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We present a broad study of linear, clustered, noble gas puffs irradiated with the frequency doubled (527 nm) Titan laser at Lawrence Livermore National Laboratory. Pure Ar, Kr, and Xe clustered gas puffs, as well as two mixed-gas puffs consisting of KrAr and XeKrAr gases, make up the targets. Characterization experiments to determine gas-puff density show that varying the experimental parameter gas-delay timing (the delay between gas puff initialization and laser-gas-puff interaction) provides a simple control over the gas-puff density. X-ray emission (>1.4 keV) is studied as a function of gas composition, density, and delay timing. Xe gas puffs produce the strongest peak radiation in the several keV spectral region. The emitted radiation was found to be anisotropic, with smaller X-ray flux observed in the direction perpendicular to both laser beam propagation and polarization directions. The degree of anisotropy is independent of gas target type but increases with photon energy. X-ray spectroscopic measurements estimate plasma parameters and highlight their difference with previous studies. Electron beams with energy in excess of 72 keV are present in the noble gas-puff plasmas and results indicate that Ar plays a key role in their production. A drastic increase in harder X-ray emissions (X-ray flash effect) and multi-MeV electron-beam generation from Xe gas-puff plasma occurred when the laser beam was focused on the front edge of the linear gas puff.

X-ray spectroscopy is an indispensable tool in the study of highly ionized high-Z plasmas. A new non-local thermodynamic equilibrium (non-LTE) model for M-shell xenon was developed, encompassing the 9-14 A wavelength range. We present comparison of this new M-shell xenon model to experimental data from reversed polarity gas-puff Z-pinch 1 and laser-irradiated gas-puff 2 xenon experiments. The model matches experimental spectral features which provides estimates of useful plasma properties, such as electron temperature, density, and presence of hot electrons. Specifically, the new M-shell xenon model is compared with x-ray spectra produced from the SHOTGUN-III device at Nihon University- Japan and from the Titan laser at Lawrence Livermore National Laboratory. Notably results include a robust description of ionization stages from Zn-like to Ar-like xenon and evidence of the effects of hot electrons in the reversed polarity gas-puff Z-pinch experiment, highlighted by the comparison of both experiments. Future applications of this model are discussed.

In previous studies using the University of Nevada, Reno's (UNR's) high-impedance Zebra Marx generator (1.9 Ω, 1.7 MA, 100 ns), Double Planar Wire Arrays (DPWAs) proved to be excellent radiators, and Double Planar Foil Liners (DPFLs) proved useful for future inertial confinement fusion applications. This article presents the results of joint UNR/UM (University of Michigan) experiments with aluminum (Al) DPWAs, Al DPFLs, and tungsten (W) DPWAs using UM's Michigan Accelerator for Inductive Z-Pinch Experiments (MAIZE) generator, a low-impedance Linear Transformer Driver (LTD) (0.1 Ω, 0.5–1 MA, and 100–250 ns). The main goals of this study were twofold: the first was a pioneering effort to test whether a relatively heavy Al DPFL could successfully be imploded on a low-impedance university-scale LTD like the MAIZE generator, and, if so, to analyze the results and make comparisons to the optimized, lighter DPWA configurations that have been previously studied. The DPWAs consisted of two planes of micrometer-scale diameter Al or W wires, while the DPFLs consisted of two planes of micrometer-scale thickness Al foils. Diagnostics include filtered Si-diodes, an absolutely calibrated filtered PCD, x-ray pinhole cameras, spectrometers, and gated optical self-emission imaging. The implosion dynamics and radiative properties of Al DPWAs and DPFLs and W DPWAs on the MAIZE LTD are discussed and compared. Time-dependent load inductance calculations derived from measurements of the load current and a MAIZE circuit model provide a relative measurement of pinch strength. In experiments on MAIZE, W planar wire arrays exhibited a higher peak load inductance throughout the pinch than Al DPWAs and DPFLs, while x-ray pulses from Al DPFLs had the longest emission duration.

The use of laboratory experiments as plasma creating sources is a valuable tool for understanding astrophysical observations. Recently plasma created through irradiation by lasers with relativistic intensities has been used to study effects of hot electrons and X-ray pumping on X-ray formation of multiply charged ions spectra. This paper discusses the formation of K-shell Fe spectra recorded from a plasma irradiated by 35 fs pulses with intensities of 1021 W/cm2. Modeling of the spectra suggests three different regions of plasma radiation including a cold ~10 eV region, a mild ~700 eV region, and a hot ~3500 eV region. The influence of hot electrons and X-ray pumping is discussed and a comparison with K-shell Fe spectra from a 1 MA X-pinch experiment is included to highlight the differences due to the shorter time frame of the laser–plasma interaction experiment.

Experiments of x-ray emission from Ar, Kr, and Ar/Kr gas jet mixture were performed at the UNR Leopard Laser Facility operated with 350 fs pulses at laser intensity of 2 × 1019 W/cm2 and 0.8 ns pulses at an intensity of 1016 W/cm2. Debris free x-ray source with supersonic linear nozzle generated clusters/monomer jet with an average density of ≥1019 cm−3 was compared to cylindrical tube subsonic nozzle, which produced only monomer jet with average density 1.5–2 times higher. The linear (elongated) cluster/gas jet provides the capability to study x-ray yield anisotropy and laser beam self-focusing with plasma channel formation that are interconnecting with efficient x-ray generation. Diagnostics include x-ray diodes, pinhole cameras and spectrometers. It was observed that the emission in the 1–9 keV spectral region was strongly anisotropic depending on the directions of laser beam polarization for sub-ps laser pulse and supersonic linear jet. The energy yield in the 1–3 keV region produced by a linear nozzle was an order of magnitude higher than from a tube nozzle. Non-LTE models and 3D molecular dynamic simulations of Ar and Kr clusters irradiated by sub-ps laser pulses have been implemented to analyze obtained data. A potential evidence of electron beam generation in jets' plasma was discussed. Note that the described debris-free gas-puff x-ray source can generate x-ray pulses in a high repetition regime. This is a great advantage compared to solid laser targets.

We begin with a brief review of the work on x-ray spectroscopy and imaging of tungsten (W) single wires, wire arrays, X-pinches and their applications [1]–[6], and move on to the most recent results. Two sets of the new experiments performed in 2017 on two university-scale Z-pinch generators with different architecture will be considered: W Double Planar Wire Arrays (DPW A) at the University of Michigan's (UM) low-impedance Linear Transformer Driver (LTD) MAIZE generator and W X-pinches at the University of Nevada, Reno's (UNR) high-impedance Marx bank Zebra generator. Though a comprehensive set of diagnostics was implemented in both types of experiments, here we will focus mostly on x-ray spectroscopy and imaging results and their interpretation, as well as applications to electron beam studies and spectropolarimetry of W pulsed-power plasmas. Two axially-resolved spectrometers were implemented: the first was the x-ray convex crystal spectrometer with a potassium acid phthalate (KAP) crystal (2d = 26.63 A and R=51 mm) for the spectral region between 4 - 10A and another spectrometer with a lithium fluoride (LiF) convex crystal (2d = 4.027 A and R=25.4 mm) for hard x-ray radiation in a spectral band 1 - 2.4 A. X-ray time-integrated pinhole cameras recorded the images with cutoff energies of 1.4 and 3.5 keV. The very complex soft x-ray M-shell W spectra recorded by the KAP spectrometers are modeled and studied in detail to provide valuable information about “hot” W plasmas and electron beams. The analysis of the hard L-shell W spectra recorded by the LiF spectrometers from much cooler W plasma as well as from the anode is applied to the studies of electron beams, and to explore the possible development of hard x-ray spectropolarimetry of W plasmas. In this regard, the results for W DPW As on UM-MAIZE and W X-pinches on Zebra at UNR are evaluated, compared, and discussed.

