The Breakdown of High-Voltage Discharge Neutron Tubes

High voltage breakdown occurs in neutron tubes, as well as in many vacuum devices. For practical reasons, it is important to know the origin of the breakdown. So, an experimental investigation has been performed on diode devices under a few ps pulse condition. Conditioning and deconditioning phenomena have been characterized, the arcing rate was considered from a probability point of view for a given voltage. The arcing rate is a decreasing function of the number of applied pulses, and increases exponentially with the tube current under deuterium pressure. Breakdowns occur more often after a thermal stress or an ac glow discharge. The most important breakdown origins are reviewed for the experimental configuration tested. Electrical charge measurements along the walls and breakdown impact were used to evaluate the wall contributions, directly from the flashover, indirectly from ion focusing, and so increasing the cathode ion bombardment density. A more fundamental study of the surface potential and of the wall surface states is now necessary, in order to explain the physical basis of electrical breakedown initiation.