Analysis of plasma detachment in the magnetic thrust chamber using full particle-in-cell simulation

Abstract

A magnetic nozzle, which is a convergent-divergent magnetic field to control a plasma flow, has been investigated for application to plasma propulsion systems in spaceships. In the magnetic nozzle, plasma thermal energy is converted to one-directional kinetic energy by Lorentz force to generate thrust. Although magnetic field structure and strength are optimized for improvement of the thrust performance, it is essential to understand physical processes of plasma ejection from the nozzle, because the plasma may flow back along lines of magnetic field if the directed plasma continues being strongly magnetized. It is assumed, for one of the scenarios to explain a plasma detachment, that a plasma detaches from magnetic field when a cyclotron radius exceeds a scale length of magnetic field in size. Hence, we investigate a plasma detachment condition by analyzing parameters of the plasma for unmagnetization. We assumed individual particle motion of a fully ionized plasma in the magnetic nozzle and conducted a full particle-in-cell simulation in a two-dimensional coordinate system. We calculated a ratio of cyclotron radius to a scale length of the magnetic field. The ratio increased in a downstream due to variation of magnetic field induced from a diamagnetic cavity, suggesting unmagnetization.

Magnetic Nozzle and RPA Simulations vs. Experiments for a Helicon Plasma Thruster Plume

“…Numerical models for the magnetized plasma plume expansion through a magnetic nozzle are of different types. A first approach is that of the kinetic approaches, which can be split into methods solving a simplified Boltzmann's equation for the ion and electron distribution functions in a low dimensional space (typically 1D, [18]), and full particle-incell (PIC) models [19,20], featuring particle ions/electrons, collisions through Montecarlo approaches [21], and generally limited to 2D to reduce the computational cost. An alternative approach, which is computationally cheaper, is that of hybrid codes, in which electrons are modeled as a fluid, while neutrals and ions are followed as macro-particles of a PIC sub-model featuring Montecarlo collisions.…”

A Central-Cathode Electrostatic Thruster Featuring a High-Temperature Superconducting Applied Field Module

“…They made the electrostatic assumption and derived a self-similar scaling law to reduce computation time. Kojima et al used a collisionless PIC code to investigate plasma detachment from a magnetic nozzle [100]. They found that ion demagnetisation led to ion detachment, but in order to study electron detachment their code must be modelled on a larger spatial scale.…”

“…In a stream of work parallel to the directed study of the AF-MPDT and HET, there has been considerable effort to study the impact of a magnetic nozzle on the flow of plasma from a plasma source, particularly in the past 15 years [122] [123] [100]. There has been a concerted effort to develop a theory of plasma within a magnetic nozzle, where a simplified plasma source model is assumed and all efforts are concentrated into how the plasma interacts with the nozzle itself [124].…”