Kinetic electron model for plasma thruster plumes

Abstract

A paraxial model of an unmagnetized, collisionless plasma plume expanding into vacuum is presented. Electrons are treated kinetically, relying on the adiabatic invariance of their radial action integral for the integration of Vlasov's equation, whereas ions are treated as a cold species. The quasi-2D plasma density; self-consistent electric potential; electron pressure, temperature, and heat fluxes are analyzed. In particular, the model yields the collisionless cooling of electrons, which differs from the Boltzmann relation and the simple polytropic laws usually employed in fluid and hybrid PIC/fluid plume codes.This article presents a quasi-2D kinetic model of a plasma plume and uses it to characterize several features of the electron expansion. The model assumes a collisionless, unmagnetized, quasineutral, steady-state plasma, providing a good description of the plume far-region. The integration of the electron model relies on the first-order

Macroscopic and parametric study of a kinetic plasma expansion in a paraxial magnetic nozzle

“…For instance, the intermediate value α = 7/2, extracted from figure 10(c), o yieldsγ ≈ 1.2, a value close to some experimental evidence [26][27][28][29]39]. Implementing the crude closure (37) in the energy equation (33) yields the known law between the electric potential fall and the polytropic coefficient, [34] e|φ…”

“…This fact must be taken in to account when comparing convergent-divergent MN models with divergence-only MN models such as those of Refs. [31,34]. In particular, the comparison of the present model with the convergent-only MN of Ref.…”

“…computed in Ref. [34], for instance. The advantage of the flux-based law proposed here is that it is easily extended to a weakly collisional plasma expansion.…”

Three dimensional fluid-kinetic model of a magnetically guided plasma jet

“…Unfortunately, this kinetic model brings up a new issue: there are islands in the VDF phase space containing trapped electrons, disconnected from the boundary conditions of the problem, so their VDF is unknown. Incidentally, this model is fully analogous to that of an unmagnetized plasma plume [41]. A posterior time-dependent kinetic paraxial model has demonstrated the formation of trapped populations in the transient period of formation of the MN [32].…”

On electron boundary conditions in PIC plasma thruster plume simulations

“…Extensive numerical efforts devoted to the characterization of the properties of plasma thruster plumes can be found in the literature; see, for example, references [16][17][18][19][20] and those cited in [15,21]. The treatment of electrons varies from kinetic (solving Vlasov-Boltzmann directly or using the Particle-in-Cell (PIC) method [22]) to fluid approximations that rely on an isothermal or polytropic closure of the equations.…”