Bulletin of the American Physical Society
2005 47th Annual Meeting of the Division of Plasma Physics
Monday–Friday, October 24–28, 2005; Denver, Colorado
Session CO3: Z-pinches, X-pinches, and Dense Plasma Focus |
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Chair: Daniel Sinars, Sandia National Laboratories Room: Adam's Mark Hotel Governor's Square 15 |
Monday, October 24, 2005 2:00PM - 2:12PM |
CO3.00001: Jet formation in multi-wire X-pinch Erik Shipton, David Haas, Greg Andreev, Kathy Wagschal, Zaid Karim, Farhat Beg Experiments have been performed to study jet formation using a compact x-pinch pulser, which produces 80 kA current in 40 ns. X-pinch consisting of various wire materials including tungsten, molybdenum, iron and aluminum were used. Number of wires, x-pinch angle and length were varied to study jet formation. The jets were observed to be formed about 5 ns after the current start. The wires connected to the cathode were observed to expand faster. Detailed results will be presented at the meeting. [Preview Abstract] |
Monday, October 24, 2005 2:12PM - 2:24PM |
CO3.00002: Generation of electron and ion beams in X pinches. Y.S. Dimant, T.A. Shelkovenko, S.A. Pikuz, D.A. Hammer X pinches employed for x-ray generation represent excellent objects to study the details of plasma pinch processes. An X pinch is produced by passing a high current through two or more metal wires that cross and touch at a single point in the middle. During its evolution, the X-pinch forms in the middle a small Z pinch that is unstable and forms a cascade of smaller and denser necks. In the final phase, the pinch disrupts and produces extremely short and localized bursts of intense soft x-ray radiation, followed immediately by a $\sim$ 1 ns burst of higher energy x-rays that is attributed to energetic electrons accelerated in the gaps that appear in the X-pinch plasma structure after its soft x-ray burst. The behavior of the energetic particles that produce intense x-rays requires a kinetic description. Using a simplified kinetic approach and available results of recent MHD simulations, we will discuss the dynamics of energetic electron and ion beams formed around the central axis of the X-pinch, where the magnetic field does not prevent kinetic runaway in the applied strong electric field. Recent measurements of the cross-wire voltage and beam currents allow us to more accurately compare our theoretical estimates with observations. [Preview Abstract] |
Monday, October 24, 2005 2:24PM - 2:36PM |
CO3.00003: Spectroscopy and implosion dynamics of combined W and Al X-pinches and their comparison with W wire arrays produced on the UNR 1 MA z-pinch generator A. Safronova, V. Kantsyrev, D. Fedin, A. Esaulov, F. Yilmaz, N. Ouart, T. Hoppe, G. Osborne, V. Nalajala, S. Pokala, I. Shrestha, J.P. Apruzese Experiments on the 1 MA Zebra generator at UNR with combined planar-loop X-pinches composed from high-Z (W) and low-Z (Al) materials provide a unique opportunity to study M-shell radiation of W. In particular, X-pinches with a 35 $\mu $m W wire in the top loop and a 99 $\mu $m Al wire in the bottom loop as well as reversed, Al at the top and W at the bottom, of the same diameter, were analyzed and compared. In addition, wire arrays with 5 $\mu $m W wires coated with 5{\%} NaF were investigated and compared with X-pinches. Spatially-resolved and integrated x-ray spectral data and time-resolved and integrated pinhole x-ray images accumulated in these experiments were analyzed. Modeling of K-shell radiation from Al, Mg, and Na ions provides K-shell plasma parameters. Modeling of M-shell radiation from W provides parameters for M-shell plasmas. Based on this modeling, Al and W radiation is analyzed and compared for different wire loads. The importance of using different materials, dopants, and load configurations for understanding the radiative properties of W is illustrated. Work supported by the DOE/ NNSA under UNR grant DE-FC52-01NV14050 and by Sandia National Laboratories under DOE contract DE-AC04-94AL85000. [Preview Abstract] |
