Monochromatic X-ray self-emission imaging of imploding wire array Z-pinches on the Z accelerator

A monochromatic X-ray self-emission imaging diagnostic has been developed for the Z accelerator, which drives 20 MA in 100 ns to implode wire array Z-pinches, generating up to 250 TW of soft X-ray radiation. This instrument reflects eight pinhole images from a flat Cr/C multilayer mirror (MLM) onto a 1-ns time-resolved microchannel plate detector. The MLM reflects 277-eV photons with ∼5-eV bandwidth and 20% peak reflectivity, and an aluminized parylene filter shields the detector from visible light. High-energy bremsstrahlung X-rays do not follow the reflected beam path, and so the background on the shielded detector is reduced compared to a standard pinhole camera. The MLM-reflected images offer low-photon-energy spectral resolution that filtration alone cannot, yielding high-quality images of the final stages of the Z-pinch implosion. Initial data on Z from a Cu wire array will be presented. Observed phenomena include implosion instabilities, zippered implosion of a piston onto a precursor column during the onset of stagnation, accretion of trailing colder mass during the X-ray pulse, and cathode reemission. The inferred implosion velocity is significantly less than thin-shell implosion model calculations, and well below what is required for efficient Cu K-shell radiation. Instability-dominated, bright-spot Cu K-shell emission is seen on a second adjacent eight-frame filtered pinhole camera that is in the same beamline.