Spectral diagnostics of plasma in the zone of its destructive interaction with heat-resistant materials

Abstract

The results of a complex study of the destructive effect of a nitrogen plasma jet at atmospheric pressure onto the surface of the MPG-6 graphite are presented. The space-time changes in the rate of decrease in the samples material, the temperature of their surface, the electron temperature of plasma in the oncoming flow and the plasma composition in the region of ‘injection’ were all experimentally determined. Using spectroscopic methods with high spatial (50 μm) and time (0.5 s) resolutions changes in the concentration of emitting carbon atoms (line CI 247.9 nm) and CN (transition B2Σ+ − X2Σ+) near the surface of isotropic graphite were recorded, which occur in the process of intense and long (100–150 s) exposure of graphite to a nitrogen plasma jet. The change in the vibrational and rotational temperatures of the radical CN and the molecular ion in the near-surface region of the plasma is determined by the method of 2D matrix spectroscopy. An analysis of the relative populations of the excited NI states in the interaction region at the quasistationary stage of sample heating revealed spatial-temporal changes in the electron temperature in the near-surface plasma, indicating an increase in its enthalpy caused by the rapid exothermic CN + N → C + N2 substitution process, which leads to a decrease in the heat flow acting on sample. The analytical solution of the problem of temperature change in a relaxing nitrogen plasma jet in the absence of graphite confirmed the experimentally observed slow cooling of it, caused by a number of exothermic recombination processes taking place in the plasma.