Monday, October 24, 2005 2:36PM - 2:48PM |
CO3.00004: Time Gated Imaging of Cylindrical Wire Array Z-Pinches Using X-Pinch Backlighting Jon Douglass, John Greenly, David Hammer, Ryan McBride, Sergei Pikuz, Tanya Shelkovenko X-Pinch radiography has been used routinely at Cornell for more than 10 years to produce high quality x-ray images with excellent spatial and temporal resolution [T.A. Shelkovenko \textit{et al}., Phys. Plasmas \textbf{8}, 1305-1318 (2001).]. This imaging technique is being used on the COBRA accelerator at Cornell to study the early stages of wire-array Z-pinches. The configuration is similar to those used at the on the Angara-5-1 facility [E.V. Grabovskii \textit{et al}., Plasma Physics Reports 30, 121--127 (2004).] and on MAGPIE [S.V. Lebedev \textit{et al}., Rev. Sci. Instrum., 72, 671-673 (2001).]. Images have been obtained that show the evolution of wire structure and instabilities. X-pinch wire parameters are varied in order to shift the timing of the x- pinch x-ray burst relative to the start of the z-pinch current pulse. The ability to control x-pinch radiation timing will be discussed along with the dynamics of the exploding wires in the wire-arrays. This research was supported by the Stewardship Sciences Academic Alliances program of the National Nuclear Security Administration under DOE Cooperative agreement DE-FC03-02NA00057.~~ [Preview Abstract] |
Monday, October 24, 2005 2:48PM - 3:00PM |
CO3.00005: Effect of material on precursor flow conditions and column formation in cylindrical wire arrays S. Bott, S. Lebedev, S. Bland, J. Chittenden, M. Sherlock, M. Haines, D. Ampleford, G. Hall, C. Jennings, J. Rapley, J. Palmer The ablation phase of wire arrays drives streams of material to the common axis for long periods prior to implosion. Flow conditions determine the density profile encountered by the imploding array, influencing trajectory and hence kinetic energy at stagnation, and are entirely determined by array material. The effect of atomic mass on the formation of the precursor column is investigated experimentally. Variations in the column diameter, formation time, and expansion rates are found to be related to the radiative cooling and collisionality of precursor streams. The column formation mechanism is shown to be a radiatively-driven collapse resulting from rising on-axis density. Agreement with a kinetic model is found. Insulated wires will also be investigated. Precursor plasma flow will be compared to uncoated arrays to determine how this will alter array pre-fill and implosion trajectory. Research sponsored by Sandia National Laboratory, the SSAA program of NNSA under DOE Cooperative Agreement DE-FC03-02NA00057. [Preview Abstract] |
Monday, October 24, 2005 3:00PM - 3:12PM |
CO3.00006: Dependence of z-pinch mass ablation rate on wire size and inter-wire gap Edmund Yu, Bryan Oliver, Pavel Sasorov, Dan Sinars, Mike Cuneo, Tom Mehlhorn A wire array z-pinch spends 60-80\% of its lifetime in a mass ablation phase, during which wire cores remain stationary while burning off hot coronal material. Experiments have demonstrated a dependence of the mass ablation rate on wire size and inter-wire gap [1,2]. We present a highly simplified model of wire ablation which attempts to capture the dominant physics driving this dependence. Comparison between theory, simulation, and experiment are presented. \newline \newline [1] S.V. Lebedev et al., Nucl. Fusion, 44, S215(2004) \newline [2] D.B. Sinars et al., (submitted for publication) [Preview Abstract] |
Monday, October 24, 2005 3:12PM - 3:24PM |
