Bulletin of the American Physical Society
50th Annual Meeting of the Division of Plasma Physics
Volume 53, Number 14
Monday–Friday, November 17–21, 2008; Dallas, Texas
Session JO5: X-Pinches and Z-Pinches |
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Chair: Michael Cuneo, Sandia National Laboratories Room: Reunion C |
Tuesday, November 18, 2008 2:00PM - 2:12PM |
JO5.00001: Nested X Pinches on the COBRA Generator David Hammer, Tatiana Shelkovenko, Sergei Pikuz, Ryan McBride, Patrick Knapp, Harold Wilhelm, Daniel Sinars Recent results of X pinch studies on the COBRA generator at Cornell University (peak current up to 1.2~MA and rise time of 100~ns) are presented. Increasing of the pulser current requires the use of loads with higher mass per unit length. Such loads can be made by increasing the number of wires or the wire diameters, which leads to increasing the size and complexity of the wire crossing region. Using an initial configuration of wires (before their twisting), similar to nested arrays enables the assembly of a more-nearly symmetric configuration at the X pinch crossing region. It also enables an investigation of multilayered X pinches. We will present experimental results obtained from X pinches with different configurations, including X pinches with different materials in the inner and outer wire layers. [Preview Abstract] |
Tuesday, November 18, 2008 2:12PM - 2:24PM |
JO5.00002: Bright Spots in X-pinch Plasmas at 6 MA D.B. Sinars, D.J. Ampleford, E.P. Yu, C.A. Jennings, M.E. Cuneo, D.F. Wenger, S.A. Pikuz, T.A. Shelkovenko, S.N. Bland, J.P. Chittenden Bright, $\sim$1 $\mu$m, 10-100 ps x-ray sources with extreme plasma parameters are routinely created using X-pinch plasmas driven by 0.2 MA. Modeling suggests that even more extreme plasma parameters might be possible at higher current. We present data from the first 6 MA X-pinch experiments on the SATURN facility at Sandia National Laboratories. The mass required to pinch near peak current was surprisingly low ($\sim$14 mg/cm vs. $\sim$3 mg/cm at 1 MA) and the smallest x-ray source measured was $\sim$60 $\mu$m in size. Following up on recent work by Pikuz et al. at 1 MA, experiments in September will use nested-array X-pinch implosions to improve the symmetry. [Preview Abstract] |
Tuesday, November 18, 2008 2:24PM - 2:36PM |
JO5.00003: Large scale parallel computing simulations of wire array Z-pinches Jeremy Chittenden, Nicolas Niasse, Andrea Ciardi Until recently simulations of wire array Z-pinches have been undertaken in a piece-wise fashion, modelling either only part of the array volume, or modelling different aspects of the array behaviour separately. Recent simulations of a single wire in the array suggest that the short wavelength modulations of the ablating plasma observed in experiments are the result of a modified m=0 like instability. In order to simulate the growth of magneto-Rayleigh-Taylor instabilities during the implosion phase, a separate calculation is usually performed in which estimates for the structure of the modulated ablation are used to provide the initial seed perturbation for the implosion. Improvements to the parallel computing architecture of the Gorgon 3D resistive MHD code, however, mean that is now possible to run with large enough computational grids to encompass the entire volume of the array whilst retaining sufficient resolution to model the spontaneous development of the modulated ablation structure from microscopic noise. Thus we can model the evolution of the wire array from the point of initial plasma formation, right through the implosion, without imposing any predetermined perturbation or structure. A detailed comparison of synthetic diagnostic images with data from MAGPIE experiments is used to test this method. Preliminary data from similar simulations of Z experiments are also presented. [Preview Abstract] |
Tuesday, November 18, 2008 2:36PM - 2:48PM |
