Non-local electron energy probability function in a plasma expanding along a magnetic nozzle

Boswell, Roderick; Takahashi, Kazunori; Charles, Christine; Kaganovich, Igor

doi:10.3389/fphy.2015.00014

Cited by 35 publications

(27 citation statements)

References 15 publications

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“…In the laboratory system containing the vacuum chamber boundary, the upstream tail electrons overcoming the potential drop of the DL are trapped by the sheath and come back to the source side via the acceleration by the DL. The detailed axial measurement of the EEPFs has shown such a behavior of the electrons, while the low-energy part is confined by the electrostatic potential structure (Boswell et al 2015). In such a situation, the potential structure affects the shape of the EEPF (called a non-local effect).…”

Section: Electron Dynamicsmentioning

confidence: 99%

“…However, it is rarely Maxwellian in low-pressure, non-equilibrium, laboratory plasmas as observed in a number of experiments, while the precise measurement of the EEPF has not been successfully performed in Little and Choueiri (2016). Even in the non-Maxwellian EEPFs, the nearly isothermal polytropic index ∼ 1.17 has been obtained, but it strongly depends on the shape of the EEPFs , which is affected by a non-local effect of the ambipolar, CFDL, and sheath electric fields as demonstrated by the detailed axial measurement of the EEPFs (Takahashi et al 2007;Boswell et al 2015). It should be mentioned that the electrons are well known to be nearly isothermal in low-pressure laboratory plasmas, when they are…”

Section: Electron Thermodynamics In the Magnetic Nozzlementioning

confidence: 99%

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Helicon-type radiofrequency plasma thrusters and magnetic plasma nozzles

Takahashi

2019

Rev. Mod. Plasma Phys.

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182

111

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Development of electrodeless radiofrequency plasma thrusters, e.g., a helicon thruster, has been one the of challenging topics for future high-power and longlived electric propulsion systems. The concept simply has a radiofrequency plasma production/heating source and a magnetic nozzle, while it seems to include many aspects of physics and engineering issues. The plasma produced inside the source is transported along the magnetic field lines and expands in the magnetic nozzle, where the plasma is spontaneously accelerated into the axial direction along the magnetic nozzle, yielding a generation of the thrust force. Hence, the plasma transport and spontaneous acceleration phenomena in the magnetic nozzle are key issues to improve the performance of the thrusters. Since the thrust is equal in magnitude and opposite in direction to momentum flux exhausted from the system, the direct measurement of the thrust can reveal not only the thruster performance but also fundamental physical quantity of plasma momentum flux. Here studies on fundamental physics relating to the thruster development and the technology for the compact and efficient system are reviewed; the current status of the thruster performance is shown. Finally, a recently proposed future new application of the thruster is also discussed.

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Section: Electron Dynamicsmentioning

confidence: 99%

Section: Electron Thermodynamics In the Magnetic Nozzlementioning

confidence: 99%

Helicon-type radiofrequency plasma thrusters and magnetic plasma nozzles

Takahashi

2019

Rev. Mod. Plasma Phys.

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182

111

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“…In recent years, there has been a growing interest in the flow of plasma through magnetic nozzle (MN) to analyze various research fields such as plasma jet thrusters for spacecraft [1][2][3][4][5][6][7][8], and solar wind from the Sun [9][10][11]. Particularly, in the case of electrodeless thruster, MNs are proposed as next-generation electric propulsion system due to its advantages in terms of lifetime and economic efficiency of the device without erosion of generation and acceleration electrode [12][13][14][15][16]. Accordingly, there has been a significant interest in the MN to elucidate the physics of plasmas expanding in divergent magnetic fields for electric propulsion systems and laboratory plasmas [17][18][19][20][21][22][23][24][25].…”

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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“…Hence an investigation of interrelation between the solar wind and laboratory plasmas can contribute to a better interpretation of the physics for both systems. Electrons in magnetically expanding low-pressure plasmas (Takahashi et al 2009;Boswell et al 2015) and in the solar wind share the following similarities: (1) they are confined along magnetic field lines; (2) they are nearly collisionless, due to the long mean free path in the lowpressure condition;…”

Section: Introductionmentioning

confidence: 99%

A Polytropic Model for Space and Laboratory Plasmas Described by Bi-Maxwellian Electron Distributions

Zhang

Charles

Boswell

2016

ApJ

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Non-local electron energy probability functions (EEPFs) are shown to have an important effect on the thermodynamic behavior of plasmas in the context of solar wind and laboratory plasmas. A conservation relation is held for electron enthalpy and plasma potential during the electron transport. For an adiabatic system governed by non-local electron dynamics, the correlation between electron temperature and density can be approximated by a polytropic relation, with different indexes demonstrated using three cases of bi-Maxwellian EEPFs. This scenario differs from a local thermodynamic equilibrium having a single polytropic index of 5/3 for adiabaticity.

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Non-local electron energy probability function in a plasma expanding along a magnetic nozzle

Cited by 35 publications

References 15 publications

Helicon-type radiofrequency plasma thrusters and magnetic plasma nozzles

Helicon-type radiofrequency plasma thrusters and magnetic plasma nozzles

Thermodynamics of a magnetically expanding plasma with isothermally behaving confined electrons

A Polytropic Model for Space and Laboratory Plasmas Described by Bi-Maxwellian Electron Distributions

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