Electron density measurements on radiographic diodes

A Mach-Zehnder interferometer was applied to radiographic diode studies conducted on the high-impedance Mercury pulsed-power generator. The interferometer was fielded in both quadrature and high-sensitivity arrangements to measure the density of the expanding electrode plasmas in a self-magnetic pinch diode. A phase shift corresponding to an electron density on the order of 10¹⁵ cm^∓3 was observed at several locations across the gap during the x-ray pulse, rising to a value of 5x10¹⁵ cm⁻³ at the time of impedance collapse. Measurements were also made of a plasma pre-fill with a chord-integrated density of 10¹⁴ cm⁻² that was injected prior to several of the pulses and affected the diode impedance. The reported work represents significant progress in the effort to overcome the challenges associated with measuring the electron density of radiographic diodes.