secElec

secElec

This kind of ParticleSource algorithm allows Vorpal to model the generation of secondary electrons being produced by impact with electrons or ions on metal surfaces.

For electrons, the determination of number, energy spectrum, and angular distribution of these secondary electrons can be found in [FP02a].

When the incident particles are ions, secondary electron emission and neutral desorption yields are calculated due to ion-target interactions. The secondary electron yield for most models depends on the projectile energy and angle of incidence, and the target material. Ion-induced secondary electron emission is proportional to electronic stopping, so stopping power \(dE/dx\) is calculated to compute secondary electron yields. Similarly, neutral desorption depends on nuclear stopping powers. The stopping power calculation is appropriate for both cold solids and dense plasmas, and is comprised of contributions from bound electrons, free electrons, and nuclear collisions. Further details are provided in [SVC+06].

Note

When dealing with incident particles of electrons, to emit secondary electrons in a different species than the primary impacting electrons, include the secElec ParticleSource block in the secondary species and reference the ptclAbsorber from the primary species. For example: ptclAbsorber = primaryElectrons.topAbsorber

Note

When dealing with incident particles of ions, there are two ways to emit secondary electrons in a different species.

1) Include the secElec ParticleSource block in the secondary species and reference the ptclAbsorber from the primary species. For example: ptclAbsorber = primaryIons.topAbsorber

2) Include the secElec ParticleSource block in the primary ion species and use the parameter secondarySpecies to reference the secondary species. This parameter ONLY works for incident ions. For example: secondarySpecies = electrons

This particle source is available with a VSimVE or VSimPD license.

secElec Parameters

ptclAbsorber (string, required)

Name of the absorber that absorbs the electrons and from which the secondaries will be emitted.

material (string, optional, default = copper)

When using electrons as the incident particle, material choices are one of:

• copper

• stainless (stainless steel)

When the incident particle is an ion, the choices are:

• hydrogen

• helium

• carbon

• nitrogen

• oxygen

• sodium

• aluminum

• silicon

• phosphorus

• argon

• iron

• nickel

• copper

• silver

• gold

• uranium

• air

• water

• stainless (stainless steel)

direction (vector, optional)

Direction vector should point along the outward-facing normal of the ParticleSource.

emissionProb (real, optional)

Specifies the probability for emission of secondaries from a material surface. For the constant probability model, a single electron is emitted with a given probability independent of all other factors, such as the incident energy, material and primary ion properties, etc.

ptclCountType (string, optional, default = emitCounting)

Describes how the emission of multiple secondary electrons is handled. This parameter is optional, and defaults to emitCounting. Valid types are:

• emitCounting (default)

  Emit multiple macroparticles.

• noCounting

  Emit single particle.

• vwCounting

  Emit single variable-weight particle and increase its weight by the number of secondaries.

• taggedVwCounting

  Emit single variable-weight, tagged particle and increase its weight by the number of secondaries.

emittingSurface (float, optional)

Physical position of the emitting surface in the direction of emission. If this parameter is not specified, it is calculated to be the appropriate edge of the grid. It is ignored when emitting from a grid boundary.

secondarySpecies (string, optional)

This parameter is only valid for primary ions and will be ignored if primaries are electrons. secondarySpecies sets the electron species to emit the secondaries into.

suppressEnergy

By default, emission does not occur if the electric field has sign that would immediately force the emitted particle back into the surface (default value is suppressEnergy=0). This parameter can be used to control this feature. If an emitted particle is desired, regardless of the sign of the electric field, then set this parameter to a very large number, e.g., suppressEnergy=1.0e32.

More specifically, emission occurs when the particle charge, times the local field strength, times a characteristic length based on the grid, e.g., q*E*dx, is less than the suppressEnergy. The local field strength is interpolated on the emission surface. In higher dimensions, the characteristic length is the diagonal across the cell. The units of the suppressEnergy are electronVolts.

ignoreProb (float, default = 0)

Float value representing probability to ignore an absorbed electron so it can be used for another process. This should be a value between 0 and 1.

gridBoundary (string)

If the particle absorber is on a gridBoundary, the name of the gridBoundary used by that particle absorber must also be specified in the ParticleSource block.

Example secElec Block

<ParticleSource leftSecondaryEmitter>
    kind = secElec
    minDim = 1
    ptclAbsorber = primaries.leftAbsorber
    direction = [-1. 0. 0.]
    material = copper
</ParticleSource>