Electron flow and impedance of an 18-blade frustum diode

A new, large-area, high-uniformity, flash x-ray source that efficiently couples electrical energy to photon energy has been successfully constructed and tested on the 1-MV, 2-MA electron accelerator SPEED (short pulse experimental electron device). The source employs 18 individual blade diodes arranged in the configuration of a frustum. Each blade was magnetically isolated on the real-cathode side of an anode foil, but not on the virtual-cathode side. The operation of the diode was heavily diagnosed using 24 Rogowski coils, a vacuum voltage monitor, p-i-n diode detectors, an 80-element TLD array, and a fast-framing x-ray pinhole carnera. The individual blade diodes were found to exhibit line pinching, end-to-end pinching, and minimal electron reflexing through the Ta anode foil, with a radiation yield that agreed with Monte Carlo simulations. The end-to-end pinch location could be controlled by tapering the anode–cathode gap. The impedance depended on only the smallest spacing, and was independent of pinch location.