The Charged Particle Tracing (cpt) interface (
), found under the
AC/DC>Particle Tracing branch (
) when adding a physics interface, is used to model charged particle orbits under the influence of electromagnetic forces. In addition, it can also model bidirectional coupling between the particles and fields. Some typical applications are particle accelerators, vacuum tubes and ion implanters. The physics interface supports time-domain modeling only in 2D and 3D.
When this physics interface is added, these default nodes are also added to the Model Builder:
Wall and
Particle Properties. Then, from the
Physics toolbar, add other nodes that implement, for example, boundary conditions and release features. You can also right-click
Charged Particle Tracing to select physics features from the context menu.
The Label is the default physics interface name.
The Name is used primarily as a scope prefix for variables defined by the physics interface. Refer to such physics interface variables in expressions using the pattern
<name>.<variable_name>. In order to distinguish between variables belonging to different 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 physics interface in the model) is
cpt.
The Formulation,
Relativistic Correction,
Store extra time steps for wall interactions, and
Maximum number of secondary particles settings are the same as for
The Mathematical Particle Tracing Interface, except that only the
Newtonian,
Newtonian, first order, and
Massless formulations are available.
Select a Particle release specification:
Specify release times (the default) or
Specify current. This setting affects the way particle-field interactions are modeled, and also affects the values of certain built-in accumulated variables.
If Specify release times is selected, then each model particle is treated as the instantaneous position of one or more charged particles for the purpose of modeling particle-field interactions. This means, for example, that if the
Space Charge Density Calculation node is used, the space charge density is only nonzero in mesh elements that are currently occupied by particles.
If Specify current is selected, then for the purpose of modeling particle-field interactions, each model particle traces a path that is followed by a number of charged particles per unit time. This means that the charge density computed by the
Space Charge Density Calculation feature is nonzero in all mesh elements that the particle trajectories pass through, not just at the instantaneous positions of the particles. In other words, the particles leave behind a trail of space charge as they propagate.
The Specify current option is primarily used to model charged particle beams in which the charge and current density do not change over time. Changing the
Particle release specification affects some inputs in the settings windows for release features such as the
Release and
Inlet nodes. In addition, the
Surface Charge Density node is only available with the
Specify release times option, while the
Current Density,
Heat Source, and
Etch nodes are only available with the
Specify current option.
The Maximum number of consecutive null collisions (dimensionless) is a positive integer. The default is 100. This value is used to cap the number of collisions that a single particle can undergo within a single time step taken by the solver when performing a Monte Carlo collision simulation. This value is only used in the model if the
Collisions node is present and
Null collision method, cold gas approximation is selected from the
Collision detection list.
The dependent variables (field variables) are the Particle position,
Particle position components,
Particle velocity, and
Particle velocity components. The degrees of freedom for particle velocity are only used if
Newtonian, first order is selected from the
Formulation list. The name can be changed but the names of fields and dependent variables must be unique within a model.