A high power diode includes a cathode for emitting a primary electron discharge, an anode, and a porous dielectric layer, e.g. a honeycomb ceramic, positioned between the cathode and the anode for receiving the primary electron discharge and emitting a secondary electron discharge. The diode can operate at voltages 50 kV and higher while generating an electron beam with a uniform current density in the range from 1 A/cm.sup.2 to >10 kA/cm.sup.2 throughout the area of the cathode. It is capable of repetitively pulsed operation at a few Hz with pulse duration from a few nanoseconds to more than a microseconds, while the total number of pulses can be >10.sup.7 pulses. The diode generates minimal out-gassing or debris, i.e. with minimal ablation, providing a greater diode lifetime, and can operate in a high vacuum environment of 10.sup.-4 Torr. The high power diode is useful in many applications requiring a high current electron beam. Exemplary applications include x-ray photography of large samples, polymerization processes, sterilization of biological and chemical agents, irradiation of food, and as a pump for lasers, e.g. excimer lasers such as krypton fluorine (KrF) lasers.