Effect of amplitude and inclination of magnetic field on low-current vacuum arc

This paper dealt with the investigation of a vacuum arc of the length 0 <= h <= 10 mm With the current 30 <= T <= 300 A, which burned at electrodes of HCOF Cu and CuCr30 composition. The dependence of such characteristics as mean current passed by a cathode spot I, and average arc-burning voltage U on the amplitude of the induction vector of external uniform magnetic field (B) over right arrow = (B) over right arrow (n) + (B) over right arrow (t) and its inclination angle a to the axis perpendicular to the electrode surfaces was investigated. At alpha -> pi/2, I-s has been found to be strongly dependent on the amplitude of vector B, but at moderate values of a, the dependence of I. on B practically vanishes. The arc voltage was noisy. The low-frequency (10(4) - 10(5) Hz) variation of the arc voltage at fixed I and B was found to correlate with the structure of the cathode attachment-the number of separately existing spots. Depending on are current I and on a, variation of the number of spots may bring about both growth and drop of the low-frequency voltage by as much as similar to Volt. The dependence of average arc voltage U on B-n at fixed current I was studied at different values of B-t. The curves have been shown to distinctly split into three portions: a rapid drop (portion 1), a constancy (portion 2), and a slow (square-rootlike) growth (portion 3) of the voltage. Transition from portions 1 to 2 takes place at certain values of magnetic-field inclination angle cc, and transition from portions 2 to 3 at alpha(2). It has been shown that alpha(2) is strongly dependent on the electrode material, whereas a, is practically independent of it. The characteristic values of a have been found to be (weakly) dependent on the arc length. The obtained results are of interest not only for better understanding of the processes in low-current arcs but also for the explanation of regularities that define the behavior of high-current vacuum arcs stabilized by axial magnetic fields.