Experimental study of the dynamics of fast gas heating in a low-pressure DC discharge in nitrogen

This paper discusses the experimental studies of the gas heating dynamics of a low-pressure DC discharge in nitrogen. The time evolution of the discharge current, the electric field, and the gas temperature in the positive column of a pulsed DC discharge in nitrogen for a gas pressure of 1.5 Torr and a current density of 0.1-6 A cm−2 were measured. The gas temperature in the discharge was equal to the rotational temperature in the A 3 u + and a 1 g metastable electronic states of nitrogen. The rotational temperature in the A 3 u + state was found from the spectra of the first positive system of N2, which were recorded by using intracavity laser absorption spectroscopy. The rotational temperature in the a 1 g state was determined from the VUV emission spectra of the Lyman-Birge-Hopfield system of N2. The gas temperatures obtained by these two spectroscopic methods were in good agreement. It was found that two phases with different gas heating rates exist during a discharge pulse. In the first phase, the gas heating was relatively slow. With increasing current density, the duration of the first heating phase decreased from 150 s at 0.2 A cm−2 to 10 s at 2.5 A cm−2. In the second phase, fast gas heating occurred. The gas heating rate in the second phase increased with increasing discharge current, and was equal to 10 K s−1 for a current density of about 2 A cm−2. The relation between the rate of the fast heating and the density of deposited power obeyed a power law. In 300 s, the gas was heated in the discharge up to about 400, 1500, and 3000 K for current densities of 0.2, 1, and 2.5 A cm−2, respectively. These experimental data can be the basis for verification of kinetic models for gas heating dynamics in a low-pressure discharge in nitrogen.