No abstract

Nanosecond repetitively pulsed (NRP) discharges were used to generate atmospheric pressure plasmas in air or nitrogen preheated at 1000 K. In order to understand the physico-chemical mechanisms that control the number densities of active species, in situ optical diagnostic techniques were developed. The ground state of atomic oxygen was measured by two-photon absorption laser induced fluorescence (TALIF), the density of N2(A) was measured by cavity ring down spectroscopy (CRDS) and the densities of N2(B) and N2(C) were measured by optical emission spectroscopy (OES). Temporally and spatially resolved density measurements were performed in the main operating regimes of the NRP discharge, namely the diffuse and filamentary regimes. The diagnostic techniques and associated challenges are presented and the effects of these discharges on the chemistry are discussed.

In atmospheric-pressure air preheated to 1000 K, nanosecond repetitively pulsed (NRP) discharges are shown to generate three plasma discharge regimes. In addition to the well-known corona and spark regimes, there exists a glow-like regime that develops through an initial cathode-directed streamer, followed by a return wave of potential redistribution. The applied electric field is then switched off before the formation of the cathode fall, resulting in an 'imminent' glow discharge. Previously, this regime had been observed only at 2000 K in air at atmospheric pressure. Measurements of the plasma dynamics, current-voltage characteristics, gas temperature and plasma chemistry of the excited species N 2 (B), N 2 (C), N + 2 (B), NO(A) and O(3p 5 P) in the pulsed glow regime are presented. Using 10 ns pulses applied repetitively at 30 kHz, we find that this glow regime generates an estimated electron number density of 10 13 cm −3 , while consuming only 1-10 µJ per pulse and heating the gas by less than 200 K.