Bulletin of the American Physical Society
55th Annual Meeting of the APS Division of Plasma Physics
Volume 58, Number 16
Monday–Friday, November 11–15, 2013; Denver, Colorado
Session TO4: Z-Pinch and Dense Plasma Focus |
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Chair: Daniel Sinars, Sandia National Laboratories Room: Plaza D |
Thursday, November 14, 2013 9:30AM - 9:42AM |
TO4.00001: Spectroscopic magnetic field measurements of the drive current on the Z machine S.B. Hansen, M.R. Gomez, D.J. Ampleford, T.J. Awe, D.E. Bliss, A.L. Carlson, M.E. Cuneo, C.A. Jennings, A.J. Harvey-Thompson, B. Jones, P.F. Knapp, D.C. Lamppa, R.D. McBride, S.A. Slutz, D. Schroen, K. Tomlinson Azimuthal magnetic fields greater than 250 T (2.5 MG) have been directly measured for the first time on the Z Machine at Sandia National Laboratories through Zeeman splitting of the optical 3s -- 3p absorption lines of neutral sodium. The measurements, made by aiming a streaked optical spectrometer with few-{\AA} spectral resolution and ns-scale time resolution at a 100 ng/cm$^{2}$ Na deposit on the surface of a cylindrical target, show increasing Zeeman splitting over $\sim$ 20 ns at the foot of the 100-ns risetime current pulse. Magnetic fields greater than 1 kT could be produced at a typical initial target radius of $\sim$ 5 mm if the Z machine's nominal peak current of 27 MA is delivered to the target without loss. However, even modest current losses can significantly reduce the drive at the target and degrade its predicted performance. Validation of simulations has thus been complicated by the absence of a direct measurement of the drive current. Experiments are underway to extend the Zeeman-splitting field measurements to peak current, enabling direct measurements of the drive over the entire implosion. [Preview Abstract] |
Thursday, November 14, 2013 9:42AM - 9:54AM |
TO4.00002: Ablation Flow Interactions in Wire Array Z-Pinches on the MAGPIE generator George Swadling, Sergey Lebedev, Gareth Hall, Francisco Suzuki-Vidal, Guy Burdiak, Nicolas Niasse, Louisa Pickworth, Jonathon Skidmore, Philip De Grouchy, Essa Koory, Lee Suttle, Matthew Bennett, Jianqiang Yuan, Adam Harvey-Thomson We present the results of experiments investigating the interactions of ablations streams in aluminium and tungsten wire array z-pinches. These experiments were carried out on the 1.4MA, 240ns MAGPIE generator at Imperial College London. The primary diagnostics used for these studies were an optical Thomson scattering diagnostic and an end-on aligned, two colour, Mach-Zehnder imaging interferometer. In aluminum arrays, the interactions of the ablation flows produces a dense network of oblique shocks. Measurements of the geometry of these shocks allows us to place limits on the plasma parameters of the flows. In tungsten arrays the data shows a prolonged period of collisionless flow. No shock structures were observed, the flow densities varied smoothly between the ablation streams and the inter-wire regions. The region about the axis appears azimuthally isotropic, and Thomson scattering measurements indicate significant interpenetration of the flows in this region. [Preview Abstract] |
Thursday, November 14, 2013 9:54AM - 10:06AM |
TO4.00003: ABSTRACT WITHDRAWN |
Thursday, November 14, 2013 10:06AM - 10:18AM |
TO4.00004: Comparison of 1D stagnation solutions to 3D wire-array Z pinch simulations in absence of radiation Edmund Yu, Alexander Velikovich, Yitzhak Maron In the idealized picture of a Z pinch, a cylindrically symmetric plasma shell implodes towards axis. In this 1D (radial) picture, the resulting stagnation is very efficient: all the kinetic energy of the shell converts to internal energy, as for instance in the Noh shock solution or the homogeneous stagnation flow. If we generalize the problem to 2D by deforming the shell from perfectly circular to oblate, the resulting stagnation will not be as efficient. As in the Hiemenz flow, in which a jet of fluid strikes a rigid flat boundary and squirts out to the sides, the more complicated flows allowed in 2D allow flow kinetic energy to redirect rather than stagnate. With this picture in mind, we might expect the stagnation of a wire-array Z pinch, which in actuality forms a highly distorted 3D imploding plasma, to dissipate its kinetic energy inefficiently due to the lack of symmetry, and be indescribable by means of the idealized 1D stagnation solutions. On the other hand, one might expect that if the imploding plasma is sufficiently messy, the non-uniformities might ``wash out,'' allowing a quasi-1D description of the averaged quantities of plasma. In this work we explore this idea, comparing predictions of 1D stagnation solutions with 3D simulation. [Preview Abstract] |
