simpleSec

This particle source is an implementation of a simplified secondary electron emission model. This model emits exactly zero or one electron macroparticle for each incident (primary) macroparticle that is absorbed. The primary particle can be an electron species or an ion species.

If the primary macroparticle is constant weight, then a single secondary electron macroparticle with the same weight is emitted with a probability p specified by the emissionProb attribute, and the primary is simply absorbed with probabilty 1.0 - p.

If the primary macroparticle is variable weight, then a single (variable weight) secondary electron macroparticle is always emitted, with a weight equal to the primary particle’s weight multiplied by emissionProb.

When the ptclAbsorber is a gridBoundary, the secondary electron macroparticle is emitted from the surface in the direction such that it’s velocity tangential to the surface is unchanged, but the normal component is reversed (specular emission). If the ptclAbsorber is defined on a slab instead of on a gridBoundary, then the emission direction is selected by the setting of the direction attribute to be the outward-facing normal (eg. pointing out of the simulation domain) and secondary electron emission will be along the negative of this direction.

The energy (in Joules) of an emitted secondary electron macroparticle is specified by the emittedEnergy attribute if the attribute randomEnergy=0. If the attribute randomEnergy=1, then the emitted energy is uniformly distributed in the range [0, emittedEnergy]. The attribute randomEnergy defaults to 0.

Secondary electron emission may be suppressed by suppressEnergy, which may be set to an arbitrarily high number if emission is always required regardless of local field.

Note

To emit particles in a different species than the primary impacting species, include the simpleSec ParticleSource block in the secondary species and reference the ptclAborber from the primary species. For example: ptclAbsorber = electrons.topAbsorber

This kind of particle source is available with a VSimMD or VSimPD license.

simpleSec Parameters

ptclAbsorber (string, required):
Name of the particle absorber that absorbs the primary incident particles, and from which the secondaries will be emitted. The absorber must be of kind = absAndSav.
emittedEnergy (float, required):
The energy in Joules of the emitted electrons or the top of the range of energies if randomEnergy is set to 1.
randomEnergy (boolean, optional):
If randomEnergy is set to 1, the ParticleSource will emit the secondary electrons with a uniformly distributed random energy between 0 and the energy given in the input file from the emittedEnergy parameter.
suppressEnergy (float, optional):

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.

emittingSurface (string, optional):
The physical position of the emitting surface in the direction of emission
direction (float vector, optional):
A vector denoting the normal pointing out of the simulation domain (eg into the metal or domain edge), i.e., away from the direction of emission from the emittingSurface. direction is ignored if the ptclAbsorber is a gridBoundary.
gridBoundary (string, optional):
Only necessary if the ptclAbsorber is on a gridBoundary. The name of the gridBoundary used in the ptclAbsorber must also be specified in the ParticleSource block.
emissionProb (float, required):
The probability that a single secondary electron macroparticle is emitted for constant weight primary particles. The fraction of the primary macroparticle weight that the emitted secondary electron macroparticle will have for variable weight particles.

Example simpleSec Block to emit secondary electrons in the same Species as the primary electrons

<ParticleSource simpleSecondaryEmitter>
  kind = simpleSec
  emissionProb = 0.25
  ptclAbsorber = cutcellBndry
  gridBoundary = plane
  emittedEnergy = EMIT_ENERGY
</ParticleSource>

Example simpleSec Block to emit secondary electrons in a different Species as the primary electrons

<Species electrons>
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<ParticleSink topAbsorber>
  kind = absAndSav
  minDim = 2
  lowerBounds = [0  NY  0]
  upperBounds = [NX NY1 NZ]
</ParticleSink>
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</Species>


<Species secondaryElectrons>
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<ParticleSource simpleSecondaryEmitter>
  kind = simpleSec
  emissionProb = 0.5
  ptclAbsorber = electrons.topAbsorber
  emittedEnergy = EMIT_ENERGY
  direction= [0. 1. 0.]
  emittingSurface = $YSTART + LY-0.5*DY$
</ParticleSource>
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</Species>