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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.

Experiments with various wire loads from mid-atomic-number wires, which were performed on the university-scale 1-MA Zebra generator at the University of Nevada, Reno, during the last few years, are analyzed to assess the highest electron temperature reached. In particular, the results from experiments with planar wire arrays (PWAs) were considered. Load materials from mid-atomic-number such as stainless steel, Alumel, Cu, brass, Mo, and up to Ag were used to generate L-shell plasmas and to study plasma parameters. Though the full diagnostic set was utilized, the main focus was on X-ray spectroscopic data and on the non-local thermodynamic equilibrium kinetic modeling. As a result, the scaling of the maximum Te with the load material atomic number is presented for the first time in the range from Fe to Ag for L-shell plasmas from PWAs. The highest values of the electron temperature in L-shell plasmas, which are estimated from the modeling, were from both Ag PWAs and X-pinches. This work is important for the development of efficient X-ray radiators on university-scale Z-pinch generators. [ABSTRACT FROM PUBLISHER]

Experiments with single-planar wire arrays (SPWA) and double PWAs (DPWAs) with brass 310 wires were carried out on the 1-MA Zebra generator at the University of Nevada, Reno. Brass 310 (70% Cu and 30% Zn) PWAs have either 10 or 16 wires with diameters of 10.9 or 7.62 µm, respectively. The diagnostic suite included a bolometer, fast X-ray detectors, an axially resolved time-integrated spectrometer, a time-gated spectrometer, a time-gated pinhole camera, and a streak camera. A wire dynamic model was applied to study implosion characteristics, and non-LTE Cu and Zn kinetic models were used to model L-shell radiation from brass. The analysis of the time-gated spectra showed a correlation between the modeled electron temperature and the X-ray signal, and it agrees well with the maximum values from the time-integrated spatially resolved spectra. Modeling of time-gated and time-integrated spectra from brass PWAs indicates stronger opacity effects in L-shell lines for DPWAs. [ABSTRACT FROM AUTHOR]

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]

We present experiments performed on the 1 MA COBRA generator using a low density, annular, gas-puff z-pinch implosion as an opening switch to rapidly transfer a current pulse into a single metal wire on axis. This gas-puff on axial wire configuration was studied for its promise as an opening switch and as a means of enhancing the x-ray output of the wire. We demonstrate that current can be switched from the gas-puff plasma into the wire, and that the timing of the switch can be controlled by the gas-puff plenum backing pressure. X-ray detector measurements indicate that for low plenum pressure Kr or Xe shots with a copper wire, this configuration can offer a significant enhancement in the peak intensity and temporal distribution of radiation in the 1–10 keV range. [ABSTRACT FROM AUTHOR]