Load impedance dynamics in the RITS-6 self-magnetic -pinch diode

Abstract

The self-magnetic-pinch (SMP) diode is being developed on the Radiographic Integrated Test Stand (RITS-6) at Sandia National Laboratories. The time history of SMP load impedance is affected by the evolution of populations of high-energy electrons and ions from the cathode and anode, respectively, as well as by electrode plasma evolution. Framing camera images of optical emission spectra from electrode plasmas has been measured [1], and anode plasma dynamics has been modeled [2]. Experimental data suggest that the interaction of high-energy and anode plasma ions can result in premature impedance collapse. These effects vary with the cathode radius and anode-cathode (A-K) gap. There is experimental evidence that changes to the anode material composition can affect the load impedance evolution. The standard anode structure consists of thin Al foil placed 0.8 mm in front of a Ta plate. We are experimenting with Al coatings placed directly upon the Ta surface, as well as with ‘limited anodes’, where the Al foil/Ta plate is replaced with a graphite plate of similar electron range, and with either tungsten or tantalum insert at small radius. Preliminary results with the Al-coated Ta anode indicate equivalent or better impedance history compared to the standard anode. Experiments with anode materials modifications are ongoing, and latest results will be presented.