A special form of vacuum discharge with a cold flat cathode and an anode in the form of a tip with a radius of rounding of the tip of 0.1 mm was studied. The discharge occurred at a slow convergence of the electrodes to the touch, with the voltage at the electrodes was 100 – 300 V. Anodes of cadmium, copper and molybdenum were used at currents from 3 A to 100 mA (Cd). At the same time, in most cases, no traces of noticeable erosion were observed at the cathode (Fig. 4), for comparison in Fig. 5 shows what the cathode surface looks like after a conventional arc discharge with a cathode spot. Thus, in this special form of discharge, the current is provided entirely by the plasma formed at the anode, and the cathode is simply a collector of particles, that is, it plays a passive role.

If our assumptions about the nature of the current flow in such a discharge are correct, this should mean that in a cathode spot discharge it is not necessary to require the cathode spot to provide the entire discharge current by means of a mechanism of electronic emission from the cathode surface. The function of the cathode process in the discharge can simply be to provide injection into the plasma clot interval, after which the electrons are directed to the anode and the ions return to the cathode, thus closing the discharge current.

Fig. 4. Tungsten cathode after a single discharge with a copper tip anode, a current of 1.5 A and a duration of 800 ns.

Fig. 5. Tungsten cathode after a single discharge with a cathode spot, a current of 2.5 A and a duration of 180 ns.