Cathode spot motion and burning voltage of low current vacuum arc with electrodes of copper-chromium composition in magnetic field

The study dealt with the cathode spot (CS) motion and the burning voltage of a low-current vacuum arc with electrodes of composition CuCr30, subjected to a magnetic field. The arcs with current 25 ≪ I ≪ 35 A burned in longitudinal (normal to the cathode surface) and transversal (tangential) fields as well as in those with the induction vector inclined by angle 5° ≪ ϕ ≪ 65° to the cathode surface. Use was made of electrodes with diameter 30 mm and gap 4 mm. The field components, longitudinal B_n, and transversal B_r, varied independently in the range from 0 to 0.12T each. The superposition of the transversal magnetic field on the arc has been found to considerably increase both the constant component and noise level of the voltage. If such arc is superposed also with the longitudinal field, both the constant component and noise level decrease and at B_n ˜ B_r, the voltage across the arc is weakly dependent of B_r. The velocity of the retrograde (anti-Ampere) CS motion grows approximately in proportion to the growth of the transversal field induction. The proportionality factor is ˜200 m/(s.T). The increase in the longitudinal field induction causes a reduction in the magnitude of the velocity vector and its rotation with respect to the anti-Ampere direction through angle θ, its value being proportional to field inclination angle ϕ. The results obtained were compared with the data in references.