CO3.00007: WITHDRAWN - Dynamics of Precursor Coronal Plasmas and Wire Ablation in Wire Array Z-Pinches B.V. Oliver, E.P. Yu, T.A. Mehlhorn, P. Sasorov The radial acceleration of low density (relative to the wire core) coronal plasmas, towards the axis of wire-array Z pinches, is observed in a variety of experiments on various pulsed-power accelerators [S. V. Lebedev, et al., Phys. Rev. Lett. 85, 98 (2000); V.V. Aleksandrov, et al., Fizika Plazmy 27, 99 (2001); M.E. Cuneo, et al., Bull. Am. Phys. Soc. 43, 234 (2001)]. The dynamics of these coronal plasmas play an important role in the distribution of both current and mass prior to the run in phase of the full array. An extension of previously reported 1-D theory of coronal plasma dynamics to include two dimensional effects and the role of the core state in the plasma production/ablation process is presented. The plasma production rate can be determined either by electron thermal and or radiation conduction from the coronal plasma to the wire core. In either case electron thermal conduction is necessary. For very high current parameter regimes (e.g. $>$ 20 MA), details of the core state need to be considered in the analysis. Two dimensional considerations suggest a weak scaling of ablation rate with the ratio of wire core diameter to inter-wire gap and suggest that strong two-dimensional effects reduce the production rate. It is concluded that to accurately model wire ablation, the material properties of both the ablated plasma and the wire core need to be determined. [Preview Abstract] |
Monday, October 24, 2005 3:24PM - 3:36PM |
CO3.00008: Studies of Al and W wire array z-pinches, and the role of ``magnetic bubbles'' in energy deposition at 1 MA Cobra generator V. Kantsyrev, A. Safronova, D. Fedin, A. Esaulov, V. Nalajala, N. Ouart, F. Yilmaz, T. Hoppe, G. Osborne, K. Williamson, J. Greenly, J. Douglass, R. McBride, L. Maxson, D. Hammer, A. Velikovich Implosions of cylindrical arrays with eight 12.5 $\mu $m Al or 5.1 $\mu $m W wires were studied on the 1MA, 100-150 ns rise time COBRA generator. X-ray and EUV detectors, time-gated cameras, spectrometers, backlighters and electrical diagnostics were used. Total radiation yields$_{ }$of 2.8 and 3.7 kJ, and total radiated powers of 15 GW and 25 GW were measured for Al and W, respectively. The keV yield for W arrays was lower than for Al. The Al spectra have shown T$_{e}$ from 200 eV to 300 eV. X-ray spectra from W arrays included very weak spectral features that were compared with results from W/Mo X-pinch experiments. Relatively uniform plasma columns (life-time 5-10 ns) were observed on time-gated images during the initial implosion stage for both Al and W. Studies of the possible role of ``magnetic bubbles'' on energy deposition were initiated based on the plasma resistance compared with the nonlinear resistance predicted by theory, total radiation yield, and the time-gated and backlighting images. This work was sponsored by NNSA through DOE Coop. Agreement DE-F03-02NA00057 and in part by the DOE/ NNSA under UNR grant DE-FC52-01NV14050. [Preview Abstract] |
Monday, October 24, 2005 3:36PM - 3:48PM |
CO3.00009: Wire Fixturing in High Wire-Number Z-Pinch Implosions Important for Reproducibility and High Power T.W.L. Sanford, R.C. Mock, J.F. Seamen, M.R. Lopez, R.G. Watt, G.C. Idzorek, D.L. Peterson Dynamic Hohlraums (DH) [1] driven by W wire-array Z pinches are being developed and used as intense black-body x-ray sources for high temperature radiation flow and ICF experiments on Z. They are currently the most energetic and intense pulsed-power driven radiation sources in the laboratory for these applications. Three methods for positioning and holding the wires in place, within these loads, have been developed: the ``flop-over'' [2], the ``hang-down'' [2], and the ``weightless''. The shot-to-shot variation in magnitude and shape of the radial and top-bottom axial powers and spectra are used to establish the efficacy of each wire-fixturing method. Comparisons among the 3 fixturing techniques illustrate the importance of good wire-cathode contact. In general, poor wire-electrode contact leads to a less coherent implosion, and to excessive W-wire plasma flowing across the REHs (radiation exit holes) located at either end of the DH, increasing the opacity of the REH, with subsequent lowering of axial power. [1] T. W. L. Sanford. et al, \textit{Phys. Plasmas} \textbf{9}, 3573 (2002). [2] T. W. L. Sanford. et al, \textit{Digest Tech. Papers, IEEE Inter. Conf. On Pulsed Power} (Dallas, TX, 2003), pp 733-6. $^{\ast }$Sandia is a multiprogram laboratory operated by the Sandia Corporation, a Lockheed Martin Company, for the U.S. Department of Energy under Contract No. DE-AC04-94AL85000\textbf{.} [Preview Abstract] |
