Investigation of arc roots of constricted high current vacuum arcs

The anodic and cathodic are roots of constricted high current vacuum arcs w ere investigated with a fast framing charge-coupled device camera of 1 mu s exposure time, The experiments were performed with cup-shaped contacts, wi th sinusoidal currents of amplitudes between 20 and 100 kA, and a sine half wave duration of 10-12 ms. The arcs were drawn by contact separation and ac celerated by the Lorentz force between the are current and the transverse m agnetic field generated by the contrate contact. The anode and cathode are roots behave reproducibly and are scaleable within the range of currents in vestigated, Both types of are roots are elliptical, with a major to minor a xis ratio of 1.4. The major axis points are in the direction of are propaga tion. Anodic and cathodic are root cross-sectional areas as a function of c urrent can both be described by a potential law with a common exponent of 0 .76, For currents of 20-100 kA, mean current densities of 81-121 and 41-60 kA/cm(2) were found in anode and cathode are roots, respectively, Estimatio ns of their temperature and vapor densities were performed. For the investi gated current range T-A approximate to 3300-3600 K, n(A) approximate to 1.6 * 10(19) -2.2 * 10(19) cm(-3) and T-C approximate to 3200-3400 K, n(C) app roximate to 0.8 * 10(19) - 1.2 * 10(19) cm(-3) were found for anode and cat hode, respectively.