3D simulation of arcs in internal and external magnetic fields

The general impact of Lorentz forces on arcs due to external magnetic fields and due to the fields produced by the arc itself is well known and profitably used in a number of applications. However, the interplay of external and internal fields or the interaction with the gas flow can lead to a complex arc behaviour. Examples are arcs moving on rails, rotating arcs in external fields or arc instabilities. Most of these cases cannot be treated in 2D models, and their numerical study in 3D represents a challenge. Time-dependent 3D simulations solving the Magneto-hydrodynamic (MHD) equation system are applied here to study the behavior of high-pressure arcs in detail. As examples a convection stabilized arc in a nozzle arrangement showing a helical instability and a high-current arc rotating in an external radial magnetic field are studied. The interaction of main forces in the momentum balance and dominant contributions in the power balance are discussed. Results are validated by measurements taken from the literature.