Ionization and recombination in nanosecond repetitively pulsed microplasmas in air at atmospheric pressure

Abstract

We confine the nanosecond repetitively pulsed discharge (NRP) to the micrometer scale, in a 200-µm discharge gap in air at atmospheric pressure and room temperature, focusing on measurements of the electron number density and electron temperature. The Stark broadening of H, O and N atomic lines and electrical conductivity both show that the electron number density reaches a maximum value of 1×10 19 cm -3 . Boltzmann plots show the electron temperature to be 72 kK several nanoseconds after the end of the pulse of applied electric field.We will use these results to determine the mechanism responsible for electron loss during the early recombination phase (t < 500 ns) and comment on the degree of ionization and dissociation.

Ionization Mechanism in a Thermal Spark Discharge

“…All electronic states of the ions are assumed to follow a Boltzmann distribution at Te. The measured electronic temperature (Te = 35,000 K) corresponds to values usually reported in thermal spark literature [9,12,13]. In the following, we discuss the determination of N + and O + number density.…”

“…The electron number density, measured by Stark broadening of N + , reached ne = 9×10 18 cm -3 , representing an ionization of 36%. Such high electron number densities and temperatures were also measured by other teams in pin-to-pin configurations [10][11][12][13][14] and nanosecond Dielectric Barrier Discharges [15,16].…”

Experimental study of energy delivered to the filaments in high pressure nanosecond surface discharge

“…Extremely high electron density, n e = 10 18 − 10 19 cm −3 and slow electron density decay, tens of nanoseconds, were reported for N 2 :H 2 mixture [4]. During last 3 − 5 years, a few groups [6][7][8] observed similar high densities of electrons with a slow decay rate in atmospheric pressure plasma pin-to-pin discharges driven by repetitive high frequency (typically at least tens of kHz) nanosecond pulses; constriction of the discharges corresponding to sharp increase of the electron density in a nanosecond time scale has been experimentally observed. Filamentary surface dielectric barrier discharge provides similar plasma properties in the filaments but instead of a single shot channel, multiply equidistant filaments (30-50 in our case) appear along the edge of the high-voltage electrode.…”

Filamentary nanosecond surface dielectric barrier discharge. Plasma properties in the filaments

“…The decay of the electron density was slow, a few tens of nanoseconds. Later experimental observations of nanosecond repetitive plasma (NRP) at atmospheric pressure [11][12][13] also report densities of electrons on the level n e ∼ 10 18 − 10 19 cm −3 , constriction of the discharge channel, high electron temperatures reaching a few electronvolts and slow plasma decay, tens of nanoseconds. The authors of [14] measured the ultra-fast gas heating observed by optical emission spectroscopy on the axis of the streamer before the constriction of the channel.…”