A Fluid Model of the Sheath Formation in Front of an Electron Emitting Electrode with Space Charge Limited Emission Immersed in a Plasma that Contains a One‐Dimensional Mono‐Energetic Electron Beam

Gyergyek, T.; Kovačič, J.; Čerček, M.

doi:10.1002/ctpp.201010026

Cited by 13 publications

(19 citation statements)

References 35 publications

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“…This result has been observed for collecting Langmuir sheaths 32,33 and predicted for emissive sheaths using fluid theory. 34 As the emitted electron temperature is increased, the sheath potential drops slightly at first, though still remaining close to the beam energy. The increased emitted electron temperature increases the emitted electron flux.…”

Section: Maxwellian Plasma With Electron Beammentioning

confidence: 97%

Effects of emitted electron temperature on the plasma sheath

et al. 2014

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It has long been known that electron emission from a surface significantly affects the sheath surrounding that surface. Typical fluid theory of a planar sheath with emitted electrons assumes that the plasma electrons follow the Boltzmann relation and the emitted electrons are emitted with zero energy and predicts a potential drop of 1.03Te/e across the sheath in the floating condition. By considering the modified velocity distribution function caused by plasma electrons lost to the wall and the half-Maxwellian distribution of the emitted electrons, it is shown that ratio of plasma electron temperature to emitted electron temperature significantly affects the sheath potential when the plasma electron temperature is within an order of magnitude of the emitted electron temperature. When the plasma electron temperature equals the emitted electron temperature the emissive sheath potential goes to zero. One dimensional particle-in-cell simulations corroborate the predictions made by this theory. The effects of the addition of a monoenergetic electron beam to the Maxwellian plasma electrons were explored, showing that the emissive sheath potential is close to the beam energy only when the emitted electron flux is less than the beam flux.

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Section: Maxwellian Plasma With Electron Beammentioning

confidence: 97%

Effects of emitted electron temperature on the plasma sheath

et al. 2014

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“…For aerospace applications, measurements of the plasma potential enable the deduction of the electric field that accelerates ions and heats electrons in plasma thrusters and their plumes [7]. Although the potential can be measured with Langmuir probes in some plasmas, these techniques fail in many circumstances, such as in the presence of flowing plasma typical for aerospace applications, and are subject to large uncertainties, such as in the presence of magnetic fields [5,[8][9][10]. Energy analyzers or laser-induced fluorescence can be used to determine ion velocities [11], which can be used to deduce the plasma potential.…”

Section: Introductionmentioning

confidence: 99%

Recommended Practice for Use of Emissive Probes in Electric Propulsion Testing

Sheehan

Raitses

Hershkowitz

et al. 2017

Journal of Propulsion and Power

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This article provides recommended methods for building, operating, and taking plasma potential measurements from electron-emitting probes in electric propulsion devices, including Hall thrusters, gridded ion engines, and others. The two major techniques, the floating point technique and the inflection point technique, are described in detail as well as calibration and error-reduction methods. The major heating methods are described as well as the various considerations for emissive probe construction. Special considerations for electric propulsion plasmas are addressed, including high-energy densities, ion flows, magnetic fields, and potential fluctuations. Recommendations for probe design and operation are provided.

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“…and that all the emitted electrons leave the wall with the negligible initial velocity, though their initial velocity may influence the sheath. [4,9] Then the energy of the emitted electrons in the sheath can be written as,…”

Section: Sheath Modelmentioning

confidence: 99%

“…The characteristics of a plasma sheath located between a plasma and a material surface play an important role in the plasma heat flow to the material surface during plasma-wall interaction. Several key factors influence the sheath structure, including electron emission, [1][2][3][4][5][6][7][8][9][10][11] magnetic field, [11][12][13][14][15] ion temperature, [13][14][15] and collision. [15][16][17] The most important one is the electron emission from plasma-wall interaction.…”

Section: Introductionmentioning

confidence: 99%

“…The investigation of the plasma sheath in the presence of secondary electron emission (SEE) has been carried out based on several models. [1][2][3][4][5][6] However, many models consider cold ions, whereas the effect of ion temperature has not been studied systematically. For the edge plasma in fusion devices, the ion temperature is comparable to or higher than the electron temperature.…”

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confidence: 99%

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Heat flow through a plasma sheath in the presence of secondary electron emission from plasma‐wall interaction

Zhao

2017

Contributions to Plasma Physics

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KEYWORDSenergy transmission coefficient, plasma sheath, secondary emission electron, sputtering yield INTRODUCTIONThe characteristics of a plasma sheath located between a plasma and a material surface play an important role in the plasma heat flow to the material surface during plasma-wall interaction. Several key factors influence the sheath structure, including electron emission, [1][2][3][4][5][6][7][8][9][10][11] magnetic field, [11][12][13][14][15] ion temperature, [13][14][15] and collision. [15][16][17] The most important one is the electron emission from plasma-wall interaction. It greatly reduces the sheath potential so that the thermal insulation may become substantially low because the potential drop across the sheath is a potential barrier for the incoming plasma electrons. The emission electron flux through the sheath may be regulated by the space-charge-limited (SCL) effect. The investigation of the plasma sheath in the presence of secondary electron emission (SEE) has been carried out based on several models. [1][2][3][4][5][6] However, many models consider cold ions, whereas the effect of ion temperature has not been studied systematically. For the edge plasma in fusion devices, the ion temperature is comparable to or higher than the electron temperature. [18][19][20][21] In addition, it is shown from sheath model results that the ion temperature influences the sheath properties. [13][14][15] Since the ion temperature in the tokamak edge region is important for the estimation of heat flux flowing to material surface and modelling plasma-wall interaction processes including impurity sputtering, [19] here we describe a plasma sheath with thermal ions in the presence of SEE. When heat flows through the plasma sheath, the sheath energy transmission coefficient , defined as the energy flux normalized by the particle exhaust flux times the electron temperature at the sheath entrance, [22] is used to estimate the energy flux flowing to the target plate in fusion device experiments and to provide boundary conditions in fusion plasma edge fluid codes.increases when SEE is taken into account or as the ion temperature is increased for a given SEE coefficient. [23] Another important physical process affected by the sheath structure is impurity production. Intrinsic impurities (e.g., Be, C, Mo, and W) are produced through erosion during the energy load on the plasma-facing material. The impurity sputtering yield depends

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A Fluid Model of the Sheath Formation in Front of an Electron Emitting Electrode with Space Charge Limited Emission Immersed in a Plasma that Contains a One‐Dimensional Mono‐Energetic Electron Beam

Cited by 13 publications

References 35 publications

Effects of emitted electron temperature on the plasma sheath

Effects of emitted electron temperature on the plasma sheath

Recommended Practice for Use of Emissive Probes in Electric Propulsion Testing

Heat flow through a plasma sheath in the presence of secondary electron emission from plasma‐wall interaction

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