Self-magnetic-pinched diode studies for radiographic applications

Summary form only given. The self-magnetic-pinch diode is a high-impedance (/spl sim/30-Ohm), low R/D (typically 4-mm/8-mm) pinched-beam diode that shows promise for high-power X-radiography. Ultimate development of this diode depends critically on the diode impedance behavior, the angular distribution of the electron beam on the anode converter, and the size of the resulting pinch. The first determines the operating range of applicable drivers, the second determines the conversion efficiency, and the last determines the radiographic spot size. Several approaches to improving performance are under study at AWE, SNL, and NRL, including optimized cathode geometry, structured anodes, and a possible plasma prefill. These studies require both informative diagnostics and effective code modeling capability. We have begun a combined experimental and theoretical study of this diode on the 1.8-MV Gamble II generator. A reentrant parallel load diverts most of the machine current, resulting in typical diode parameters of 1.7 MV and 30-60 kA. The electron-incidence-angle-distribution is diagnosed using an array of photodiodes and a low-Z converter. The spot size is diagnosed using a rolled edge and film (time-integrated) or and array of p-i-n's (time-resolved). Coarser features of the beam focusing are diagnosed using a fast scintillator behind the converter and a fast framing camera. Dense electrode plasmas are characterized using a holographic interferometer. Lower-density-regions of the electrode plasmas are measured using a sensitive quadrature interferometer and a multi-channel heterodyne interferometer.