Electron dynamics in an e-beam ring diode

Modular e-beam ring diodes like the Large-Area Bremsstrahlung source (LAB) used on Maxwell Laboratory's Blackjack facility offer distinct advantages over other designs. When inductances are properly tuned, these sources are very reliable and can be arranged concentrically to illuminate a large area. Several important aspects of these sources need to be addressed before they can be made optimally compact; e.g. the effect of cathode tip geometry and gap closure on e-beam dynamics and diode impedance. Basic trends are also needed for incorporation into multiple-ring circuit models. In this study the authors employ the 2D electromagnetic particle-in-cell code ELECTRA whose equilibrium formulation allows fast calculation of the steady state e-beam configuration. Results of a number of simulations are presented showing the effects of geometry and gap closure on the performance of the diode