[Show abstract][Hide abstract] ABSTRACT: Linear Discriminant Analysis (LDA) is applied and compared with the Principal Component Analysis (PCA) and the Hand He-like line ratio diagnostics to investigate the electron beam effects on the laser produced K-shell Al synthetic spectra 1,2. 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=3x10 21 cm-3 in the presence of electron beams with fraction of f~0.05 and energy centered at ~10 keV.
[Show abstract][Hide abstract] ABSTRACT: 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.
High Energy Density Physics 04/2015; 15. DOI:10.1016/j.hedp.2015.04.006 · 1.23 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: A compact Z-pinch x-ray hohlraum design with parallel-driven x-ray sources is experimentally demonstrated in a configuration with a central target and tailored shine shields at a 1.7-MA Zebra generator. Driving in parallel two magnetically decoupled compact double-planar-wire Z pinches has demonstrated the generation of synchronized x-ray bursts that correlated well in time with x-ray emission from a central reemission target. Good agreement between simulated and measured hohlraum radiation temperature of the central target is shown. The advantages of compact hohlraum design applications for multi-MA facilities are discussed.
Physical Review E 12/2014; 90(6-1):063101. DOI:10.1103/PhysRevE.90.063101 · 2.29 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Detection of low-energy ions via Thomson parabola mass analyzer in the absence of any additional electrical systems is examined. Numerous low-energy ions were recorded on UF-4 solid state emulsion films. Kinetic energies between 1 and 4 keV of ions generated by YAG laser focused on Al and Ti targets were obtained using Thomson parabola measurements. Characteristics of ion tracks on the UF-4 detector are discussed in terms of pressure ranges of vacuum chamber. Moreover, differences in charges of ions between this study and previous spectroscopic measurements are discussed.
[Show abstract][Hide abstract] ABSTRACT: Experiments performed at the Leopard Laser Facility at the Nevada Terawatt Facility of the University of Nevada, Reno have produced K-shell Mg spectra with complex satellite features. K-shell Mg spectra were collected from experiments comprised of three different conditions related to laser pulse and contrast. Two spectrometers were fielded: a survey convex spectrometer with a potassium hydrogen phthalate (KAP) crystal (R ~ 300) and a high resolution focusing spectrometer with spatial resolution using a spherically bent mica crystal (R ~ 3000). These spectra included dielectronic satellite (DS) lines that were investigated using the quasi-relativistic many-body perturbation theory (MZ) code for previously identified transitions from autoionizing 2lnl' states in He-like Mg and new transitions involving autoionizing 1s3lnl' states in Li-like Mg and 1s3l3l'3l'' in Be-like Mg calculated using the Hartree–Fock-relativistic method (COWAN code). Radiative and non-radiative data are combined to obtain branching ratios, intensities and effective emission rate coefficients of DS lines. Synthetic spectra were matched to experimental data to identify strong satellite structures to the Heβ (7.8507 Å) and Lyα (8.4192 Å) resonance transitions.
Journal of Physics B Atomic Molecular and Optical Physics 02/2014; 47(6):065001. DOI:10.1088/0953-4075/47/6/065001 · 1.98 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: 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.
Physics of Plasmas 02/2014; 21(3). DOI:10.1063/1.4865368 · 2.14 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Implosions of brass wire arrays on Zebra have produced L-shell radiation as well as inner-shell Kα and Kβ transitions. The L-shell radiation comes from ionization stages around the Ne-like charge state that is largely populated by a thermal electron energy distribution function, while the K-shell photons are a result of high-energy electrons ionizing or exciting an inner-shell (1s) electron from ionization stages around Ne-like. The K- and L-shell radiations were captured using two time-gated and two axially resolved time-integrated spectrometers. The electron beam was measured using a Faraday cup. A multi-zone non-local thermodynamic equilibrium pinch model with radiation transport is used to model the x-ray emission from experiments for the purpose of obtaining plasma conditions. These plasma conditions are used to discuss some properties of the electron beam generated by runaway electrons. A simple model for runaway electrons is examined to produce the Kα radiation, but it is found to be insufficient.
