Plasma Model
Use the Plasma Model node to set the electron transport properties, material properties, and model inputs.
Model Inputs
This section has fields and values that are inputs to expressions that define material properties. If such user-defined property groups are added, the model inputs display here. Initially, this section is empty. The input depends on which Transport Settings are selected in the Plasma interface.
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Enter a Temperature T (SI unit: K) for the gas mixture used to compute the gas density and species transport properties.
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Enter an Absolute pressure pA (SI unit: Pa) to compute the gas density and the Maxwell–Stefan diffusivities.
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If the Convection check box is selected, enter coordinates for the Velocity field u (SI unit: m/s).
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If the Compute tensor electron transport properties or the Compute tensor ion transport properties property is activated enter an expression for the Magnetic flux density B (SI unit: T). This usually comes from a magnetostatic model, and is used to compute anisotropic transport properties for electrons and ions.
If Global is selected in Diffusion model this section has the following fields:
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Enter the temperature of the background gas in Temperature T (SI unit: K).
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If the Reactor type is set to Closed reactor or Constant mass enter an Initial pressure p0 (SI unit: Pa). If the Reactor type is set to Constant pressure enter an Absolute pressure pA (SI unit: Pa).
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Enter an Absolute electron Flux |Γe| (SI unit: 1/(m2.s)) if there are reaction rate constants defined using Townsend coefficient.
Electron Density and Energy
Select an option from the Electron transport properties list — Specify mobility only (the default), From electron impact reactions, From electron energy distribution function, Specify all, Use lookup tables, or Mobility from electron energy distribution function.
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The options available depend on whether the Use reduced electron transport properties physics interface property is selected and on what option is selected for Electron energy distribution function property. If the physics interface property Compute tensor electron transport properties is selected then only one field appears for the DC or reduced DC electron mobility, μdcNn. The other transport properties are computed using Einstein’s relation. The option From electron energy distribution function is only available if Maxwellian, Druyvesteyn, or Generalized are selected. The option Mobility from electron energy distribution function is only available when the Boltzmann equation, two-term approximation (linear) or Boltzmann equation, two-term approximation (quadratic) are selected.
Tensor Transport Properties
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For Specify mobility only enter a value or expression for the Electron mobility μe (SI unit: m2/(V·s)). Select Isotropic, Diagonal, Symmetric, or Anisotropic based on the model. The electron diffusivity, energy mobility and energy diffusivity are automatically computed using Einstein’s relation for a Maxwellian EEDF:
(6-2)
For Use reduced electron transport properties enter the Reduced electron mobility μeNn (SI unit: 1/(V·m·s)). The actual electron mobility is then computed by dividing the reduced electron mobility by the neutral number density.
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With From electron impact reactions the electron mobility is computed from
(6-3)
where ν is the total electron collision frequency computed from
(6-4)
where rj (unit: mol/(m3·s)) is a reaction rate, ce (unit: mol/m3) is the electron molar concentration, and the sum is over all electron impact collisions. The electron diffusivity, energy mobility and energy diffusivity are automatically computed using Einstein’s relation for a Maxwellian EEDF:
(6-5)
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With From electron energy distribution function the electron transport properties are computed directly from the EEDF using the following:
(6-6)
(6-7)
(6-8)
(6-9)
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For Specify all enter values or expressions for all of the properties, which can be either scalars or tensors. The appropriate values for the transport properties can be computed with The Boltzmann Equation, Two-Term Approximation Interface. For all of the properties, select Isotropic, Diagonal, Symmetric, or Anisotropic from the list based on the model, then enter values or expressions for all of these properties:
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Electron mobility μe (SI unit: m2/(V·s))
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Electron diffusivity De (SI unit: m2/s)
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Electron energy diffusivity Den (SI unit: m2/s)
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Electron energy mobility μen (SI unit: m2/(V·s))
For Use reduced electron transport properties enter:
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Reduced electron mobility μeNn (SI unit: 1/(V·m·s))
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Reduced electron diffusivity DeNn (SI unit: 1/(m·s))
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Reduced electron energy diffusivity DenNn (SI unit: 1/(m·s))
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Reduced electron energy diffusivity μenNn (SI unit: 1/(V·m·s))
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For Use lookup tables enter or load a lookup table with the transport properties as listed above versus mean electron energy (eV).
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With Mobility from electron energy distribution function the electron mobility is computed directly from the EEDF using
(6-10).
The electron diffusivity, energy mobility and energy diffusivity are computed using Einstein’s relation
(6-11)
See the Theory for the Boltzmann Equation, Two-Term Approximation Interface for more information.
 
For the Use reduced electron transport properties physics interface property, the appropriate values for the transport properties can be computed with The Boltzmann Equation, Two-Term Approximation Interface and written out to a text file. The text file can then be loaded in for each electron transport property.
Mean electron energy specification
This section is available when the Mean electron energy is set to Local field approximation and if Maxwellian, Druyvesteyn, or Generalized are selected from the Electron energy distribution function property. Select how to provide the relation between the reduce electric field and the mean electron energy from the Specify using list — Expression or Use lookup table.
If Global is selected in Diffusion model enter an Electric potential V (SI unit: V) used to compute the reduced electric field.
Density
Select an option from the Mixture density list — Ideal gas or User defined. For User defined enter a value for ρ (SI unit: kg/m3).
For Ideal gas it computes the expression for the gas density automatically using the ideal gas law, based on the composition of the mixture. The density is a function of the mean molecular weight:
where pA is the absolute pressure, T is the temperature, R is the universal gas constant and M is the mean molecular weight given by:
Total Mass flow
If Global is selected in Diffusion model and the Reactor type is set to Constant mass or Constant pressure enter the Number of SCCM units for the reactor feed. The Feed mole fraction of individual species can be set in the Species node ().
Mean electron energy
This section is available if Global is selected in Diffusion model and Mean electron energy is set to Local energy approximation or Fix mean electron energy. If Fix mean electron energy is selected enter the Mean electron energy ε (unit: V). If Local energy approximation is selected:
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Enter the Power absorbed Pabs (SI unit: W) by the plasma.
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The Mean kinetic energy lost per electron lost εe (unit: V).
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The Mean kinetic energy lost per ion lost εi (unit: V).
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The Initial mean electron energy ε0 (unit: V).
EEDF Inputs
This section is available if Global is selected in Diffusion model, Mean electron energy is set to Local field approximation, and Electron Energy Distribution Function is set to Boltzmann equation, two-term approximation (linear) or Boltzmann equation, two-term approximation (quadratic). Enter values or expressions for each of the following:
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Enter the Reduced electric field E/N (SI unit: V·m2) for which the Boltzmann equation in the two-term approximation is solved.
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Enter a EEDF initial mean electron energy ε0 (unit: V) to set the value of the mean electron energy of the Maxwellian EEDF used as initial condition.