The results of the 2017 experiments with tungsten (W) Double Planar Wire Arrays (DPWA) at the University of Michigan's (UM) low-impedance Linear Transformer Driver (LTD) MAIZE generator ( $(0.1 \Omega, 0.5-1 Ma$ , and 100–250 ns) are presented and analyzed. For these experiments, the peak of generator current was typically near 500 kA. Observations were made previously and tested for Al DPWAs on MAIZE1. It was earlier determined that DPWA implosion dynamics depend strongly on the aspect ratio $\phi,$ defined as array width to inter-planar gap, which ranged from 0.82 to 2.33, with array masses ranging from 55 to $76 \mu \mathrm{g}/\text{cm}$ . New calculations were made to derive the time-dependent inductance throughout implosions on the MAIZE generator (using the formalism in ref.2), which were then used to calculate implosion characteristics and the dynamic plasma radius. This information can be used to better optimize future DPWA loads and measure the strength of the pinch. The diagnostics include an absolutely calibrated filtered photoconducting detector - PCD (>2.4 keV, time resolution 0.5 ns) and Si-diodes (> 1.4 ke V, time resolution > 1 ns), x -ray pinhole cameras, spectrometer, and 12-frame optical shadowgraphy system. The results are compared to those obtained earlier at the University of Nevada, Reno's (UNR) high-impedance Marx bank Zebra generator ( $1.9 \Omega, 1 \text{MA}, 100 \text{ns}$ ).

Results of the research with triple planar wire arrays (TPWAs) made of uniform Mo or from combined Mo and Al planes obtained on the University of Nevada, Reno (UNR) Zebra generator are presented. The combined loads consisted of either two Mo planes on the outside with Al in the center or two Al planes on the outside with Mo in the center. Different wire diameters of Mo and Al were used to keep the planes approximately the same mass Also, the change of inter-planar gap was investigated: decreasing the inter-planar gap from 3.0 mm to 1.5 mm led to a higher yield of 25 kJ (up from 16 kJ), close to the highest yield from Mo double planar wire arrays. The question of how Mo and Al plasmas mix is raised and is examined and as a result it is demonstrated that L-shell Mo (∼1000 eV) and K-shell Al (∼400 eV) plasmas have very different electron temperatures. Additionally, time-gated K-shell Al and Mg plasma parameters were modeled, giving important information on the time-evolution of such plasmas. The future work on radiation from mixed higher and lower atomic number wire arrays is discussed.

Since the first wire-array tungsten (W) experiments on Z at SNL, where the record x-ray power of 200 TW and x-ray yield of nearly 2 MJ were achieved 1, such arrays were actively studied and considered for various applications including inertial confinement fusion (ICF) 2. More recently, W Double Planar Wire Arrays (DPWAs) were suggested and tested for indirect drive ICF 3. DPWA consists of two parallel planes of wires of the same (uniform) or different (mixed) wire materials. W DPWAs have previously demonstrated the highest (among PWAs) radiation yield (up to 30 kJ), compact size (few mm), and strong electron beams at the Universityscale high-impedance generator 3. During the last few years we have reported on the outcome of the experiments with uniform and mixed Al and stainless steel DPWAs on the University of Michigan’s low-impedance Linear Transformer Driver (LTD) MAIZE generator. Here we present the results of the most recent campaign with W and W/Al DPWAs recorded using filtered x-ray diodes, x-ray spectrometers and pinhole cameras, and a twelve frame shadowgraphy system. For the first time, implosion of W wire arrays on LTD generator in USA was demonstrated and analyzed. In particular, uniform W and mixed W/Al DPWAs with a mass up to 87 μg arranged in various configurations were successfully imploded at the current of 0.5 MA during $\sim 210$ns. The most interesting results were obtained with W/Al DPWAs where a long-term standing shock wave was consistently formed at the W side, which was also observed at the high-impedance Zebra generator at UNR. In addition, soft (4-7 A) and hard (1-2.4 A) line radiation was substantially suppressed by including the Al plane.

An exploration of the implosion properties and X-ray radiation pulses from tungsten-based planar wire array Z-pinch experiments is presented, with an emphasis on loads mixed with aluminum. These experiments were carried out on Zebra, the 1.0 MA pulse power generator at the Nevada Terawatt Facility. A suite of diagnostics was used to study these plasmas, including X-ray and EUV Si diodes, optical imaging, laser shadowgraphy, and time-gated and time-integrated X-ray pinhole imagers and spectrometers. Specifically, loads with relatively large inter-wire gaps where tungsten is placed in the center of a planar configuration composed primarily of aluminum showed unusual characteristics. These loads are shown to generate a “bubbling” effect in which plasma from the ablation of outer aluminum wires is temporarily hindered from converging at the center of the array where the tungsten wire is located. Reproduction of these experiments with variations to load geometry, materials, and mass distribution are also presented and discussed in an attempt to better understand the phenomenon. In addition, a theoretical model has also been applied to better understand the dynamics of the implosions of these loads. Applications of this effect to radiation pulse shaping, particularly with multi-planar arrays, are also discussed.

International audience; Double Planar Wire Arrays (DPWA), which consist of two parallel rows of wires, have previously demonstrated high radiation efficiency, compact size, and usefulness for various applications in experiments on a University-scale high-impedance Z-pinch generator1. Recently, we successfully performed two experimental campaigns with PWAs on the University of Michigan's low-impedance MAIZE (Linear Transformer Driver (LTD)-driven generator, 0.1ohm, 0.5-1 MA, 100-180 ns) in collaboration with the UM team. The details and the analysis of the results of the first experimental campaign can be found in Ref. [2]. The second experimental campaign was focused on studying the implosion and radiative characteristics of DPWAs using a diagnostic set similar to the first campaign, including: filtered X-ray diodes, X-ray spectrographs and pinhole cameras, and a new four-frame shadowgraphy system with 2-ns, 532 nm frequency doubled Nd:YAG laser. Here we present the results of four, mixed-DPWA shots with the load consisting of one plane with 6 Al wires of 10¿¿m diameter and another plane of 6 stainless steel wires of 5.1 ¿¿m diameter. The rise-time of the current varies between 175 and 225 ns and shadowgraphy images cover the broad span of time from as early as 116 ns to as late as 304 ns. The shadowgraphy images show ablating and imploding mixed DPWAs that are very different from the images of uniform DPWAs. There is a clearly observed asymmetry of implosions of two wire array planes dependent on the material of each plane, (early time images in particular), captured also by X-ray pinhole images. WADM is used for the analysis of shadowgraphy images. X-ray spectra display both K-shell Al and L-shell Fe features analyzed with non-LTE modeling. Advantages of using mixed wire arrays are discussed. [1] V. L. Kantsyrev et al, Phys. Plasmas 15, 030704 (2008). [2] A.S. Safronova, V.L. Kantsyrev, M.E. Weller, V.V. Shlyaptseva, I.K. Shrestha, M. Lorance, M. Schmidt-Petersen, A. Stafford. M. Cooper, A.M. Steiner, D.A. Yager-Elorriaga, S.G. Patel, N.M. Jordan, R.M. Gilgenbach, A.S. Chuvatin, IEEE TPS, Special Issue on Plenary and Invited papers from ICOPS 2015, to be published, April 2016. * This work was supported by NNSA under DOE Cooperative Agreement DE-NA0001984.

