Experimental study of cathode spot motion and burning voltage of low-current vacuum arc in magnetic field

This experimental study dealt with cathode spot (CS) motion and the burning voltage of a low-current vacuum arc with electrodes of HCOF Cu and with a composition of CuCr30, subjected to a magnetic field. Arcs with current of I≈30 A burned in axial and transverse fields as well as with the induction vector inclined at an angle 5°<φ<65° to the cathode surface. Butted-end electrodes were used with diameter 30 mm and gap h=4 mm. The field components, axial B_n and transverse B_t, were varied independently over a wide range. The superposition of a transverse magnetic field on the arc was found to considerably increase both the constant component and noise level of the voltage U. If this arc is also superposed with an axial field, both the constant component and noise level decrease. With growing B_n, the dependencies of the U(B_n) at different values of B_t converge to a single curve that is typically V-shaped. This is similar to the dependence of the voltage across a high-current vacuum arc with fixed current in an external axial magnetic field on the magnetic field induction. The velocity of the retrograde CS motion grows approximately in proportion to the growth of the transverse field. The proportionality factor is ∼60 m/(s·T) for Cu and ∼200 m/(s·T) for CuCr. Increase of the axial field causes a slight reduction in the magnitude of the velocity vector and its rotation with respect to the retrograde direction through an angle θ, its value being proportional to the field inclination angle φ. The results obtained were compared with the data in references.