Bulletin of the American Physical Society
53rd Annual Meeting of the APS Division of Plasma Physics
Volume 56, Number 16
Monday–Friday, November 14–18, 2011; Salt Lake City, Utah
Session GO6: Z Pinches |
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Chair: Stephanie Hansen, Sandia National Laboratories Room: Ballroom G |
Tuesday, November 15, 2011 9:30AM - 9:42AM |
GO6.00001: Simulation Dynamics of a Multi-Material Pinch for Neutron Production on the Refurbished Z Simulator Y.K. Chong, A.L. Velikovich, J.W. Thornhill, J. Giuliani, C.A. Coverdale Previous Radiation MHD (RMHD) simulation studies of deuterium (D) double-shell gas-puff Z-pinch implosions driven by the Sandia refurbished Z have shown that their performance can be substantially affected by an introduction of a dense high-Z gas at the outer shell. One of the physical mechanisms playing an important role in the process is the development of multi-D structure {\&} nonuniform gradients due to the RT instabilities. Here, we present the results from the simulations of the multimaterial (MM) gas puff Z-pinch loads from the multiphase version of the Mach2-DDTCRE code. The MM radiation transport is included to account for the radiation emission, absorption {\&} transport from/into different materials. We will investigate the effects of different load materials/configurations such as argon-on-D on the multi-D structures, nonuniform gradients {\&} RT formation/development. We will then characterize various performance metrics, in particular the neutron yields, of the loads as a function of mass ratio and/or radius. A comprehensive analysis of 1D/2D RMHD results will be also made to gauge the operation parameter regime {\&} design of MM gas-puff loads. [Preview Abstract] |
Tuesday, November 15, 2011 9:42AM - 9:54AM |
GO6.00002: Analyzing Spatially Resolved Z-pinch Spectra to Determine the Nature of ``Bright Spots''* J.P. Apruzese, J.L. Giuliani, J.W. Thornhill, D.J. Ampleford, B. Jones, C.A. Coverdale Wire array Z-pinch implosions which access the K-shell stages of their load elements are usually characterized by spatially nonuniform emission. But, is the existence of the ``bright spots'' due to density enhancement, higher temperature, or some combination of the two? Does the answer vary with atomic number of the load? To investigate this issue we have analyzed spatially resolved spectra from Cu and Al pinches driven by the Z generator. Correlation studies and regression analyses from the derived conditions are employed in order to infer the cause(s) of the local enhancements of K-shell powers. \\[4pt] *Work supported by U. S. Department of Energy, National Nuclear Security Administration. 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. DOE's NNSA under contract DE-AC04-94AL85000. JPA is a consultant to NRL through L3 Communications, Chantilly, VA 20151 [Preview Abstract] |
Tuesday, November 15, 2011 9:54AM - 10:06AM |
GO6.00003: Analysis of Radiation from Implosions of Stainless Steel Wire Arrays on Zebra and Comparison with Laser Plasma Experiments on Leopard at UNR*. A.S. Safronova, V.L. Kantsyrev, I. Shrestha, V.V. Shlyaptseva, M.E. Weller, G.C. Osborne, K.M. Williamson, A. Stafford, S.F. Keim, A.Ya. Faenov, A.A. Esaulov, P. Wiewior, N. LeGalloudec, Y. Paudel, C.A. Coverdale, A.S. Chuvatin The implosions of Stainless Steel (SS) Wire Arrays are extensively studied at SNL and also have applications in astrophysics. The analysis of radiation from low-number-wire SS Single and Nested Cylindrical, and Planar Wire Array experiments on the 1 MA Zebra is presented. The major focus is on x-ray imaging and spectra, total radiation yields, and fast, filtered x-ray detector data. The results of Leopard laser experiments with a flat 25 $\mu $m Fe target in the nanosecond (ns) and 350 femtosecond (fs) pulse regimes are discussed and compared with Z-pinch data. This comparison focuses mainly on L-shell Fe radiation and provides an excellent benchmark to the Z-pinch results. Good agreement with laser data is demonstrated in the ns regime, but a substantial difference is observed for the fs pulse. * This work was supported by NNSA under DOE Coop. Agreements DE-FC52-06NA27588, 27586, and 27616. SNL is a multi-program laboratory managed and operated by Sandia Corp., a wholly owned subsidiary of Lockheed Martin Co., for the U.S. DOE under Contract DE-AC04-94AL85000. [Preview Abstract] |
Tuesday, November 15, 2011 10:06AM - 10:18AM |