A gas jet containing a mixture of monomers and clusters was characterized and studied as an x-ray radiation source produced by a TW-class laser pulse. Gas jet parameters such as average density and cluster size were measured at the UNR Radiation Physics Laboratory using both optical interferometry and Rayleigh scattering techniques, respectively. Several noble gases were used in the gas jet: Ar, Kr, and Xe. Additionally, mixtures of two or three of those gases were also tested. By changing the gas jet backing pressure as well as the gas delay time between jet initiation and laser interaction with the jet, both the density and cluster size of the gas jets can be varied. Having control over the composition, density, and cluster size of the gas jets is important when considering them as targets for intense laser pulses. Our gas jets were irradiated with the 1057 nm short pulse (350 fs) UNR Leopard laser with an intensity of 1019 W/cm2 in the focus spot. Time resolved diagnostics included filtered Si-diode detectors (1.4–9 keV), filtered absolutely calibrated PCDs (>2.4 keV), and Faraday cups. An x-ray spectrometer and two three-channel x-ray pinhole cameras provided time integrated diagnostics on the gas jet plasma. Anisotropy of x-ray radiation with respect to laser beam polarization was observed in all spectral regions. The coefficient of conversion of laser energy into x-rays was measured with a maximum of 10−3. Most importantly, the mixtures of two or three gases each produced higher x-ray yields than the pure gases. Non-LTE modelling and a molecular dynamics (MD) code have been employed to determine plasma and cluster parameters. Electron temperatures and densities of the laser plasma of the mixed gases were higher than the pure gases.

Many aspects of physical phenomena occurring when an intense laser pulse with subpicosecond duration and an intensity of ${10}^{18}--{10}^{19}\phantom{\rule{0.16em}{0ex}}\mathrm{W}/{\mathrm{cm}}^{2}$ heats an underdense plasma in a supersonic clustered gas jet are studied to determine the relative contribution of thermal and nonthermal processes to soft- and hard-x-ray emission from debris-free plasmas. Experiments were performed at the University of Nevada, Reno (UNR) Leopard laser operated with a 15-J, 350-fs pulse and different pulse contrasts (${10}^{7}$ or ${10}^{5}$). The supersonic linear (elongated) nozzle generated Xe cluster-monomer gas jets as well as jets with Kr-Ar or Xe-Kr-Ar mixtures with densities of ${10}^{18}--{10}^{19}\phantom{\rule{0.16em}{0ex}}{\mathrm{cm}}^{\ensuremath{-}3}$. Prior to laser heating experiments, all jets were probed with optical interferometry and Rayleigh scattering to measure jet density and cluster distribution parameters. The supersonic linear jet provides the capability to study the anisotropy of x-ray yield from laser plasma and also laser beam self-focusing in plasma, which leads to efficient x-ray generation. Plasma diagnostics included x-ray diodes, pinhole cameras, and spectrometers. Jet signatures of x-ray emission from pure Xe gas, as well as from a mixture with Ar and Kr, was found to be very different. The most intense x-ray emission in the 1--9 KeV spectral region was observed from gas mixtures rather than pure Xe. Also, this x-ray emission was strongly anisotropic with respect to the direction of laser beam polarization. Non-local thermodynamic equilibrium (Non-LTE) models have been implemented to analyze the x-ray spectra to determine the plasma temperature and election density. Evidence of electron beam generation in the supersonic jet plasma was found. The influence of the subpicosecond laser pulse contrast (a ratio between the laser peak intensity and pedestal pulse intensity) on the jets' x-ray emission characteristics is discussed. Surprisingly, it was found that the x-ray yield was not sensitive to the prepulse contrast ratio.

The relative amount of Kα radiation emitted by partially ionized copper and zinc from planar wire arrays on the 1 MA Zebra generator at the University of Nevada, Reno, does not correspond to the composition (70% copper, 30% zinc) of the array's brass wires. For example, the copper Kα line at 8 keV was observed to be much stronger than would be expected from zinc's Kα radiation at 8.6 keV, but this ratio also reversed, more emission from zinc than from copper, during the X-ray pulse. An excess of Kα photons from copper is consistent with a beam of electrons with energies above copper's K-edge but below that of zinc, but the opposite case is perplexing. Preferential ablation of Zn over Cu early in the current pulse could be a contributing factor, but opacity effects are not. Synthetic spectra for brass computed by a non-LTE collisional-radiative model that includes an electron beam component compare well with observed K-shell spectra, and suggest the parent ions of the Kα emission. These ionization stages are consistent with L-shell spectra. This comparison also indicates that the total energy in the electron beam increases towards the end of the radiation pulse while the electron temperature decreases. The crucial diagnostic in this measurement is a time-resolved X-ray spectrometer based on a LiF crystal.

The LTE Saha–Boltzmann plasma ionization balance model and the Braginskii plasma electric resistance model are compared with the results by a suite of codes based on the average-atom model, which is a quantum-mechanical version of the Temperature Dependent Thomas–Fermi Theory. The analysis is focused on low-Z Al, mid-Z Cu and higher-Z Mo plasmas over broad ranges of electron temperature Te and electron number density ne. Calculations of mean ion charge by these two LTE models are compared to the results produced by non-LTE atomic kinetic codes. The applicability of the LTE and non-LTE models to the description of the radiative properties of highly-radiating z-pinch plasmas is also discussed. Two different approaches to the calculation of plasma resistance and their effects on line radiation mechanisms are analyzed.

Proton radiography is a very powerful diagnostic but in some high debris environments it may be challenging to get a good signal-to-noise ratio radiograph to gain insights into the electric and magnetic field topology, and thus the basic physics. Such environments are produced for example on z-pinches and also on lasers such as the National Ignition Facility. We demonstrate here the feasibility of clean, very high signal-to-noise ratio proton radiographs in extremely hostile environments.

Spectral tungsten data taken on an electron beam ion trap (EBIT) at Lawrence Livermore National Laboratory are analyzed between 3 and 8 Å for electron beam energies between 2.5 and 4.1 keV. The advantage of using charge state balancing with the experimental EBIT spectra for the identification of lines is employed and discussed. Theoretical Hebrew University Lawrence Livermore Atomic Code (HULLAC) modeling is then benchmarked against the experimental EBIT results. In particular, Co-, Ni-, Zn-, Cu-, Ga-, and Ge-like transitions were modeled independently using HULLAC to aid in charge state balancing. This model is then compared with Z-pinch plasma data collected on Zebra, the 1.6 MA pulse power generator located in the Nevada Terawatt Facility at the University of Nevada, Reno. The model is used to calculate charge balance and average ionization levels of these experimental plasma results, with particular focus on planar tungsten arrays.

