Two-dimensional spectral line emission reconstruction as a plasma diagnostic

A technique for reconstructing point-by-point light emission from a plasma using a series of one-dimensional, line-of-sight measurements is described. The method, an adaptation of tomographic x-ray scans, does not assume any symmetry in the plasma, unlike an Abel inversion. Results from the Tormac IV toroidal bicusp device are presented, in which plasma light was collected by a 16-channel polychromator with 0.4-A resolution and a 1-micros time response. Reconstructed plasma light emission with spatial, temporal, and wavelength resolution is then calculated. The profiles of reconstructed spectral lines (Stark broadened H(beta) and Doppler broadened He II 4686-A lines from the 90% H, 10% He plasma) are used to monitor local plasma density and temperature. A spatial resolution of 2 cm in a 14 x 24 cm vessel, which is determined by the number of angles that the plasma is viewed from, is realized. This technique is particularly useful when a high-temperature plasma is surrounded and obscured by a low-temperature, highly emissive plasma near the vessel walls.