Thursday, November 14, 2013 10:18AM - 10:30AM |
TO4.00005: Acceleration of Hydrogen Ions up to 30 MeV and Generation of 3x10$^{12}$ Neutrons in Megaampere Deuterium Gas-Puff Z-Pinch D. Klir, J. Cikhardt, J. Kravarik, P. Kubes, K. Rezac, O. Sila, A. Shishlov, R. Cherdizov, F. Fursov, V. Kokshenev, B. Kovalchuk, N. Kurmaev, A. Labetsky, N. Ratakhin, H. Orcikova, K. Turek Fusion neutrons were produced with a deuterium gas-puff z-pinch on the GIT-12 generator at the Institute of High Current Electronics in Tomsk. The peak neutron yield from DD reactions reached $Y_{n}=(2.9\pm 0.3)\times 10^{12}$ at 100 $\mu$g/cm linear mass density of deuterium, 700 ns implosion time and 2.7 MA current. Such a neutron yield means that the scaling law of deuterium z-pinches $Y_{n}\propto I^{4}$ was extended to 3 MA currents. The further increase of neutron yields up to $(3.7\pm 0.4)\times 10^{12}$ was achieved by placing a deuterated polyethylene catcher onto the axis. Maximum neutron energies of 15 and 22 MeV were observed by radial and axial nToF detectors, respectively. A stack of CR-39 track detectors showed up to 40 MeV deuterons (or 30 MeV protons) on the z-pinch axis. Since the energy input into plasmas was 70 kJ, the number of DD neutrons per one joule of stored plasma energy exceeded the value of $5\times 10^7$. This value implies that deuterium gas-puff z-pinches belong to the most efficient plasma-based sources of DD neutrons. [Preview Abstract] |
Thursday, November 14, 2013 10:30AM - 10:42AM |
TO4.00006: New Regimes of Implosions of Larger Sized Wire Arrays With and Without Modified Central Plane at 1.5-1.7 MA Zebra A.S. Safronova, V.L. Kantsyrev, A.A. Esaulov, M.E. Weller, I. Shrestha, V.V. Shlyaptseva, A. Stafford, S.F. Keim, E.E. Petkov, M. Lorance, A.S. Chuvatin, C.A. Coverdale, B. Jones The recent experiments at 1.5-1.7 MA on Zebra at UNR with larger sized planar wires arrays (compared to the wire loads at 1 MA current) have demonstrated higher linear radiation yield and electron temperatures as well as advantages of better diagnostics access to observable plasma regions. Such multi-planar wire arrays had two outer wire planes from mid-Z material to create a global magnetic field (gmf) and mid-Z plasma flow between them. Also, they included a modified central plane with a few Al wires at the edges to influence gmf and to create Al plasma flow in the perpendicular direction. The stationary shock waves which existed over tens of ns on shadow images and the early x-ray emissions before the PCD peak on time-gated spectra were observed. The most recent experiments with similar loads but without the central wires demonstrated a very different regime of implosion with asymmetrical jets and no precursor formation. This work was supported by NNSA under DOE Cooperative Agreement DE-NA0001984 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 Company, for the U.S. Department of Energy's National Nuclear Security Administration under Contract DE-AC04-94AL85000. [Preview Abstract] |
Thursday, November 14, 2013 10:42AM - 10:54AM |
TO4.00007: High gain fusion in a Staged Z-pinch Paul Ney, Hafiz Rahman, Frank Wessel, Radu Presura The implosion of a Staged Z-pinch$\footnote{H. U. Rahman, F. J. Wessel, and N. Rostoker. Staged z-pinch. PRL, 74:714, 1995.}$ is simulated for the Sandia National Laboratories, ZR accelerator. The pinch is comprised of a silver (Ag) plasma shell, 3-mm outer radius, 0.01-cm thick, imploding onto a uniform fill (target) of deuterium-tritium (DT); the Z-R parameters are: 130 ns, 27 MA, 22 MJ; the 2-1/2 D, radiation-MHD code is MACH2. Magnetosonic shock waves generated during implosion propagate at different speeds in the liner and target, producing a shock front at the interface, and a conduction channel ahead of the liner. The interface remains stable even as the outer-surface of the liner is RT unstable. At peak compression target plasma hot spots trigger ignition with a fusion yield of 200 MJ and a net-energy gain approaching 10. The stability remains robust and the gain is unaffected for perturbations ranging from 2-5\%. [Preview Abstract] |
Thursday, November 14, 2013 10:54AM - 11:06AM |
