Search

Implosion characteristics of cylindrical arrays of aluminum (Al) or tungsten (W) wires with low number of wires were studied on the 1-MA 100-150-ns current rise time COBRA generator at Cornell University using X-ray/extreme ultraviolet detectors, time-gated cameras, spectrometers, and electrical diagnostics. Total radiation yields [E.sub.T] of 2.8 and 4.1 kJ were measured for Al and W, respectively. The yield above 0.75 keV for W arrays was lower than for Al. Al spectra imply [T.sub.e] of 250-280 eV. X-ray spectra in the 2-3-keV range from W arrays showed only very weak spectral lines. A relatively uniform precursor plasma column was observed on time-gated images in the initial implosion phase for both Al and W. Rapid radiation cooling of W plasmas after precursor plasma formation leads to a decrease of plasma [T.sub.e] before the stagnation phase of the implosion. No evidence of the increased energy deposition that could be associated with the single-shell or closed toroidal magnetic structures models was found. Index Terms--Wire arrays, X-ray imaging, X-ray source, X-ray spectroscopy, Z-pinch.

In the following experiments, we studied implosions of different wire arrays and X-pinches produced on the 1-MA Zebra generator at the University of Nevada, Reno. Diagnostics included both spatially-resolved and time-gated X-ray imaging and spectroscopy, and laser probing. In particular, we compared planar wire arrays, to which little energy could be coupled via the conventional magnetic-to-kinetic conversion mechanism, to cylindrical wire arrays of comparable dimensions and mass. The planar wire arrays were shown to radiate much higher peak power and more energy in subkiloelectronvolt and kiloelectronvolt spectral ranges than cylindrical wire arrays. We tested the theoretical conjecture that enhanced resistivity due to the small-scale inhomogeneity of wire-array plasmas has a major effect on dynamics, energy coupling and radiation performance of wire-array Z-pinches. The study of Al, Alumel, and W cylindrical wire arrays shows a wide variety of characteristic behaviors in plasma implosions discussed hereinafter. Additional experimental results for symmetric and asymmetric, uniform stainless steel, Cu, Mo, combined Al/Mo, Mo/Al, Al/W, W/Al, and Mo/W X-pinches are also presented. New data for the total radiation yield are obtained. The planar structures of X-pinch plasma and the corresponding electron beam was observed for most of X-pinches. The generation of hot spots along original wires positions--cooler than those from the cross-wire region--and arc structures with hot spots between wires were found for X-pinches composed from Al, Cu, and W wires. Index Terms--Wire arrays, X-pinches, X-ray imaging, X-ray spectroscopy, Z-pinch.

We analyzed the characteristics of energetic electron beams produced by implosions of multiplanar wire arrays, nested cylindrical wire arrays (NCWAs), and compact cylindrical wire arrays (CCWAs), as well as X-pinches. In this paper, filtered soft and hard X-ray (HXR) diodes, spatially resolved time-integrated and time-gated spatially integrated LiF crystal spectrometers, and a Faraday cup were fielded to study the time evolution and spatial distribution of electron beams. Observed Faraday cup signals (electron cutoff energy, with EB from 42 to 250 keV) always coincide with HXR signals, and their pulse shape is similar to the shape of HXR pulses. The dependence of the total energy of the electron beam (Eb) on the wire material and the geometry of the wire-array load was studied. The electron-beam energies increase with the atomic number of the wire material. Aluminum tracer wires were found to decrease Eb in loads with Cu, Mo, or W wires. The intensity of cold K- and L-shell time-gated spectra correlate with corresponding amplitudes of HXR peaks and Faraday cup signals. The timing of correlation between the onset of energetic electron beams, HXR generation, and appearance of trailing mass for NCWAs and CCWAs is presented and discussed. [ABSTRACT FROM AUTHOR]