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 BP6: Poster Session I: Z-Pinches and High Energy Density Plasmas; Simulation and Modeling of Magnetic Confinement; Stellarators |
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Room: Marsalis A/B, 9:45am - 12:45pm |
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BP6.00001: Z-PINCHES, AND HIGH ENERGY DENSITY PLASMAS |
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BP6.00002: Recent Wire-Array Z-Pinch Experiments at Imperial College Gareth Hall, Sergey Lebedev, Jeremy Chittenden, Simon Bland, Francisco Suzuki-Vidal, Adam Harvey-Thompson, George Swadling, Nicolas Niasse, James Palmer Recent wire-array Z-pinch experiments performed on the MAGPIE generator at Imperial College are presented. Experiments have been conducted using a variety of array configurations, including radial wire arrays, cylindrical arrays, and coiled arrays. This research was sponsored by Sandia National Laboratories, Albuquerque; and the NNSA under DOE Cooperative Agreement DE-F03-02NA00057. [Preview Abstract] |
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BP6.00003: Temperature, Density, and Opacity Gradients of K-Shell X-Ray Sources at the Z Accelerator C.A. Coverdale, C. Deeney, J.P. Apruzese, B. Jones, P.D. LePell, A.S. Safronova, N. Ouart X-ray spectroscopy is a valuable tool for inferring properties of imploding and stagnated z-pinch plasmas. In experiments at the Z accelerator, time-integrated and time-gated spatially resolved spectra have been collected for Al (1.7 keV), SS (6.7 keV), and Cu (8.4 keV) z pinches. These spectra have been analyzed to study temperature and density gradients, using K-shell spectra for Al, SS, and Cu, and L-shell spectra from Cu. The quantitative features of the gradients will be presented, and the results compared with time-gated pinhole images that show different physical characteristics for 277 eV radiation relative to $>$ 1 keV radiation. The gradients observed in the K-shell and L-shell spectra will be compared as well. The effects of opacity have been directly observed for Al K-shell, and gradients in the opacity detailed. Opacity effects are not observed for SS or Cu. Sandia is a multi-program laboratory operated by Sandia Corporation, a Lockheed Martin Company, for the United States Department of Energy under Contract DE-AC04-94AL85000. [Preview Abstract] |
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BP6.00004: Impact of Dielectronic recombination on Ionization dynamics and Spectroscopy of Z-pinch Stainless Steel plasma A. Dasgupta, J. Davis, J.L. Giuliani, R.W. Clark, K.G. Whitney The implosion dynamics of an array of stainless steel (SS) wires on the Z and/or ZR accelerator produces an abundances of radiation from the K- and L-shell ionization stages. We will evaluate the contributions of dielectronic recombination (DR) process to the K-shell yield and its role in cooling the plasma and influencing the recombination rate of the recombining plasma. As the plasma assembles on axis, a number of time resolved snapshots will provide temperature and density profiles and size of the emitting region. We will analyze the ionization dynamics and generate K- and L-shell spectrum using the temperature and density conditions generated in Z and/or ZR accelerator describing the implosion with a 1-D non-LTE radiation hydrodynamics model. The non-LTE populations will be obtained by using detailed atomic models that include all important excitation, ionization, and recombination processes. In particular, we will investigate the effects of DR which is the most important recombination process for moderate to high Z plasma such as iron at moderate densities, on the generated spectrum. [Preview Abstract] |
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BP6.00005: Two-Dimensional Radiation MHD Modeling of Stainless Steel Wire Array Z-Pinch Implosions J.W. Thornhill, J.L. Giuliani, J.P. Apruzese, Y.K. Young, J. Davis, A. Dasgupta, R.W. Clark, K.G. Whitney, B. Jones, C.A. Coverdale, D.J. Ampleford, M.E. Cuneo, C. Deeney A 2D radiation MHD modeling capability was developed to study large diameter wire array Z-pinch experiments. This model incorporates into the Mach2 MHD code a self-consistent calculation for non-LTE kinetics and ray trace based radiation transport.\footnote{J. W. Thornhill, J. P. Apruzese, \textit{et. al.,} Phys. Plasmas \textbf{8}, 3480 (2001).} Such a method is necessary for modeling opacity effects and the high temperature state of K-shell emitting loads. This model is used to investigate ways to mitigate the reduction in K-shell emission caused by unstable plasma implosion behavior. This behavior is especially present in implosions of the large diameter loads needed to match the electrical energy of the Z machine to an appropriate massed load for producing K-shell emission. Non-1D behavior can have many sources, but here we focus on 2D behavior seeded by radiative losses. However, efforts that mitigate the deleterious effects of unstable plasma behavior due to this mechanism are also relevant to other sources of non-ideal plasma implosion behavior. [Preview Abstract] |
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BP6.00006: Two-Dimensional Radiation Transport in Cylindrical Geometry: Ray-Tracing Compared to Monte Carlo Solutions for a Two-Level Atom J.P. Apruzese, J.L. Giuliani Radiation plays a critical role in the dynamics of Z-pinch implosions. Modeling of Z-pinch experiments therefore needs to include an accurate but efficient algorithm for photon transport. Such algorithms exist for the one-dimensional (1D) approximation. In the present work, we report progress toward this goal in a 2D (r,z) geometry, intended for use in radiation hydrodynamics calculations of dynamically evolving Z pinches. We have tested a radiation transport algorithm that uses discrete ordinate sets for the ray in 3-space, and the multifrequency integral solution along each ray. The published solutions of Avery et al. [1] for the line source functions are used as a benchmark to ensure the accuracy of our approach. We discuss the coupling between the radiation field and kinetics that results in large departures from LTE, ruling out use of the diffusion approximation. [1] L. W. Avery, L. L. House, and A. Skumanich, JQSRT \underline {9}, 519 (1969). [Preview Abstract] |
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BP6.00007: Charge balancing and identification of prominent spectral features of M-shell W plasmas G.C. Osborne, A.S. Safronova, U.I. Safronova, V.L. Kantsyrev, K.M. Williamson, I. Shrestha, P. Beiersdorfer Charge balancing and identification of prominent spectral features in M-shell tungsten between 3 and 9 {\AA} has been performed for LLNL EBIT data collected at varying electron beam energies between 2.3 and 4.2 keV. Previous research [G.C. Osborne et al, RSI (2008, in press)] focused on the analysis of spectra corresponding to beam energies of 2.9 and 4.1 keV, while this paper mainly focuses on lower beam energy configurations. Diagnostic of these spectra is challenging due to numerous lower than Ni-like ionization stages within a relatively narrow region, so a procedure was developed utilizing a theoretical model for charge state balancing. Atomic data was calculated separately for transitions 3$\to $4 and 3$\to $5 from each ionization stage, including Co-Ge-like W ions using the HULLAC code. The synthetic spectra calculated at higher electron density as well as identified EBIT spectra then are used to identify spectral features and to determine charge balance of M-shell W spectra from Z-pinch plasmas produced on 1 MA Zebra generator at UNR. Work was supported by DOE under grant DE-FG02-08ER54951 and NNSA Coop. Agr. DE-FC52-06NA27588 and DE-FC52-06NA27586. Work at LLNL was performed under auspices of the DOE under contract DE-AC52-07NA2344. [Preview Abstract] |
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BP6.00008: Dynamics of electrode plasmas leading to current losses in post-hole-convolutes on the Z and ZR accelerators D.V. Rose, D.R. Welch, E.A. Madrid, R.E. Clark, W.A. Stygar, M.E. Cuneo The Z and ZR accelerators at Sandia National Laboratories utilize vacuum post-hole-convolutes, which join several magnetically insulated transmission lines (MITLs) in parallel, to drive $z$-pinch loads at current levels between 19 and 24~MA. Outer ($r\simeq 70$~cm) and inner ($r=6$~cm) MITL $B$-dot probes are used to determine current losses in the combined MITL and convolute regions of the Z and ZR accelerators. It has been observed that current losses of 1.0 to 1.5~MA occur for initial load inductances of $\sim 2.5 - 3.0 $~nH. For initial load inductances of $\sim 5.5 - 6.0$~nH, current losses of 5~MA or larger are observed. The assumption is that higher initial load inductances result in larger voltages in the MITLs and convolutes, which in turn results in more rapid electrode plasma formation. These issues are being addressed in 3D EM PIC simulations that include electrode plasma formation and dynamics [D. V. Rose, \textit{et al.}, Phys.\ Rev.\ ST-AB \textbf{11}, 060401 (2008)]. The simulations have indicated that only small electrode plasma desorption rates ($\le 0.01$ monolayers/nanosecond) are required to obtain current losses of order 1.5~MA on Z. New ZR convolute designs attempt to reduce the measured current losses. These designs are also being analyzed using PIC simulations. [Preview Abstract] |
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BP6.00009: Magnetic Flux Advection in Ablation Streams of Wire Array Z-Pinches John Greenly, Matthew Martin, Isaac Blesener, David Chalenski, Patrick Knapp, Bruce Kusse Magnetic probes are used to measure the field advected inward toward the axis of wire-array Z-pinches on the COBRA 1 MA driver. The probes are 0.7 mm outer diameter, with area $\sim $0.1 mm$^{2}$. The probes are insulated by Kapton tubing and reliably give signals that track the ablation and implosion phases. Pairs of probes are placed at different radial locations inside the array. Typically, probes 2 mm inside the wires (e.g., at 4 mm radius in a 6 mm radius, 16 wire array), show a nearly linearly rising field throughout the ablation phase, from the onset of inward ablated flow until the start of the final implosion. Nearer the axis (at 2 mm radius) the magnetic field begins to rise later, then rises faster than at 4 mm for some time, but then ceases to rise for a significant time interval before implosion while the field at 4 mm is still linearly rising. This appears to be the signature of deceleration and stagnation of the ablation streams at the precursor column near the axis. These results will be compared with analytic modeling and with the results of computer simulations. [Preview Abstract] |
