Electron Properties in Collisionless Mesothermal Plasma Expansion: Fully Kinetic Simulations

Hu, Yuan; Wang, Joseph

doi:10.1109/tps.2015.2433928

Cited by 45 publications

(34 citation statements)

References 23 publications

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“…The polytropic exponent γ e in the equation describes the exchange of heat between a magnetically expanding plasma and the system, and various kinetic modeling approaches have been established to explore the physical meaning of MN devices by relating the thermodynamic model to the MN phenomena, e.g. plasma detachment, plume divergence efficiency, and thruster gain [26][27][28][29][30][31].…”

Section: Introductionmentioning

confidence: 99%

Thermodynamics of a magnetically expanding plasma with isothermally behaving confined electrons

Kim

Ryu

et al. 2018

New J. Phys.

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Thermodynamics of a magnetically expanding plasma (magnetic nozzle (MN)) has been investigated considering the existence of confined electrons bouncing back and forth inside a potential well formed by a combination of external magnetic field and self-generating ambipolar electrostatic potential. The properties of confined electrons are distinguished from that of the adiabatically expanding electrons with γ e ≈5/3 by the separate measurement of each species using a double-sided planar Langmuir probe. Relationship between the electron pressure versus electron density averaged over electron energy probability functions (eepfs) clearly reveals that the confined electrons in MN have a nearly isothermal characteristic. Existence of isothermally behaving confined electrons together with adiabatically expanding electrons separates the MN system into two regions with different thermodynamic properties; one is a nearly adiabatic region located near the nozzle throat and the other is nearly isothermal region located far from the nozzle. A transition of electron thermodynamic property along a distance from the nozzle throat can be explained with conservation of magnetic moment of electrons bounced back by ambipolar electrostatic potential. Coexistence of the nearly adiabatic electrons with Maxwellian eepf and the nearly isothermal electrons with high energydepleted eepf makes the overall eepf shape low energy-populated eepf, indicating a need for careful analysis on the measured eepfs near the nozzle throat. In spite of significant contribution of confined electrons to eepf and overall electron thermodynamics, it is found that the confined electrons behaving isothermally do not contribute to the generation of ambipolar electrostatic potential which is important for ion acceleration in MN. The present study suggests that ion acceleration should not be directly inferred from the value of polytropic exponent γ e because thermodynamic property of a MN is influenced by isothermally behaving confined electrons as well as adiabatically expanding electrons.

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Section: Introductionmentioning

confidence: 99%

Thermodynamics of a magnetically expanding plasma with isothermally behaving confined electrons

Kim

Ryu

et al. 2018

New J. Phys.

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“…The most common electron fluid model is the Boltzmann relation (BR). In the BR model it is assumed that the electrons are isothermal, the pressure is described by an ideal gas and the electron drift velocity can be neglected [11,12].…”

Section: Theorymentioning

confidence: 99%

A Particle-in-Cell solver based on a high-order hybridizable discontinuous Galerkin spectral element method on unstructured curved meshes

Pfeiffer

Hindenlang

Binder

et al. 2019

Computer Methods in Applied Mechanics and Engineering

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A high-order hybridizable discontinuous Galerkin spectral element method (HDGSEM) for Particle-In-Cell (PIC) schemes is presented for the simulation of electrostatic applications on three-dimensional unstructured curved meshes.The electrostatic Poisson equation is solved and optionally a Boltzmann relation for the electron species can be used which leads to non-linear source terms.The hybridizable formulation reduces the total number of unknowns of the field solver, allowing the simulation of large problems. The implementation of the HDGSEM solver in a PIC code is described and validated using several test cases with successive increasing complexity. It is shown that the high-order convergence properties are retained on curvilinear meshes, likewise when material jumps are introduced. The simulation of an ion optic illustrates the applicability of the presented method for complex geometries and large problem sizes.

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“…Mora and Pellat () examined the use of equation for electrons in the derivation of the self‐similar solution of collisionless plasma expansion into a vacuum and found that the exact electron density differs from that predicted based on equation . Hu and Wang (, , ) carried out full particle PIC simulations of the emission and expansion of plasma plumes and found that the electron temperature is anisotropic and the electron velocity distribution function (VDF) is non‐Maxwellian in most of the plume region.…”

Section: Introductionmentioning

confidence: 99%

The Breakdown of the Fluid Approximation for Electrons in a Plasma Wake

Wang

2018

JGR Space Physics

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A comparative study using a fluid-based analytic solution, hybrid particle-ion fluid-electron particle-in-cell (PIC), and fully kinetic PIC is carried out to examine a collisionless, mesothermal plasma flow over a large, unbiased plate. We find that the plasma wake may be characterized into two regions based on the electron characteristics: a fluid electron expansion region and a kinetic electron expansion region. In the fluid electron expansion region, the electrons may be considered to be an equilibrium fluid and all the three approaches lead to a similar result. In the kinetic electron expansion region, the local electron velocity distributions are strongly non-Maxwellian and the commonly used fluid approximation for electrons breaks down. The results also show that the error of the hybrid PIC simulation strongly correlates with a nonequilibrium parameter based on the weighted deviation of the electron velocity distribution from the equilibrium. Plain Language SummaryThe formation of a plasma wake behind a large moving object is applicable to many problems in space science and engineering, ranging from the ionospheric plasma flow around spacecrafts to the solar wind flow around asteroids. A common approach used in almost all previous studies of plasma wakes is to assume that electrons can be modeled as a fluid, in order to simplify analyses and save on computational time in simulations. While the assumption of fluid electrons has been widely adopted, its validity has never been carefully examined. This paper presents the first study on the validity of the fluid approximation of electrons when applied to a collisionless plasma wake. The results show that these wakes consist of two regions: a fluid electron expansion region and a kinetic electron expansion region. The electrons in the kinetic expansion region are in a nonequilibrium state, and their microscopic characteristics lead to anisotropic and complex macroscopic properties. Thus, the commonly used fluid approximation for electrons breaks down in this region. The conclusions of this study will have an immediate impact on all ongoing studies of space plasma interactions with spacecraft and solar wind interactions with small asteroids. Key Points:• The validity of the commonly used fluid electron model in a collisionless plasma wake is investigated • The plasma wake consists of a fluid electron expansion region and a kinetic electron expansion region • The fluid electron model breaks down in the kinetic expansion region due to nonequilibrium electrons

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Electron Properties in Collisionless Mesothermal Plasma Expansion: Fully Kinetic Simulations

Cited by 45 publications

References 23 publications

Thermodynamics of a magnetically expanding plasma with isothermally behaving confined electrons

Thermodynamics of a magnetically expanding plasma with isothermally behaving confined electrons

A Particle-in-Cell solver based on a high-order hybridizable discontinuous Galerkin spectral element method on unstructured curved meshes

The Breakdown of the Fluid Approximation for Electrons in a Plasma Wake

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