Arc movement in a transverse magnetic field at atmospheric pressure

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Abstract
The velocities of d.c. arcs moving in the forward direction in a transverse magnetic field, in air at atmospheric pressure, have been measured at arc currents up to 700 amp, and magnetic fields up to 0.1 Wb/m2.The results confirm the findings of an earlier investigation1 where the driving field was due to current flowing in the electrodes, that the arc movement is chiefly controlled by cathode surface processes. It is affected by a variety of factors, some of which have not been sufficiently appreciated or controlled in previous investigations.The cathode movement and the resulting track on the surface is either continuous or discontinuous. In the case of the former mode, cathode surface phenomena alone are decisive. In the latter mode, even though jumps of random length occur, the movement is still definite and consistent and depends upon a combination of cathode-root and arc-column processes. Thus, the overall arc movement is at all times controlled and repeatable within surprisingly small limits, any scatter being due mainly to differences in cathode surface layers.Above about 40 amp, the velocity of the cathode root, and thus that of the whole arc, is independent of arc current, whether its movement is continuous or discontinuous.

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