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BP6.00010: Studies of x-ray and XUV radiation from wire-array z-pinches on COBRA using an x-ray streak camera P.-A. Gourdain, S.A. Pikuz, T.A. Shelkovenko, P.F. Knapp, D.A. Hammer, D.B. Simar Time- and space- resolved short-wavelength radiation from wire-array z-pinches has been studied using a low-magnification Kentech x-ray streak camera in experiments on the 1 MA COBRA pulsed power generator at Cornell University. In the x-ray spectral band, a standard photochode and imaging slit were used to record one-dimensional images in the axial direction. Axial and radial images of wire arrays were recorded in XUV radiaion using an open pinhole and a specially made transparent mesh-type photocathode. The development of the precursor plasma and hot spots in the stagnated plasma have been observed. The images were compared with results obtained with an optical streak camera and 4-frame gated microchannel plate imager. [Preview Abstract] |
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BP6.00011: Time Resolved Optical Spectroscopy Experiments on the 500 kA XP Pulsed-Power Generator K.S. Bell, S.A. Pikuz, T.A. Shelkovenko, R.D. McBride, I.C. Blesener, P.F. Knapp, D.A. Hammer, J.B. Greenly, Y. Maron Recent experiments on the 500 kA XP pulsed-power generator at Cornell University have explored the properties of optical spectra emitted by single exploding wires and wire-arrays carrying less than 13 kA and 50 kA per wire, respectively. We are studying the wire's time resolved visible spectra in order to identify the levels of current per wire that visible spectroscopy might provide a means to measure magnetic field strength[1]. We have also investigated the dependence of single wire visible spectra on the current, which was measured using a calibrated non-integrating Rogowski coil. PCDs and XRDs were employed to gather information about the temporal structure of the wire radiation. 1. E. Stambulchik, K. Tsigutkin, and Y. Maron. Phys. Rev. Lett. 98, 225001 (2007). This research was supported by DOE grant DE-FG03-98ER54496, Sandia National Laboratories contract AO258, and the NNSA Stockpile Stewardship Academic Alliances program under DOE Cooperative Agreement DE-FC03-02NA00057. [Preview Abstract] |
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BP6.00012: Axial X Pinch Backlighting on COBRA Isaac Blesener, John Greenly, Sergey Pikuz, Tatiania Shelkovenko, David Hammer, Bruce Kusse X pinch backlighting is a useful imaging technique whereby two or more wires are crossed at a single point and driven with a high current (300-500 kA). At the crossing point, a micron-scale sub-nanosecond x-ray source is produced that acts as a point source and can be used for point-projection imaging. Axial x pinch backlighting is a new technique that allows an end-on image of Z pinches. New load geometry was developed at Cornell University to allow all standard diagnostics to be used on the same shot as the axial x pinch backlighting diagnostic. High density plasma features have been observed that correlate well with XUV self-emission images previously recorded on COBRA and simulation results from GORGON. Data and images will be presented illustrating the latest results from COBRA. Future applications include the possibility of shockwave imaging in the center of thing foil cylinders. [Preview Abstract] |
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BP6.00013: X-Pinch Measurements Performed on a 1-microsecond Current Generator. Richard Appartaim, Bulmuo Maakuu A 320 kiloamp, 1-microsecond current generator based on a simple L-C discharge has been used to drive 2-wire and 4-wire X-pinches of tungsten, aluminum, titanium, etc., with diameters ranging from 13--25 microns. We report the results of measurements of the characteristics and dynamics of the X-pinch using silicon p-n junction photodiodes, a diamond radiation detector, pinhole cameras, x-ray spectroscopy and interferometry. The time duration of the observed x-ray pulses as well as the difference in the spectral sensitivities of the silicon and diamond radiation detectors provide a way to determine what fraction of the emitted x-rays is soft (e.g. with photon energy from 1 keV to 5 keV that may be emitted from high temperature plasmas at the hot spots) and what fraction is due to dense plasma interactions with electron beams accelerated across mini-diodes near the X-pinch crossing point. We address this issue as well as present the results of spectroscopic measurements of plasma parameters. [Preview Abstract] |
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BP6.00014: Experimental Investigations of the Ablation of Wire Arrays on the 250 kA GenASIS Machine S.C. Bott, D.M. Haas, Y. Eshaq, U. Ueda, R.E. Madden, G. Collins, F.N. Beg We present investigations of exploding wire experiments on a recently completed linear transformer driver (LTD) in the High Energy Density Physics laboratory at UCSD. The GenASIS machine delivers $>$250kA in 130ns to short circuit and $>$200kA to a wire array load, via a conical constant gap power feed. Measured load currents compare favorably to circuit modeling. This new generator facilitates ablation studies of multiple wire cylindrical arrays with $>$25 kA/ wire, and we present laser Schlieren imaging, along with radial and axial electron density profiles inferred from interferometry for Al and W arrays, which are compared to analytical theory. In addition, conical wire arrays are used to generate supersonic plasma jets. We present characterization of high atomic number jets along with estimates of the local sound speed and Mach number. [Preview Abstract] |
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BP6.00015: Development of the Zebra load region for increased capability plasma diagnostics and improved Leopard laser access Alexey Astanovitskiy, R. Presura, V.V. Ivanov, A. Haboub, C. Plachaty, J.M. Kindel A new geometry for the load area in the Zebra (1MA pulse generator) is developed. It will form the basis for future experiments requiring Leopard (1057nm, 50TW laser) to Zebra coupling and give extended capability to z-pinch diagnostics. This required the development of a new current return, which allows laser access and installation of the OD 4'' parabolic mirror for the x-ray radiography, isochoric heating and magnetized plasma experiments, and accommodates wire-array z-pinch loads, to which the laser may then be coupled. In addition, this configuration allows diagnostics access close to the plasma, leading to a significant increase of the spatial resolution for imaging of z-pinches, as well as the photon flux in imaging and spectroscopy of laser produced plasmas. These diagnostics will allow coupling of the Leopard beam for x-ray laser probing of the pinch plasma and we will test point-projection x-ray backlighting of the pinch plasma. [Preview Abstract] |
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BP6.00016: A comparative analysis of implosion dynamics of triple planar wire arrays of Mo and Al on the 1 MA, 100 ns UNR Zebra generator M.E. Weller, A.S. Safronova, V.L. Kantsyrev, A.A. Esaulov, K.M. Williamson, I. Shrestha, G.C. Osborne, N.D. Ouart, M.F. Yilmaz, V. Shlyaptseva Implosion dynamics of three different triple planar wire arrays (TPWA) that were performed on the 1 MA, 100 ns UNR Zebra generator will be compared: the first consisting of pure Mo, the second consisting of 68{\%} Mo and 32 {\%} Al (5052), with Mo on the outside, and the third consisting of 35{\%} Mo and 65{\%} Al (5052), with Mo on the inside. In particular, experimental results for x-ray time-integrated, spatially-resolved spectra and pinhole images, x-ray time-gated pinhole and spectra images, laser shadowgraphy, optical streak camera images, PCD signals, and total energy will be fully compared and analyzed. Plasma parameters derived from non-LTE models of Mo, Al, and Mg will be presented and discussed. [Preview Abstract] |
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BP6.00017: Observation of Cascade Implosions in Star-Like Wire-Array \textit{Z}-Pinches on the Zebra Generator A. Haboub, V.V. Ivanov, A.L. Astanovitskiy, S.D. Altemara The dynamics of implosions in Al and W star-like wire arrays were investigated in the 1-MA Zebra generator. The hydrodynamic mode of implosion was confirmed by several optical plasma diagnostics, including five-frame laser probing of z-pinch in three directions, an optical streak camera, and a time-gated (ICCD). In low wire-number star-like arrays the imploding plasma starts on the edge wires, cascades from wire to wire accelerating toward the center, and forms moving plasma columns with a smooth leading edge. The hydrodynamic regime of collision presumably mitigates the instabilities, improves the homogeneity of the imploding plasma, and increases the radiated power in the star-like wire array. Work was supported by the DOE/NNSA under UNR grant DE-FC52-06NA27616. [Preview Abstract] |
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BP6.00018: Theory of Contact Resistance Wilkin Tang, Y.Y. Lau, R.M. Gilgenbach, M.R. Gomez, J. Zier Electrical contact is an important issue for high power microwave sources, wire-array Z pinches, field emitters, and metal-insulator-vacuum junctions. Because of the surface roughness on a microscopic scale, true contact between two pieces of metal occurs only on the asperities of the two contacting surfaces. This gives rise to contact resistance [1]. We have developed a novel analytic theory of contact resistance of an asperity of transverse dimension (a) and finite axial length (h) connecting two metal blocks. For asperity of rectangular, cylindrical or funnel shape, we find that the contact resistance is of the form R[1+p(h/a)] where R is the corresponding h=0 ``a-spot'' theory limit of Holm [1] and Timsit [2], p has a simple form which we have verified against electrostatic code results. This higher-dimensional treatment links the contact resistance to the geometrical deformations in response to an applied pressure, and to the hardness of the material. This work is supported by Sandia, AFOSR, AFRL, L-3, and Northrop-Grumman. [1] R. Holm, Electric Contact (Springer-Verlag, 1967). [2] R. S. Timsit, IEEE Trans. Components Packaging Tech. 22, 85 (1999). [Preview Abstract] |
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BP6.00019: Z-Pinch Wire-Electrode Contact Resistance Studies Using Weighted and Soft Metal Gasket Contacts* M.R. Gomez, J.C. Zier, A.F. Thurtell, D.M. French, R.M. Gilgenbach, W. Tang, Y.Y. Lau The contact made between z-pinch wires and electrodes has a significant effect on both the energy deposited in the wires and the uniformity of the expansion profile of the wires. We have shown that using soft metal gaskets can improve wire-electrode contact significantly over typical weighted contacts. Images of wire expansion profile and wire plasma emission will be presented for single and double wire shots on a 16 kA, 100 kV 4-stage Marx bank with 150 ns risetime. Bench resistance measurements for aluminum, stainless steel, and tungsten wires with diameters ranging from 7.5 um to 30 um will be presented. These measurements utilized both soft metal gasket contacts (gaskets include: indium, silver, aluminum, tin, and lead) and double-ended wire weight contacts (weights ranged from 0.4 g to 1.9 g). *This research was supported by U. S. DoE through Sandia National Laboratories award document numbers 240985, 768225, 790791 and 805234 to the University of Michigan. MRG supported by NNSA Fellowship and JCZ supported by NPSC Fellowship sponsored by Sandia National Labs. [Preview Abstract] |
