Simulation tools for pinched-electron-beam radiographic diodes

We describe capabilities of an integrated software suite to simulate pinched-electron-beam diodes for pulsed radiography. In contrast to other reported work using particle-in-cell methods, we employ a ray-tracing code (trak) with advanced capabilities for modeling beam-generated magnetic fields. Ray tracing is a direct approach to a steady-state solution and involves less work than a particle-in-cell calculation. The second software component, gambet, is a new Monte Carlo code for radiation transport that incorporates effects of the complex electric and magnetic fields at the radiation target. The ray-tracing approach exhibits good convergence in calculations for the diode geometry of the compact radiography (CRAD) program at Lawrence Livermore National Laboratory. With a 1.5 MV, 30 ns driver, we predict that the diode can produce a beam with axial length ∼1  mm that generates isotropic bremsstrahlung radiation exceeding 1 rad at 1 m. The ray-tracing procedure encounters convergence problems when applied to the rod-pinch geometry, a configuration used in several pulsed radiographic machines. We observe a fundamental difference in the nature of electron orbits in the two diodes. There is an increased chance for particle-orbit feedback in the rod pinch, so that equilibrium solutions are sensitive to small changes in emission characteristics.