Recent progress in the development of immersed diodes

Sandia National Laboratories is investigating and developing high-dose, high-brightness flash radiographic sources. One of the diodes we are developing is the immersed or B/sub z/ diode. These diodes employ large-bore, high-field solenoid magnets to help produce an intense electron beam from a needle-like cathode "immersed" in the strong B/sub z/ field of the magnet. Both simulation and experiments suggest that the capability of these diodes to achieve high dose from a small spot has been limited by deleterious effects associated with nonprotonic anode plasmas evolving from the electron target or high-atomic-number (high-Z) converter. We are in the process of developing and testing the next generation of immersed diodes. The goals of these diodes are to improve our understanding of the evolution of the anode plasmas and avoid or delay the onset of nonideal diode behavior by controlling the amount of nonprotonic species accelerated off the anode. These diodes employ improved plasma diagnostics for studying the evolution of the anode plasmas and novel cryogenic concepts for forming solid hydrogenous anodes. Recent progress in the development, testing and understanding of immersed diodes at Sandia is described.