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BP6.00020: Design Studies of Magneto-Rayleigh-Taylor Instabilities on Thin Foils Jacob Zier, Matthew Gomez, Yue Ying Lau, Ronald Gilgenbach, Wilkin Tang, David French, Michael Cuneo, John Luginsland Thin foils are not widely used as z-pinch loads currently. However, they might be necessary to achieve the required mass for higher current x-ray sources, and they also offer useful options for x-ray pulse shaping [1]. This paper reports a preliminary design study on the dominant instability, the magneto-Rayleigh-Taylor instability (MRTI). Planar Al foils 400 nm thick will be used, driven by the 1-MA linear transformer driver (LTD), MAIZE, at U of Michigan. Inductance considerations and a planar foil load design are presented along with MRTI theory. Laser diagnostic images of 400 nm Al foil shots on the (U of M) MZP4 accelerator are also presented. [1] T.J. Nash, C. Deeney, G.A. Chandler \textit{et a.l}, Phys. Plasmas 11, L65 (2004). [Preview Abstract] |
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BP6.00021: Overview of FRC Translation Experiments for Magnetized Target Fusion T.P. Intrator, G.A. Wurden, P.E. Sieck, W.A. Waganaar, X. Sun, A. Lynn, M. Gilmore, T. Awe, R.E. Siemon, J. Degnan, E.L. Ruden, M. Domonkos, P. Adamson, T.C. Grabowski, D. Gale, M.H. Frese, S.D. Frese, J.F. Camacho, S.K. Coffey, N.F. Roderick, D.J. Amdahl, P. Parks We present and overview the experimental high density Field Reversed Configurationi (FRC) approach for application to a physics demonstration of magnetized target fusion (MTF). This MT target plasma continues to be developed at the Los Alamos FRC experiment FRXL. The first translated FRXL FRC data will be shown, where the translation speeds exceed 15cm/usec, which yields a translation time substantially shorter than the FRC lifetimes. The conical theta coil is expected to generate toroidal magnetic field and helicity and increase stability and lifetime. The implications of the present data for MTF experiments will be discussed, along with the hardware, diagnostics, and pre-compression plasma formation and trapping experiments. [Preview Abstract] |
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BP6.00022: Plasma-Jet Magneto-Inertial Fusion Investigations John Santarius, Carol Aplin Several issues related to using plasma jets to implode a Magneto-Inertial Fusion (MIF) liner onto a magnetized plasmoid and compress it to fusion-relevant temperatures[1] are explored. One simple problem modeled is pure plasma jet convergence and compression without a target present. More elaborate cases with a target present explore how well the target's magnetic field reduces thermal conduction and the liner's inertia provides transient plasma stability and confinement. The investigation uses UW's 1-D Lagrangian radiation-hydrodynamics code, BUCKY, which solves single-fluid equations of motion with ion-electron interactions, PdV work, table-lookup equations of state, fast-ion energy deposition, and pressure contributions from all species. Extensions to the code include magnetic field evolution as the plasmoid compresses plus dependence of the thermal conductivity and fusion product energy deposition on the magnetic field. \newline[1] Y.C. F. Thio, et al., ``Magnetized Target Fusion in a Spheroidal Geometry with Standoff Drivers,'' in Current Trends in International Fusion Research, E. Panarella, ed. (National Research Council of Canada, Ottawa, Canada, 1999), p. 113. [Preview Abstract] |
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BP6.00023: Recent Numerical Studies of High-Z Plasma in the HyperV Plasma Guns L. Wu, M. Phillips, F.D. Witherspoon Previous numerical studies on plasma jets at HyperV Technologies focused mainly on carbon/hydrogen plasmas, since ablative polyethylene was the main source of plasma in the experiments to date. However, recent interest in using high-Z plasmas to form imploding plasma shells for MIF and other HEDP applications, has led us to begin modeling high-Z gases such as argon and xenon in the HyperV plasma gun geometry. The computational work is performed on our new cluster using the latest version of Lsp, which provides some more efficient algorithms that allow for longer gun simulation times. Numerical studies on hydrogen plasma with this improved code have shown more accurate results. Ablation and secondary (or restrike arcs) are also being investigated to determine their effect on the plasma dynamics. Results of these simulations will help provide benchmarking data for planned experiments. Work supported by the U.S. DOE Office of Fusion Energy Sciences. [Preview Abstract] |
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BP6.00024: Simulation of Plasma Jet Driven MTF Roman Samulyak, Wen Wu, Paul Parks Numerical simulations of the supersonic plasma jet driven MTF have been performed using the FronTier code. The plasma jet MTF concept uses a spherical array of converging high Mach number plasma jets to form a ``plasma liner'' that further converges to compress a magnetized plasma target to fusion conditions. We present 2D and 3D fluid dynamic simulations of a single plasma jet prior to merging, and 1D and 2D simulations of the imploding liner. 2D simulations of the implosion focus on the formation and evolution of the Rayleigh Taylor instability and its impact on the increase of the liner density and ram pressure. Work on 3D simulations of the merging of jets and formation of oblique shocks is underway. FronTier simulations of detached jets, performed with explicit tracking of material interfaces, are compared to FLUENT simulations in order to quantify the role of numerical diffusion. Results of numerical studies are compared with theoretical predictions of [P.B. Parks, Phys. Plasmas 15, 062506 (2008)]. [Preview Abstract] |
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BP6.00025: MHD effects in laser-produced plasmas Oleg Polomarov, Riccardo Betti The implementation of the magneto-hydrodynamic (MHD) module in the arbitrary Lagrange-Eulerian (ALE) hydro-code for laser-plasma simulation DRACO [1] is described. Using a two-dimensional axysimmetric description, the magnetic field is decomposed in an azimuthal component B$_{\phi }$ and a poloidal component B$_{p}$=B$_{R}$\textbf{e}$_{R}$+B$_{Z}$\textbf{e}$_{Z}$. The latter is computed using a vector potential function. MHD block accounts for convection, diffusion and generation of the magnetic field by the thermoelectric/magnetic effects caused by the non-parallel temperature and density gradients and the Nernst term. The effect of the magnetic field on the transport coefficients for MHD equations is explicitly taken into account and the influence of the strong magnetic field on hydrodynamics and heating of the laser imploded plasma pellets are studied. The work is supported by the U.S. Department of Energy under Cooperative Agreement Nos. DE-FC02-04ER54789 and DE-FC52-08NA28302. 1. P. B. Radha\textit{ et al}., Phys. Plasmas \textbf{12}, 056307 (2005). [Preview Abstract] |
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BP6.00026: Three-dimensional Resistive Magnetohydrodynamics in Hydra Joseph Koning, Gary Kerbel, Michael Marinak The Magnetohydrodynamics package in the ALE radiation-hydrodynamics code Hydra implements the three-dimensional resistive magnetic diffusion equations in the small Hall limit. The diffusion equations are discretized, on semi-structured grids, using a vector finite element method with H(curl), H(div) and H(grad) conforming spaces, resulting in a method that is second order accurate in space and fully implicit in time. Coupling of the MHD forces and Joule heating to the hydrodynamics package is accomplished through a split scheme. The package includes a second-order accurate advection method utilizing an exact DeRham complex to preserve the divergence free magnetic induction. Several improvements to the package have been applied, including matrix monotonicity constraints, a scalable iterative solution method and an arbitrary linear circuit source. This work is proceeding to create an MHD package that incorporates the full Ohm's law. [Preview Abstract] |
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BP6.00027: Advances in HYDRA and its application to simulations of Inertial Confinement Fusion targets M.M. Marinak, G.D. Kerbel, J.M. Koning, M.V. Patel, S.M. Sepke, P.N. Brown, B. Chang, R. Procassini, S.A. Veitzer We will outline new capabilities added to the HYDRA 2D/3D multiphysics ICF simulation code. These include a new S$_{N}$ multigroup radiation transport package (1D), constitutive models for elastic-plastic (strength) effects, and a mix model. A Monte Carlo burn package is being incorporated to model diagnostic signatures of neutrons, gamma rays and charged particles. A 3D MHD package that treats resistive MHD is available. Improvements to HYDRA's implicit Monte Carlo photonics package, including the addition of angular biasing, now enable integrated hohlraum simulations to complete in substantially shorter time. The heavy ion beam deposition package now includes a new model for ion stopping power developed by the Tech-X Corporation, with improved accuracy below the Bragg peak. Examples will illustrate HYDRA's enhanced capabilities to simulate various aspects of inertial confinement fusion targets.\newline This work was performed under the auspices of the Lawrence Livermore National Security, LLC, (LLNS) under Contract No. DE-AC52-07NA27344. The work of Tech-X personnel was funded by the Department of Energy under Small Business Innovation Research Contract No. DE-FG02-03ER83797. [Preview Abstract] |
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BP6.00028: Improvements in Modeling Au Sphere Non-LTE X-ray Emission Mordecai Rosen, Howard Scott, Laurance Suter, Stephanie Hansen We have previously reported on experiments at the Omega laser at URLLE, in which 1.0 mm in diameter spheres, coated with gold, were illuminated at either 10$^{14}$ W/ cm$^{2}$ (10 kJ / 3 ns) or 10$^{15}$ W/ cm$^{2}$ (30 kJ / 1 ns). Spectral information on the 1 keV thermal x-rays, as well as the multi-keV M-band were obtained. (E. Dewald, M. D. Rosen, et al to be published in PoP). We compared a variety of non-LTE atomic physics packages to this data with varying degrees of success. In this paper we broaden the scope of the investigation, and compare the data to newer models. One is a vastly improved Detailed Configuration Accounting (DCA) method. The other model involves adjustments to the standard XSN non-LTE model which lead to a better match of coronal emission as calculated by XSN to that calculated by a more sophisticated stand-alone model known as SCRAM. We show some improvements in the agreement with Omega data when using either of these new approaches. [Preview Abstract] |
