A mathematical model a a diffuse vacuum arc in an axial magnetic field (AMF) has been developed with the ultimate aim to predict the limit of the diffuse mode operating range as well as contribute to a better understanding of the mechanisms that cause the arc to switch from the diffuse mode to a different (more confined) mode. The focus is on the interelectrode plasma region, from the mixing region of the cathode spots to the anode. The model is based on a 2D two-fluid hydrodynamic description of the fully ionized plasma, including consideration of the energy balance equations for both ions and electrons. It incorporates the influence of an external axial magnetic field and takes full account of the effect of the self generated magnetic field, including the field components induced by the azimuthal current density. The possibility of both supersonic and subsonic plasma flow regimes is considered. Simulations results are obtained for a wide range of arcing conditions. Their analysis provides useful insights into the influence of various parameters, such as the arc current and the presence of an AMF, on plasma properties and current constriction.
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