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.

15 molecules cm -3 for air and nitrogen discharges, respectively. In nitrogen, the decay of the N 2 (A) density is shown to be a second-order process with a rate coefficient of 1.1 × 10 -9 cm 3 s -1 at 1600 K with a factor of 2 uncertainty. In air, the decay is estimated to be 1 order of magnitude faster than that in nitrogen owing to quenching by atomic and molecular oxygen. Furthermore, the rotational temperature is determined by comparison of CRDS measurements and simulations of several rotational lines of the (2 r 0) band of the first positive system of N 2 between 769.8 and 770.7 nm. The rotational and vibrational temperatures are also determined by comparison of optical emission measurements and simulations of the second positive system of N 2 between 365 and 385 nm. In these CRDS measurements, we achieved a temporal resolution down to 50 ns.

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