About Some Features of the Vacuum Arc Operation with Boron-Containing Cathodes

The report presents an experimental studies of a pulsed vacuum arc discharge operation with pure boron and lanthanum hexaboride cathodes. For the experiments reported here, the arc discharge triggering was carried out due to breakdown on a ceramic button installed in the center of the cathode surface. Pure boron and LaB6 cathodes were tested. The pure boron cathode is a cast rod. The lanthanum hexaboride cathode is a hot pressed rod with small porosity (not more than 1%). Pure boron is a non-metallic element, but a semiconductor with a very high resistivity (2 MOhm×cm) under normal conditions, therefore for the stable discharge operation requires the cathode preheating up to high temperatures. A strong temperature dependence of resistivity and relatively low thermal conductivity lead to the fact that the cathode spot is localized in one place. Lanthanum hexaboride, although it is considered a refractory ceramic material, differs from pure boron in that it has a very low resistivity under normal conditions. Therefore, there is no need to preheat of the cathode for the arc discharge operation. Another difference is that LaB6 has a metallic type of conductivity and behavior of the cathode spots on the surface of the LaB6 cathode is similar to the behavior of the spots on a pure metal cathode. The vacuum arc with boron containing cathodes is accompanied by a large flow of hot droplets – macroparticles, as well as small cathode fragments.