Dynamics of Near-Atmospheric-Pressure Hydrogen Plasmas Driven by Pulsed High Voltages

Abstract

The formation mechanism of hydrogen plasmas by nanosecond high-voltage pulses at near-atmospheric pressure was examined by particle-in-cell/Monte-Carlo-collision simulations. In the model system, plasmas were generated between parallel metal electrodes. The simulation results show the propagation of ionization fronts and the formation of non-Maxwellian electron-energy distributions. The time evolution of plasma dynamics observed in the simulations has been confirmed to be in good agreement with recent experimental results.Index Terms-Atmospheric-pressure plasmas, nanosecondpulsed discharge, plasma simulation. P LASMAS have been widely used in many fields of industrial applications. Conventionally, these applications are operated under low-pressure conditions; therefore, materials that can be treated by such plasmas have been limited to those that can be placed in a vacuum chamber. For nonconventional applications, plasmas under higher pressure have become recently an important research topic. High-voltage short pulses are often used to generate such plasmas. Plasmas generated under such conditions are of low temperature and highly collisional.In this paper, we have examined the processes of hydrogenplasma formation by the application of repetitive high-voltage short pulses to parallel metal plates, using a 1-D-in-space and 2-D-in-velocity particle-in-cell (PIC) simulation [1] with Monte Carlo collisions (MCC) and a null-collision operator [2]. The simulation code was developed by the authors.In the simulation model, a plasma is generated between a grounded anode and a cathode connected to an external voltage source. The applied voltage is a triangular pulse with a peak value of −2 kV. It is set at 0 V between t = 0 ns and t = 5 ns, increases linearly with time from t = 5 ns, peaks at t = 10 ns, then decreases with time linearly, and vanishes at t = 15 ns. This voltage variation is similar to what has been observed experimentally [3]. The electrode-gap distance is 1.2 mm. The neutral gas is assumed to be molecular hydrogen (H 2 ) at room temperature and have a pressure of 0.3 atm, following the experimental conditions in [3].A uniformly distributed plasma with a plasma density of 10 10 cm −3 at 300 K is assumed to exist at t = 0. It represents Manuscript a remnant of the previous pulsed discharge. Numerically, the initial plasma, consisting of ions and electrons, is modeled by 20 000 simulation particles for each species. The charged species of the plasma are assumed to be only electrons and H + 3 ions. The processes of electron-neutral collisions considered are elastic collisions, ionization to H + 2 (because most H + 2 ions encounter collisions with neutral atoms and turn into H + 3 ions immediately under high-pressure conditions), the vibrational excitation of ν = 0 → 1, and electronic excitations to b 3 Σ + u , B 1 Σ + u , and E, F 1 Σ + g states. Three types of ion-neutral collisions are taken into account: momentum transfer, slow H + 3 production, and H + 3 annihilation. The collision cross-sectional data fo...

Vibrational CARS measurements in a near-atmospheric pressure plasma jet in nitrogen: I. Measurement procedure and results

“…The electric field in these conduction current plateaus is measured by the E-FISH method and found to be constant during the discharge with a value around 81 Td for all conditions investigated here. These constant discharge conditions were previously observed in hydrogen plasmas (otherwise similar discharge conditions as in this work) both in simulations and measurements [53,[60][61][62]. CARS spectra were measured for three different high voltage pulses.…”

Vibrational CARS measurements in a near-atmospheric pressure plasma jet in nitrogen: II. Analysis

“…The same behaviour is also seen for different molecular species, e.g. hydrogen [24][25][26]. This promises an easy tool for estimating the amount of vibrational excitation a priori, when one is able to predict the density and electric field for the given discharge.…”

The effect of photoemission on nanosecond helium microdischarges at atmospheric pressure

“…Nonetheless, particle-based kinetic approaches, like the particle-in-cell method complemented by Monte Carlo collisions (PIC/ MCC), have also been applied in some studies, despite the high computational requirements, because they can describe non-local kinetic effects in domains with high reduced electric fields, and they provide access to the electron energy distribution function. Such studies include those of fast (subnanosecond) breakdown in high-voltage open discharges [12,13], discharge development in hydrogen microdischarges [14][15][16], as well as ionization instabilities [17] and selforganized pattern formation [18].…”