X-pinches are very good sources of x-rays and can be used for studying radiative properties of high density and temperature plasmas with scale from a few μm to several mm in size. An X-pinch is formed by the touch-crossing of two or more wires between the electrodes of a high-current pulsed-power generator. As a result of current quickly vaporizing and strongly ionizing the wire material, X-pinch yields short (few nsec) x-ray bursts from one or few bright plasma spots near the wire cross point. Other distinct features of X-pinches are strong electron beams, which make them attractive objects for x-ray spectropolarimetry, as well as plasmas jets for astrophysical applications. Recently, we spectroscopically studied x-ray L-shell and K-shell radiation from variety of X-pinches from different materials and load configurations. In the present work, the results of x-ray spectroscopy and imaging of X-pinches from stainless steel are presented. The application of these results to astrophysics is highlighted.

The spectroscopic features of implosions of Mo single- and double-planar wire arrays are studied. The experiments were performed on the 1 MA Zebra generator at UNR. Implosions of Mo planar wire arrays radiate high peak powers and produce high-temperature L-shell plasmas. In particular, plasma electron temperature of single-planar wire arrays of Mo reached ∼1375 eV. To estimate and analyze the evolution of plasma parameters in space and time, spatially resolved, time-integrated L-shell Mo X-ray spectra as well as time-gated and time-integrated pinhole images were collected and analyzed. A non-LTE kinetic model was applied to study the spatial structures, temperatures and densities of different wire loads of Mo planar wire arrays. Effects of non-Maxwellian hot electrons on L-shell radiation of Mo are discussed. Furthermore, Mo planar wire arrays generate bright spots or clusters of bright spots along the axial directions. Temperature and density gradients inside these bright spots or its clusters are also investigated. The results are compared with results of previous experiments with X-pinches on UNR Zebra and nested wire arrays at SNL-Z. Radiation magnetohydrodynamics modeling was performed to analyze the mechanisms of Z-pinch plasma heating in the presence of strong density gradients.

International audience; Single Planar Wire Arrays (SPWA) and Double Planar Wire Arrays (DPWA), which consist of one or two parallel rows of wires, respectively, have demonstrated high radiation efficiency (up to 30 kJ), compact size (1.5-3 mm), and usefulness for various applications in experiments on the high-impedance Zebra (1.9Ω, 1 MA, 100 ns). For example, DPWAs are very suitable for the new compact multi-source hohlraum concept, astrophysical applications, and as an excellent radiation source. Their implosion dynamics strongly depends on the critical load parameter, the aspect ratio Φ (width to inter-planar gap Δ) as well as on load wire material and mass. We have studied implosion dynamics and radiative properties of DPWAs at the enhanced Zebra current of 1.5-1.7 MA and have demonstrated the new regimes of implosions with asymmetric jets, no precursor formation, and very early radiation for larger sized (Δ=9 mm, Φ=0.54) and precursor formation and strong “cold” Ka emission for standard sized (Δ=6 mm, Φ=1.28) DPWAs.

International audience; A new compact Z-pinch x-ray hohlraum design with multiple parallel-driven x-ray sources was jointly proposed by the Sandia National Laboratories and the University of Nevada [1]. The first proof-of-principle experimental demonstration of the full configuration of this compact hohlraum with central reemission target and tailored shine shields (to provide a symmetric temperature distribution on the target) was achieved at the 1.7 MA UNR Zebra generator [2]. VisRad (PRISM Computational Sciences Co.), a 3-D view factor code, is used to simulate the multi-dimensional radiation environment within this new compact hohlraum configuration that incorporates multiple compact (mm-scale) planar wire array (PWA) x-ray sources that surround a reemission target in the center of the hohlraum cavity, allowing a reduction of hohlraum surface area and potentially providing a hotter x-ray environment. View factor modeling is a valuable design tool, allowing us to improve rapidly on experimental design and to demonstrate the feasibility of the concept for hohlraum and ICF studies on a 1-2 MA university-scale pulsed power platform. Double-PWA sources (DPWA) were modeled and used in experiments due to much better pulse shaping properties compared with single PWAs. Also, we are taking into account that the W DPWA is an anisotropic x-ray source and maximum radiation is emitted in the direction parallel to the wire planes. Different versions of compact hohlraum with two W DPWA sources and central cavity between them were analyzed using VisRad code. Simulations have predicted a reemission plastic target radiation temperature Trad ~ 39eV, showing good correlation to experimental data 37 3 eV The possibility of optimization of new compact configuration was demonstrated by changing relative volume of central cavity. Special emphasis is made on Trad uniformity at the reemission target surface by analysis of compact holraum configuration of 6 or more - PWA pinches proposed in Ref. [2] to reach better symmetry of hohlraum exposure. The scaling of this 6 DPWA sources hohlraum configuration using VisRad for higher current 20 MA generators (as Sandia National Laboratories Z facility) show that central target Trad ~ 85 eV is reachable. VisRad simulation has shown that x-ray power flux in new compact hohlraum might be ~1.3 times higher if W sources will be changed with Au sources.

International audience; Oral presentation Load Current Multiplier (LCM) continues to be successfully applied on Zebra at UNR. Here we consider further, expanded applications of LCM. Time-shaping of magnetic pressures on pulsed facilities is useful for such a number of High Energy Density Physics (HEDP) applications such as dynamic material properties studies1,2, high gain ICF research3 and instability growth studies4. The Dynamic LCM (DLCM) technique was recently developed for profiling the dynamic pressure ramp with good reproducibility on the microsecond SPHYNX generator (left plot)2. The present report analyses applications of this technique on Pulse Forming Line (PFL) nanosecond generators. The right plot presents simulated load currents Id and load liner accelerations ad for a 0.2 Ω PFL with the voltage Veq. without (dashed lines) and with (solid lines) DLCM for the imploding solid-state load of Ref. 2. DLCM here is an additional compact (5×10 cm) hardware installed between the PFL and the load with an imploding annular plasma shell inside. We report circuit analysis and MHD simulations that identify critical DLCM and load configuration parameters allowing to control the load current ramp. We demonstrate that not only the load magnetic pressure time-dependence can be controlled in the HEDP loads above but also the load current amplitude can be increased with respect to the direct PFL-driven case (right plot).

Some aspects of physical phenomena occurring when an intense laser pulse with sub-ps duration and intensity > 1018-1019 W/cm2 heats under-dense plasma in supersonic clusters/gas jet from gas-puff system were studied to determine the relative contribution of these processes to soft and hard x-ray emission from debris-free plasmas. Experiments were performed at the UNR Leopard laser operated with 15J / 350 fs and different pulse contrast (107 or 10−5). The supersonic linear (elongated) nozzle generated Ar and Kr clusters/monomer jets as well as jets with Ar/Kr or Ar/Kr/Xe mixtures with density > 1019 cm3. In prior laser heating experiments, all jets were probed with optical interferometry and Rayleigh scattering to measure jet density and cluster distribution parameters. The elongated jet provides the capability to study laser beam self-focusing in plasma that is interconnecting with efficient x-ray generation. The laser radiation flux density in the focal spot was up to 2 × 1019 W/cm2. Plasma diagnostics included x-ray diodes, pinhole cameras and spectrometers. Jet signatures of x-ray emission from pure Ar carrier gas as well as from mixture with lower Kr concentration and Ar/Kr mixture with adding Xe gas, were found to be very different. The most intense x-ray emission was observed in a wide spectral region 1–9 keV from these gas mixtures compared to pure Ar or pure Kr carrier gases. Also, this x-ray emission was strongly anisotropic depending on the direction of laser beam polarization. Non-LTE models have been implemented to analyze the x-ray spectra. It was shown that Ar/Kr jet plasma was hotter than that from pure Kr. X-ray spectra of Ar carrier gas (only “cold” Ka line) were similar to the spectra obtained early from subsonic tube nozzle (no clusters in jet). It can be explained by the fact that Ar in Ar/Kr mixture did not generate clusters as opposed to Kr. Evidence of electron beam generation in supersonic jets' plasma was found. Influence of fs laser pulse contrast level on x-ray emission characteristics is discussed. Future research will focus on the study of cluster formation in linear supersonic jets with Ar carrier gas and Kr and Xe impurities, varying its parameters for optimization of x-ray yield and power. Another goal is to determine optimal conditions for possible application of x-ray source with gas mixture jets at larger sub-ps laser facilities.

