Anode heating/cleaning and its effects on diode impedance in Self-Magnetic Pinch (SMP) Experiments*

The SMP diode is fielded on both the RITS-6 (3.5-8.5 MV) and Mercury (5.5 MV) accelerators, located at Sandia and the Naval Research Laboratory, respectively. This diode utilizes a hollowed metal cathode to produce focused electron beams ($<$3 mm diameter) onto a high-Z converter for flash x-ray applications. We observe on some shots unexplained impedance collapse beyond what may be attributed to normal A-K gap closure. This could be caused by gas evolution off the as-provided hardware making up the anode and cathode. The goal of heating the anode is to remove gases trapped within the bulk of the Ta anode, and so reduce the volume of evolving gases near the A-K gap. Two heating techniques have been investigated, a short-pulse ($\sim$1 sec) resulting in high Ta temperature ($\sim$3000 $^{\circ}$C), and a longer ($\sim$100 sec) heating of the Ta to lower peak temperature ($\sim$1000 $^{\circ}$C). Initial experiments indicate a modest improvement to diode performance. Additional experiments are ongoing, and latest results will be reported.\\[4pt] *Sandia National Laboratories is a multi-program laboratory managed and operated by Sandia Corporation, a wholly owned subsidiary of Lockheed Martin Corporation, for the U.S. Department of Energy's National Nuclear Security Administration under contract DE-AC04-94AL85000.