Temperature measurements of the background gas and metastable argon atoms in N₂/Ar nanosecond repetitively pulsed discharges

Abstract

Characterization of plasma properties that underpin kinetic processes in nanosecond repetitively pulsed discharges (NRPDs) is necessary to understand and manipulate the behavior of these discharges for a wide variety of applications. Here, the neutral gas temperature in N2 and 50% N2/50% Ar NRPDs during the discharge is determined by characterizing the rotational temperature of rovibrational spectra from the N2 2nd positive system. At the conditions investigated, it is shown that the timescale for rotational-translational relaxation is shorter than the effective lifetime of the N2(C) state, thereby, rendering the rotational temperature measurements a reasonable representation of the background gas temperature. The measurements show that the translational temperature of ground state nitrogen molecules does not increase significantly above ambient temperature during the discharge generated at a constant pressure of 20 Torr, 10 kHz pulse repetition frequency, and pulse energy of 50 μJ. An absorption based detection technique with a 2 ns time-resolution used to measure the translational temperature history of the metastable argon atoms (Ar(1s3)) in the N2/Ar NRPDs shows that the Ar(1s3) atoms and the neutral background gas are in thermal non-equilibrium during the discharge. Furthermore, the addition of nitrogen gas is shown to significantly reduce the translational energy enhancement of the metastable argon atoms produced in the N2/Ar discharges compared to that in pure argon discharges.