GO6.00004: Experimental Study of an Inverse Wire Array Z-Pinch Operating as a Current Switch Sergey Lebedev, A. Harvey-Thomson, G.N. Hall, E.M. Waisman, E. Khoory, G. Burdiak, J.P. Chittenden, P. de Grouchy, F.A. Suzuki-Vidal, G. Swadling, S.N. Bland, L. Pickworth, J. Skidmore, L. Suttle We will present experiments on the MAGPIE facility (1.5MA, 250ns) in which an inverse wire array [1] (with the wires acting as a return current cage placed around a central current conductor) operated as a fast current switch. This allowed to significantly reduce the rise-time of the current pulse ($<$100ns) delivered to a separate, standard imploding wire array z-pinch load. Experimental studies of the operation of this arrangement as a current switch will be discussed and new measurements of current switching into the load array will be presented. We will also discuss how pre-conditioning of the load array wires by the current pre-pulse [2] depends on wire materials (Al, Cu, W) used in the load and the exploding wire arrays. \\[4pt] [1] A. Harvey-Thompson, S.V. Lebedev, S.N. Bland et al., PoP 16, 022701 (2009).\\[0pt] [2] A. Harvey-Thompson, S.V. Lebedev, G. Burdiak, et al., PRL 106, 205002 (2011) [Preview Abstract] |
Tuesday, November 15, 2011 10:18AM - 10:30AM |
GO6.00005: Investigation of the Internal Structure of the Dense Z-Pinch V.V. Ivanov, J.P. Chittenden, S.D. Altemara, N. Niasse, P. Hakel, R.C. Mancini, D. Papp, A.A. Anderson, A.L. Astanovitskiy, V. Nalajala UV laser probing at the wavelength of 266 nm was applied for investigation of wire-array Z-pinches at the Zebra generator. A fine structure of the 1 MA stagnated pinch was observed in unprecedented details. Kink instability with loop-like structures, disruptions, and micropinches were observed in Z-pinches at the peak of the x-ray pulse and later in time. Micropinches with the diameters of 60-90 $\mu $m are located inside necks of lower-density plasma. Instability with a period of 70-200 $\mu $m was observed on the edges of Z-pinches. Micron-scale density perturbations were observed in the precursor plasma and in the current carrying areas of the dense pinch. A homogeneous Z pinch plasma column was observed in star wire arrays. Development of instabilities was compared with 3D MHD Gorgon simulations. The Gorgon modeling is in good agreement with implosion and stagnation scenarios observed in two very different cylindrical and star wire arrays. [Preview Abstract] |
Tuesday, November 15, 2011 10:30AM - 10:42AM |
GO6.00006: Advanced Kr Atomic Structure and Ionization Kinetics for Pinches on ZR Arati Dasgupta, Robert Clark, John Giuliani, Nick Ouart, Jack Davis, Brent Jones, Dave Ampleford, Stephanie Hansen High fluence photon sources above 10 keV are a challenge for HED plasmas. This motivates Kr atomic modeling as its K-shell radiation starts at 13 keV. We have developed atomic structure and collisional-radiatve data for the full K-and L-shell and much of the M-shell using the the state-of-the-art Flexible Atomic Code. All relevant atomic collisional and radiative processes that affect ionization balance and are necessary to accurately model the pinch dynamics and the spectroscopic details of the emitted radiation are included in constructing the model. This non-LTE CRE model will be used to generate synthetic spectra for fixed densities and temperatures relevant for Kr gas-puff simulations in ZR. [Preview Abstract] |
Tuesday, November 15, 2011 10:42AM - 10:54AM |
GO6.00007: Experimental Comparison of Radiative Characteristics and Implosion Dynamics of Planar Foils and Single Planar Wire Arrays in Current Region 0.9-1.6 MA on the UNR Zebra generator* V.L. Kantsyrev, A.S. Chuvatin, L.I. Rudakov, A.S. Safronova, A.A. Esaulov, G.C. Osborne, I. Shrestha, V.V. Shlyaptseva, H.A. Zunino, M.E. Weller, A. Stafford, S.F. Keim Foil liners are good objects for the investigation of dissipation mechanism of magnetic energy and as possible alternative loads for wire-arrays at multi-MA generators. Performance of Al planar foils was compared with single planar wire-arrays (SPWAs) in 0.9 -- 1.6 MA current region. Using time-gated and time-integrated x-ray, optical and laser diagnostics, the implosion dynamics and radiative characteristics are studied from current start to pinch stagnation. Foils radiate at 80{\%} of the total yield and power of SPWAs. Moreover, anisotropic emission from planar foils was observed similar to SPWAs [V. Kantsyrev \textit{et al}., Bull. Amer. Phys. Soc., v. 55, 244 (2010)]: the total yield registered orthogonally to the foil plane was higher than along the plane. Possible magnetic energy dissipation mechanism, numerical modeling and future experiments will be discussed. *This work was supported by NNSA under DOE Cooperative Agreements DE-FC52-06NA27586, DE-FC52-06NA27588, and in part by DE-FC52-06NA27616. [Preview Abstract] |
Tuesday, November 15, 2011 10:54AM - 11:06AM |
