The External Current Density node adds an externally generated current density Je, which appears on the right-hand side of the equation that the Magnetic Fields interface defines.

Add a contribution as a Harmonic Perturbation by right-clicking the parent node or clicking Harmonic Perturbation in the Physics toolbar. For more information see Harmonic Perturbation — Exclusive and Contributing Nodes in the COMSOL Multiphysics Reference Manual.

Enter a value or expression for each component of the External current density Je (SI unit: A/m2). The defaults are 0 A/m2.

The external current density does not contribute to the losses (due to Joule heating), since there is no electric field associated with it. To include the contribution to the losses from the external current density, select the Add contribution of the external current density to the losses check box. Then select an option from the External losses list — From domain conductivity (the default) or User defined. If From domain conductivity is selected, the heat source is computed using the conductivity specified in the material model feature (such as Ampère’s Law) that is applied in the domain. For User defined, enter a value for Qe (SI unit: W/m3) to specify a user-defined heat source.