Slower impedance collapse with hot anode and enhanced emission cathode

As most high power diodes, our nominally 1 kA and 300 kV diode shorts out during the pulse. This so-called impedance collapse can be affected by the anode temperature and by surface conditions on the carbon fiber cathode. With the tantalum anode at room temperature, impedance collapse occurs after about 200 ns. Collapse takes 100 ns longer when the anode is hot, 800-1200 K. Covering the carbon fibers in the cathode with cesium iodide delays collapse by another 100 ns. These observations are consistent with pre-shot removal of loosely bound adsorbates off the anode by the high temperature, and with easier electron emission from the cathode out of smaller, less violent explosive emission spots.