In a tangential magnetic field the electrons flowing from the cathode spot towards the anode are deflected by the Lorentz force. The surplus electric charges accumulate at the plasma-electrode boundary (positive at the retrograde side of the spot and negative at the opposite side), thus forming a Hall electric field. This field increases the cathode voltage drop at the retrograde side and reduces it at the amperian side; the difference between the cathode voltage drops between these two sides being delta Vc. It is shown that since the Hall parameter omega e tau e increases with the distance from the spot, the main contribution to delta Vc is made by the rather distant (up to a distance of the order of the interelectrode gap) additional electric charges. The formula describing arc velocity is obtained on the basis of the hypothesis of the leading role of the cathode voltage drop asymmetry formed by the Hall field. This formula describes the experimental data on the velocity in the weak magnetic field as well as on the magnitude of magnetic field for which the velocity saturates. It also describes, in accordance with the experiment the velocity decrease with interelectrode gap decrease, in addition to the external gas and superimposition of magnetic field normal to the cathode surface.

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