GO6.00008: End-On Laser Interferometry of Wire Array Z-Pinch Implosions on the MAGPIE Generator George Swadling, Sergey Lebedev, Jeremy Chittenden, Gareth Hall, Francisco Suzuki-Vidal, Adam Harvey-Thompson, Nicolas Niasse, Guy Burdiak, Essa Khoory, Louisa Pickworth, Philip de Grouchi, Lee Suttle New end-on measurements have taken of the areal electron density distribution of wire array z-pinches during the ablation phase. These measurements have been used to investigate the differences in dynamics between aluminium and tungsten arrays. The experiments were carried out on the 1.4 MA peak current, 240ns rise-time MAGPIE generator at Imperial College, London. The measurements were taken using a two colour Mach-Zender style imaging interferometer. Probing is provided by the 2nd and 3rd harmonics (532nm and 355nm) of a pulsed Nd:YAG laser with a pulse duration of 500ps. Analysis of the results is presented and comparisons made to both the rocket model and simulations produced using the GORGON MHD code. [Preview Abstract] |
Tuesday, November 15, 2011 11:06AM - 11:18AM |
GO6.00009: Mitigation of 3D Magneto-Taylor instabilities in cylindrical liner, isentropic compression experiments Marcus Weinwurm, Jeremy Chittenden, Simon Bland Recent experiments and computational modelling at Sandia National Laboratory have led to the development of techniques for designing current pulse shapes which provide shock-less compression and acceleration of cylindrical liners. This technique allows the equation of state of the liner material to be studied under dynamic pressure loading of several Mbar. In addition, such an imploding liner could potentially be used to compress other materials to high pressure, allowing, for example, the behaviour of hydrogen-helium mixtures to be studied at temperatures and pressures comparable to the centre of Jupiter. In this paper we study the susceptibility of such designs to the magneto-Rayleigh-Taylor instability using the 3D MHD code Gorgon. The seeding of instabilities by surface machining perturbations and by the strong variations of resistivity with density and temperature, are evaluated early in the compression. The propagation and correlation of instabilities around the azimuth later in time is also studied. Finally the potential for designing implosions, in which the inner surface of the liner remains free from penetration by the instability, is evaluated. [Preview Abstract] |
Tuesday, November 15, 2011 11:18AM - 11:30AM |
GO6.00010: Thin Foil Copper Liner Initiation Experiments Isaac Blesener, Bruce Kusse, John Greenly, Kate Blesener, David Hammer, Brent Blue Solid liners are an increasingly attractive load design for pulsed power drivers, with applications in both Z pinches and alternative fusion concepts. Next generation pulsed power drivers will need increasingly massive loads to match the implosion time of the Z pinch with the current pulse. Solid liners present a relatively simple load design that could replace wire arrays for fast Z pinch studies. Additionally, fusion concepts such as MAGnetized Liner Intertial Fusion (MAGLIF) are designed to use solid liners to compress the fusion fuel. One problem that has hindered the performance of solid liners in the past is non-uniform initiation, or current filamentation. A series of experiments on the 1 MA, 100 ns COBRA generator show that at high enough current density rise times (dJ/dt), copper liners initiated nearly instaneously and uniformly along the azimuth. The threshold for these experiments for uniform initiation was found to be $\frac{dJ}{dt}\geq3.5\times10^{16}\frac{A}{cm^{2}s}$. [Preview Abstract] |
Tuesday, November 15, 2011 11:30AM - 11:42AM |
GO6.00011: 3 Dimensional Magneto-hydrodynamic modeling of liner implosions on the Z Generator C.A. Jennings, D.B. Sinars, R.D. McBride, S.A. Slutz, M.E. Cuneo, M.C. Herrmann, J.P. Chittenden Metal liners imploded by a fast rising ($<$100ns) current to compress a magnetized, preheated fuel offer the potential to efficiently reach fusion conditions [S.A. Slutz et al. Phys. Plasmas 17, 056303 (2010)]. Maintaining the integrity of the imploding liner is critical to effective fuel compression. Experiments at Sandia National Laboratories diagnosing the development of Magneto-Rayleigh-Taylor (MRT) instabilities in Beryllium and Aluminum liners have provided a valuable dataset for validating simulations. We present 3 dimensional, MHD simulations of liner implosions, demonstrating good agreement with radiographic data. We then use our model to explore how the choice of a 2 or 3 dimensional geometry affects the growth of simulated MRT instabilities, and examine how the presence of an axial magnetic field can affect the development and growth of these instabilities. * 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. [Preview Abstract] |
Tuesday, November 15, 2011 11:42AM - 11:54AM |
