Droplet spot as a new object in physics of vacuum discharge

It is established experimentally that the burning of a low-current (several and tens of amperes) pulsed (microseconds) vacuum discharge is accompanied by the formation of plasma microbunches around some of the droplets leaving the cathode spot. The parameters of these bunches (electron concentration $n_e\sim10^{26} m^{-3}$ and equilibrium temperature $T_e\sim1\,$eV) are close to the parameters of cathode-spot plasma. The data obtained suggest that the initial temperature of droplets and the thermionic emission from them play a key role in the formation of such plasma microbunches. By analogy with the well-known cathode and anode spots in vacuum discharges, these droplet plasma formations are classified as «droplet spots.» This work reports the first results on studying the formation dynamics and the characteristics of the droplet spots. It is noted that the concept of droplet spots will require a certain refinement of the plasma formation mechanism in vacuum discharges.