Micropinch Formation Dynamics in Hybrid X-pinches

An X-ray streak camera with a temporal resolution of 17 ps was used to investigate the micropinch formation dynamics in Cu and Ni hybrid X-pinches on a 400 kA peak current, 50 ns rise time pulsed-power machine. The focus was on L-shell radiation with energies below 1 keV before the X-pinch continuum burst which signals X-pinch micropinch formation to determine imploding plasma conditions just before stagnation. No Li-like copper lines were observed in Cu spectra prior to micropinch formation. Analysis of Ne-like copper lines pre-continuum indicates an average electron temperature of ~200 eV and 4.5x1028 𝑚−3 electron density. The spectra suggest that the electron temperature jumps to ~1 keV inferred from the continuum and the postcontinuum line emission. There was no sign of a rapid temperature change or a substantial surge in radiation emission during the 200 ps pre-continuum X-ray burst to support a major role in micropinch formation for the radiative collapse process. Two-dimensional extended MHD simulations coupled to a collisional-radiative spectral analysis code were used to help develop a new hypothesis that does not involve radiative collapse to explain micropinch formation. These simulations highlight the role of the rapid radial implosion and compression of high-temperature, low-density plasma, the axial outflow of the cold wire core, the dynamo term in the generalized ohms law, and the importance of dynamic pressure of the imploding Cu plasma in the final phase of the micropinch formation process.