Suppression of ion emission and pinching using heated tantalum anodes in high-power electron-beam diodes

Summary form only given. Tantalum anodes used as X-ray sources in high-power electron-beam diodes can be copious sources of ions. The part of the total current carried by ions effectively reduces the X-ray production efficiency. Tantalum absorbs gas, even at elevated temperatures (maximum at 1300 K). These gases are released and ionized when a powerful e-beam vaporizes the tantalum foil, and the low-Z impurities (hydrogen, carbon, etc.) form an ion beam that can become a substantial fraction of the diode current. Gases on the surface can be removed by moderate heating prior to a shot, but gases entrained in the interior of a tantalum sheet require higher temperatures (2300 K or greater) to remove them. A pulsed resistive heating technique has been developed to heat tantalum X-ray converters in situ and the effects investigated on the Gamble II generator (1.5 MV, 0.7 MA, 60 ns) at the Naval Research Laboratory.