Generation and focusing of high energy, 35-kA electron beams for pulsed-diode radiographic machines: theory and experiment

Cathode ball and anode planar-foil geometries used to generate self-focused beams onto X-ray conversion targets via beam-induced ionization in gas cells have been investigated since the early 1970's by J.C. Martin et al. at Aldermaston, U.K. The building of a succession of increasingly higher voltage, pulsed-diode machines tailored for flash X radiography has resulted. Given sufficient dose to penetrate an object, the spot size of the X-ray source generally determines the resolution of a radiograph. Reported are particle-in-cell code simulations applied to beam generation in the A-K gap and the self-focusing onto the target. A Monte Carlo code for neutron, photon, and electron transport converts the beam particles at the target to photons with transport to a film plane used to calculate the spot size. Comparisons are made to experiments using the Ector (3.5-4 MeV) and PIXY (4-8 MeV) pulsed-diode radiographic machines at Los Alamos.<>