| Popis: |
Summary form only given. Precursor plasmas, both the early time precursor flow of mass and the accumulation of this material on axis, have been observed on many z-pinch experiments at various facilities, including low current ( 15 MA, Z) facilities. The impact of these precursors on stagnated plasmas, and targets such as those used for inertial confinement fusion experiments, is still under evaluation. Experiments have been performed at the University of Nevada, Reno 1-MA, 100 ns Zebra facility to study these precursor plasmas with stainless steel and copper wire arrays. The wire array loads ranged from 8-16 mm in diameter, with wire numbers from 14 to 6 wires. The impact of initial load mass, initial load diameter, and initial load material on the precursor has been evaluated through spectroscopy, shadowgraphy, and fluence measurements. The time-history and radiated output of the precursor have been measured, with significant radiation observed in the precursor at photon energies > 1 keV. Plasma parameters, extracted from modeling of the spatially resolved time-integrated L-shell spectra, have shown that multiple temperatures and densities are necessary to describe the measured spectra at each spatial location. This may be due to different plasma conditions in the precursor than in the stagnated plasma. Time-resolved spectra have been collected to investigate this possibility and will be presented. Shadowgraphy has been fielded to study the precursor formation on the axis, and the structures observed in this plasma column will be compared with shadowgraphy and x-ray images of the stagnated plasmas. The differences in spatial and temporal plasma conditions and x-ray pulse shapes observed for the various materials and initial load configurations will be discussed. |
