Electron Temperature Distribution Measurements in Clouds of Polystyrene Pellets Ablating in LHD Heliotron Plasma

Abstract

Two methods for measuring the spatial distribution of the temperature of electrons in a cloud near a polystyrene pellet that ablates in LHD heliotron plasma are described. The first method is based on measuring the ratio of the local emission-coefficient values at wavelengths of 486 ± 5 nm (the H_β line) and 630 ± 5 nm (continuum). The second (new) method is based on the measurement of radiation distributions of the H_β line in the direction along the magnetic field. Both the methods use an assumption about the partial local thermodynamic equilibrium in the cloud and show close results. It is shown for the first time that the temperature of cloud electrons increases from 0.8 eV in the immediate vicinity of the pellet surface to 6.0–7.0 eV at a distance of 6–8 mm from the pellet in the direction along the magnetic field, which agrees with the experimentally observed longitudinal distribution of the H_β radiation in the cloud.