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BP6.00029: Benchmarking statistical averaging of spectra with HULLAC Marcel Klapisch, Michel Busquet Knowledge of radiative properties of hot plasmas is important for ICF, astrophysics, etc When mid-Z or high-Z elements are present, the spectra are so complex that one commonly uses statistically averaged description of atomic systems [1]. In a recent experiment on Fe[2], performed under controlled conditions, high resolution transmission spectra were obtained. The new version of HULLAC [3] allows the use of the same model with different levels of details/averaging. We will take advantage of this feature to check the effect of averaging with comparison with experiment. [1] A Bar-Shalom, J Oreg, and M Klapisch, \textit{J. Quant. Spectros. Rad. Transf.} \textbf{65}, 43 (2000). [2] J. E. Bailey, G. A. Rochau, C. A. Iglesias et al., \textit{Phys. Rev. Lett.} \textbf{99}, 265002-4 (2007). [3]. M. Klapisch, M. Busquet, and A. Bar-Shalom, \textit{AIP Conference Proceedings} \textbf{926}, 206-15 (2007). [Preview Abstract] |
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BP6.00030: A proposed experimental investigation of a sub-sonic Marshak wave Stephan MacLaren An experiment has been proposed to investigate the behavior of a diffusive x-ray driven heat wave using a laser halfraum and a high-Z aerogel. This problem has been solved analytically in one dimension from a few specific cases to a much more general problem.[1][2][3] The experiment has been designed to optimize comparisons with a 1-D analytic solution. Specifically, a 48-beam, 7ns laser pulse from the National Ignition Facility (NIF), shaped to produce a power-law time dependence for the radiation temperature, is used to create a uniform radiation temperature bath for a 0.5 g/cc, 150 micron slab of Ta$_{2}$O$_{5}$ foam. Driven by NIF over this distance, the shock separates from the temperature front by $>$2 ns, improving the accuracy of the timing measurements. Results from radiation-hydrodynamics simulations will be presented, along with the analytic predictions of the temperature front from the solutions of Refs [2] and [3]. Additionally, these solutions offer a prediction of the shock arrival time due to the time dependent ablation pressure; these predictions will also be compared with simulation. Finally, the impact of a simultaneous match of these two arrival times between theory and experiment on the knowledge of the material properties of the Ta$_{2}$O$_{5}$ foam will be discussed. [1] Marshak, R.E., Phys. Fluids \textbf{1} (1), 1958, 24. [2] Pakula, R. and R. Sigel, Phys. Fluids \textbf{28} (1), 1985, 232. [3] Hammer, J.H., and M.D. Rosen, Phys Plasmas \textbf{10} (5), 2003, 1829. [Preview Abstract] |
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BP6.00031: Determining Spatial Dependence of Plasma Conditions in HEDP Experiments Based on Space-Resolved Spectral Data Joseph MacFarlane, I. Golovkin, P. Woodruff, J. Bailey, G. Rochau We discuss the analysis of space-resolved spectral data obtained in a series of Ar-doped DD capsule implosion experiments carried out at the Sandia Z Facility. The 1-D space-resolved Ar K-shell spectra obtained in these dynamic hohlraum experiments -- which supply data for the spatial dependence of line intensities, line ratios, and line widths of the Ar He-like and H-like lines -- provide valuable constraints on the variation of plasma conditions (e.g., electron density and temperature) in the imploded core. In our analysis, we use the SPECT3D Imaging and Spectral Analysis package to compute high-resolution space-resolved spectra for a variety of plasma distributions. In the present analysis, non-LTE atomic level populations and emergent spectra are computed for spherically symmetric plasma grids with temperature and density distributions specified by analytic functions. In particular, we study the sensitivity of the simulated space-resolved data (line widths, intensities, and ratios) to the variation in the density and temperature profiles. [Preview Abstract] |
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BP6.00032: Verification and Validation of the VULCAN Lagrange-ALE HEDP Code J.M. Reynolds, J.H. Cooley, T.O. Masser, J.G. Wohlbier, B.D. Lansrud-Lopez, R.B. Lowrie, M. Kenamond, J. Waltz We present a V and V study of the VULCAN 3T physics and grey radiation diffusion packages in regimes relevant to HEDP. Cases where the material penetration of the radiation front is either supersonic or subsonic are considered. Computations of the Marshak thermal diffusion problem are verified against analytical solutions. Simulations that model supersonic radiation transport in heated foam cylinders are validated against published results [1]. Radiation-driven planar shock wave simulations are compared to semi-analytical solutions [2]. Simulations of an Omega experiment where a shock is driven through a Be disk are verified against the time history of the front position, the mean shock velocity, and the breakout time. Comparisons of our calculations are made to computations from the cassio Eulerian-AMR code. LA-UR-08-04737. [1] C.A. Back, et al., Physics of Plasmas, 7, 2126 (2000). [2] R. Lowrie and J.D. Edwards, Shock Waves, 18, 129 (2008). [Preview Abstract] |
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BP6.00033: The Rad Hydro for Roadrunner Code Project J. Wohlbier, B. Bergen, W. Dai, A. DuBois, D. DuBois, T. Kelley, R. Lowrie, R. McClarren Los Alamos National Laboratory is receiving and testing Roadrunner, the first supercomputer to sustain a petaflop [1]. Roadrunner consists of a cluster of Opterons, with each Opteron core accelerated by one Cell Broadband Engine processor with enhanced double precision capability. We are developing a rad hydro code for this new architecture that takes into account that Roadrunner is just the first of many multi-core, heterogeneous architectures to come. The design has a block AMR direct Eulerian hydrodynamics scheme with separate electron and ion temperatures, working with tabular equations of state, and using various radiation transport schemes. Planned radiation transport schemes are grey diffusion, multi-group diffusion, and IMC transport. Software for Roadrunner and future heterogeneous architectures requires specialized, non-portable code. We are using tools--the SIMD Abstraction Layer (SAL) [2] and the Cell Isolation Kit (CIK) [2]--that aid writing architecture independent software. We report on our plans and progress on the Rad Hydro for Roadrunner project. [1] http://www.top500.org [2] Tim Kelley, private communication. [Preview Abstract] |
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BP6.00034: Verification and Validation of cassio, an HEDP Code from the Crestone Project Thomas Masser, John Wohlbier, James Reynolds, Robert Lowrie, James Cooley, Jacob Waltz The Crestone Project at Los Alamos National Laboratory produces cassio, an HEDP code. Currently cassio implements radiation hydrodynamics on an Eulerian AMR mesh along with a three temperature (3T) plasma physics model. A 3T model treats a plasma as a single species fluid with separate electron and ion temperatures, and uses a radiation diffusion model, where a radiation temperature characterizes the radiation energy density. We provide details of verification and validation studies for the 3T model implemented in cassio, as well as code comparison studies with VULCAN, an ALE HEDP code. For verification, we compare code solutions to available semi- analytical results of 3T Sod problems for radiation hydrodynamics with heat conduction and electron-ion coupling. For validation, we simulate recent laboratory-astrophysics jet experiments at the Omega laser facility. We also study a typical ICF capsule implosion. For all of the problems considered above, we compare the simulation results of cassio and VULCAN. [Preview Abstract] |
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BP6.00035: Addition of Implicit Monte Carlo Radiation Transport and Validation of 3D Hydrodynamics in \textit{DRACO} Milad Fatenejad, Timothy Collins, Gregory Moses, Patrick McKenty We will describe two new advancements which have been made to the \textit{DRACO} Lagrangian radiation-hydrodynamics code. First, the 3D hydrodynamics module has been validated using analytic formulas; second, we have added Implicit Monte Carlo (IMC) radiation transport in 2D $r$-$z$ geometry. Previous results demonstrated the ability to model 3D Richtmyer-Meshkov (RM) instabilities [Fatenejad and Moses, \textit{Bull. APS} \underline{51}, 209(2006)] using \textit{DRACO}. New results validate simulations of the growth of 3D RM and Rayleigh-Taylor (RT) instabilities via comparisons with theoretical growth rates and 2D calculations. The IMC model now implemented in \textit{DRACO} was originally developed by Fleck and Cummings [\textit{JCP} \underline{8}, 313(1971)]. The IMC code is validated using comparisons with diffusion theory and numerical results presented in the original paper. Finally, comparison of a 2D symmetric direct drive target implosion using IMC to an identical simulation using no radiation transport and diffusion theory will be presented. [Preview Abstract] |
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BP6.00036: Modeling laser-plasma interactions of an entire NIF beam using all of Blue Gene Light C.H. Still, D.E. Hinkel, A.B. Langdon, S.H. Langer, E.A. Williams In 2010, there will be an experimental campaign to achieve ignition on the National Ignition Facility (NIF) using $\sim $1.2 MJ of laser energy. In preparation for such a campaign, ignition targets are being carefully analyzed with regard to laser-plasma interactions. We use pF3d$^{1}$ to perform these calculations$^{2}$ of ignition point designs$^{3}$ on near whole-beam volumes, dubbed ``letterboxes'', in which the entire extent of the beam is used in the radial direction, and enough of the beam in the azimuthal direction to achieve sufficient speckle statistics. These letterbox calculations require tens of thousands of CPU days on large massively parallel computers, and until recently, simulating an entire beam volume has been out of reach. In this presentation, we report on results obtained from the first ever simulation of an entire NIF outer beam volume propagating in a CH-ablator ignition point design at 300 eV using 196,608 CPUs of Blue Gene/L, one the world's fastest supercomputers.$^{4 }$We also describe progress in benchmarking our letterbox simulations with this entire beam run. This work performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344. 1. R. L. Berger \textit{et al.,} \textit{Phys. Plasmas} \textbf{5}, 4337, (1998); C. H. Still, et. al, \textit{Phys. Plasmas} \textbf{7}, 2023 (2000). 2. D. E. Hinkel \textit{et al}., ``Analyses of laser-plasma interactions in National Ignition Facility ignition targets'', \textit{Phys. Plasmas} \textbf{15}, 056314 (2008). 3. D. A. Callahan \textit{et al}., \textit{Bull. Am. Phys. Soc.}\textbf{52}, 316 (2007). 4. http://www.tops500.org [Preview Abstract] |