Physics of Plasmas 02/2014; 21(3). DOI:10.1063/1.4865370 · 2.14 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: This article reports on the joint success of two independent lines of research, each of them being a multi-year international effort. One of these is the development of innovative sources, such as planar wire arrays (PWAs). PWAs turned out to be a prolific radiator, which act mainly as a resistor, even though the physical mechanism of efficient magnetic energy conversion into radiation still remains unclear. We review the results of our extensive studies of PWAs. We also report the new results of the experimental comparison PWAs with planar foil liners (another promising alternative to wire array loads at multi-mega-ampere generators). Pioneered at UNR, the PWA Z-pinch loads have later been tested at the Sandia National Laboratories (SNL) on the Saturn generator, on GIT-12 machine in Russia, and on the QiangGuang-1 generator in China, always successfully. Another of these is the drastic improvement in energy efficiency of pulsed-power systems, which started in early 1980s with Zucker's experiments at Naval Research Laboratory (NRL). Successful continuation of this approach was the Load Current Multiplier (LCM) proposed by Chuvatin in collaboration with Rudakov and Weber from NRL. The 100 ns LCM was integrated into the Zebra generator, which almost doubled the plasma load current, from 0.9 to 1.7 MA. The two above-mentioned innovative approaches were used in combination to produce a new compact hohlraum radiation source for ICF, as jointly proposed by SNL and UNR [Jones et al., Phys. Rev. Lett. 104, 125001 (2010)]. The first successful proof-of-the-principle experimental implementation of new hohlraum concept at university-scale generator Zebra/LCM is demonstrated. A numerical simulation capability with VisRaD code (from PRISM Co.) established at UNR allowed for the study of hohlraum coupling physics and provides the possibility of optimization of a new hohlraum. Future studies are discussed.
Physics of Plasmas 02/2014; 21(3). DOI:10.1063/1.4865367 · 2.14 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: The study of radiation from different wire materials in wire array Z-pinch plasma is a very challenging topic because it is almost impossible to separate different plasmas at the stagnation. A new approach is suggested based on planar wire array (PWA) loads to assess this problem. Multi-planar wire arrays are implemented that consist of few planes, each with the same number of wires and masses but from different wire materials, arranged in parallel rows. In particular, the experimental results obtained with triple PWAs (TPWAs) on the UNR Zebra generator are analyzed with Wire Ablation Dynamics Model, non-local thermodynamic equilibrium kinetic model, and 2D radiation magneto-hydrodynamic to illustrate this new approach. In TPWAs, two wire planes were from mid-atomic-number wire material and another plane was from alloyed Al, placed either in the middle or at the edge of the TPWA. Spatial and temporal properties of K-shell Al and L-shell Cu radiations were analyzed and compared from these two configurations of TPWAs. Advantages of the new approach are demonstrated and future work is discussed.
Physics of Plasmas 02/2014; 21(3). DOI:10.1063/1.4864335 · 2.14 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Various configurations of planar wires arrays (PWA) made from wires in a broad range of atomic numbers up to 74 (W) have been extensively tested on Zebra generator at the University of Nevada, Reno. In this work, we present the results of our experiments with PWA made of the wires with an even higher atomic number, specifically 79 (Au). Two different configurations (single and double PWAs) are considered. The diagnostic set included: x-ray detectors, laser shadowgraphy, time-gated and time-integrated x-ray pinhole cameras, time-integrated spatially resolved and time-gated spatially integrated x-ray spectrometers, and a bolometer. The total x-ray yield was measured along and perpendicular to the load plane and reached the highest value measured on Zebra so far for the single PWA (perpendicular to the plane, 32 kJ). Theoretical tools included non-LTE kinetic and wire ablation dynamic models. The full set of data using aforementioned diagnostics is analyzed and specific implosion and radiative characteristics of Au PWAs. The application of gold PWAs in compact hohlraum configurations on Zebra is highlighted. VisRad (Prism Computational Sciences), a 3-D view factor code, is used to simulate the multi-dimensional radiation environment with a special emphasis on radiation temperature calculations and uniformity at the re-emission target surface.
[Show abstract][Hide abstract] ABSTRACT: University-scale Z-pinch generators are able to produce High Energy Density (HED) plasmas in a broad range of plasma parameters under well-controlled and monitored experimental conditions suitable for radiation studies. The implosion of X-pinch and wire array loads at a 1 MA generator yields short (1-20 nsec) x-ray bursts from one or several bright plasma spots near the wire cross point (for X-pinches) or along and near Z-pinch axis (for wire arrays). Such X- and Z-pinch HED plasma with scales from a few µm to several mm in size emits radiation in a broad range of energies from 10 eV to 0.5 MeV and is subject of our studies during the last ten years. In particular, the substantial number of experiments with very different wire loads was performed on the 1 MA Zebra generator and analyzed: X-pinch, cylindrical, nested, and various types of the novel load, Planar Wire Arrays (PWA). Also, the experiments at an enhanced current of 1.5-1.7 MA on Zebra using Load Current Multiplier (LCM) were performed. This paper highlights radiative signatures of X-pinches and Single and Double PWAs which are illustrated using the new results with combined wire loads from two different materials.
