Plasma and beam dynamics in selfmagneticpinch electron beam diodes

Summary form only given. The self-magnetic-pinch diode is being developed as an intense electron beam source for high-power X-ray radiography. The diode geometry includes a ~5-cm long tapered cathode stalk, ~4-mm radius, with a rounded and hollow tip from which a high-current hollow electron beam is emitted. The beam is accelerated and focuses across a small (<1 cm) vacuum gap to a high-atomic-number planar target (anode) from which bremsstrahlung radiation is produced. This diode has been experimentally optimized for electrical operating parameter ranges of 1-5 MV, >50 kA, and pulse widths of 10-50 ns. Experimental data suggests that the hollow cathode region acts to inhibit the enhancement of bipolar flow by expanding electrode plasmas, thus extending the impedance lifetime of the diode. Hybrid electromagnetic particle-in-cell simulations are being used to study the dynamical evolution of cathode and anode plasmas in several of the experimentally tested cathode configurations. Computational models of plasma evolution from solid surfaces are presently under development that will allow detailed comparisons with measured data including electron beam spot size on the anode and temporal impedance history