Linear Discriminant Analysis (LDA) is applied and compared with the Principal Component Analysis (PCA) and the H- and He-like line ratio diagnostics to investigate the electron beam effects on the laser produced K-shell Al synthetic spectra1,2. The experiments were performed at the Leopard Laser Facility of NTF/UNR (1.057 μm Ti:Sapphire/Nd:glass laser system) with 0.8 ns pulses with 15 J of energy, focused into 10 μm diameter spot on the 50 μm thick flat Al foil target. The spectrum was obtained by the high resolution focusing spectrometer with spatial resolution using a spherically bent mica crystal. The plasma electron temperature, density and electron beam fractions of laser produced K-shell Al plasma (Shot 556) were extracted using coefficients of discriminant and principal components produced from the non-LTE collisionally radiative K-shell Al model. The modeled plasma electron temperatures and densities are about Te∼270 eV and ne=3×1021 cm−3 in the presence of electron beams with fraction of f∼0.05 and energy centered at ∼10 keV.

Experiments with X-pinches made with both Mo and W wires have been performed on 1-MA pulsed power generators at Cornell University and University of Nevada, Reno. X-ray images and spectra have been studied and compared for three different configurations of X-pinch loads with Mo and W wires. For all X-pinches, the image size decreases with decreasing wavelength and photoconducting diode (PCD) signals show multiple bursts except for one variant of the mixed Mo and W configurations. Time-gated, as well as time-integrated, images indicate the presence of radiation from energetic electrons. Previous experience with application of L-shell Mo modeling to various Z- and X-pinch experiments helped to determine plasma parameters in the X-pinches studied here, and permitted identification of M-shell W spectral features useful for plasma parameter estimation

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 ET 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 Te 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 Te 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

A Faraday rotation diagnostic was applied for the investigation of magnetic fields in plasma of 1-MA wire arrays and X-pinches. Laser-probing diagnostics at the Zebra generator include a four-channel polarointerferometer and a four-frame shadowgraphy. The Faraday rotation diagnostic consists of shadow and Faraday channels, shearing air-wedge interferometer, and an additional schlieren channel. The implosion dynamics of the wire arrays were studied. A current in the plasma column of Al low-wire number arrays was found by the Faraday rotation diagnostic. Optical diagnostics showed a turbulent plasma and bubblelike objects in the plasma column of Al wire arrays. The Faraday rotation diagnostic demonstrated a complicated structure of magnetic fields in X-pinch plasma

Dense z-pinches produced by 100 ns implosions of wire arrays or gas puffs produce substantial soft X-ray power. One class of z-pinch radiation sources includes low- to moderate-atomic-number K-shell radiators, such as aluminum and iron. These loads are designed for 1–10 keV K-shell X-ray generation, and offer opportunities for crystal spectroscopy that can reveal fundamental properties of the plasma when studied using plasma spectroscopic modeling. Typically these plasmas are characterized by ion densities of ∼ 10 20 cm - 3 , diameters of 1–5 mm, electron temperatures up to several keV, and a range of opacities of the K-shell lines. Measurements from wire arrays on Sandia's 20 MA Z accelerator are presented along with collisional radiative and hydrodynamic simulations. The impact of opacity and 3D structure on non-LTE, non-diffusive radiation transport and X-ray production is discussed.

The presence of collimated 1.5–2.0 MeV electron beams in 0.9–1.0 MA high-Z X-pinch plasmas leads to the generation of an anisotropic hard x-ray radiation (more than 50–100 keV) in the crossing point of the wires, with a 1–2 mm size source and a time duration of 100–150 ns. The side-on measured electron temperature is higher than the end-on. Introducing of a synchrotron radiation in a side-on direction is used for the explanation of the phenomenon. The new results of time-resolved 0.16–10 keV x-ray imaging and spectroscopic study of the development of jets and hot spots in X-pinches are presented. The plasma parameters varied significantly for consecutive x-ray bursts (hot spots) during the same X-pinch discharge. A minimum duration of x-ray pulses was 1.1 ns. The x-ray energy output was up to 10–11 kJ, and a maximum power can reach up to 3×1011 W. The X-pinch coupled with the x-ray glass-capillary converter for collecting and focusing of x rays can generate soft x-ray energy density up to (1–10) J/cm2, an...

The University of Nevada, Reno has developed a collisional-radiative atomic kinetics model that has successfully described the spectra produced by widely different multicharged ion experiments. The application of the model to experiments that highlight the importance of particular kinetics effects, including time-dependence and non-Maxwellian electron distribution functions, will be presented. These experiments include ion beam collision and high-temperature femtosecond laser and X-pinch plasma experiments. Adequate descriptions of ion beam collision spectra and x-ray yield require time-dependent treatment of radiative cascades from high-n capture states. Spectra from plasmas with significant fractions of hot electrons, such as those produced by fs lasers and X-pinches, require calculation of hot electron effects on collisional rates. The kinetics model presented here extracts as much information as possible from advanced experimental diagnostics such as time- and space-resolved spectral measurements.

The complex measurements with spectral, temporal, and spatial resolution are very important in studies of properties of radiation from hot dense plasmas (Te up to 1.5 keV, Ne up to 1022 cm−3) generated by a pulse-powered Z-pinch machine with Imax∼0.9–1.0 MA and a current risetime of 100 ns. Plasma radiation from Ti, Fe, Mo or W X-pinches has been studied. The analysis and comparison of 1D TGS images in a spectral region 20–80 A with time-integrated and time-resolved images from pinhole cameras show differences in sizes and positions of images depending on the wavelength. A comparison of these data with data obtained from absolutely calibrated PCD, XRD, and the bolometer shows the input of radiation from this spectral range into the total yield. The temporal behavior and spatial structure were found to be different in keV and sub-keV regions along an anode–cathode gap.

X-ray spectra of high energy density (HED) Z-pinch plasmas have been analyzed by means of a comprehensive kinetic modeling. A new diagnostic, x-ray spectropolarimetry, was applied to study anisotropy of Z-pinch plasma. This diagnostic is based on theoretical modeling of polarization-dependent spectra measured simultaneously by spectrometers with different sensitivity to polarization. Specifically, K-shell emission from Ti X-pinches was recorded simultaneously with identical LiF crystal spectrometers with the dispersion plane perpendicular and parallel to the discharge axis. Spectroscopic results from seven Ti X-pinch shots have been analyzed. Similar K-shell Ti polarization-dependent spectra generated by a quasi-Maxwellian electron beam at the LLNL EBIT-II electron beam ion trap have been studied. Further, the EBIT-II M-shell W spectra have proved to be important in the development of M-shell diagnostics of HED Z-pinch plasma. The advantages provided by electron beam ion trap data in the interpretation of HED Z-pinch spectra will be presented.

