| Popis: |
Summary form only given. The development of coronal plasmas and other phenomena that occur early in Z-pinch implosions may significantly affect overall Z-pinch performance. At the University of Michigan, experiments have been performed to measure the composition of the coronal plasma surrounding metal wires, with focus on the presence and importance of wire impurities. A single wire Z-pinch, driven by a 2 kA, 500 ns half period current pulse, exhibits hydrodynamics of the early-time coronal plasma. Diagnostics include optical emission spectroscopy (OES) with gated ICCD or PM tube, as well as resonant and non-resonant laser imaging. OES data show that C and H are important to the development of the coronal plasma and the current. At the time of voltage collapse, singly and doubly ionized carbon emission lines dominate the spectra. Effects of wire cleaning on coronal plasma development are also presented, as well as the effects of initial wire morphology on the seeding of plasma instabilities. In addition to single-wire experiments, multi-wire experiments are being started to study coronal plasma formation, wire-wire merging, and global plasma structures. In conjunction with the multi-wire experiments, computer modeling of the inductive current distribution in the multi-wire geometries is presented. The effect of wire misplacement on pinch symmetry has been modeled. This research is directed toward improving the understanding of early-time plasma physics in Sandia's Z-machine and benchmarking ALEGRA models of wire initiation. |
