Motion of a Short Arc in a Magnetic Field

Abstract

When an electric arc with an evaporating cathode (e.g., copper) is exposed to a strong transverse magnetic field in atmospheric air, its motion can be made to change from the conventional to the reverse direction by reducing sufficiently the electrode separation.The effect is discussed in terms of an earlier idea based on the resultant magnetic field acting on the cathode region. This field is composed of the applied field and the "loop" field of the curved current path above the cathode spot. At low pressure, an increase of the former is accompanied by a rapid increase of the latter and thus the resultant field changes its sign. Here at high pressure and constant external field, the change of sign at small electrode separation is caused by a forced reduction of the radius of curvature of the deflected positive column.