International audience; Double Planar Wire Arrays (DPWA), which consist of two parallel rows of wires, have demonstrated high radiation efficiency (up to 30 kJ), compact size (1.5-3 mm), and pulse shaping capabilities in experiments at 1 MA Zebra. DPWAs are also very suitable for the new compact multi-source hohlraum concept. It was shown that their implosion dynamics strongly depends on the critical load parameter, the aspect ratio (width to inter-planar gap Δ). Recently, we studied larger sized DPWAs at the increased current of 1.5-1.7 MA that provided enhanced energy coupling in plasma and better diagnostic access to observable plasma regions. The new regimes of implosions with asymmetric jets, no precursor formation and very early radiation for larger sized DPWAs (Δ=9 mm) with low aspect ratio of 0.54 were demonstrated. As a development of this work, new experiments at the enhanced current with the DPWAs from Alumel (mostly Ni) with Δ=6 mm and higher aspect ratio were performed. The different implosion and radiative signatures were observed that are presented and analyzed such as formation of the precursor in the middle of the array, no “foot” pulse emission but a very broad XRD signal, and L-shell radiation before the XRD peak but not so early as for larger PWAs. Also, simultaneously with soft x-ray L-shell Ni radiation, hard x-ray K-shell Ni radiation was recorded in a broad range from 13 ns before up to 18 ns after the XRD peak showing the temporal evolution of characteristic “cold” Ni Kα emission as well as some adjacent spectral features from hotter plasmas. Non-LTE modeling of such K-shell features provided time history of ionization balance of Ni ions and is compared with results of L-shell modeling.

The development of efficient x-ray probes with photon energies 1–20 keV became important for high-energy density physics (HEDP) research at larger scale facilities such as OMEGA and NIF. The goal of our studies is better understanding of the mechanisms of the laser energy to x-ray conversion efficiency (both thermal and non-thermal) and the directionality of x-rays. Experiments were performed at the UNR Leopard laser operated with 350 fs or 0.8 ns pulses. The supersonic linear nozzle (generated Ar clusters/monomer mixture with density up to 2 × 1019 cm−3) was compared to the cylindrical tube sub-sonic nozzle. The linear (elongated) cluster/gas jet is more uniform than the cylindrical one in experiments with the laser beam orthogonal to the jet axis. Additionally, the elongated jet provides capability to study laser beam self-focusing (when laser beam propagates along a jet plane) and plasma channel formation that are interconnecting with efficient x-ray generation. The laser radiation flux density in the focal spot was up to 2 × 1019 W/cm2 (fs pulse). Diagnostics included x-ray diodes, pinhole cameras and spectrometers. Signatures of x-ray emission from linear and tube nozzles were found to be very different. It was observed that emission in the 1–55 keV region was strongly anisotropic depending on the direction of laser beam polarization for fs laser pulse and supersonic linear nozzle. Energy radiated in the 1–3 keV region by a linear nozzle was an order of magnitude higher than from a tube nozzle. Non-LTE models have been implemented to analyze the spectroscopic data. It was shown that plasma from the linear nozzle was by an order of magnitude hotter than one from the tube nozzle. Evidence of electron beam generation in jets' plasma was found. Observed effects are explained by presence of Ar clusters in the jet from the linear nozzle. Future research will focus on study of cluster formation in different linear nozzles with Ar and mixture of Ar/Kr jets with varying of its parameters for optimization x-ray yield and power.

Brass wire array implosions on Zebra have produced characteristic K-shell emission. These Kα and Kβ photons are a result of high-energy electrons (>∼10 keV) ionizing or exciting a 1s bound electron from ionization stages around the Ne-like charge states. The electron beam was measured using a Faraday cup. The K- and L-shell radiation was captured using time-gated and time-integrated spectrometers. The L-shell radiation comes from ionization stages around the Ne-like charge state that is mostly populated by a thermal electron energy distribution function. X-ray imaging was accomplished using time-integrated and time-gated pinhole cameras, with one camera using a Ross filter pair to image the K-shell emission. The diagnostic suite included various filtered x-ray diodes, bolometers, and laser shadowgraphy. A multi-zone non-LTE kinetics pinch model with radiation transport is used to obtain the plasma conditions by matching the observed x-ray emission. Monte-Carlo simulations are employed to infer information about the electron energy distribution function for the runaway electrons.

International audience; Summary form only given. High Energy Density (HED) plasmas were produced in two sets of experiments: using a Z-pinch generator and a high power laser at the Nevada Terawatt Facility (NTF) of the University of Nevada, Reno (UNR). Each experiment has its unique characteristics and can be used to gain better understanding of HED plasmas. X-pinch experiments were performed at enhanced current on the Zebra generator using the Load Current Multiplier (LCM) and generated radiation yield up to 19 kJ/cm. These experiments used Ti alloy wires (6% Al, 4% V) for a first look at X-pinches at 1.5-1.7 MA at UNR. A full set of diagnostics was fielded including time-integrated spatially-resolved (TISR) and time-gated spatially-integrated (TGSI) x-ray spectrometers, time-integrated and time-gated pinhole x-ray cameras, and shadowgraphy. Many interesting results were found such as: i) the appearance of characteristic emission of Ti (wire material) and Fe (anode) in different orders of reflection at 30 ns prior to the first x-ray burst that was recorded for the next 15 ns, ii) prominent K-shell Al radiation despite the low percentage of Al in the alloy in both TGSI and TISR spectra, iii) K-shell Al radiation that corresponds to 400-550 eV plasmas starting near the first x-ray burst. Additionally experiments using the Leopard laser were performed on flat Al targets using a 0.8 ns pulse duration and two different target thicknesses (10 and 50 μm) that produced K-shell Al spectra of higher electron density. K-shell Al spectra of X-pinches, both TGSI and TISR, were modeled and compared with the laser-produced plasma results. The advantage of using alloyed Ti wires to study K-shell HED plasmas is highlighted. Future work is discussed.

The studies of polarization properties of mid-Z a High Energy Density (HED) plasmas are challenging and extremely important, because of, for example, its relevance to hot electron beam studies for Inertial Confinement Fusion (ICF) research. Such plasmas can be produced by high power lasers and Z-pinch generators. Plasma Polarization Spectroscopy (PPS) is able to provide more information about HED plasmas, including existence, directionality, and energy of particle beams, compared to traditional spectroscopy. In particular, such PPS studies with X-pinches on 1 MA Zebra at UNR have provided the evidence of anisotropy in Z-pinch plasmas in the form of electron beams [1, 2]. They involved the simultaneous measurement of x-ray polarization-dependent spectra by two spectrometers with different sensitivity to polarization and their modeling. The further development of such PPS studies for HED plasmas demands the comprehensive analysis of polarization properties of x-ray lines prominent in such plasmas. The present work reviews our previous results on x-ray line polarization of X-pinch plasmas and spectroscopically evaluates our recent results on K- and L-shell radiators from Z-pinch plasmas. It focuses on new theoretical predictions of polarization properties of x-ray K- and L-shell lines prominent in Z-pinch plasmas as well as in HED plasmas in general. The calculations of atomic characteristic and polarization data are performed using the FAC [3] and MZ [4] codes as well as theoretical approach from Ref. [5]. X-ray line polarization of both resonance lines and dielectronic satellite lines are considered. These results suggest the promising candidates for PPS of mid-Z a HED plasmas which include the lines that have maximum values of polarization, the stronger dependence on the energy of electron beam, and that are almost non-polarized. In addition, the important depolarization effects in plasmas are estimated and discussed.

