The Electric Particle Field Interaction multiphysics coupling () computes the space charge density due to particles and assigns it to a dependent variable that is defined on the domain mesh elements that contain the particles. It also applies the accumulated space charge density as a source when computing the electric potential.

The computation of the space charge density is controlled by the Particle release specification list in the settings window for the Charged Particle Tracing interface. If Specify release times is selected, each particle contributes to the space charge density based on its instantaneous location. If Specify current is selected, each model particle is treated as representing a number of charged particles per unit time, leaving behind a contribution to the space charge density in mesh elements it has previously passed through.

The Label is the default multiphysics coupling name.

The Name is used primarily as a scope prefix for variables defined by the coupling node. Refer to such variables in expressions using the pattern <name>.<variable_name>. In order to distinguish between variables belonging to different coupling nodes or physics interfaces, the name string must be unique. Only letters, numbers, and underscores (_) are permitted in the Name field. The first character must be a letter.

The default Name (for the first multiphysics coupling in the model) is epfi1.

Enter a Charge multiplication factor n (dimensionless). The default value is 1 × 106. If the Particle release specification in the settings window for the Charged Particle Tracing interface is set to Specify release times, the Charge multiplication factor indicates the number of real particles represented by every model particle for the purpose of computing the space charge density.

Select the Use cumulative space charge density check box to enable the following inputs, which are used to accelerate the convergence of models with bidirectionally coupled particle-field interactions.

Enter the Number of iterations β (dimensionless). The default value is 1. During the iterative solver loop set up by the Bidirectionally Coupled Particle Tracing study step, the contribution of the particles to the space charge density will be linearly ramped up for iteration numbers less than β. This improves the probability of stable convergence for models in which overestimation of the space charge density may lead to nonphysical particle motion. This is often true when using the Space Charge Limited Emission feature, since overestimation of the space charge density in the vicinity of the cathode may cause a nonphysical reversal in the direction of the initial particle velocity.

Select an option from the Weights for subsequent iterations list: Uniform (the default), Arithmetic sequence, or Geometric sequence. For Geometric sequence enter the Common ratio r (dimensionless). The default value is 1.5. The contribution of charged particles to the space charge density is treated as a cumulative average of the solutions for all iteration numbers greater than β, and these settings control how the cumulative average is computed.

This section defines the physics involved in the multiphysics coupling. By default, the applicable physics interface is selected in the Source and Destination lists.

You can also select None from either list to uncouple the node from a physics interface. If the physics interface is removed from the Model Builder then the applicable list defaults to None as there is nothing to couple to.