JO5.00004: Fourier analysis of bubble dynamics in a wire-array Z pinch implosion Edmund Yu, Michael Cuneo In the simplest picture of a Z pinch, wires are Ohmically heated and converted into a plasma sheath, which then implodes radially inwards due to the jxB force. Of critical importance is the width of the imploding plasma sheath, since a narrow sheath leads to higher radiated power. Recent simulations and experimental radiography suggest this simple picture is actually quite a bit more complicated. The imploding plasma sheath is an inherently 3D object and constitutes a web-like network of bubbles, on which bubble growth is governed by both the magnetic Rayleigh-Taylor instability as well as jxB forces. An important (but experimentally unknown) parameter affecting the dynamics of the sheath is the degree of azimuthal correlation C, which relates to the average azimuthal extent of each bubble. In this work we perform a Fourier analysis on radiographs generated from 3D simulations to glean information on the time evolution of the dominant (axial and azimuthal) bubble wavelengths, and compare with the corresponding experimental radiographs. This data can help us understand the dynamics of the plasma sheath and constrain the azimuthal correlation C. [Preview Abstract] |
Tuesday, November 18, 2008 2:48PM - 3:00PM |
JO5.00005: Development of the Axial Instability in Low Wire Number Wire Array Z-Pinches P.F. Knapp, K.S. Bell, I.C. Blesener, D.A. Chalenski, J.B. Greenly, M.R. Martin, R.D. McBride, S.A. Pikuz, T.A. Shelkovenko, D.A. Hammer, B.R. Kusse We are investigating the development of the axial instability that occurs on wires in wire-array Z-pinches, which manifests itself as a modulation of the size of the coronal plasma. The modulation is evidently a result of non-uniform ablation of material from the wire core. It is known that the wavelength of this modulation reaches a constant as the pinch develops that is a strong function of the material and little else, thus it is known as the fundamental mode. In these experiments we have been imaging individual wires with laser shadowgraphy primarily in low wire number, large wire diameter arrays made with Al, Cu, Ag and other wires. We document the development of this modulation from the beginning of plasma formation and show the wavelength and amplitude growth as a function of time. The magnetic field is also measured using B-dot probes inside the array. The change from a closed to an open field topology and its relation to the instability growth will be discussed.This research was supported by the Stewardship Sciences Academic Alliances program of the National Nuclear Security Administration under DOE Cooperative agreement DE-FC03-02NA00057 and by Sandia National Laboratories contract AO258. [Preview Abstract] |
Tuesday, November 18, 2008 3:00PM - 3:12PM |
JO5.00006: ABSTRACT WITHDRAWN |
Tuesday, November 18, 2008 3:12PM - 3:24PM |
JO5.00007: Experiments Investigating the Interaction between Precursor Plasma from Wire Arrays and On-axis Foam Targets at 1 MA. J. Palmer, S. Lebedev, J. Chittenden, S. Bland, F. Suzuki-Vidal, G. Hall, S. Bott, M. Sherlock, D. Ampleford Low density cylindrical plastic foam targets are placed on the axis of several configurations of wire array z-pinch (e.g. the dynamic hohlaum). These targets can be preconditioned by the precursor plasma produced by wire array z-pinches prior to the array imploding. Experimental data has shown precursor plasma produced from both low current low wire-number arrays and high current high wire-number arrays. Experiments were carried out on the 1 MA pulsed power generator MAGPIE, where targets were placed on the axis of non-imploding tungsten wire arrays. Data showed the target diameter was reduced, probably due to a snow-plough like compression, and that the precursor plasma formed a boundary layer at the surface of the target. This boundary layer evolved in a similar way to the precursor plasma column that forms on the axis of bare arrays however, its formation was more rapid than the precursor column and it developed an axial modulation with wavelength approximately one millimetre. Diagnostics were; x-pinch back-lighting; pin-hole imaged XUV/soft x-ray framing cameras; laser probing (shadowgraphy and interferometry); optical streak photography; VUV time and spatially (1D) resolved spectroscopy; filtered diamond photo-conducting diodes. [Preview Abstract] |
