Rod pinch radiography source optimization at 2.3 MV

Summary form only given, as follows. Rod pinch diodes have shown considerable promise as high-brightness flash X-ray sources for penetrating dynamic radiography for a variety of DOE Defense Programs applications. The rod pinch diode uses a small diameter (0.4 - 2 mm) anode rod extended through a cathode aperture. When properly configured, the electron beam born off of the aperture edge can self-insulate and pinch onto the tip of the rod creating an intense, small X-ray source. Experiments have been performed on Sandia´s SABRE accelerator (2.3 MV, 40 Ohms, 60 ns) to search a wide parameter space to optimize the source by maximizing the figure of merit (dose/spot diameter/sup 2/) and minimizing the diode impedance droop. Many diode parameters have been examined in detail including rod diameter, rod length, rod material, cathode aperture diameter, and vacuum pressure. The best configuration tested so far uses a 0.5 mm diameter gold rod, a 6 mm rod extension beyond the cathode aperture (diameter = 8 mm), to produce 3.5 rad at 1 m from a 0.8 mm X-ray spot. A large experimental database has been developed to benchmark computer codes so that physics details can be extracted in this complex beam-plasma environment. Further physical insight is necessary to extend the rod pinch operations to higher voltages.