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BP6.00037: Absorption, imprint, and heat transport of optically smoothed KrF laser radiation in direct-drive ICF Michael Keskinen, Denis Colombant, Jason Bates, Andrew Schmitt Accurate models of absorption, imprint, and heat transport from optically smoothed lasers are important to maximize gain in direct-drive inertial confinement fusion. Nonuniform single beam imprint can lead to reduction in target yield, depending on the degree of optical smoothing, and can seed Rayleigh-Taylor growth in the acceleration phase. Optically smoothed laser radiation, e.g., induced spatial incoherence (ISI), fluctuates on a coherence time scale. We have developed a time-dependent electromagnetic full-wave Maxwell solver. The electromagnetic wave solver can simulate the propagation and absorption of different wave polarizations for normal and oblique incidence for smooth and rippled critical surfaces. In addition it can model ISI effects. We apply the results to shock ignition and high-Z targets and discuss implications for heat transport. [Preview Abstract] |
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BP6.00038: SIMULATION AND MODELING OF MAGNETIC CONFINEMENT |
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BP6.00039: Progress report on PIXIE3D, a fully implicit 3D extended MHD solver Luis Chacon Recently,\footnote{L. Chac\'on, {\em Phys. Plasmas} {\bf 15}, 056103 (2008); invited talk at DPP07} an optimal, massively parallel implicit algorithm for 3D resistive magnetohydrodynamics (PIXIE3D) was demonstrated. Excellent algorithmic and parallel results were obtained with up to 4096 processors and 138 million unknowns. While this is a remarkable result, further developments are still needed for PIXIE3D to become a 3D extended MHD production code in general geometries. In this poster, we present an update on the status of PIXIE3D on several fronts. On the physics side, we will describe our progress towards the full Braginskii model, including: electron Hall terms, anisotropic heat conduction, and gyroviscous corrections. Algorithmically, we will discuss progress towards a robust, optimal, nonlinear solver for arbitrary geometries, including preconditioning for the new physical effects described, the implementation of a coarse processor-grid solver (to maintain optimal algorithmic performance for an arbitrarily large number of processors in massively parallel computations), and of a multiblock capability to deal with complicated geometries. [Preview Abstract] |
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BP6.00040: Fourth order discretization of anisotropic heat conduction operator Natalia Krasheninnikova, Luis Chacon In magnetized plasmas, heat conduction plays an important role in such processes as energy confinement, turbulence, and a number of instabilities. As a consequence of the presence of a magnetic field, heat transport is strongly anisotropic, with energy flowing preferentially along the magnetic field direction. This in turn results in parallel and perpendicular heat conduction coefficients being separated by orders of magnitude. The computational difficulties in treating such heat conduction anisotropies are significant, as perpendicular dynamics numerically is polluted by the parallel one. In this work, we report on progress of the implementation of a fourth order, conservative finite volume discretization scheme for the anisotropic heat conduction operator into the extended MHD code PIXIE3D [1]. We will demonstrate its spatial discretization accuracy and its effectiveness with two physical applications of interest, both of which feature a strong sensitivity to the heat conduction anisotropy: the thermal instability and the neoclassical tearing mode. [1] L. Chacon Phys. Plasmas 15, 056103 (2008) [Preview Abstract] |
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BP6.00041: NIMEQ: MHD Equilibrium Solver for NIMROD E.C. Howell, C.R. Sovinec Development of a Grad-Shafranov solver within the framework of the NIMROD code (nimrodteam.org) is described. The solver will facilitate two-fluid studies of spheromak plasmas including the effects of realistic simply connected geometries. The solver utilizes the existing high order polynomial finite element basis employed by NIMROD, which avoids numerical noise that is created when interpolating other equilibria data onto a NIMROD grid. A direct solve is preformed for the quantity$\Psi $/r$^{2}$. The Grad-Shafranov operator is converted to a total divergence, allowing the use of conventional boundary and regularity conditions. A Picard scheme is used to advance the nonlinear iteration. The solver is benchmarked on analytical cylindrical profiles, and convergence studies on stability results test accuracy. Results on equilibria in SSPX geometry with parameterized profiles are also described. [Preview Abstract] |
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BP6.00042: Preconditioning for Three-Dimensional Two-Fluid NIMROD Applications C.R. Sovinec, E.D. Held A new parallel preconditioner implementation for Krylov-space matrix-solves in nonlinear 3D two-fluid simulations with the NIMROD code (nimrodteam.org) is presented. The implementation takes advantage of the typically small perturbation size. The large axisymmetric component provides diagonal dominance for matrices partitioned into Fourier-component blocks. An inner preconditioner iteration using limited Fourier-component coupling in Gauss-Seidel-like relaxation with diagonal blocks solved by SuperLU-DIST [Li and Demmel, ACM Trans. Math. Software 29, 110 (2003)] is then effective for the two-fluid magnetic advance, provided that a realistic level of electron inertia is used to limit R-mode frequencies. Generating and multiplying matrix elements for a limited number of off-diagonal blocks is shown to scale with processor number as the number of Fourier components is increased in research-relevant sawtooth and ELM computations. [Preview Abstract] |
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BP6.00043: Anisotropic Heat Transport in the Presence of Resonant Magnetic Perturbations Scott Kruger, Eric Held Heat transport in the H-mode tokamak edge is significantly modified by the presence of resonant magnetic perturbations. Application of collisional transport models to this problem ignores the fact that temperatures at the top of the edge pedestal may be several keV. Here, we compare the effective radial heat transport predicted by local (diffusive) and nonlocal [1] (integral) forms for the parallel heat flux. Accurately predicting this effective radial heat transport becomes important when significant magnetic field line stochasticity is present, as in the case of overlapping magnetic perturbations. For such cases, the integral form for the parallel heat transport correctly assesses the effects of temperature perturbations all along the magnetic field line and yields predictions that vary substantially from the diffusive closure, which relies only on the local temperature gradient. Quantitative comparisons of effective radial transport are given for single helicity and multiple helicity magnetic perturbations in cylindrical and toroidal geometry, with emphasis given to a toroidal case with a narrow pedestal width and a high temperature at the top of the pedestal. \\[0pt] [1] E. D. Held, J. D. Callen, C. C. Hegna, C. R. Sovinec, T. A. Gianakon, and S. E. Kruger, Phys Plasmas, 11, 2419 (2004). [Preview Abstract] |
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BP6.00044: Parallel heat flow and stress tensor in toroidal plasmas Mukta Sharma, E.D. Held, J.Y. Ji Closures for the parallel conductive heat flux and stress are derived using a Chapman-Enskog-like approach that maintains a maximal ordering between parallel streaming, particle trapping and collisional effects. The distribution function is written as the sum of a dynamic Maxwellian and a kinetic distortion, $F=\sum_{l} P_l (v_\| /v) F_l$, where the parallel gradient operator acts on both the coefficients, $F_l$, and the Legendre polynomials, $P_l (v_\| (x)/v)$. A moment approach is used to treat ${\hat b} \cdot {\vec \nabla} B$ terms as well as the linearized Coulomb collision operator.\footnote{J.-Y. Ji and E. D. Held, Phys. Plasmas {\bf 13}, 102103 (2006).} The Lorentz scattering term acting on $F$ is inverted along with the free streaming term and the coupled ODE system for the $F_l$'s is diagonalized. Integrating the separated ODEs along magnetic field lines and taking the necessary moments yields the desired closures. This general approach allows examination of the closures in all collisionality regimes. Results are compared with previous bounce-averaged theories. [Preview Abstract] |
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BP6.00045: Extended MHD Effects on RMPs and ELMs H.R. Strauss, G.-Y. Park, C.S. Chang, L. Sugiyama, J. Breslau, R. Maingi M3D studies of Resonant Magnetic Perturbations (RMP) in DIII-D equilibria indicate that in the absence of plasma rotation, the vacuum RMP magnetic field penetrates the plasma and causes the magnetic field to be stochastic in a wide layer. Parallel thermal conduction cools the plasma in the stochastic layer. When the plasma rotates toroidally and / or poloidally, with sufficient speed, the RMP penetrates only a thin edge layer. The pressure gradient is reduced in this layer, which can stabilize Edge Localized Modes (ELMs). This resembles the behavior of RMPs when there is high edge collisionality, $\nu_* > 1.$ There is advection of density at the edge, as well as some density reduction in the plasma core, but not the large density pump out that has been observed at low edge collisionality $\nu_* < 1.$ In NSTX, RMPs have been found ineffective in ELM suppression. Applying an RMP can cause ELMs to occur in an otherwise ELM free discharge. It is possible that these ELMs in NSTX are produced by resistive tearing and ballooning modes. Resistive modes can be stabilized by two fluid drifts. The stabilization depends on edge collsionality. It is possible that the RMP cools the edge and increases collisionality, destabilizing the resistive ELMs. [Preview Abstract] |
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BP6.00046: FRC Formation and Translation Simulations with Anisotropic Viscosity G.A. Cone, R.D. Milroy, C.C. Kim FRC plasmoid formation and translation are simulated using a modified version of the NIMROD code. These modifications allow for the prescription of an initial vacuum magnetic field suitable for theta-pinch formation or importation of a prescribed FRC equilibrium. Modified boundary condition routines allow for time varying ``pusher coils'' to translate the FRC. The FRC simulations are performed in the context of several operational FRC devices: PHD, TCS-U, and FRX-L. The formation simulations studied apply to all generic theta-pinch formed FRCs and both uniform and conical theta-pinch formation schemes are simulated. Salient features include the generation of toroidal plasma flow and toroidal magnetic flux with the Hall and $\nabla P_\textrm{e}$ terms included in Ohm's law. The translation simulations are initialized from a presupposed magnetic equilibrium. Pusher coils translate the FRC in a peristaltic fashion and proper timing of coil firing is critical; this is especially true for shaped translation tubes such as the PHD device. Simulations of FRC translation including a shaped boundary approximating that of the PHD device are investigated. Of key interest in FRC translation is the impact of anisotropic viscosity on the translation efficiency. Results of translation simulations using varying ratios of parallel to perpendicular viscosity are discussed. [Preview Abstract] |
