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 les h les 10 mm with the current 30 les I les 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_s and average arc-burning voltage U on the amplitude of the induction vector of external uniform magnetic field Boarr = Boarr_n + Boarr_t and its inclination angle alpha to the axis perpendicular to the electrode surfaces was investigated. At alphararrpi/2, I_s has been found to be strongly dependent on the amplitude of vector B, but at moderate values of alpha, the dependence of I_s on B practically vanishes. The arc voltage was noisy. The low-frequency (10⁴-10⁵ 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 arc current I and on alpha, variation of the number of spots may bring about both growth and drop of the low-frequency voltage by as much as ~volt. The dependence of average arc voltage U on B_n at fixed current J 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 alpha₁ and transition from portions 2 to 3 at alpha₂. It has been shown that alpha₂ is strongly dependent on the electrode material, whereas alpha₁ is practically independent of it. The characteristic values of alpha 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 r- egularities that define the behavior of high-current vacuum arcs stabilized by axial magnetic fields.