impactExcitation

impactExcitation

Works with VSimPD license.

This kind MonteCarlo interaction models electron-impact excitation collisions with a background neutral gas. In this collision, the incident electron first loses the energy corresponding to the excitation energy threshold and is scattered after the collision. The scattered electron energy is given by:

\[\epsilon_{sc} = \epsilon_{inc} - \epsilon_{ex}\]

where \(\epsilon_{inc}\) and \(\epsilon_{ex}\) are the incident electron energy and the excitation threshold energy, respectively. For a user defined cross section with an OAFunc function, the excitation threshold energy must be explicitly specified in the input file through the excitationThreshold parameter, otherwise Vorpal uses the threshold limit from the EEDL data set.

The final direction of the incident electron is given by the scattering angle X defined as:

\[\cos \chi = \frac{2 + \epsilon_{sc} - 2(1+\epsilon_{sc})^{R_1} }{ \epsilon_{sc} }\]

and the azimuthal angle \(\varphi = 2 \pi R_2\). In the above equations \(R_1\) and \(R_2\) are two random numbers uniformly distributed between 0 and 1.

Note

This feature replaces the impactExcitation feature previously implemented in Vorpal ionization.

impactExcitation Parameters

crossSection (string, required)

Cross section to be used in the interaction. Possible values are builtIn, eedl, and functionDefined. See below for required parameters for each choice.

impactSpecies (string, required)

Name of the incident particles described by a species block in the input file.

neutralGas (string, required)

Name of the Fluid block describing the background neutral gas. For more information on the kinds of allowed neutral Gases, please see Working with neutralGas Fluids and the gasKind Parameter.

neutralGasTemp (real, optional, default = 300.)

Temperature of the background neutral gas in Kelvin. This parameter is used to determine the incident ion velocity relative to the neutral gas atoms and the final ion velocity.

isNeutralGasFluid (string, optional, default = true)

Defines whether the neutral gas tracked is a fluid background or not. The default is true, i.e. the neutral gas is fluid. When this option is false, the kinetic neutral species and its gas type must be defined using inNeutrals and inNeutralsGasType.

inNeutrals (string)

Name of the impact kinetic neutral particle described by a species block in the input file. This attribute is required when isNeutralGasFluid is set to false.

inNeutralsGasType (string)

Type of the impact kinetic neutral gas particle. This attribute is required when isNeutralGasFluid is set to false.

depleteBackgroundGas (string, optional, default =  true)

A flag to modify the background fluid gas density when performing the interaction.

leaveIncidentUnchanged (bool, optional, default = false)

When enabled, this parameter leaves the impact (incident) particle unchanged after the collision is processed. This is helpful when the scattering effect of the incident particle is treated as a bulk effect, such as in the nullBgAbsorber.

force1D (integer, optional, default = 0)

Force the interaction to occur in 1D, i.e. the scattered angle of the electron after the interaction is always 0.

excitationThreshold (real)

The excitation threshold energy (in eV). To be set in the case the cross section is user defined with an OAFunc block. This value is used to determine the scattered electron energy in the excitation collision.

excAtomSpecies (string)

Name of the excited atom species, product of the excitation of an atom of the background neutral gas. To track the excited atom as separate species, this string must be included in the Interaction block. By ignoring this parameter makes the interaction not to track the excited atom in simulation.

builtIn Parameters

Please see Types of collisions for the available builtIn gases.

eedl Parameters

If the eedl cross section type is used, the following parameters must be set:

crossSectionDataFile (string)

Points to the file containing the EEDL data.

functionDefined Parameters

If the functionDefined cross section type is used, the following parameters must be set:

OAFunc (block, required)

An OAFunc block of name crossSectionFunc must be used inside the Interaction block. The OAFunc block allows the user to define its own cross section for the interaction, either through a two-column data file or through an expression. The kinds of OAFunc available for this interaction are interpolatedFromFile, LXcatFile, or expression. The OAFunc must return the value of the cross section in m².

Please see OAFunc Block for more information on the OAFunc block.

crossSectionVariable (string, optional, default = energy)

Used in the case when an OAFunc function is given for the cross section to specify whether the parameter of the function is either the:

• Relative collision velocity magnitude of the incident particle in m^-1: crossSectionVariable = velocity

• Kinetic energy of the incident particle in eV: crossSectionVariable = energy

Example impactExcitation Block

<Interaction CuExcitation>
  kind = impactExcitation
  neutralGas = CuNeutralGas
  impactSpecies = electrons
  crossSection = eedl
  crossSectionDataFile = eedlCu.dat
</Interaction>