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BP6.00047: Results from the PSI-Center Interfacing Group B.A. Nelson, C.C. Kim, R.D. Milroy, T.R. Jarboe The Interfacing Group of the Plasma Science and Innovation Center (PSI-Center - http://www.psicenter.org) facilitates simulations of collaborating Innovative Confinement Concept (ICC) experiments. Present collaborating experiments include the Bellan Plasma Group (Caltech), FRX-L (Los Alamos National Laboratory), HIT-SI (Univ of Wash - UW), LDX (M.I.T.), MST, Pegasus (Univ of Wisc-Madison), PHD (UW), SSPX (Lawrence Livermore National Laboratory), SSX (Swarthmore College), TCS (UW), and ZaP (UW). LDX simulations study stability of marginally-stable equilibria as additional heating increases pressure gradients. Simulations of translating FRCs, such as PHD, have recently started, using equilibria from a mimetic-operator Grad-Shafranov solver. Output files from NIMROD and its nimplot postprocessor suite are interfaced to the powerful 3-D visualization program, VisIt (http://www.llnl.gov/visit). Results from these simulations, as well as an overview of the Interfacing Group status will be presented. [Preview Abstract] |
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BP6.00048: Kinetic Studies of ICC Devices using High Order PIC in Finite Elements Charlson C. Kim We present progress on the implementation of a full Lorentz particle in cell (PIC) module for the NIMROD code. This is an extension of the drift kinetic $\delta\!f$ PIC module already in place in NIMROD.\footnote{C.~C.~Kim and the NIMROD Team, ``Impact of velocity space distribution on hybrid kinetic-magnetohydrodynamic simulation of the $(1,1)$ mode'', Phys. Plasmas {\bf 15}, 072507, (2008)} The Lorentz force PIC (LFP) module will be used to study the effects of energetic ions in innovative confinement concept (ICC) devices - particularly their impact on stability and confinement in the context of the hybrid kinetic-MHD model. As an initial step in development, we demonstrate the LFP module as tracer particles to study various ICC topologies and the resultant phase space. To couple the kinetic physics of the particles back into the MHD fluid model of NIMROD we calculate the energetic particle stress tensor moment on NIMROD's high order finite element, pseudospectral grid. This work will lead to a $3D$ nonlinear MHD code that self consistently includes the effects of an energetic tail. Representative ICC devices modeled are FRCs, RFPs, spheromaks and dipole configurations. [Preview Abstract] |
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BP6.00049: Application of Mimetic Operators to Tetrahedral Mesh MHD Codes George Marklin, Tom Jarboe Mimetic operators are numerical approximations to the grad, div and curl operators that 'mimic' the orthogonality properties of their analytic counterparts, div(curl)=0 and curl(grad)=0. They define different components of vector fields at different parts of the mesh and can be viewed as a special type of finite element basis and can be defined to arbitrarily high order. They have been used in electromagnetic simulation codes for many years. This poster will show how they can be defined to lowest order on a tetrahedral mesh and applied to Taylor state computations and to the induction equation in an MHD simulation. They have the advantage of being able to exactly maintain zero divergence in both the magnetic field and current density and to make an exact separation of static and inductive electric fields. Mimetic Operators can also be used in the momentum equation and the results will be compared to other commonly used methods like the finite volume and discontinuous Galerkin methods. The new code will be used to run simulations of the HIT-SI experiment with insulated conductor boundary conditions and different injector configurations and results compared to the experiment and to simulations done with the NIMROD code. [Preview Abstract] |
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BP6.00050: Development and verification of HiFi -- an adaptive implicit 3D high order finite element code for general multi-fluid applications V.S. Lukin, A.H. Glasser, W. Lowrie, E. Meier, U. Shumlak, M. Sato A three-dimensional (3D) implicit high order finite (spectral) element code HiFi, based on the well established two-dimensional SEL code [1], is now operational and continues to be developed at the PSI-Center of the University of Washington. The distinguishing capabilities of the code include fully 3D adaptive spectral element spatial representation with flexible multi-block geometry, highly parallelizable implicit time advance, and general flux-source form of the PDEs and boundary conditions that can be implemented in its framework. The two-dimensional version of the code has been extensively verified and used for simulations of various multi-fluid plasma physics phenomena, including magnetic reconnection, cylindrical tokamak sawtooth oscillations and FRC translation. The 3D code verification studies and the latest status of the code development effort will be presented. [1] V.S. Lukin, Ph.D. Dissertation, Princeton University (2007). [Preview Abstract] |
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BP6.00051: Scalable Parallel Computation for Extended MHD Modeling of Fusion Plasmas Alan H. Glasser Parallel solution of a linear system is scalable if simultaneously doubling the number of dependent variables and the number of processors results in little or no increase in the computation time to solution. Two approaches have this property for parabolic systems: multigrid and domain decomposition. Since extended MHD is primarily a hyperbolic rather than a parabolic system, additional steps must be taken to parabolize the linear system to be solved by such a method. Such physics-based preconditioning (PBP) methods have been pioneered by Chac\'on, using finite volumes for spatial discretization, multigrid for solution of the preconditioning equations, and matrix-free Newton-Krylov methods for the accurate solution of the full nonlinear preconditioned equations. The work described here is an extension of these methods using high-order spectral element methods and FETI-DP domain decomposition. Application of PBP to a flux-source representation of the physics equations is discussed. The resulting scalability will be demonstrated for simple wave and for ideal and Hall MHD waves. [Preview Abstract] |
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BP6.00052: Verification studies of the three-dimensionsl high order finite (spectral) element HiFi code and mesh generator integration Weston Lowrie, Vyacheslav Lukin, Uri Shumlak Verification studies of the recently developed three-dimensional (3D) high order finite (spectral) element HiFi code are presented. The code is based on the two-dimensional (2D) SEL code [1]. A semi-structured CUBIT mesh generator has been interfaced with the code, such that CAD based drawings can easily be used to specify simulation geometries. Various logical to physical grid mappings with severe distortions are tested to better understand the limits of the grid mapping. Resistive MHD is used in these studies. Further developments of the 3D HiFi code are also discussed. In particular, the use of new linear and non-linear solvers is investigated to improve the efficiency and scalability of the code. [1] V.S. Lukin, Ph.D. Dissertation, Princeton University (2007) [Preview Abstract] |
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BP6.00053: Multi-Fluid Effects and Open Boundaries in FRC Translation Simulations Eric Meier, V.S. Lukin, Richard Milroy, Uri Shumlak Multi-fluid effects are important in modeling many plasma physics phenomena. In particular, predictive modeling of Emerging Concept and Innovative Confinement Concept experiments often requires multi-fluid physics because of the relatively cool, often weakly-magnetized nature of the plasmas. To meet this need, neutral fluid effects and phenomenological Chodura resistivity have been added to the SEL code [Reference: V.S. Lukin, Ph.D. Dissertation, Princeton University (2007)]. This multi-fluid capability is now available in both visco-resistive MHD and Hall MHD models. Comparative results from FRC translation simulations with multi-fluid effects are shown. To simulate truncated domains without disruptive boundary effects, ``open'' boundary capability is under development and progress is presented. [Preview Abstract] |
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BP6.00054: Between Shots TRANSP Web Service E. Feibush, R. Andre, C. Ludescher-Furth, S. Kaye, D. McCune Running TRANSP between NSTX shots requires rapid data preparation and job submittal. A web service with a graphical user interface and data visualization has been developed to meet these goals. The underlying data preparation system has a command line interface written in Python and runs on a PPPL compute server. The display client is a Java program (ElVis) that sends requests to the data preparation system. As the run data is prepared, graphs are created and sent to the client for display. Flux surface plots are displayed and animated over time. The most commonly used control options are implemented in the UI as buttons and text fields. A time slice or time dependent run can be prepared. The command line interface is available in the client program for expert users to apply advanced settings, to prototype new UI buttons, and to run scripts. The client program contains a simple text editor for modifying the TRANSP namelist. When data preparation is complete the run is submitted to the TRANSP production system. The initial version has been deployed and is being tested in the control room setting. Results will be discussed in the poster presentation. Work performed at PPPL under the auspices of U.S. DOE Contract DE-AC02-76CH03073. [Preview Abstract] |
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BP6.00055: Status of TRANSP and PTRANSP D. McCune, R. Andre, E. Feibush, K. Indireshkumar, C. Ludescher-Furth, L. Randerson, H. St. John, G. Bateman, F. Halpern, A. Kritz, L. Lodestro, W. Meyer, D. Pearlstein The PPPL TRANSP code suite is a set of tools for time dependent simulation of axisymmetric tokamak plasmas. While the code has historically been used primarily for analysis of experimental results, predictive modeling enhancements to TRANSP have been carried out under the PTRANSP project. TRANSP and PTRANSP are now both deployed as Fusion Grid services at PPPL, supporting an international user base. The status of TRANSP and PTRANSP code development, as well as trends in production use, are presented. New and developing features, such as the solution of free boundary MHD equilibria, the use of advanced solvers for prediction of the evolution of plasma density, angular momentum, and temperature profiles, are emphasized. The status of MPI parallelization of TRANSP components is described. A recent positive development has been the beneficial collaboration between TRANSP/PTRANSP and SciDAC FSP prototype projects SWIM and FACETs, with code components being shared effectively across all of these efforts. PPPL work performed under auspices of DOE contract DE-AC02-76CH03073; LLNL work performed under auspices of DOE contract DE-AC52-07NA27344. [Preview Abstract] |
