plasma imposes addi- tional requirements on the measurement system: the recording time of plasma radiation should be shorter than the characteristic time of fluctuations. Therefore, there is often no point in solving traditionally the inverse problems in plasma OES or such a solution is impossible because of the large errors, excessive complexity of the recording systems, and stringent requirements imposed on them. As a consequence, there are practi- cally no OES methods for measuring local parameters in space and time of the low-temperature plasma of