TO4.00008: A novel investigation of the ion temperature and hydromotion of stagnating z-pinch plasma using Stark-broadened line shapes Dror Alumot, Eyal Kroupp, Evgeny Stambulchik, Dmitry Osin, Alexander Starobinets, Vladimir Bernshtam, Leonid Weingarten, Yitzhak Maron, Ingo Uschmann, Amnon Fisher In imploding plasmas, there is a severe lack of detailed experimental data on the thermalization processes that govern the ion temperature at stagnation, and on the energy delivered to radiation. Here, we report on a novel spectroscopic system, used to determine the temporally-resolved ion temperature and total ion kinetic energy, as well as the electron temperature and density. We use a neon Z-pinch, imploding under a 500-kA, 500-ns current pulse, and observe a hot-and-dense plasma core stagnating on axis for $\sim$ 10 ns. A two-spectrometer diagnostic system is employed, simultaneously recording two groups of optically-thin lines: He-like satellites to Ly$_\alpha$ and high-\textit{n} H-like Ly$_\delta$ and Ly$_\epsilon$ lines, with ultra-high resolutions in spectrum, time and space. The ion temperature is obtained, as a function of time, by analyzing the ion-correlation-affected shapes of the Stark-broadened high-\textit{n} lines. The total Doppler width yielded the total ion kinetic energy. The ion temperature is found to be substantially lower than the hydrodynamic-motion energy, the dissipation time of which is determined as well. [Preview Abstract] |
Thursday, November 14, 2013 11:06AM - 11:18AM |
TO4.00009: Numerical simulation of the wire array load for Z pinch and optimal load design based on PSPICE Hailong Zhao, Jianjun Deng, Wenkang Zou, Ganghua Wang, Mingxian Kan In order to maker better understand of the Z pinch implosion performed on Yang generator, the key point is to make numerical simulations about the pinch load. A zero dimensional load model of the wire array Z pinch is designed using PSPICE to simulate the implosive process, comparisons between the calculated results and experimental data prove the load model to be correct. With this model, optimal load designs are performed for PTS facility, factors influencing the simulation results are discussed, and comparison between results are analyzed to give out appropriate parameters useful for experiments. [Preview Abstract] |
Thursday, November 14, 2013 11:18AM - 11:30AM |
TO4.00010: Study of Bright Spots in Wire-Array Z-Pinches V.V. Ivanov, D. Papp, A.A. Anderson, B. Talbot, A.L. Astanovitskiy, V. Nalajala, O. Dmitriev, J.P. Chittenden, N. Niasse Bright areas with a high plasma density and temperature (hot spots) were observed in all kinds of Z-pinches. Hot spots may be interpreted as results of the collapse of the plasma necks due to plasma outflowing and radiative losses of energy. We studied bright radiating spots in cylindrical and planar wire-arrays at the 1 MA Zebra generator using x-ray streak cameras synchronized with laser diagnostics, x-ray time-gated pinhole camera and spectroscopy. Hot spots in Al wire arrays generate x-ray bursts with durations of 0.4-1ns in the soft range and 0.1-0.4ns in the keV range. UV two-frame shadowgraphy shows spatial correlation of hot spots with micropinches. Hot spots can generate continuum radiation with energy \textgreater 2.5keV. An analysis of x-ray streak images shows that hot spots can generate \textgreater 20{\%} of the x-ray energy of the Z pinches. [Preview Abstract] |
Thursday, November 14, 2013 11:30AM - 11:42AM |
TO4.00011: Computational modeling of Krypton Gas Puffs on Z C.A. Jennings, D.J. Ampleford, A.J. Harvey-Thompson, B. Jones, S.B. Hansen, D.C. Lamppa, M.R.L. Jobe, T. Strizic, M.E. Cuneo Large diameter multi-shell gas puffs rapidly imploded by high current ($\sim$ 20MA, $\sim$ 100ns) on the Z generator are able to produce high-intensity K-shell radiation. Experiments are underway to produce Krypton K-shell emission at $\sim$ 13keV, although efficiently radiating at these high photon energies represents a significant challenge. This necessitates the careful design and optimization of the distribution of gas in these loads. To facilitate this we hydro-dynamically model the flow of gas out of the nozzle, before imploding that mass distribution using a 3-dimensional resistive, radiative MHD code (GORGON). Modeled gas profiles have been validated against 2-dimensional interferometric measurements of the gas distribution from these nozzles, and MHD calculations are validated against power, yield, spectral and imaging diagnostics of previous gas puff implosions on Z. This approach enables us to iterate between modeling the implosion and modeling gas flow from the nozzle to optimize radiative output from this combined system. Guided by our implosion calculations we have redesigned the gas nozzle to better optimize Krypton K-shell output and the evaluation of these designs is the subject of ongoing experiments. [Preview Abstract] |
Thursday, November 14, 2013 11:42AM - 11:54AM |