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BP6.00056: Rotation Modified Equilibrium Solutions in TRANSP/PTRANSP R. Andre, D. McCune, J. Menard, L. LoDestro, D. Pearlstein Neutral beam injection is used with NSTX to achieve high beta discharges. This can lead to significant toroidal rotation such that the centrifugal pressure becomes a significant fraction of the total plasma pressure. Under these conditions, it has been shown that the particle densities are no longer flux surface functions with a resulting modification of the equilibrium solution. While TRANSP/PTRANSP has traditionally supported an additional contribution to the plasma pressure due to rotation, the total pressure has been assumed to be a flux surface quantity. Accounting for the radial dependence of the pressure caused by rotation requires a modification to the underlying Grad-Shafranov equation. This poster will describe the status of adding the rotation terms to the TEQ and other equilibrium solvers in TRANSP/PTRANSP and the effect they have on the flux surface representation in NSTX. The rotation is assumed to be purely toroidal with the rotation frequency and species temperatures represented as flux surface quantities. [Preview Abstract] |
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BP6.00057: NUBEAM as TRANSP parallel service and component for SWIM or FACETS K. Indireshkumar, Long-Poe Ku, D. McCune, L. Randerson, A. Pletzer, A. Malony, A. Morris, S. Shende The PPPL Monte-Carlo module NUBEAM is a package for modeling fast ion species in an axisymmetric tokamak. Since its parallelization in 2006, it has been deployed as part of the TRANSP Parallel Service at PPPL. The recently updated parallel service allows for concurrent running of multiple processes consisting of serial TRANSP client jobs sharing a multi-processor server for the NUBEAM code; performance characteristics of the parallel server will be described in this poster. NUBEAM has also been configured to run simulations for the SWIM project. We have recently performed the first 16-processor TSC/TRANSP simulation of the 200s approach to flattop of an ITER hybrid scenario discharge in the SWIM framework.Currently efforts are underway to incorporate NUBEAM as a formal component in the FACETS and SWIM SciDAC frameworks, coupled through the SWIM Plasma State interface similar to other tokamak heating and current drive models in these projects. This poster will discuss performance scaling, computing/communication costs and physics benefits of parallelized NUBEAM as a component in TRANSP parallel services and SWIM/FACETS. [Preview Abstract] |
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BP6.00058: Particle, momentum and thermal transport in the PTRANSP code G. Bateman, F.D. Halpern, A.H. Kritz, A.Y. Pankin, T. Rafiq, D.C. McCune, R.V. Budny, K. Indireshkumar The combined effects of particle, momentum and thermal transport are investigated in tokamak discharges using a coupled system of transport equations implemented in the PTRANSP integrated modeling code. The magnetic diffusion equation is advanced separately, along with the evolution of the equilibrium. Simulations are carried out using theory-based models to compute transport, sources and sinks. Boundary conditions are either read from data or computed using a pedestal model for H-mode discharges. Different techniques are explored for controlling numerical problems [1] in time-dependent simulations that include sawtooth oscillations and other rapid changes in the profiles. Results for the density, temperature and toroidal angular velocity profiles are compared with experimental data. \newline [1] S.C. Jardin et al, ``On 1D diffusion problems with a gradient-dependent diffusion coefficient''; G.V. Pereverzev and G. Corrigan, ``Stable numeric scheme for diffusion equation with a stiff transport''; both papers to appear in Comp. Phys. Comm. (2008). [Preview Abstract] |
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BP6.00059: PTRANSP study of energy confinement associated with toroidal rotation in tokamak discharges F.D. Halpern, A.H. Kritz, G. Bateman, A.Y. Pankin, T. Rafiq, D.C. McCune, R.V. Budny PTRANSP integrated modeling simulations are carried out for existing tokamak devices and ITER in order to study the effects of toroidal rotation on the thermal energy confinement in H-mode discharges. These simulations include self-consistent computation of toroidal momentum transport, thermal transport, and particle transport. The toroidal rotation frequency is evolved by balancing momentum diffusion and convection against the source of neutral beam torque. The toroidal angular momentum diffusion coefficients are computed using the GLF23 model or the new Weiland model. Objectives of this work include examining the parametric dependence of the simulated energy and momentum confinement times as a function of the beam driven torque density. PTRANSP simulations indicate that the flow shear driven by toroidal rotation could increase the fusion performance of ITER. It is shown that the improvement in thermal energy confinement depends on the choice of the edge boundary condition for the toroidal rotation frequency. [Preview Abstract] |
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BP6.00060: A new drift wave model for anomalous transport: Verification and validation using the PTRANSP code A.H. Kritz, F.D. Halpern, G. Bateman, A.Y. Pankin, T. Rafiq, D.C. McCune, R.V. Budny Recent developments in the PTRANSP integrated modeling code allow comparison of predicted plasma profiles obtained using different anomalous transport models. A new multi-mode model for drift-wave turbulence driven transport is introduced. The new model is based on the Weiland model for ITG and TEM and includes contributions from the Horton model for ETG modes. Results obtained with this new model are compared in PTRANSP simulations with those obtained using GLF23, MMM95 and the mixed-Bohm/gyro-Bohm model. Transport equations are solved self-consistently with sources and sinks of particles, angular momentum, thermal energy, and non-inductively driven current. The density, temperature, and width of the H-mode pedestal are predicted using a theory based model, while the edge rotation is taken from experimental data. An objective of this work includes the validation of the models for anomalous transport. This objective is pursued by comparing simulation results for the density, momentum and temperature profiles against experimental data. [Preview Abstract] |
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BP6.00061: Comparison of kinetic MHD simulation results between gyrokinetic PIC and gyro-reduced-MHD codes Hiroshi Naitou, Kenichi Kobayashi, Hiroki Hashimoto, Takehisa Andachi, Shinji Tokuda, Masatoshi Yagi To understand the MHD phenomena which can be explained only by extended or kinetic MHD simulation is crucial in tokamak experiments. We have developed a Gpic-MHD code and a GRM code. Gpic-MHD code is the electromagnetic gyrokinetic particle-in-cell code with delta-f method and specialized for MHD. GRM code is the gyro-reduced-MHD code based on the equations for the electrostatic potential, the longitudinal component of the vector potential, the electron density, the ion fluid velocity along the magnetic field, and the perturbed ion temperature. The equation for the perturbed ion temperature is added to include the ion Landau damping effect Both codes have single and multi- helicity versions. The simulation results of m/n=1/1 kinetic internal kink mode are compared. Gpic-MHD results are more stable than GRM results because the shifted electron Maxwell distribution used in the Gpic-MHD code includes anisotropy in the pressure term. Parallelization performance will be presented as well as the discussion about incorporating advanced algorithms such as a split-weight-scheme to the Gpic-MHD code. [Preview Abstract] |
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BP6.00062: STELLARATORS |
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BP6.00063: The HSX Experimental Program F.S.B. Anderson HSX has demonstrated reductions in neoclassical particle, heat, and momentum diffusivity through quasisymmetry. The Pfirsch- Schluter and bootstrap currents have been measured with pickup coils and analyzed with the V3FIT code. Their structure is consistent with the quasihelical structure; the time evolution of the bootstrap current is being modeled. The radial electric field plays a central role in neoclassical transport, and through ExB shear, in anomalous transport. Use of the 2D Wieland transport model for TEM/ITG turbulence predicts well the electron temperature profile outside r/a ~0.3, and inside if turbulence suppression by ExB shearing is included. The peaked electron temperature (2.5 keV with 100 kW injected power) is indicative of an internal transport barrier. Our program is focusing on modeling and measurement of the electric fields through use of the PENTA code and a CHERS diagnostic. GNET is being used to look at ECRH/ICRF driven fluxes. The focus is now shifting toward anomalous transport and enhanced confinement regimes through increased turbulence measurements and variation of the electric field through attainment of the ion root. [Preview Abstract] |
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BP6.00064: Neoclassical Predictions of ``Electron Root'' Plasmas at HSX Jeremy Lore, David Anderson, Alexis Briesemeister, Joseph Talmadge, Kan Zhai, Walter Guttenfelder, Don Spong Recent neoclassical transport calculations at HSX for discharges with very peaked electron temperature profiles (T$_{e}$(0)$>$2.5keV) show predictions of large ($>$400V/cm) radial electric fields in the plasma core. The existence of this ``electron root'' is due to the ion poloidal resonance with T$_{e}>>$T$_{i}$, and it is predicted to have an effect on both neoclassical and anomalous transport. Calculations were made using the DKES code [1], which uses a non-momentum conserving collision operator. Initial results will be shown from the PENTA code [2] based on a moments method which recovers the effects of momentum conservation by including effects of the parallel flows. Results of plasma density and ECRH power scans will be presented as investigations into the experimental existence of the `electron root' and possible internal transport barrier formation. [1] W.I. van Rij and S.P. Hirshman, Phys. Fluids B \textbf{1}, 563 (1989) [2] D.A. Spong, Phys. Plasmas \textbf{12}, 056114 (2005) This work is supported by DOE Grant DE-FG02-93ER54222. [Preview Abstract] |
