Diagnostics of a nanosecond atmospheric plasma jet. Electron and ro-vibrational excitation dynamics

Abstract

Atmospheric repetitive He discharge with 10 ns current peak width and 3 × 10 11 V s−1 voltage front rise working in jet geometry is studied. The first part of the study is devoted to electrical and optical discharge characterization including voltage-current behavior, emission dynamics, as well as ro-vibrational dynamics of N2, N 2 + and OH molecules. It is found that He atoms get excited at the very early stage, as a result of ionization wave formation. This process follows by excitation of O, N2 and N 2 + . It is also shown that a rather small (0.1%–1%) air admixtures facilitate gas breakdown, as revealed by shortening of the discharge current risetime. The rotational excitation of N 2 + always overtakes He excitation by about 5 ns, with rotational temperature peaking at about 650 K and decaying afterwards, whereas rotational temperature of N2 always remains constant equal to about 300 K. This value is associated with gas kinetic temperature since the electron-rotational (e-R) excitation process is too slow, so it cannot be activated during the plasma phase and no additional change in rotational excitation of N2 happens. Nitrogen molecules remain vibrationally excited in the discharge, post-discharge and jet areas after the plasma pulse which is likely a result of ionization wave propagation. Upon water vapor injection the apparent OH rotational distributions reveal double Boltzmann slope representing thermalized and non-thermalized OH groups. Rotational temperature of the thermalized group correlates with the one of N 2 + showing, however, much longer relaxation time, whereas for the non-thermalized group it remains above 1 eV at all conditions. The obtained results confirm that the studied ns- discharge is a good candidate for temperature-sensitive applications, such as the bio-sample treatment. Further analysis related to the ionization waves, electron density and electric field behavior is undertaken in the second part.

Breakdown modes in nanosecond pulsed micro-discharges at atmospheric pressure

“…Moreover, the shorter rise time also contributes to a faster propagation speed of the ionization wave [92]. Therefore, at relatively low pulse voltages, even if no runaway electrons are generated, a fast ionization wave may still occur, thereby shortening the gas breakdown time [93].…”

Orbits and chaos of a two‐fluid magnetized plasma oscillator subjected to parametric excitation with square delayed feedback

“…Dubinov [12] developed the non-linear theory of ion-acoustic waves in two-species isotropic collisionless plasma, derived the differential equation describing the profile of the ion concentration, and calculated profiles of the concentration in the periodic ion-acoustic wave and soliton. Britun et al [13] devoted to electrical and optical discharge characterization including voltage-current behavior, emission dynamics, as well as ro-vibrational dynamics of a nanosecond atmospheric plasma. They found that rather small air admixtures facilitate gas breakdown.…”

“…Britun et al. [13] devoted to electrical and optical discharge characterization including voltage‐current behavior, emission dynamics, as well as ro‐vibrational dynamics of a nanosecond atmospheric plasma. They found that rather small air admixtures facilitate gas breakdown.…”