Aerosol microparticles and emission characteristics of the pulsed high-current vacuum diode in a microsecond range

Vacuum electrical breakdown of extended gaps (tens of cm and more) by a high voltage (1-2 MV) microsecond pulses and the cold cathode material influence on an electron beam formation have been investigated. It has been established, that drop fraction (aerosol microparticles) of a cathode torch influences essentially on the vacuum electrical breakdown development for microsecond pulse duration. The characteristic sizes of the microparticles are experimentally measured and calculated. The main part of the microparticles has a size about the length of Fermi electron's free run in metals. The radius of graphite particles exceeds by almost three orders that of the metal (Al, Fe, Cu). In the case of graphite cathodes, the diode operation can be optimized for receiving extreme beam parameters. It has been calculated that the deformation of a potential barrier in a vicinity of the cathode raises considerably the probability of electron tunneling. It can lead to the development of explosive electron emission.