B. LeGalloudec

Design and Testing of a Load Current Multiplier on Zebra Facility

The Load Current Multiplier concept (LCM) was validated for the first time on a high‐voltage nanosecond pulse‐power generator. The designed new device allowed to increase the load current from the nominal 0.8–0.9 MA up to 1.6 MA in static loads with constant inductance and up to 1.4 MA in a planar wire‐array plasma loads. These results were achieved without modifying the generator energetic or architecture. LCM allowed both the load magnetic energy increase and the increase of soft X‐ray radiation from z‐pinch plasmas.

Implosion dynamics and Spectroscopy of X-pinches and Wire arrays with doped Al wires on the UNR 1MA Z-pinch generator

The study of implosion dynamics and spectroscopy of X‐pinches and wire arrays with Al wires alloyed or coated with other near‐Z or higher‐Z materials is discussed. In particular, X‐pinches from two combined Al 5056 and Mo wires and composed from four identical Al 5056 (5%Mg) wires and Cu clad Al (90% Al and 10%Cu) are studied. In addition, wire arrays with Alumel wires (95% Ni and 5% Al) and with Al 5056 wires (uncoated) and coated with 5% NaF are investigated. Spatially‐resolved and integrated x‐ray spectral data and time integrated and time‐gated pinhole x‐ray images accumulated in these X‐pinch and wire array experiments on the UNR 1MA Zebra generator are analyzed. Modeling of K‐shell radiation from Mg provides K‐shell plasma parameters for all Al 5056 wire experiments, whereas modeling of L‐shell radiation from Ni, Cu, and Mo provide parameters for L‐shell plasmas. The importance of using different materials or dopants for understanding of implosion dynamics of different wire materials is illustrated.

Grazing incidence extreme ultraviolet spectrometer fielded with time resolution in a hostile Z-pinch environment

This recently developed diagnostic was designed to allow for time-gated spectroscopic study of the EUV radiation (4 nm < λ < 15 nm) present during harsh wire array z-pinch implosions. The spectrometer utilizes a 25 μm slit, an array of 3 spherical blazed gratings at grazing incidence, and a microchannel plate (MCP) detector placed in an off-Rowland position. Each grating is positioned such that its diffracted radiation is cast over two of the six total independently timed frames of the MCP. The off-Rowland configuration allows for a much greater spectral density on the imaging plate but only focuses at one wavelength per grating. The focal wavelengths are chosen for their diagnostic significance. Testing was conducted at the Zebra pulsed-power generator (1 MA, 100 ns risetime) at the University of Nevada, Reno on a series of wire array z-pinch loads. Within this harsh z-pinch environment, radiation yields routinely exceed 20 kJ in the EUV and soft x-ray. There are also strong mechanical shocks, high velocity debris, sudden vacuum changes during operation, energic ion beams, and hard x-ray radiation in excess of 50 keV. The spectra obtained from the precursor plasma of an Al double planar wire array contained lines of Al IX and AlX ions indicating a temperature near 60 eV during precursor formation. Detailed results will be presented showing the fielding specifications and the techniques used to extract important plasma parameters using this spectrometer.

New results on planar wire array implosions and their comparison with cylindrical wire arrays on the 1 MA zebra generator

Summary form only given. Planar wire arrays were shown to produce the strong power and yield in EUV/X-ray region. The new results of the total radiation yield Et, time-resolved sub-keV and keV outputs, X-ray spectra and images from ten wire planar arrays from low-to high-Za materials were collected recently on Zebra at UNR. Data were compared with the similar mass cylindrical wire arrays results. Planar arrays were characterized by a short rise-time of a single radiation peak: up to 8 ns for sub-keV radiation and near 2 ns in keV and harder X-ray regions, and much higher peak power compared to cylindrical arrays usually having precursor and main peak with a fastest rise-time >10-15 ns. The largest Et>18 kJ was found for Cu and Mo planar arrays (up to 25% from an energy delivered to a load) that is higher than a maximum Etap15-16 kJ for Cu or 10 kJ for Alumel (Ni) cylindrical arrays. The radiating imploding plasma is strongly inhomogeneous. The plasma (few-mm thick in the EUV/sub-keV region) has within itself hundred-mum scale structures on the axis (in several keV quanta). The electron temperatures up to 800-1000 eV were estimated for Mo planar arrays that are much higher than for cylindrical arrays and comparable with the values for X-pinches. The implosion dynamics of wire arrays were studied using spectral and imaging techniques. The results were compared with radiation and MHD modeling

