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

Abstract

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 and metastable electronic states of nitrogen. The rotational temperature in the 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 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 μs at 0.2 A cm−2 to 10 μs 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 μs−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 μs, 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.