Modeling of thermalization phenomena in coaxial plasma accelerators

Abstract

Coaxial plasma accelerators are electromagnetic acceleration devices that employ a self-induced Lorentz force to produce collimated plasma jets with velocities ~50 km s −1 . The accelerator operation is characterized by the formation of an ionization/thermalization zone near gas inlet of the device that continually processes the incoming neutral gas into a highly ionized thermal plasma. In this paper, we present a 1D non-equilibrium plasma model to resolve the plasma formation and the electron-heavy species thermalization phenomena that take place in the thermalization zone. The non-equilibrium model is based on a self-consistent multi-species continuum description of the plasma with finite-rate chemistry. The thermalization zone is modelled by tracking a 1D gas-bit as it convects down the device with an initial gas pressure of 1 atm. The thermalization process occurs in two stages. The first is a plasma production stage, associated with a rapid increase in the charged species number densities facilitated by cathode surface electron emission and volumetric production processes. The production stage results in the formation of a two-temperature plasma with electron energies of ~2.5 eV in a low temperature background gas of ~300 K. The second, a temperature equilibration stage, is characterized by the energy transfer between the electrons and heavy species. The characteristic length scale for thermalization is found to be comparable to axial length of the accelerator thus putting into question the equilibrium magnetohydrodynamics assumption used in modeling coaxial accelerators.

Transient phenomena during dense argon micro-plasma formation

“…One can obtain from the ideal gas law the requirement that the ionization degree should be smaller than T g /T e , where T e is the electron temperature. As was discussed in [17], the conventional approach is invalid for non-equilibrium plasmas having high ionization degree, namely, larger than T g /T e . In such plasmas, the electron pressure can become comparable or even exceed the background gas pressure.…”

“…One important effect discussed in [17] in the context of plasma thermalization phenomenon was not considered in [15]. Indeed, highly ionized non-equilibrium plasmas with the ionization degrees exceeding a few percent are characterized by rather high electron pressure.…”

Multi-physics modeling of a spark plasma jet igniter

“…Modeling the streamer-spark-arc transition from nonequilibrium to equilibrium mode is still a challenging task not well solved. Pioneering works modeling the thermalization can be found in [11,17]. In our work the thermal discharge lasts a much longer time, requiring a quite large change in the model (from a two-temperature model with fixed EEDF to a single temperature model with the magnetic field, thermal chemistry and strongly changed EEDF), thus we skip the transition moment, the commercial software COMSOL Multiphysics is used for the thermal arc gas heating stage.…”

“…The plasma spark jet igniter is a promising igniter configuration as it combines the aforementioned three effects. The working procedures of a spark jet igniter are very similar to a plasma synthetic jet actuator used in the field of plasmaassisted flow [6][7][8][9][10][11]. A typical spark jet igniter consists of a discharge chamber with one side open that contains two electrodes separated by an insulator.…”

Effects of flow collisionality on ELM replication in plasma guns

“…The MHD governing equations are a 'single-fluid' description of a quasi-neutral high density plasma [28,29]. The high pressure (>1 atm) operational regime, underlying breakdown and ionization in plasma guns, ensures short energy transfer mean free paths and thus rapid temperature equilibration between all constituent species [30]. Hence, the local thermodynamic equilibrium (LTE) approximation is used to define plasma composition and its thermodynamic properties.…”