Radiative Properties, Structure, and Dynamics of Asymmetric and Symmetric, Uniform and Combined X-Pinches on 1MA Zebra Generator

Experimental results of studies of the 1MA symmetric and asymmetric, uniform stainless steel, Cu, Mo, combined Al/Mo, Mo/Al, Al/W, W/Al, and Mo/W X‐pinches are presented. Implosions of X‐pinches are studied by spatially‐resolved and time‐gated x‐ray imaging, spectroscopy, and laser probing diagnostics. New data for the total radiation yield are obtained. The planar‐shape structures of X‐pinch plasma and the corresponding electron beam is observed for the most of X‐pinches. The effects of generation of hot spots along original wires positions that are cooler than that from the cross‐wire region and arc structures from hot spots between wires are found for X‐pinches composed from Al, Cu and W wires.

Enhanced magnetic energy released in solid-state and plasma loads on a nanosecond pulse power generator

The requirements on lossless power transport through vacuum interface and MITLs limit from above the physical volume and hence inductance of the vacuum part of pulse power generators. This in turn limits the generator-to-load energy coupling and hence the magnetic energy available in vacuum loads used in high energy density physics research. We obtained on Zebra generator (1.9 Ohm, 1 MA, 100 ns) an enhanced load magnetic energy corresponding to the load current increase from the nominal 0.95 MA to 1.65 (plusmn0.05) MA. This improvement was achieved without changing the generator architecture, but through better generator-to-load energy coupling using the new Load Current Multipliers (LCM) technique. The average experimental load-to-generator current amplitude ratio in LCM with both a 7 nH constant-inductance load and with z-pinch loads was 1.7plusmn0.2. We report on new generator electrotechnical parameters with LCM and on characterization of the plasma dynamics and radiative properties of planar wire-array z-pinches at the achieved enhanced load magnetic energy level.

Spectroscopic Modeling and Comparison of Radiation from X-Pinches and Wire Arrays Produced on the 1 MA Pulsed Power Generator at UNR

Summary form only given. X-ray spectra and images from Al (with 5% of Mg and some with 5% of NaF dopants) and Cu (pure and with 4% of Ni) wire arrays and X-pinches were accumulated in experiments on the 1 MA pulsed power generator at UNR. In particular, axially and radially resolved K-shell X-ray spectra of Al, Mg, and Na and L-shell X-ray spectra of Cu and Ni were recorded by a KAP crystal (in a spectral region from 6 to 15 Aring) through different slits from 50 mum to 3 mm. In addition, spatially integrated harder X-ray spectra were monitored by a LiF crystal. Non-LTE kinetic models of Al, Mg, and Na, and of Cu and Ni provided spatially resolved electron temperatures and densities for experiments with Al and Cu loads, respectively. Advantages of using alloys and dopants with small concentrations for spectroscopic plasma diagnostics will be presented. Dependence of the plasmas spatial structures, temperatures, and densities from wire material and load configurations, sizes, and masses will be discussed

Study of Radiative Properties and Implosion Dynamics of Different Wire Arrays and Asymmetric and Symmetric Two-and Four-Wire X-Pinches on the UNR 1 MA Generator

Summary form only given. Experimental results of complex studies of the Al wire arrays at UNR 1 MA generator with different configurations and symmetric and asymmetric Cu, Mo, W, Al/Mo, Al/W, Mo/W X-pinches in EUV to hard X-ray spectral region are presented. Implosions of Z-pinch loads were studied by spatially- and time-resolved X-ray and laser probing diagnostics, EUV spectroscopy, spectroscopic modeling, and MHD simulation. In particular, data were obtained on investigation of wire-array initiation and radiation properties of Al cylindrical and linear wire arrays. New data were obtained on current distribution in imploding plasmas. In addition, X-ray radiation and electron beam characteristics from different X-pinches with two or four wires were studied. Dynamics of spatial and temporal development of a structure of X-ray emitting regions (0.05-5 keV), temporal characteristics of X-ray pulses, X-ray radiation output and electron beam characteristics were analyzed. The planar type structure of X-pinch plasmas and electron beams were observed. Comparisons with MHD modeling of certain types of wire arrays and X-pinches are presented. The competing mechanisms of generation of hot spots and the dissipation of the initial discharge X-pinch energy are discussed.