protonImpactIonization

Proton Impact Ionization

Works with a VSimPD license. Collision of the form

\[H^+ + B \rightarrow H^+ + B^+ + e\]

Any RxnProcess Block block which points to a productGenerator of kind = protonImpactIonization should have the Reactants and Products in the order

reactants = [impactingProton speciesLosingElectron]
products = [impactingProton ionizedSpecies Electron]

The ionized species will maintain the same velocity as the species losing the electron, and the balance of energy will be subtracted from the impacting proton only. The Electron is emitted isotropically (in the lab frame) with an energy distribution given by Eq.1 in M. Rudd, “User-Friendly Model for the Energy Distribution of Electrons from Proton or Electron Collisions.” Nuclear Tracks and Radiation Measurements, Vol.16, No 2/3, pp. 213-218, 1989. The differential cross-section, essentially the energy probability distribution, is given by:

\[\sigma(\omega) = \frac{S}{I} \frac{F_1 + F_2\omega}{(1 + \omega^3) [1 + \exp{\alpha(\omega - \omega_c) / \nu}]}\]

where \(I\) is the ionization energy, \(\omega=W/I\) is the reduced emitted electron energy, \(\omega_c\) is the kinematic cutoff energy, \(\nu\) is the reduced proton speed, and \(S, F_1, F_2, \alpha\) are fitting parameters which depend on the target neutral species and proton energy. Fig. 150 shows a sample electron energy distribution from a 65keV proton beam impacting neutral H2 gas.

../_images/protonImpactElectronDist.png — Fig. 150 Emitted electron energy distribution for a 65keV proton beam impacting hydrogen gas

protonImpactIonization Attributes

neutralSpeciesType (string, optional, default = H2): The neutral species, which can be a kinetic species or a neutral fluid. The only currently supported type is H2.

Example protonImpactIonization Block

<RxnProductGenerator productGenerator>
  kind = protonImpactIonization
  #neutralSpeciesType = H2
</RxnProductGenerator>