negativeIonDetachment

negativeIonDetachment

Works with VSimPD license.

This kind of MonteCarlo interaction models electron detachment from a negative ion impact collision with a background neutral gas. In this kind of collision, the incident negative ion loses the electron and becomes a neutral particle. The detached electron’s energy is calculated with two options. Option 1 (the default) uses the relation given in Reiser’s book [Rei08]:

\[T_{e} = \frac{2.}{3.0} \sqrt{\frac{T_{inc}T_{thr}}{m_{ratio}}}\]

where:

\(T_{e}\) the detached electron energy in eV

\(T_{inc}\) the incident negative ion energy in eV

\(T_{thr}\) the threshold energy in eV (~15.0 eV rough estimate)

\(m_{ratio}\) the mass ratio of incident ion and electron which is given by:

\[m_{ratio} = \frac{m_{ion}}{m_e}\]

In option 2, the detached electron energy is given by the energy specified by the user in the input block. This option is enabled when the attribute useThermalDist is set to 1 in the Interaction block. The detached electron velocity is set based on the mean velocity vbar and the width of the electron thermal velocity distribution vsig.

negativeIonDetachment Parameters

crossSection (string, required)

cross-section to be used in the interaction. Possible values are builtIn, 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.

detachmentThreshold (real, optional, default = 0.0)

Negative ion threshold energy (in eV) for detachment reaction.

detachedElectronSpecies (string, required)

Name of the detached electron species, product of the ion detachment reaction.

detachedNeutralSpecies (string, optional)

Name of the neutral species. If this is not set then the neutral species resulting from electron detachment is not tracked.

crossSecScaleFactor (real, optional, default = 1.0)

A factor to scale the cross-section values.

useThermalDist (integer, optional, default = 0)

A flag to turn-on thermal distribution energy for detached electrons. If this flag is not set, then the electron energy value is based on the expression given by Reiser’s book.

vbar (real, required)

Mean value of the electron thermal-distribution energy. This parameter is required when useThermalDist flag is set to 1.

vsig (real, required)

Widths of detached electron thermal energy. This parameter is required when useThermalDist flag is set to 1.

builtIn Parameters

The cross-section data for these interactions are based on ORNL’s Atomic Data for Fusion [BHF+90].

Please see Types of collisions for the available builtIn gases.

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 negativeIonDetachment Block

<Interaction HminusIonDetachment>
  kind = negativeIonDetachment
  neutralGas = H2NeutralGas
  impactSpecies = Hminus
  crossSection = builtIn
  detachedElectronSpecies = electrons
  detachedNeutralSpecies = Hneutral
  detachmentThreshold = 0.75
</Interaction>