Monday, October 24, 2005 3:48PM - 4:00PM |
CO3.00010: Magnetohydrodynamic turbulence model James Hammer K-epsilon models find wide application as approximate models of fluid turbulence. The models couple equations for the turbulent kinetic energy and dissipation rate to the usual fluid equations, where the turbulence is driven by Reynolds stress or buoyancy source terms. We generalize to the case with magnetic forces in a Z-pinch geometry (azimuthal fields), using simple energy arguments to derive the turbulent source terms. The field is presumed strong enough that 3 dimensional twisting or bending of the field can be ignored, i.e. the flow is of the interchange type. The generalized source terms show the familiar correspondence between magnetic curvature and acceleration as drive terms for Rayleigh-Taylor and sausage instability. The source terms lead naturally to a modification of Ohm's law including a turbulent electric field that allows magnetic field to diffuse through material. The turbulent magnetic diffusion parallels a corresponding ohmic heating term in the equation for the turbulent kinetic energy. [Preview Abstract] |
Monday, October 24, 2005 4:00PM - 4:12PM |
CO3.00011: Time- and space-resolved Si emission measurements of the Z-pinch dynamic hohlraum Gregory A. Rochau, J.E. Bailey, K.J. Peterson, G.S. Dunham, P.W. Lake, S.A. Slutz, J.J. MacFarlane, Y. Maron Simulations of the Z-pinch dynamic hohlraum predict a radiating shock in the 14mg/cc CH$_2$ foam that reaches T$_e >$ 600eV with a peak hohlraum temperature of T$_r >$ 200eV. To test these simulations, an advanced diagnostic technique has been developed that relies on the measurement of time- and space- resolved Si line emission in combination with 2-D collisional- radiative calculations to infer the conditions of the dynamic hohlraum interior. The line emission originates from Si atoms doped over the central 3 - 6mm height of the foam, and is recorded on an elliptical spectrometer with 1-D spatial resolution imaging through a slot aperture on the top of the dynamic hohlraum. The 2-D calculations assume a 2 or 3 region model of the Si-doped CH$_2$ foam conditions, and include non- local photo-pumping processes that are determined to have an important influence on the observed spectra. The time- and space-resolved conditions of the dynamic hohlraum interior inferred from this technique are presented and compared with 2- D rad-hydro simulations. [Preview Abstract] |
Monday, October 24, 2005 4:12PM - 4:24PM |
CO3.00012: Using a Z-pinch precursor plasma to produce a cylindrical, hotspot ignition, ICF Jeremy Chittenden, Peter Vincent, Christopher Jennings, Andrea Ciardi We show that if the same precursor plasma that exists in metal wire arrays can be generated with a Deuterium-Tritium plasma then this precursor provides an ideal target for a cylindrical magneto-inertial ICF scheme. The precursor is generated from a fraction of the mass of the array which arrives on the axis early in time and remains confined at high density by the inertia of further material bombarding the axis. Later on, the main implosion of the DT Z-pinch produces a dense, low temperature shell which compressively heats the precursor target to high temperatures and tamps its expansion. The azimuthal magnetic field in the hotspot is sufficient to reduce the Larmor radius for the alpha particles to much less than the hotspot size, which dramatically reduces the $\rho $R required for ignition. A computational analysis of this approach is presented, including a study of the thermonuclear burn wave propagation. The robustness of the scheme with respect to instabilities, confinement time and drive parameters is examined. The results indicate that a high energy gain can be achieved using Z-pinches with 50-100 MA currents and a few hundred nanosecond rise-times. This work was partially supported by the U.S. Department of Energy through cooperative agreement DE-FC03-02NA00057. [Preview Abstract] |