GO6.00012: Experimental Measurements of the Convolute Plasma on the Z-Machine* M.R. Gomez, R.M. Gilgenbach, M.E. Cuneo, R.D. McBride, G.A. Rochau, B. Jones, D.J. Ampleford, D.B. Sinars, J.E. Bailey, W.A. Stygar, M.E. Savage, M. Jones, A.D. Edens, M.R. Lopez, E. Stambulchik, Y. Maron, D.V. Rose, D.R. Welch Post-hole convolutes are used in large pulsed power devices to combine the current from several self-magnetically insulated transmission lines at the load. The efficiency of Z's post-hole convolute has decreased with increasing electrical power. Losses as high as 20{\%} of the peak current have been recorded on the most lossy shots. Spectroscopic measurements of the plasma that forms in the convolute are underway. Initial results show that there is a strong correlation between convolute plasma density and the load. This presentation will cover convolute plasma behavior and loss current for several load configurations on the Z-Machine. *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. [Preview Abstract] |
Tuesday, November 15, 2011 11:54AM - 12:06PM |
GO6.00013: Plasma Parameters from Optical Emission Spectroscopy of Single Wire Aluminum Plasmas Kate Blesener, Sergei Pikuz, Tania Shelkovenko, Isaac Blesener, David Hammer, Yitzhak Maron, Vladimir Bernshtam, Ramy Doron, Leonid Weignarten, Yuri Zarnitsky We are studying plasmas created by exploding aluminum wires on the 10 kA Low Current Pulser LCP3 at Cornell University, employing both high- and low-resolution time gated emission spectroscopy at visible wavelengths to determine the plasma parameters as a function of radial position and time. With high spectral resolution, we can determine the electron density profile, and we are studying the magnetic field in the plasma. To study the magnetic field we are using the new Zeeman Broadening technique developed at the Weizmann Institute of Science with lower energy densities [1]. We are using the low spectral resolution configuration to determine the ionization state, electron temperature, and electron density with greater time resolution. This research is supported by the DOE/NNSA joint program in HEDLP under contract DE-SC0002263 and by the NNSA SSAA program under DOE Cooperative Agreement DE-FC03-02NA00057. \\[4pt] [1] E. Stambulchik, \textit{et al.} Phys. Rev. Lett. \textbf{98}, 225001 (2007). [Preview Abstract] |
Tuesday, November 15, 2011 12:06PM - 12:18PM |
GO6.00014: Deuterium Gas-Puff Z-Pinch on GIT-12 Generator Daniel Klir, Jozef Kravarik, Pavel Kubes, Karel Rezac, Alexander Shishlov, Vladimir Kokshenev, Nicolai Ratakhin, Boris Kovalchuk, Aleksey Labetsky, Nikolay Kurmaev, Fedor Fursov Deuterium gas-puff experiments have been carried out on the GIT-12 generator at the High Current Electronics Institute in Tomsk. During the initial experiment in May 2011, we used mainly double shell gas puffs with the outer and inner diameter of 100 and 30~mm, respectively. Single shell and shell-on-solid fill gas puffs were, however, also tested. The linear mass density of deuterium varied between 50 and 80 $\mu$g/cm. When a plasma-opening-switch (POS) was used, the current reached the peak of above 2.5~MA within 300~ns. The peak neutron yield from D(d,n)$^{3}$He reactions exceeded 10$^{11}$. In all shots, the neutron emission started during the stagnation. At the beginning of the neutron production, there was the correlation between the neutron emission and soft X-rays. Nevertheless, the peak of the neutron emission occurred 50~ns after the soft X-ray peak. At this very moment, hard X-rays above 1~MeV were detected. In the case of POS, $>800$~keV widths of side-on neutron spectra implied $>200$~keV deuterons moving in the radial direction. [Preview Abstract] |
Tuesday, November 15, 2011 12:18PM - 12:30PM |
GO6.00015: Laser-produced Plasmas X-ray Source and Its Application to Rayleigh Taylor Instability Study Ruirong Wang, Wei Wang, Jiaqin Dong Several experiments have been performed on the SG-II laser facility to understand x-ray source and to test radiography concepts. Through the use of a novel time-integrated, space and energy-resolved x-ray spectrometer and pinhole camera, potential Helium-like Titanium K alpha x-ray backlighting (radiography) line source is studied as a function of laser wavelength, the pre-pulse to main pulse intensity contrast, and the laser intensities. One-dimensional radiography using a grid consisting of 5$\mu $m Au wires on 16-$\mu $m period and the pinhole-assisted point projection were tested. The measurements show that the relative x-ray line emission conversion efficiency from the incident laser light energy to Helium-like Titanium K-shell spectrum increases significantly with pre-pulse intensity, increases rapidly with decreasing laser wavelength, and increases moderately with increasing main laser intensity. It is also further demonstrated that the level of the pinhole-assisted point projection will be a novel and simple two-dimensional imaging diagnostic technique for inertial confinement fusion experiments. [Preview Abstract] |
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