Tuesday, November 18, 2008 3:24PM - 3:36PM |
JO5.00008: Origin of the interaction pulse in Nested Wire Array Z-pinches D.J. Ampleford, C.A. Jennings, M.E. Cuneo, M.C. Jones, D.B. Sinars, S.N. Bland, G.N. Hall, S.V. Lebedev, J.P. Chittenden, F. Suzuki-Vidal, S.C. Bott The interaction pulse emitted by nested wire array z-pinches on the Z-generator is critical to achieving the required x-ray pulse shape for z-pinch driven ICF schemes. We discuss data from the MAGPIE generator which indicates this interaction pulse is likely to be caused by the presence of the inner array creating bow shocks in the ablation streams from the outer array, and hence enhancing the prefill density at this location. As the outer array implodes, it snowplows the prefilled material, radiating excess kinetic energy as snowplow radiation. The enhanced density due to shocked prefill around the inner wires boosts the snowplow, and is seen as the interaction radiation pulse. This understanding agrees with data from Z, which indicates that the interaction pulse is independent of the inner array parameters, and decreases with increasing outer array mass. Comparisons of this model to recent data on the refurbished Z generator will also be discussed. [Preview Abstract] |
Tuesday, November 18, 2008 3:36PM - 3:48PM |
JO5.00009: Radiated X-ray Power and Energy current scaling at 80ns implosion times Michael Mazarakis, Michael Cuneo, William Stygar, Henry Harjes, Daniel Sinars, Brent Jones, Christopher Deeney, Eduardo Waisman, Thomas Nash, Kenneth Struve, Dillon McDaniel The results of our current scaling experiments with the Z accelerator for the compact, single, 20-mm diameter, 10-cm long wire arrays, are compared with the predictions of the W.A. Stygar \textit{et al.} [Phys. Rev. E \textbf{69}, 046403 (2004)] and [Phys. Rev. E \textbf{72}, 026404 (2005)] heuristic model for ablation dominated pinches. We also derive an empirical predictive relation that connects the power-scaling exponent with the array parameters. Utilizing the results of the present work with those of W.A. Stygar \textit{et al.} and T. Nash \textit{et al.} [Phys. Plasmas \textbf{11}, 5156 (2004)] we evaluate the proportionality constant of the heuristic model. [Preview Abstract] |
Tuesday, November 18, 2008 3:48PM - 4:00PM |
JO5.00010: Dynamics and scaling of z-pinch K-shell x-ray sources B. Jones, D.J. Ampleford, M.E. Cuneo, S.C. Jones, C.A. Coverdale, C. Deeney, E.M. Waisman, J.E. Bailey, G.A. Rochau, C.A. Jennings, J.W. Thornhill, J.P. Apruzese, R.W. Clark, K.G. Whitney, J. Davis, J.L. Giuliani, Y. Maron, V. Fisher, V. Bernshtam, A. Starobinets, J.P. Chittenden Fast z-pinch implosions provide high fluence 1-10 keV photon energy radiation environments. We discuss recent work with $\sim $6.7 keV stainless steel and 8.4 keV Cu wire array sources on Sandia's Z machine pulsed power driver. Implosion dynamics are investigated along with scaling of K-shell yield with atomic number and coupled energy. L-shell radiative cooling can remove energy from the plasma and limit K-shell yield scaling at high mass, high generator current, and moderate atomic number. These K-shell line sources also provide an opportunity for spectroscopic diagnosis of high energy density plasma conditions. [Preview Abstract] |
Tuesday, November 18, 2008 4:00PM - 4:12PM |
JO5.00011: Progress report on new results of the study of multi-planar and compact cylindrical wire arrays at 0.8-1.3 MA current at UNR Zebra generator V.L. Kantsyrev, A.S. Safronova, A.A. Esaulov, R. Presura, K.M. Williamson, I. Shrestha, N.D. Ouart, M.F. Yilmaz, P.G. Wilcox, G.C. Osborne, M.E. Weller, V. Shlyaptseva, L.I. Rudakov The studies that include the measurements of radiation yields, time-gated spectra and images, streak camera and laser probing images, spectral modeling, and magnetostatic and MHD simulations focus on Z-pinch plasma implosion and radiation features (including bright spots properties). The experiments with small size (3-10 mm) single-, double-, triple-, cross- planar, and compact cylindrical wire arrays from various materials at nominal as well as enhanced currents up to 1.3 MA were performed on the Zebra generator. The largest x-ray yields and powers were ranged for W and Mo. Observed multi-step precursor formation in multi-planar arrays may open new paths for radiation pulses shaping. Implosion and spectroscopic features specific for enhanced currents are discussed. [Preview Abstract] |
