The Particle–Field Interaction, Relativistic Interface
The Particle–Field Interaction, Relativistic () multiphysics interface combines the Charged Particle Tracing, Electrostatics, and Magnetic Fields physics interfaces. The Electric Particle–Field Interaction and Magnetic Particle–Field Interaction multiphysics coupling features are added automatically. The Particle–Field Interaction, Relativistic interface is used to model beams of relativistic charged particles. The particles generate space charge density and current density terms as they propagate through domains. The space charge density and current density are then used to compute electric and magnetic forces, respectively, which are exerted on the particles. This physics interface requires both the AC/DC Module and the Particle Tracing Module.
When a predefined Particle–Field Interaction, Relativistic interface is added from the AC/DC ()>Particle Tracing branch () of the Model Wizard or Add Physics windows, Electrostatics, Magnetic Fields, and Charged Particle Tracing interfaces are added to the Model Builder. A Multiphysics Couplings node is also added, which automatically includes the Electric Particle–Field Interaction and Magnetic Particle–Field Interaction multiphysics coupling features.
On the Constituent Physics Interfaces
The Electrostatics interface is used to compute the electric field, the electric displacement field and potential distributions in dielectrics under conditions where the electric charge distribution is explicitly prescribed. The formulation is stationary but for use together with other physics, also eigenfrequency, frequency-domain, small-signal analysis and time-domain modeling are supported in all space dimensions. The physics interface solves Gauss’ law for the electric field using the scalar electric potential as the dependent variable.
The Magnetic Fields interface is used to compute magnetic field and induced current distributions in and around coils, conductors, and magnets. Depending on the licensed products, stationary, frequency-domain, small-signal analysis and time-domain modeling are supported in 2D and 3D. Note that the frequency- and time-domain formulations become ill-posed when approaching the static limit. You may extend the useful frequency range downward by adding a low conductivity. The physics interface solves Maxwell’s equations formulated using the magnetic vector potential and, optionally for coils, the scalar electric potential as the dependent variables.
The Charged Particle Tracing 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. The physics interface solves the equation of motion for charged particles subjected to electromagnetic forces.
Settings for Physics Interfaces and Coupling Features
When physics interfaces are added using the predefined couplings, for example Particle–Field Interaction, Relativistic, specific settings are included with the physics interfaces and the coupling features. However, if physics interfaces are added one at a time, followed by the coupling features, these modified settings are not automatically included.
For example, if single Electrostatics, Magnetic Field, and Charged Particle Tracing interfaces are added, COMSOL Multiphysics adds an empty Multiphysics Couplings node. You can choose from the available coupling features but the modified settings are not included.
Coupling features are available from the context menu (right-click the Multiphysics Couplings node) or from the Physics toolbar, Multiphysics menu.
Table 6-2: Modified Settings for a Particle Field Interaction, Relativistic Interface.
Physics Interface or Coupling Feature
Modified Settings (if any)
Electrostatics
No changes.
Magnetic Fields
No changes.
Charged Particle Tracing
For the Charged Particle Tracing interface, under Particle Release and Propagation, the Particle release specification is set to Specify current, and the Relativistic correction check box is selected.
The Electric Force and Magnetic Force nodes are added to the Charged Particle Tracing interface. The Domain Selection for each node is the same as that of the Charged Particle Tracing interface.
Electric Particle Field Interaction
The Domain Selection is the same as that of the participating physics interfaces.
The corresponding Electrostatics and Charged Particle Tracing interfaces are preselected in the Electric Particle Field Interaction section.
Magnetic Particle Field Interaction
The Domain Selection is the same as that of the participating physics interfaces.
The corresponding Magnetic Fields and Charged Particle Tracing interfaces are preselected in the Electric Particle Field Interaction section.
Physics Interfaces and Coupling Features
Use the online help in COMSOL Multiphysics to locate and search all the documentation. All these links also work directly in COMSOL Multiphysics when using the Help system.
Coupling Features
The Magnetic Particle–Field Interaction coupling is described in this section. The Electric Particle Field Interaction and Space Charge Limited Emission coupling feature nodes are described for The Particle–Field Interaction, Nonrelativistic Interface.
Physics Interface Features
Physics nodes are available from the Physics ribbon toolbar (Windows users), Physics context menu (Mac or Linux users), or right-click to access the context menu (all users).
In general, to add a node, go to the Physics toolbar, no matter what operating system you are using. Subnodes are available by clicking the parent node and selecting it from the Attributes menu.
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The available physics features for The Charged Particle Tracing Interface are listed in the section Domain, Boundary, Pair, and Global Nodes for the Particle Tracing for Fluid Flow Interface.
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The available physics features for The Electromagnetics Interfaces are listed in the section Domain, Boundary, Edge, Point, and Pair Nodes for the Electrostatics Interface in the COMSOL Multiphysics Reference Manual.
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The available physics features for The Magnetic Fields Interface are listed in the section Domain, Boundary, Point, and Pair Nodes for the Magnetic Fields Interface in the COMSOL Multiphysics Reference Manual.
This physics interface requires the addition of the AC/DC Module. This means that additional feature nodes are available for the Electrostatics and Magnetic Fields interfaces. These are described in the AC/DC Module User’s Guide and the information is most easily available from the online Help found when working in COMSOL Multiphysics.