Plasma dynamics of a wire-shorted rod-pinch diode for flash x-ray radiography

The rod-pinch diode (RPD) is one of the most iconic load configurations for flash x-ray radiography, which offers advantages of simple structure and high-quality x-ray spot. While physical models have been well-developed for the classic vacuum RPD since the 1970s, research remains lacking for its low-impedance variant using a metal wire to pre-short the anode-cathode gap, particularly on the plasma dynamics following electrical wire explosion (EWE) in the diode. The wire-shorted RPD features an operating impedance of <1 Ω, which is desirable on a high-current low-impedance pulse driver for high x-ray dose conversion. This work investigates the joint phenomenology from the plasma diagnostics, electrical measurements, and radiation detections of a wire-shorted RPD, offering a novel perspective on its plasma behaviors. Results from both experiment and magneto-hydrodynamic simulation show that the wire trailing mass persists throughout the x-ray emission phase, with only fractional mass adjacent to the anode pushed toward the rod tip. Unlike the micro diode at rod tip in a plasma-prefilled RPD, the much denser EWE plasma in a wire-shorted RPD forms an extended current return path prior to x-ray burst, and the electrons pinched at the rod tip are emitted from a large cathode area.