Tuesday, November 18, 2008 4:12PM - 4:24PM |
JO5.00012: Analysis of x-ray bright spots from triple and single combined Cu and Al planar wire arrays on the 1MA pulsed power generator at UNR A.S. Safronova, V.L. Kantsyrev, A.A. Esaulov, N.D. Ouart, M.F. Yilmaz, M.E. Weller, K.M. Williamson, V. Shlyaptseva, I. Shrestha, G.C. Osborne, C.A. Coverdale, C. Deeney The recently discovered implosion features of double planar wire arrays, such as the two step precursor formation with the independent implosion of wire arrays made from different materials and bright spot generation in a central precursor column early in time [Kantsyrev et al, PoP 15, 030704 (2008)], led to new experiments with combined triple planar wire arrays (TPWA). Combined TPWA include three planar wire rows that are parallel to each other and made of either Cu or Al alloyed wires. New x-ray data for two configurations (Al/Cu/Al and Cu/Al/Cu) are considered and compared with each other, with the results from combined single planar wire arrays of the same materials, and with Cu uniform cylindrical wire arrays. Emphasis is made on the study of bright spot formation, which is a signature of implosions of planar wire arrays and can be significant for other wire array configurations as well. Work was supported by NNSA/DOE under Coop. Agr. DE-FC52-06NA27588, DE-FC52-06NA27586, and in part by DE-FC52-06NA27616. Sandia is a multi-program laboratory operated by Sandia Corporation, a Lockheed Martin Company, for the US DOE under Contract DE-AC04-94AL85000. [Preview Abstract] |
Tuesday, November 18, 2008 4:24PM - 4:36PM |
JO5.00013: Implosion dynamics and x-ray generation in small-diameter wire-array z-pinches V.V. Ivanov, V.I. Sotnikov, J.M. Kindel, A.L. Astanovitskiy, A. Haboub, S.D. Altemara, A.P. Shevelko, E.D. Kazakov, P.V. Sasorov The implosion in cylindrical wire arrays with diameters from 1 to 16 mm were compared to find a transition from regimes with high kinetic energy to regimes with other mechanisms of plasma heating. The x-ray power falls in 1-2-mm loads that can be linked to the lower efficiency of plasma heating with lack of kinetic energy. The electron temperature and density of pinches also depend on the array diameter. Correlated bubble-like implosions were observed with a multi-frame shadowgraphy. The energy balance provides evidence for mechanisms of non-kinetic plasma heating in z-pinches. Formation and evolution of bright spots in Al and W z-pinches were studied with a time-gated pinhole camera. A comparison of x-ray images with shadowgrams shows that implosion bubbles produce ``necks'' and initiate bright spots in the pinch. [Preview Abstract] |
Tuesday, November 18, 2008 4:36PM - 4:48PM |
JO5.00014: Nonlinear dynamics of flute mode structures in a plasma with inhomogeneous magnetic field V.I. Sotnikov, O.G. Onishchenko, V.V. Ivanov, R. Presura, J. Kindel, J.N. Leboeuf, B.V. Oliver, T.A. Mehlhorn, C. Deeney In the past decade the problem of formation of large scale coherent structures from random perturbations as well as coexistence of these structures with short scale turbulent spectra has attracted considerable attention. We have developed an understanding of the nonlinear dynamics of compressible flute mode turbulence in a high beta plasma in the presence of a non-uniform magnetic field. Flute modes can be responsible for the intermittent convective-like transport across the magnetic field and enhanced viscous heating associated with appearance of short scales. This is important for numerous applications, including Z-pinches and laboratory astrophysics. [Preview Abstract] |
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