Monday, October 24, 2005 4:24PM - 4:36PM |
CO3.00013: Thermonuclear and Beam-Target Fusion in Deuterium Gas-Puff Z-Pinch Implosions: Theory and Modeling R.W. Clark, A.L. Velikovich, J. Davis, Y.K. Chong, C. Deeney, C.A. Coverdale, C. Ruiz, G. Cooper, J. Franklin, L.I. Rudakov Recent experiments with 8 cm diameter deuterium gas puff implosions on the Z accelerator at currents from 13 to 17 MA demonstrated reproducible production of high neutron yields, up to $\sim $3x10$^{13}$. We report the results of 1-D and 2-D radiation-hydrodynamic simulations of these experiments. The simulations predict relatively low, $\sim $10-fold, radial compression ratios, and rapid bouncing of the imploded plasma due to small radiative energy losses. Simulated spectra with argon and freon R12 dopants in the deuterium agree with the observations. Calculated temperature, density, and inertial confinement time of the stagnated plasma are consistent with the hypothesis of thermonuclear origin of the observed neutrons. The alternative assumption of beam-target neutron generation in these experiments implies an unusually high, $\sim $10{\%} efficiency of energy conversion into non-thermal deuterium ions, and multi-MA levels of the ion beam current. [Preview Abstract] |
Monday, October 24, 2005 4:36PM - 4:48PM |
CO3.00014: Computational Study of Plasma Radiation in MITL Gap Milena A. Angelova, Bruno S. Bauer, Volodymyr Makhin, Richard E. Siemon, Stephan Fuelling Magnetically insulated transmission lines (MITLs) employ the principle of magnetic insulation to efficiently transmit energy from a source to a load. They are a part of pulsed power devices such as fast z{\-}pinches and particle accelerators, which operate in the regime of extremely high voltages. Cathode plasma produced as a result of strong electric fields in MITLs may significantly decrease the amount of transmitted energy or may close the MITL gap causing an electrical termination. An understanding of plasma formation and evolution in MITL gap can help improve the efficiency of energy transmission, thereby improving the design and characteristics of some pulsed power devices. Plasma evolution in MITL gap is complex, involving several competing processes, including magnetic field-plasma interactions and plasma radiation. This study concentrates on the understanding of plasma radiation and the ways this radiation affects the plasma evolution in the MITL. This paper will present the results of one and two-dimensional magnetohydrodynamic plasma simulations as well as the development of CRE tables for plasma radiation, EOS, and transport coefficients. [Preview Abstract] |
Monday, October 24, 2005 4:48PM - 5:00PM |
CO3.00015: Shrapnel Formation in a Z-Pinch Power Plant John De Groot, N. Gronbech-Jensen The mainline z-pinch IFE power plant design has a recyclable transmission line (RTL) that drives a fusion capsule with output energy in the range of about 3 GJ. The deposition of this energy will result in the RTL close to the target being transformed to high temperature plasma. The RTL farther away from the fusion capsule will be converted to liquid and shrapnel. The shrapnel is composed of droplets, aerosols, liquid, and solid metal. Continuum theory and molecular dynamics calculations are being used to quantify the shrapnel production as a result of spallation driven by shock reflection. The study will also focus on the essential issue of the defect content in the RTL material. We are developing scaling laws that show which sections of the RTL are turned into plasma, droplets, aerosols, liquid, and solid metal. We are also evaluating the effects of post-shot EMP, plasma, droplets, and shrapnel up the RTL. [Preview Abstract] |
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