Use the Thermionic Emission node to model the release of electrons from a hot cathode. The properties specified in the Particle Properties node should be appropriate for electrons, that is, a mass of me_const and a charge number of −1.

Go to Release for information about the following sections: Released Particle Properties, Initial Value of Auxiliary Dependent Variables, and Advanced Settings.

Enter a value or expressions for the Temperature T (SI unit: K) of the cathode. If the temperature is computed by another physics interface then it can be selected from the list.

Enter a value or expression for the Metal work function Φ (SI unit: V). The default expression is 4.5 V.

Enter a value or expression for the Effective Richardson constant A∗ (SI unit: A/(m2·K2)). The default expression is 110 A/(m2·K2).

Enter a value for the Number of particles per release N (dimensionless). The default is 100.

Enter the Number of particles in velocity space Nvel (dimensionless). The default is 200. This determines the number of particle velocity vectors to sample at each release point. Therefore the total number of particles released by the feature is usually N × Nvel, but may be greater if any auxiliary dependent variables are also sampled from distributions.

The thermionic emission of electrons from the surface follows an axially symmetric probability distribution function of particle velocities that is centered about the surface normal. Select the Reverse direction check box to reverse the direction of the surface normal for the purpose of initializing the particle velocities. This is useful when releasing particles from interior boundaries where the default surface normal might not point into the desired adjacent domain. The surface normals on selected boundaries are indicated by arrows in the Graphics window.

Select an option from the Weighting of macroparticles list: Uniform current (the default), Uniform speed intervals, or Uniform energy intervals. Each model particle released by the Thermionic emission feature is a macroparticle representing a certain number of emitted electrons per unit time.

When Uniform current is selected, each model particle represents the same number of electrons and the initial particle speeds are sampled from a probability distribution function based on a population of electrons following a Maxwell-Boltzmann distribution.

When Uniform speed intervals is selected, particles are sampled from uniform intervals from 0 to a maximum speed, which is expressed in terms of the average thermal energy of the electrons. Specify the Maximum multiple of thermal energy n (default 10).

When Uniform energy intervals is selected, particles are sampled from uniform intervals from 0 to a maximum energy, which is a multiple of the average thermal energy of the electrons. Specify the Maximum multiple of thermal energy n (default 10).

For Uniform speed intervals or Uniform energy intervals each model particle can be weighted differently so that it represents a unique number of electrons per unit time. Particles that are initialized with a more probable initial speed or energy are assigned a greater weight for the purpose of computing charge density on domains and current density at boundaries.