Effect of Amplitude and Inclination of Magnetic Field on Low-Current Vacuum Arc

Experiment dealt with investigating a vacuum arc of length 0leshles10 mm with current 30lesIles150 A, which burned at electrodes of CuCr₃₀ composition. The study concerned the dependence of such characteristics as arc burning voltage U and average current passed by a cathode spot I_s on the amplitude of the induction vector of external uniform magnetic field Boarr = Boarr _n + Boarr_t and its inclination angle alpha to the arc axis. The voltage at fixed I and B was found to correlate with the structure of cathode attachment - the number of separately existing spots. Depending on alpha, variation of the number of spots may bring about both the growth and drop of the voltage by as much as ~Volt. At alpha rarr pi/2, I_s has been found to be strongly dependent on the amplitude of vector B, but at a rarr 0 the dependence of I_s on B practically vanishes. Dependence of average arc voltage U on B_n at fixed current has been studied at different values of B_t. The curves have been shown to distinctly split into three portions: rapid drop, constancy and slow (root-like) growth of the voltage. Transition from one portion to another takes place at certain values of magnetic field inclination angle alpha₁ and alpha₂. Comparison with previously published authors´ results obtained in an arc with copper electrodes has 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 and current. Obtained results are of interest not only for the insight into processes in low-current arcs, but also for explanation of regularities that define the behavior of high-current vacuum arcs stabilized by axial magnetic fields