Particle Source (TRK) - Thermionic Emissson

Simulation: Sources and LoadsParticle SourcesParticle Source on PECThermionicEdit
Simulation: Sources and LoadsParticle SourcesParticle Source on any SurfaceThermionicEdit
Simulation: Sources and LoadsParticle SourcesParticle Point SourceThermionicEdit
Simulation: Sources and LoadsParticle SourcesParticle Circular SourceThermionicEdit

The parameters for the thermionic emission model can be changed within this dialog box. A detailed model description can be got from the particle emission model overview page.

The Thermionic Emission model is subdivided into two parts:

Space charge emission.
Thermionic emission, based on the Richardson-Dushman equation.

Both emission models are calculated during the emission process. The emission model (SCL or Thermionic) with lowest emission current is finally used for the simulation.

Thermionic Emission:

The Thermionic Emission model does not calculate an initial momentum for the particles. The initial momentum has to be defined within the "Kinetic Settings" section of this dialog box.

p_emission = p_{kinetic
setting}

Space Charge Limited Emission:

The SCL Emission model automatically calculates an initial momentum for the particles. The momentum of the "Kinetic Settings" section is added to the initial momentum of the emission model.

p_emission = p_scl-model + p_{kinetic setting}

Kinetic settings

Kinetic type
Select the kinetic type for further emission properties such as the Kinetic Value (see also Kinetic Particle Settings):
Velocity, Beta, Gamma, Normed Momentum, Energy, Temperature

Distribution
Select if the kinetic settings should be Maxwellian or uniformly distributed.

Kinetic value
The kinetic start value of the emitted particles. See also the Kinetic Particle Settings page.

Kinetic spread
The energy spread (from 0 to 200 percent) offers the possibility to specify a randomly calculated emission energy. The kinetic emission type (e.g. energy, momentum) is calculated uniformly distributed in the range of:

Angle spread
Determines the maximal deviation between the particle's start angle and the plane's normal. The emitting angle is randomly chosen within the range between 0 and the given start angle limit. See also the Kinetic Particle Settings page.

Temperature
The temperature is used to specify the Maxwell-Boltzmann distribution.

Distribution bins
Specifies the number of different temperature levels within the Maxwell-Boltzmann distribution.

Thermionic emission

Temperature

Specifies the temperature of the source's surface.

Work function

Work function (in eV) for the particles from the emitting material into vacuum (band gap between emitter and vacuum). For example, the work function of Tungsten equals 4.54eV.

Richardson constant

Specifies the material constant, i.e. the linear factor of the Richardson-Dushman equation.

Calculate Richardson constant

Determines the material constant depending on the solid state parameters.

Space charge limited emission

Enable additional kinetic settings

Enable the additional settings mentioned above to increase/modify the emission energy.

Emit. potential

The potential of the emitting surface is called emitting potential. If the emitting potential is not one of the predefined potential values, choose "User defined" and enter the potential value under "Emit. potential value".

Ref. potential

Specifies the reference potential (for electron guns usually the anode's potential). If the reference potential is not one of the predefined potential values, choose "User defined" and enter the potential value under "Ref. potential value".

Virtual cathode

Specifies the distance of the emitting surface to the virtual emitting surface. Note that the virtual emitting surface is only considered for Child-Langmuir based space charge limited emission. The value represents a scaling factor which describes the virtual gap distance as a multiple of the maximal emitting mesh cell's diagonal length.

value to enter in the dialog box: dvirtual gap factor
diagmax = max ( diag( emission cells ) )
dvirtual gap = dvirtual gap factor diagmax

Preview

By pressing the Preview button one can get a visualization of the virtual cathode distance:

The calculated virtual gap distance in meter is written to the solver log-file.

Confirms the changes and closes the dialog box.

Cancel

Closes this dialog box without performing any further action.

Help

Shows this help text.