Consideration of Secondary Electron Emission Effect for Probe Measurement

Tawaraya, Takehito; Tsushima, A.; Yoshimura, S.

doi:10.1143/jjap.51.096101

Cited by 2 publications

(2 citation statements)

References 23 publications

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“…However, for a Maxwellian distribution of the electrons, it does not depend on sheath potential, but is usually a function of the electron temperature. [2,7,28] By using the Sternglass formula e ( ) = m m exp(2 − 2 √ ∕ m ), [29] where m is the maximum of e , and m is the characteristic energy corresponding to m , eff can be expressed as, [28]…”

Section: Sheath Modelmentioning

confidence: 99%

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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Section: Sheath Modelmentioning

confidence: 99%

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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“…In general, the problem should be solved with the kinetic approach, but this aspect is not yet addressed in the present paper. Experimental findings in the laboratory indicate that the actual values of δ eff do not depend on φ 0 , but are usually a function of the electron temperature T [27,28] .…”

Section: Model For Secondary Electron Emissionmentioning

confidence: 99%

Plasma Wall Potentials with Secondary Electron Emissions up to the Stable Space-Charge-Limited Condition

Seon¹,

Lee²

2013

Plasma Sci. Technol.

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Numerical solutions to floating plasma potentials for walls emitting secondary electrons are obtained for various surface materials. The calculations are made with plasma moment equations and the secondary electron emission coefficients, which were determined from recent laboratory experiments. The results estimate the wall potentials up to the physical conditions that allow stable plasma sheaths under the space-charge-limited condition. The materials often used in the laboratory, such as aluminum, silicon, boron, molybdenum, silicon dioxide, and alumina, are considered. The minimum wall potential before the onset of space-charge-limited emission is determined by the electron temperatures at which the effective secondary electron emission coefficient integrated over the velocity distributions is about 0.62. The corresponding potential is given by −eφ0 ∼ 1.87kBT. The condition for space-charge-limited emission is newly found by numerically searching for all the stable sheaths. The new condition is −eφ0 ∼ 0.95kBT , and this predicts a wall potential that is less negative than the previously found one. Calculation of the power dissipated to the wall for hydrogen plasmas shows that there is a large difference in terms of power dissipation among the considered materials in the temperature range 20∼50 eV.

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Consideration of Secondary Electron Emission Effect for Probe Measurement

Cited by 2 publications

References 23 publications

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

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

Plasma Wall Potentials with Secondary Electron Emissions up to the Stable Space-Charge-Limited Condition

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