Effects of pulsed anode heating on self-magnetic-pinch radiographic performance using NRL's Mercury IVA

Summary form only given. Previous proof-of-principle experiments at NRL used the Mercury IVA facility to test a self-magnetic-pinch (SMP) diode in conjunction with a pulsed resistive heating treatment that cleaned the SMP's anode surface. This heating treatment was tested as a method for mitigating the negative effects of low-Z ions, such as post-shot activation and potentially reduced diode impedance. These low-Z ions can form in the diode region from contaminants on the diode hardware that require in situ cleaning to remove. A more extensive series of experiments are reported here that tested 3 diode configurations with and without the heat treatment. The heat treatment resulted in improvements in spot symmetry, spot size, dose, and radiation pulse length to varying degrees depending on the particular configuration tested. The most significant improvement in dose was achieved from an SMP with a large AK-gap-to-cathodediameter ratio compared with traditional ratios, which are close to 1:1. Large ratios typically result in premature termination of the radiation pulse in the absence of heating. The heat treatment made the large ratio SMP resemble a more stable 1:1 ratio configuration in terms of pulse length, and provides evidence that supports a low-Z ion mechanism as the cause for poor SMP diode impedance at large aspect ratios [1]. The heating circuit itself was a simple resistive pulse through the tantalum anode supplied by switched batteries that drove the anode to >2300 K for approximately 0.5 seconds. Detailed results from this series of experiments will be presented.