Results of Ar gas-puff experiments performed on the high power Leopard laser at UNR are presented. The Leopard laser operated in two regimes: 350 fs, 40 TW pulse, or 0.8 ns, 25 GW pulse (pulse contrast from 10−5 to 10−7). Laser wavelength was 1.057 µm. The supersonic linear nozzle was compared with cylindrical tube sub-sonic nozzle. Flux density of laser radiation in focal spot was from 3×1016 W/cm2 (ns piulse) up to 2×1019 W/cm2 (fs pulse). The laser beam axis was positioned either along the jet plane or orthogonal to it at a distance of 1 mm from the nozzle output. Diagnostics included two sets of filtered Si-diodes (covered region from 1 to 55 keV), x-ray pinhole cameras, x-ray spectrometers, and Faraday cups. Specifically, x-ray images and structure of x-ray bursts are investigated and compared as a function of the orientation of the laser beam to the linear or cylindrical gas jet and laser pulse duration. The importance of analysis and comparison of x-ray image and x-ray burst features for a better understanding the mechanisms of the laser energy to x-ray conversion efficiency and future research directions are discussed.

X-ray spectropolarimetry is a powerful new tool for investigating the anisotropy of high-temperature plasmas. It is sensitive to the energetic electron distribution function and magnetic field, which, in general, have not been measured adequately. This diagnostic is based on the theoretical modeling of x-ray line polarization-dependent spectra measured simultaneously by spectrometers with different sensitivities to polarization. The increasing sophistication of spectroscopic monitoring of high-temperature plasmas has led to the necessity to account for both non-Maxwellian electron distribution functions and polarization properties of lines. This diagnostic can be applied to a broad range of plasmas, from low-density astrophysical plasmas to dense z-pinch plasmas. This work shows how x-ray spectropolarimetry complements the usual spectroscopic monitoring of hot plasmas and demonstrates the importance of accounting for x-ray line polarization in plasma diagnostics.

A wide variety of x-ray and extreme ultraviolet (EUV) diagnostics are being developed to study z-pinch plasmas at the Nevada Terawatt Facility at the University of Nevada, Reno. Time-resolved x-ray/EUV imaging and spectroscopy, x-ray polarization spectroscopy, and backlighting will be employed to measure profiles of plasma temperature, density, flow, and charge state, and to investigate electron distribution functions and magnetic fields. The instruments are state-of-the-art applications of glass capillary converters (GCC), multilayer mirrors (MLM), and crystals. New devices include: a novel GCC-based two-dimensional imaging spectrometer, a six-channel crystal/MLM spectrometer (“polychromator”) with a transmission grating spectrometer, and two sets of x-ray/EUV polarimeters/spectrometers. An x-pinch backlighter is under development. X-ray polarimeter/spectrometer, a survey spectrometer, a multichannel time-gated x-ray pinhole camera, and filtered fast x-ray diodes have observed the structure of Ti and Fe x pinches driven by a 0.9 MA current. X-ray yield and pulse duration depend sensitively on the wire load.

International audience; Experiments on the UNR Zebra generator with Load Current Multiplier (LCM) allow for implosions of larger sized wire array loads than at standard current of 1 MA. Advantages of larger sized planar wire array implosions include enhanced energy coupling to plasmas, better diagnostic access to observable plasma regions, and more complex geometries of the wire loads. The experiments with larger sized wire arrays were performed on 1.5 MA Zebra with LCM (the anode-cathode gap was 1 cm, which is half the gap used in the standard mode). In particular, larger sized multi-planar wire arrays had two outer wire planes from mid-atomic-number wires to create a global magnetic field (gmf) and plasma flow between them. A modified central plane with a few Al wires at the edges was put in the middle between outer planes to influence gmf and to create Al plasma flow in the perpendicular direction (to the outer arrays plasma flow). Such modified plane has different number of empty slots: it was increased from 6 up to 10, hence increasing the gap inside the middle plane from 4.9 to 7.7 mm, respectively. Such load configuration allows for more independent study of the flows of L-shell mid-atomic-number plasma (between the outer planes) and K-shell Al plasma (which first fills the gap between the edge wires along the middle plane) and their radiation in space and time. We demonstrate that such configuration produces higher linear radiation yield and electron temperatures as well as advantages of better diagnostics access to observable plasma regions and how the load geometry (size of the gap in the middle plane) influences K-shell Al radiation. In particular, K-shell Al radiation was delayed compared to L-shell mid-atomic-number radiation when the gap in the middle plane was large enough (when the number of empty slots was increased up to ten).

International audience; Silver (Ag) wire arrays were recently introduced as efficient x-ray radiators and have been shown to create L-shell plasmas that have the highest electron temperature (>1.8 keV) observed on the Zebra generator so far and upwards of 30 kJ of energy output. In this paper, results of single planar wire arrays and double planar wire arrays of Ag and mixed Ag and Al that were tested on the UNR Zebra generator are presented and compared. To further understand how L-shell Ag plasma evolves in time, a time-gated x-ray spectrometer was designed and fielded, which has a spectral range of approximately 3.5–5.0 Å. With this, L-shell Ag as well as cold Lα and Lβ Ag lines was captured and analyzed along with photoconducting diode (PCD) signals (>0.8 keV). Along with PCD signals, other signals, such as filtered XRD (>0.2 keV) and Si-diodes (SiD) (>9 keV), are analyzed covering a broad range of energies from a few eV to greater than 53 keV. The observation and analysis of cold Lα and Lβ lines show possible correlations with electron beams and SiD signals. Recently, an interesting issue regarding these Ag plasmas is whether lasing occurs in the Ne-like soft x-ray range, and if so, at what gains? To help answer this question, a non-local thermodynamic equilibrium (LTE) kinetic model was utilized to calculate theoretical lasing gains. It is shown that the Ag L-shell plasma conditions produced on the Zebra generator at 1.7 maximum current may be adequate to produce gains as high as 6 cm−1 for various 3p → 3s transitions. Other potential lasing transitions, including higher Rydberg states, are also included in detail. The overall importance of Ag wire arrays and plasmas is discussed.

We have applied a new, more efficient diagnostic technique for studies of extreme ultraviolet (EUV) radiation from multicharged ions interacting with He gas. Following single and double electron capture and one electron capture plus target-ion excitation in He2++He and Ar8++He collisions, the subsequent emitted EUV photons are analyzed with a high-resolution 2.2 m grazing incidence monochromator in conjunction with a new type of glass capillary converter (GCC) specifically designed for the EUV wavelength region. This new optical device images a horizontal cylindrical ion beam segment onto the vertical entrance slit of the monochromator. With this new imaging technique a spectral intensity enhancement of about 10 has been achieved over a distance of about 60 cm. By further optimizing this method an enhancement of the flux density of EUV radiation of about 20–30 is expected. As prototype examples, new advanced EUV spectra arising from He2++He and Ar8++He collisions are presented and discussed.

