A 2D two-fluid numerical model is developed for the description of the diffuse arc in a vacuum interrupter under the possible influence of an axial magnetic field (AMF). This model incorporates the energy balance equations for both ions and electrons and takes into account the three components of the self-generated magnetic field. The possibility of both supersonic (at low current density) and subsonic (at high current density) plasma flow regimes is considered. Data from the literature are used to specify the values of the plasma parameters near the cathode, and the boundary conditions on the anode boundary rely on a simplified model of the anode sheath. Simulation results are presented for both ion flow regimes, with special attention to the current and plasma flow features. It is shown that there is always a contraction of the current flow, whereas the dynamics of the ions throughout the interelectrode gap is strongly influenced by their flow regime near the cathode. Finally, the influence of various operating parameters (presence of an AMF, gap length) on the current constriction at the anode is discussed.

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