TO4.00012: Hard X-ray and Particle Beams Research on 1.7 MA Z-pinch and Laser Plasma Experiments Ishor Shrestha, Victor Kantsyrev, Alla Safronova, Andrey Esaulov, Mineyuki Nishio, Veronica Shlyaptseva, Steven Keim, Michael Weller, Austin Stafford, Emil Petkov, Kimberly Schultz, Matthew Cooper Studies of hard x-ray (HXR) emission, electron and ion beam generation in z-pinch and laser plasmas are important for Inertial Confinement Fusion (ICF) and development of HXR sources from K-shell and L-shell radiation. The characteristics of HXR and particle beams produced by implosions of planar wire arrays, nested and single cylindrical wire arrays, and X-pinches were analyzed on 100 ns UNR Zebra generator with current up to 1.7 MA. In addition, the comparison of characteristics of HXR and electron beams on Zebra and 350 fs UNR Leopard laser experiments with foils has been performed. The diagnostics include Faraday cups, HXR diodes, different x-ray spectrometers and imaging systems, and ion mass spectrometer using the technique of Thomson parabola. Future work on HXRs and particle beams in HED plasmas is discussed. [Preview Abstract] |
Thursday, November 14, 2013 11:54AM - 12:06PM |
TO4.00013: Direct Measurement of the Acceleration of a Probe Beam by a Dense Plasma Focus Z-Pinch J.L. Ellsworth, S. Falabella, B. Rusnak, A.E.W. Schmidt, V. Tang Dense plasma focus (DPF) Z-pinch plasmas produce multiple-MeV ions on a cm-scale length, implying electric field gradients exceeding 100 MV/m in the plasma.~ We report on the first experiments using a 4 MeV deuteron probe beam to directly measure the electric field gradients produced by the kJ-level DPF experiment at LLNL. This information can be used in conjunction with fully kinetic simulations of DPF plasmas to further our understanding of the mechanisms that produce these beams.~ An understanding of gradient formation in DPFs is necessary to optimize the gradients in these devices for compact accelerator applications. This work performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344 and supported by the Laboratory Directed Research and Development Program (11-ERD-063) at LLNL. [Preview Abstract] |
Thursday, November 14, 2013 12:06PM - 12:18PM |
TO4.00014: Neutron Emission in Deuterium Dense Plasma Foci Brian Appelbe, Jeremy Chittenden We present the results of a computational study of the deuterium dense plasma focus (DPF) carried out to improve understanding of the neutron production mechanism in the DPF. The device currents studied range from 70 kA to several MA. The complete evolution of the DPF is simulated in 3D from rundown through to neutron emission using a hybrid computational method. The rundown, pinching, stagnation and post-stagnation (pinch break-up) phases are simulated using the 3D MHD code Gorgon. Kinetic computational tools are used to model the formation and transport of non-thermal ion populations and neutron production during the stagnation and post-stagnation phases, resulting in the production of synthetic neutron spectra. It is observed that the break-up phase plays an important role in the formation of non-thermal ions. Large electric fields generated during pinch break-up cause ions to be accelerated from the edges of dense plasma regions. The dependence on current of the neutron yield, neutron spectra shape and isotropy is studied. The effect of magnetization of the non-thermal ions is evident as the anisotropy of the neutron spectra decreases at higher current. [Preview Abstract] |
Thursday, November 14, 2013 12:18PM - 12:30PM |
TO4.00015: Application of Proton Deflectometry to Z-Pinch Plasma Systems at the Mega-Ampere Scale Derek Mariscal, Chris McGuffey, Julio Valenzuela, Mingsheng Wei, Farhat Beg, Radu Presura, Showera Haque, Angel Arias, Aaron Covington, Hiroshi Sawada, Jeremy Chittenden Measuring magnetic fields in z-pinch plasmas is challenging. Typical laser-probing diagnostics are limited by the critical density and large density gradients, while electrical diagnostics have limited spatial resolution. We report the first demonstration of proton deflectometry of z-pinch plasma systems at the mega-ampere scale. The proton beam was produced using the 10J 0.3ps Leopard laser and coupled to z-pinch plasma produced by Zebra, a 1MA pulsed-power driver at the Nevada Terawatt Facility. The magnetic field distorted the proton beam profile, which was recorded on radiochromic film. The experimental data was compared against integrated modeling using the resistive MHD code, Gorgon, for Z-pinch plasmas, in combination with the hybrid PIC code, LSP, for proton-beam trajectory tracking. This comparison provided the field and current configuration for various plasma loads, including wire and foil z-pinches. [Preview Abstract] |
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