Study of gas heating mechanisms in millisecond pulsed discharges and afterglows in air at low pressures

Abstract

A self-consistent model is developed to study the temporal variation of the gas temperature in millisecond single dc pulsed discharges and their afterglows in air-like mixtures (N 2 -20%O 2 ) at low pressures. The model is based on the solutions to the time-dependent gas thermal balance equation, under the assumption of a parabolic gas temperature profile across the discharge tube, coupled to the electron, vibrational and chemical kinetics. Modelling results provide a satisfactory explanation for recently published time-resolved experimental data for the gas temperature in a 5 ms pulsed air plasma with a current of 150 mA and the corresponding afterglow at a pressure of 133 Pa (1 Torr). It is shown that the main heating mechanisms during the first millisecond of the pulse come predominantly from O 2 dissociation by electron impact through the pre-dissociative excited state O 2 (B 3 − u ) and the quenching of nitrogen electronically excited states N 2 (A 3 + u , B 3 g , a 1 − u , a 1 g , w 1 u ) by O 2 , agreeing with other studies on fast gas heating in air plasmas. As the pulse duration increases, other gas heating sources become important, namely V-T N 2 -O energy exchanges, recombination of oxygen atoms at the wall, N 2 (A) quenching by O( 3 P) and reaction N( 4 S) + NO(X) → N 2 (X, v ∼3) + O, contributing altogether to an additional smooth increase in the gas temperature until the end of the pulse. In the first instants of the early afterglow, the gas temperature decreases very rapidly as a consequence of the minor role played by electronic collisions and due to a fast decay of N 2 electronic states. For afterglow times up to 10 ms, the gas temperature continues to decrease, following the time-dependent kinetics of [N 2 (X,v)], [N( 4 S)], [O( 3 P)] and [NO(X)]. Sensitivity of the model to different input parameters such as thermal accommodation coefficient and probabilities for atomic recombination at the wall are reported.

Volume and surface propellant heating in an electrothermal radio-frequency plasma micro-thruster

“…9-16 Volume heating results from energy being redistributed between the electronic, translational, rotational, and vibrational states through elastic collisions, 9,16 ion-neutral charge exchange collisions, 10,11,15 quenching, 12,13 dissociation, and vibration-vibration (V-V) and vibration-translation (V-T) relaxation. 12,16 Surface or wall heating results from a mechanism, such as ion neutralization, 14 metastable quenching, 12,16 or vibrational de-excitation, 12,16 through collisions with the walls, which transfers energy to the surface increasing the temperature of the walls, which then transfers energy into the neutral gas through convection and conduction processes.…”

Simulation study on nitrogen vibrational kinetics in a single nanosecond pulse high voltage air discharge

“…Table III shows a classification of all reaction processes for nitrogen-oxygen mixtures. [25][26][27][28][29][30][31][32][33][34] 055209-3 Yang, Zhou, and Dong AIP Advances 6, 055209 (2016) …”

“…20,30 The rate constant for Chem-V process such as N( 4 S) + NO → O + N2(v = 3.4) is also calculated by a similar method, 39 with fraction of the released energy transferred into vibrations known from measurements. 40 The surface-vibrational (Surf-V) process is included in the 0D model by the characteristic diffusion time τ…”

“…20 The temperaturedependent heat capacity and conductivity are adopted from Ref. 30. The gas heating mechanisms 29,46 are listed in Table VI (the detail information about dominant E-V and Chem-V processes are marked in bold type).…”

“…The above approximation was generally true for discharge in flow conditions or even in static conditions when energy deposition is not too high. 30 However, the pressure may change in NPD due to gas dynamic expansion induced by fast gas heating. According to a discharge model coupled with compressible Navier-Stokes equations for the same conditions, 6,23 the pressure at the discharge center line may increase to about 150 Torr at 1 µs, followed by a decrease to 90 Torr at 5 µs, and remain 100 Torr after 10 µs.…”