[Show abstract][Hide abstract] ABSTRACT: 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.
High Energy Density Physics 12/2013; 9(4):653–660. DOI:10.1016/j.hedp.2013.06.004 · 1.23 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: The planar wire array (PWA) is a promising load for new multi-source inertial confinement fusion (ICF) hohlraums [B. Jones et al., Phys. Rev. Lett. 104, 125001 (2010)]. The hohlraum radiation symmetry is an important issue for ICF. It was found that extreme ultraviolet and sub-keV photon emission from PWAs may have considerable anisotropy in the load azimuthal plane. This experimental result is obtained on the UNR 1–1.7 MA Zebra generator. The time-dependent anisotropy effect is detected. This feature is studied in 2D numerical simulations and can be explained by initial anisotropy of implosion of those non-cylindrical loads radiating essentially as surface sources in sub-keV quanta and also by radiation absorption in cold magnetized plasma tails forming in the direction of magnetic compression.
Physics of Plasmas 07/2013; 20(7). DOI:10.1063/1.4817023 · 2.14 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: In new hohlraum configuration, multiple mm-size planar wire array (PWA)
sources surround a central cavity [B. Jones et al., PRL, v.104 (2010)].
This might provide a hotter hohlraum for ICF than the prior double-ended
scheme with cylindrical arrays. The current redistribution in two
magnetically decoupled compact Z-pinches (0.75-0.82 MA each) was
demonstrated at 1.7 MA UNR Zebra generator. Yield measurements from two
cages with PWA sources show that such plasma dissipates the magnetic
energy at stagnation as a resistor. For the first time, strong EUV
radiation, that time-correlated with sub-keV source bursts, was
registered from central cavity. The experimental cavity radiation
temperature of 37-45 eV correlates well with 39 eV from VisRaD code
(PRISM Co.) simulation. First results of new configuration optimization
are reported. The possible applications for 30-60 MA ICF experiments are
discussed. This work was supported by NNSA under DOE Coop. Agr.
DE-FC52-06NA27586, 06NA27588, and in part by DE-FC52-06NA27616. Sandia
National Laboratories is a multi-program laboratory managed and operated
by Sandia Corporation, a wholly owned subsidiary of Lockheed Martin
Corporation, for the U.S. Department of Energy's National Nuclear
Security Administration under contract DE-AC04-94AL85000.
[Show abstract][Hide abstract] ABSTRACT: 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 out- r planes.
Plasma Science (ICOPS), 2013 Abstracts IEEE International Conference on; 01/2013
[Show abstract][Hide abstract] ABSTRACT: 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.
Plasma Science (ICOPS), 2013 Abstracts IEEE International Conference on; 01/2013
[Show abstract][Hide abstract] ABSTRACT: 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.
Plasma Science (ICOPS), 2013 Abstracts IEEE International Conference on; 01/2013
[Show abstract][Hide abstract] ABSTRACT: 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.
Plasma Science (ICOPS), 2013 Abstracts IEEE International Conference on; 01/2013
[Show abstract][Hide abstract] ABSTRACT: This paper covers ongoing research on pulsed-power-produced plasmas using wire arrays and foil loads at four universities in the U.S. It is directed toward prospective and current students, as well as program managers at government agencies, and others who have a general interest in applications of pulsed power. This paper presents several pinch configurations (Z-pinches, X-pinches, planar wire arrays, radial, and suspended foils), specific physics issues (e.g., wire ablation), applications (plasma jets, X-ray hohlraums), diagnostics (e.g., ultraviolet laser probing), and modeling. The areas covered are not meant to be comprehensive, but rather, the discussion demonstrates the breadth and vibrancy of the activities at these institutions and collates extensive references on this work over primarily the past six years.
[Show abstract][Hide abstract] ABSTRACT: Abstract: Experiments with various wire loads from midatomic-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 T-e 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.