Repetitive, electron-beam diode development

We constructed a stacked-Blumlein pulse generator that can deliver pulses of nearly 200 kV to an electron beam diode load. This pulse generator has an output impedance of 100Ω and a pulse width of 80 ns. It can operate continuously at pulse repetition rates as high as 500 Hz. We discharged the pulse generator into two diodes. One had a 2.9 cm diameter sintered bronze cathode, and the other had a 4.0 cm diameter graphite cathode with points machined into it. The sintered bronze cathode turned on completely with a peak, macroscopic field of 100 kV/cm. The graphite cathode required a peak, macroscoplc field of 150 kV/cm in order to operate reproducibly. Nevertheless, only about 10% of the area of the graphite cathode emitted. The bronze cathode operated at 30 Hz, and it exhibited heat damage. Specifically, it melted in places. Conversely, the graphite cathode, operated at 50 Hz, exhibited little damage: principally, minor erosion around the perimeter.