Influence of Electron and Ion Thermodynamics on the Magnetic Nozzle Plasma Expansion

Abstract

A two-fluid 2-D model of the supersonic plasma flow in a propulsive magnetic nozzle (MN) is extended to include simple electron and ion thermodynamics to study the effects of electron cooling and ion thermal energy on the expansion. A faster electron cooling rate is seen to reduce plasma jet divergence, increase radial rarefaction, and enhance detachment from the closed magnetic lines. Ion thermal energy is converted to directed kinetic energy by the MN without the mediation of an ambipolar electric field, and alters the electric response of the plasma.

Electron Properties in Collisionless Mesothermal Plasma Expansion: Fully Kinetic Simulations

“…Merino and Ahedo [20] investigated the use of a single polytropic model with an arbitrary γ to describe electron cooling in a magnetized plasma plume. Their follow up study further suggested that electron cooling might not be captured using a single polytropic model due to the non-Maxwellian populations [24].…”

“…Gatsonis and Yin [16] addressed the collisional effect in a pulsed plasma thruster plume using a hybrid particle-fluid approach where the electron momentum equation that includes the electron-ion and electron-neutral collision terms was solved. Denavit [17], Mora and Pellat [18], Manfredi et al [19], and Merino and Ahedo [20] considered nonisothermal electrons in plasma expansion using a polytropic law to model the electrons T e n 1−γ e = const, or p e n −γ e = const (2) where p e is the pressure of the electrons and γ is the polytropic coefficient. γ = 1 corresponds to the isothermal case.…”

“…They argued that the polytropic relation p e n −γ e = const should exist for For a 1-D planar expansion, Manfredi et al [19] found that γ = 3. Merino and Ahedo [20] simulated the plasma expansion in a magnetic nozzle with a 2-D two-fluid model and studied the effects of electron cooling under a single polytropic relation. By comparing the numerical results with different γ values, they observed that the electron cooling led to lower beam divergence and facilitated plasma detachment.…”

“…By comparing the numerical results with different γ values, they observed that the electron cooling led to lower beam divergence and facilitated plasma detachment. However, the exact cooling mechanisms were not identified, and hence, the choice of γ in [20] was arbitrary.…”

Influence of the Applied Magnetic Field Strength on Flow Collimation in Magnetic Nozzles

“…It has been shown using theoretical models that the value of the polytropic exponent strongly influences the resulting behavior and performance of the MN. [33][34][35] Unfortunately, there is very little theoretical support for the polytropic law, and calculation of γ e from existing experimental data provides little consensus with values ranging from γ e ≤ 1 to γ e > 5/3. 18,36,37 RF-LP and EP measurements of the density, electron temperature, and plasma potential along the axis of the MN (see Fig.…”