Effect of boundary conditions on the heat flux to the wall in two-temperature modeling of ‘thermal’ plasmas

Pekker, Leonid; Hussary, N.

doi:10.1088/0022-3727/47/44/445202

Cited by 16 publications

(28 citation statements)

References 28 publications

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“…In previous studies of high-pressure plasmas (the plasma pressure is as large as or larger than atmospheric pressure) different sets of boundary conditions at the cathode with thermionic electron emission were constructed disregarding the cathode sheath, see for example local thermodynamic equilibrium models ( = ℎ ) [1 -5] and two temperature ( ≠ ℎ ) models [6 -18] and references therein; is the electron temperature and ℎ is the temperature of heavy particles, ions and neutrals. In recent work [19] the authors constructed sets of boundary conditions at the floating and biased walls for the case of cold walls with no thermionic electron emission or no erosion of the wall. In this work they considered the plasma in a two temperature -----------hydrodynamic approximation, ≠ ℎ , and the plasma sheath formed at the wall as the interface between the plasma and the wall, and used Godyak's collisional sheath model [20,21].…”

Section: Introductionmentioning

confidence: 99%

Boundary conditions at the walls with thermionic electron emission in two temperature modeling of “thermal” plasmas

Pekker

Hussary

2015

Physics of Plasmas

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In this paper we propose new boundary conditions at the hot walls with thermionic electron emission for two-temperature thermal arc models. In the derived boundary conditions the walls are assumed to be made from refractory metals and that the erosion of the wall is small and, therefore, is not taken into account in the model. In these boundary conditions the plasma sheath formed at the electrode is considered as the interface between the plasma and the wall. The derived boundary conditions allow the calculation of the heat flux to the walls from the plasma and consequently the thermionic electron current that makes the two temperature thermal model self consistent.

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Section: Introductionmentioning

confidence: 99%

Boundary conditions at the walls with thermionic electron emission in two temperature modeling of “thermal” plasmas

Pekker

Hussary

2015

Physics of Plasmas

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“…As in [1,2], the following assumption are made in the model: (1) the plasma is considered in twotemperature thermal approximation, ;…”

Section: Collision Sheath Model and Heat Fluxes With Thermionic Ementioning

confidence: 99%

“…Following [1,2] the enthalpy flux from the singly ionized plasma to the wall due to charged particles can be written as ,…”

Section: Collision Sheath Model and Heat Fluxes With Thermionic Ementioning

confidence: 99%

“…In [2], the wall is assumed to be made from refractory metals that the erosion of the wall is small and can be neglected. In [1], the authors used the Godyak collision sheath model [3,4], and in [2] they expanded it to the case of the electron thermionic emission. In both works [1] and [2], the Schottky effect describing the decrease in the work function of the material in a strong electric field was calculated by neglecting the friction of ions in the sheath.…”

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A Sheath Collision Model with Thermionic Electron Emission and the Schottky Correction Factor for Work Function of Wall Material

Pekker

2016

Plasma Chem Plasma Process

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This paper proposes a model that expands Godyak's collisional sheath model to the case of hot electrodes (anode or cathode) with thermionic electron emission. In the model, the electrodes are assumed to be made from refractory metals and, consequently, the erosion of the electrodes is small and can be neglected. In the frame of two temperature thermal plasma modeling, this model allows self-consistent calculation of the sheath potential drop, the Schottky correction factor for the work function of the wall material, the thermionic electron current density, and the heat fluxes of the charged particles from the plasma to the wall. The model is applied to the cathode spot at the tungsten cathode in argon. It is shown that the Schottky correction factor plays a crucial role in modeling high-intensity arcs. It is demonstrated that a virtual cathode can be formed in the atmospheric pressure argon plasma at the cathode surface temperature of 4785 K if the cathode current density is sufficiently small. The heat flux to the thermionic cathode due to charged particles and the heat flux to the plasma due to thermionic electrons are calculated. The model can be reduced to the case of the cold walls where the thermionic electron emission and the wall erosion processes are small and can be neglected. The sheath potential drop and the heat fluxes calculated by this model can be used as boundary conditions at the wall for the electric potential and for the energy equations for the electrons and heavy particles (ions and neutrals). I. IntroductionThe formation of plasma sheath at the wall plays a fundamental role in the heat flux from the plasma to the wall, thermionic electron emission, the structure of the cathode spot and anode attachment, the electrode erosion process, and other electrode process. Therefore, the plasma sheath has to be taken into account in modeling high-pressure thermal arcs (i.e., whenever the plasma pressure is as large as or larger than atmospheric pressure). In recent works [1, 2] the authors constructed boundary conditions at the wall for the electric potential and the electron and heavy particle energy equations in two temperature, , modeling of "thermal" plasmas; is the temperature of electrons and is the temperature of heavy

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“…Including the ionization energy U iz,X + of X + [46] results in the following expression forŪ X + :Ū…”

Section: B Boundary Conditionsmentioning

confidence: 99%

A Global Enhanced Vibrational Kinetic Model for High-Pressure Hydrogen RF Discharges

Averkin

Gatsonis

Olson

2015

IEEE Trans. Plasma Sci.

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A global enhanced vibrational kinetic model (GEVKM) is developed for multitemperature, chemically reacting hydrogen plasmas in inductively coupled cylindrical discharges for low-to high-pressure regimes. The species in a GEVKM are ground-state hydrogen atoms H and molecules H 2 , 14 vibrationally excited hydrogen molecules H 2 (v), v = 1 − 14, electronically excited hydrogen atoms H(2) and H(3), groundstate positive ions H + , H + 2 , and H + 3 , ground-state negative ions H − , and electrons e. The GEVKM involves volume-averaged steady-state continuity equations for the plasma species, an electron energy equation, a total energy equation, a heat transfer equation to the chamber walls, and a comprehensive set of surface and volumetric chemical processes governing vibrational and ionization kinetics of hydrogen plasmas. The GEVKM is verified and validated by comparisons with previous numerical simulations and experimental measurements of a negative hydrogen ion source in the low-pressure (20-100 mtorr), low-absorbed-power-density (0.053-0.32 W/cm 3 ) regime and of a microwave plasma reactor in the intermediate-to high-pressure (1-100 torr), high-absorbed-power-density (8.26-22 W/cm 3 ) regime. The GEVKM is applied to the simulation of a highcurrent negative hydrogen ion source (HCNHIS). The HCNHISconsists of a high-pressure (20-65 torr) radio-frequency discharge chamber in which the main production of high-lying vibrational states of the hydrogen molecules occurs, a bypass system, and a low-pressure (0.1-0.4 torr) negative hydrogen ion production region where negative ions are generated by the dissociative attachment of low-energy electrons to rovibrationally excited hydrogen molecules. The discharge pressure and negative hydrogen ion current predicted by the GEVKM compare well with the measurements in the HCNHIS.

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Effect of boundary conditions on the heat flux to the wall in two-temperature modeling of ‘thermal’ plasmas

Cited by 16 publications

References 28 publications

Boundary conditions at the walls with thermionic electron emission in two temperature modeling of “thermal” plasmas

Boundary conditions at the walls with thermionic electron emission in two temperature modeling of “thermal” plasmas

A Sheath Collision Model with Thermionic Electron Emission and the Schottky Correction Factor for Work Function of Wall Material

A Global Enhanced Vibrational Kinetic Model for High-Pressure Hydrogen RF Discharges

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