Summary form only given. Experiments on the Zebra generator with LCM (Load Current Multiplier, provides 1.5-1.7 MA) allow for implosions of larger sized wire array loads (including planar wire arrays) than at standard current of 1 MA. Advantages of larger sized planar wire array implosions include enhanced energy coupling to plasmas and better diagnostic access to observable plasma regions. A full set of diagnostics was implemented to study radiation in a broad spectral range from few Å to few hundred Å using PCD, XRD, and EUV detectors, X-ray/EUV spectrometers and X-ray pinhole cameras. In addition, laser shadowgraphy was utilized. In multi-planar wire arrays, two outer wire planes were each 4.9 mm width and made of eight mid-atomic-number (Alumel with 95% of Ni) wires with the inter-row gap increased from 3 or 6 mm (usually used at 1 MA current) up to 9 mm. A central plane located in the middle between the outer planes had empty slots and a few Al wires at the edges. Recently, we have shown that such configuration produces higher linear radiation yield. In the new experiments, the number of empty slots was further increased from 6 up to 10, increasing the gap inside the middle plane from 4.9 to 7.7 mm, respectively. This allows for more independent study of the flows of L-shell Ni plasma (between the outer planes) and K-shell Al plasma (which first fills the gap between the edge wires along the middle plane) and their radiation in space and time. When studying the combined wire arrays before, the time-gated X-ray spectra have always included radiation from both materials, even at early time. In the present work, for the first time we have observed that the K-shell Al radiation was delayed compared to L-shell Ni radiation when the number of empty slots was increased. In addition, the results of another new experiment are presented when a few Al wires on each edge were replaced by a thicker Cu wire to understand their influence on radiation from outer planes.

Summary form only given. Previous experiments on the 1 MA Zebra generator at UNR studied precursor plasmas with Ni-60 cylindrical wire arrays (CWA). Those precursor plasmas were shown to consistently have electron temperatures > 400 eV1. Continuing research on precursor plasmas at 1 MA on Zebra investigated first other mid-Z wire materials and then alternate arrays using mixed Al/mid-Z CWAs. Results found similar electron temperatures for the mid-Z elements present in the precursor with relatively colder temperatures for Al. A better understanding of the results from the mixed CWAs requires understanding pure Al CWAs. Recent experiments on Zebra using Al CWAs were performed to compare with the mixed Al/mid-Z CWAs. These CWAs consist of 6 wires evenly spaced in a 12 mm diameter, the same configuration as in previous experiments on precursor plasmas. Time-integrated spatially-resolved (TISR) and time-gated spatially-integrated (TGSI) X-ray spectral data, time-integrated and time-gated pinhole X-ray images, shadowgraphy, as well as optical streak camera images were obtained and analyzed. It was found that the Al precursor radiation starts, and stays pronounced until the main X-ray burst. This differs from the mid-Z precursors which show a defined precursor burst with an increase in radiation and decrease to zero before the main x-ray burst. Non-LTE kinetic models of Al have been applied to account for the K-shell radiation from precursor and main X-ray burst plasmas. The resulting plasma parameters from modeling of TGSI and TISR spectra together with analysis of corresponding images allow for the study of precursor plasma formation in time and in space, respectively.

Extreme ultraviolet (EUV) radiation from z-pinch plasma sources has been shown to play a substantial role in the evolution of z-pinches, contributing significant amounts of radiation in the wire ablation, stagnation, and plasma expansion phases. Recent studies of Cu z-pinch plasmas from cylindrical wire arrays have also shown that high temperatures (up to 450 eV) exist in precursor plasmas, which have applications to inertial confinement fusion. The final expansion phase has shown that substantial EUV radiation continues even after the main x-ray bursts. In this work, EUV data were analyzed with the goal of understanding how the bulk cooler plasma might represent the main contribution to the total radiative output from z-pinch plasmas. In particular, a comparison and analysis of EUV data generated by two plasma sources is shown: the first set of experiments used Cu cylindrical wire arrays on the 1.0 MA Zebra generator at UNR. In addition to EUV data, x-ray data is also analyzed which shows dominant emission of Cu XX ions. The second set used Cu flat targets and was performed at the compact laser-plasma x-ray/EUV facility “Sparky” at UNR, which is used as a unique line calibration source. Moreover, spectral data generated by Sparky generally show more and better resolved lines. Cu L-shell lines in the range of 120-160 Å, specifically CuX to CuXIII ions, are identified. To help with the identification of lines, a non-local thermodynamic equilibrium (non-LTE) kinetic model was utilized and was also used to determine plasma parameters, such as electron temperature and density. Future studies will focus on attaining time-gated EUV spectra in order to better understand its role in the evolution of z-pinch plasmas.

Summary form only given. Planar foil liners are alternative loads to wire arrays at multi-mega ampere generators as well as a promising object for the investigation of the magnetic energy dissipation mechanisms in Z-pinch plasmas. Experimental comparison of implosion dynamics and radiative mechanisms of Al planar foils and single planar wire arrays (SPWAs) of the same width and linear mass was performed for the 0.9-1.6-MA current region. Foils radiate approximately 80-90% of the total yield and power of SPWAs. The non-LTE code was applied to estimate the average electron temperature in Al planar foils that was found to be 20% higher, than that in SPWAs, and the average electron density in foils that was an order of magnitude lower than for SPWAs. Also, the foils are characterized by smaller axial gradient of electron temperature and density than SPWAs. In addition, anisotropic emission from Al planar foils was observed to be similar to Al SPWAs: the total yield registered orthogonally to the foil plane was 1.3 times higher than that along the plane (compared to 1.5 for SPWAs). The anomalous MHD resistivity consideration suggests that a significant part of foil radiation could be due to formation of strongly-inhomogeneous plasma through instabilities appearing on shadowgraphic images of a symmetric foil as a result of initial sharp edges inhomogeneity. This idea was tested in the recent experiments with modified foils where one edge was initially sharp and the other was folded with smaller initial inhomogeneity. The yield from a foil with a folded edge was 13-15% lower than that with both sharp edges as predicted by MHD modeling. Presented results on radiation from foils suggest them as potentially useful x-ray sources for various HEDP applications due to simpler load foil preparations compared to wire arrays. Preliminary results of the research we started on radiation from double foils in comparison with double planar wire arrays (DPWAs) are also discussed.

Radiative properties of plasmas from X pinches with nichrome and conichrome wires have been studied using the presented diagnostic arrangement. The experimental results have been produced at the Cornell XP facility with a peak current of 450 kA and a full width at half maximum pulse duration of 100 ns. The spatially resolved, time-integrated x-ray line spectra from the region of the X-pinch cross point have been recorded using different crystal spectrometers. In particular, K-shell and L-shell x-ray spectra of Ni and Cr have been recorded through different filters in the same pulses for X pinches from two different wire alloys. A nonlocal thermodynamic equilibrium collisional–radiative atomic kinetic model of Ni has been developed to identify the useful diagnostic spectroscopic features and to model experimental spectra. The results of the modeling and radiative properties of different materials from nichrome and conichrome alloys are compared and discussed.