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BP6.00065: The Development of ChERS and Passive Spectroscopy for Measuring Ion temperatures, Densities, and Flows in HSX A. Briesemeister, D.T. Anderson, K. Zhai, F.S.B. Anderson, J. Lore, J. Talmadge A charge-exchange recombination spectroscopy system (ChERS) is being implemented on HSX to measure ion flow speed and temperature. These flow measurements can be used to verify the value of the radial electric field, which has been predicted to be large in the core region of the plasma. Flow measurements will also be used to observe changes in viscous damping caused by breaking the symmetry of HSX's quasi-helical magnetic field structure. Careful analysis of the ChERS system is presented including effects from beam width and the different energy components of the beam. The radial distribution of ion species is predicted using coronal equilibrium as well as impurity diffusion to facilitate the use of spectroscopic measurements to estimate the effective ion charge at different radial locations within HSX plasmas using both ChERS and passive spectroscopy. This work is supported by DOE Grant DE-FG02-93ER54222. [Preview Abstract] |
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BP6.00066: Measurement {\&} Modeling of Equilibrium Currents in HSX J.C. Schmitt, J.N. Talmadge, J. Lore, S. Knowlton The Pfirsch-Schl\"{u}ter (PS) and bootstrap currents in the quasihelically symmetric stellarator HSX are unlike those of traditional stellarators and tokamaks. The lack of toroidal curvature in HSX results in a helical PS current that rotates with toroidal angle. The bootstrap current is opposite in direction to that in a tokamak and reduces the rotational transform, but increases the effective transform. Both currents are reduced in magnitude by a factor of n-m$\iota $ ($\sim $3 in HSX) compared to an equivalent tokamak. The bootstrap current induces a toroidal current that decays resistively, resulting in a current profile and rotational transform that varies during the plasma discharge. The decay rate scales with $\sim $1/Z$_{eff}$. Two Rogowski coils measure the net toroidal current. The B$_{\theta }$ and B$_{r}$ due to plasma currents are measured with an array of magnetic pickup coils. VMEC and BOOTSJ provide a self-consistent estimate of the plasma currents, a model of the resistive decay of the toroidal current is shown, and V3FIT[1] calculates the expected magnetic signals due to these currents throughout the shot. Direct comparisons of V3FIT with diagnostic data confirm the helical nature of the PS current and the evolving toroidal current. [1] Hirshman, S. P., Lazarus, E. A., Hanson, J. D., Knowlton, S. F., {\&} Lao, L. L.\textit{ Phys Plasmas,} \textbf{11}, 595 (2004). Supported by DOE grant number DE-FG02-93ER54222. [Preview Abstract] |
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BP6.00067: Limiter Experiments and Edge Magnetic Field Structure in HSX C. Clark, D.T. Anderson, F.S.B. Anderson, J. Canik When operating at 1 Tesla, density control in HSX has been challenging, and although methane carbonization has mitigated the control issue, shot-to-shot density reproducibility needs improvement. A moveable graphite limiter for use both inside, and outside of the last closed flux surface has been implemented in HSX to improve plasma performance by reducing interactions between the plasma and the steel walls of the device. The magnetic islands that define the plasma edge in QHS allow a relatively small plate with primarily poloidal extent to intercept a large fraction of field lines that start near the last closed flux surface before they reach the vessel. These islands in the edge region can be moved with respect to the vessel by a small variation in the auxiliary field, allowing the relationship between island position and limiter effectiveness to be studied. The effect of edge electric fields set up by differential biasing between the limiter and an insertable electrode will be studied using langmuir probes. [Preview Abstract] |
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BP6.00068: 5-D Kinetic Modeling of ECH Plasmas in the HSX Stellarator J.W. Radder, K.M. Likin, J.N. Talmadge, D.T. Anderson, S. Murakami The HSX electron cyclotron heating (ECH) system is being upgraded to two 200 kW, 28 GHz gyrotron sources. This new system will allow increased total available ECH power as well as increased heating flexibility with a poloidally steerable launch assembly. Kinetic simulations using the global transport code GNET will model the evolution of the perturbed electron distribution function and radial electron transport due to ECH. GNET solves a linearized drift kinetic equation in five-dimensional phase space, allowing simulations of quasihelically symmetric (QHS) as well as asymmetric magnetic configurations. GNET will be used to determine ECH-driven electron fluxes and estimate modifications to the ambipolar radial electric field obtained from neoclassical theory. GNET calculations will be presented for 2\textsuperscript{nd}-harmonic X-mode at 0.5 Tesla and 1\textsuperscript{st}-harmonic O--mode at 1.0 Tesla operations. Implications for ECE and X-ray diagnostics will also be presented. [Preview Abstract] |
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BP6.00069: EBW Heating in the Helically Symmetric Experiment Konstantin Likin On HSX the electron cyclotron resonance heating is made by the extraordinary (X) wave at 0.5 Tesla and/or by the ordinary (O) wave at 1 Tesla. The plasma density in ECRH experiments is always limited by a cut-off value. This limit has been overcome in other experiments with heating by Bernstein (B) waves. Possible heating scenarios in overdense HSX plasmas are of a great interest. A ray tracing code is used to model the propagation and absorption of electron cyclotron waves in the 3- D geometry of the HSX stellarator. The dispersion relation for the electron Bernstein wave has been incorporated into the ray tracing code. The O-X-B and/or direct X-B conversions in launching the microwave power from the low or high magnetic field sides have been explored. A target plasma can be made by a microwave source at 60 GHz while the second 28 GHz source will be used for EBW heating. The overall O-X-B conversion efficiency can be high (about 0.8) in the vicinity of the box port while the Bernstein wave in HSX plasmas (Te=2 keV) is absorbed outboard at r/ap=0.5 when Npar=0.5 and even further out at higher Npar. [Preview Abstract] |
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BP6.00070: Fast-Electron-Driven Instability in the HSX Stellarator C. Deng, D.L. Brower, D.A. Spong, B.N. Breizman, A.F. Almagri, D.T. Anderson, F.S.B. Anderson, W. Guttenfelder, K. Likin, J. Lore, J. Lu, J. Schmitt, K. Zhai Coherent, global fluctuations in the frequency range 20-120 kHz are observed in the quasi-helically symmetric HSX Stellarator. The modes have n=1 and m$>$1, peak in the plasma core and are driven by fast electrons associated with electron cyclotron resonance heating. Typically one mode is observed but under certain conditions secondary and tertiary modes are also present with frequency spacing $\sim $20 kHz. Large parallel wavenumber and lack of any frequency scaling with iota suggest the mode is not Alfvenic. Lagrangian formulation for coupled shear Alfven and acoustic waves have been investigated and modeling indicates the fluctuation may be a sound wave with weak Alfvenic coupling. Predicted mode frequencies and band spacing are consistent with observations. The measured fluctuation is very sensitive to magnetic ripple as just a 2{\%} perturbation results in the mode no longer being observed. This is expected for acoustic modes which are more sensitive to ripple by a factor 1/$\beta $ compared to Alfvenic modes.\textit{ *Supported by USDOE contracts DE-FG03-01ER54615 and DE-FG02-93EE54222.} [Preview Abstract] |
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BP6.00071: Momentum transport in stellarators and rippled tokamaks Andrei Simakov, Per Helander Drift kinetic formalism is employed to demonstrate that quasi- axisymmetry or quasi-helical symmetry is a necessary condition for intrinsic ambipolarity of collisional plasma transport in toroidal magnetic confinement configurations [1]. Only in magnetic fields possessing such a symmetry can plasma of arbitrary collisionality rotate freely and then only in the symmetry direction. In practice, the quasi-symmetry requirement sets an upper bound on the helical field ripple magnitude, which is difficult to achieve in low-collisionality plasmas. In non-quasi-symmetric cases the averaged radial electric field is expected to be primarily governed by collisional processes through parallel ion viscosity. Electrostatic turbulence that obeys the conventional gyrokinetic ordering may only affect the radial electric field locally, but not on a radial average taken over a few ion gyroradii. Finally, two-fluid equations [2] are employed to estimate the size of a tokamak toroidal field ripple capable of modifying the axisymmetric Pfirsch- Schl\"uter radial electric field predictions [3]. [1] P. Helander and A. N. Simakov, submitted to Phys. Rev. Lett. [2] P. J. Catto and A. N. Simakov, Phys. Plasmas {\bf 11}, 90 (2004). [3] P. J. Catto and A. N. Simakov, Phys. Plasmas {\bf 12}, 012501 (2005). [Preview Abstract] |
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BP6.00072: Neoclassical Viscosities and Anomalous Flows in Stellarators A.S. Ware, D.A. Spong We discuss initial work to use neoclassical viscosities calculated with the PENTA code [1,2] in a transport model that includes Reynolds stress generation of flows [3]. The PENTA code uses a drift kinetic equation solver to calculate neoclassical viscosities and flows in general three-dimensional geometries over a range of collisionalities. The predicted neoclassical viscosities predicted by PENTA can be flux-surfaced average and applied in a 1-D transport model that includes anomalous flow generation. This combination of codes can be used to test the impact of stellarator geometry on anomalous flow generation.\\ ~ [1] D. A. Spong, Phys. Plasmas {\bf 12}, 056114 (2005).\\ ~ [2] D. A. Spong, Fusion Sci. Technology {\bf 50}, 343 (2006). \\ ~ [3] D. E. Newman, et al., Phys. Plasmas {\bf 5}, 938 (1998). [Preview Abstract] |
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BP6.00073: Configurational Variations and Finite-Beta Effects on Neoclassical Viscosities and Flows in Stellarators M. Breyfogle, T. Marine, A.S. Ware, D.A. Spong The impact of magnetic geometry on neoclassical flows and viscosities for the Helically Symmetric Experiment (HSX) is investigated using the PENTA code [1,2]. Specifically, two topics are investigated: (1) finite-beta effects and (2) configurational variations. The PENTA code is used to calculate flows in HSX with the vacuum magnetic geometry and with finite-beta magnetic surfaces from the VMEC equilibrium code. This is done for the standard quasi-helically symmetric configuration of HSX, a symmetry-breaking mirror configuration and a hill configuration. The impact of these changes in the magnetic geometry on neoclassical viscosities and flows in HSX will be discussed.\\[0pt] [1] D. A. Spong, Phys. Plasmas 12, 056114 (2005). \\[0pt] [2] D. A. Spong, Fusion Sci. Technology 50, 343 (2006). [Preview Abstract] |
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BP6.00074: Analytic and computational investigation of the effect of finite parallel heat transport on the formation of magnetic islands in 3-D plasma equilibria M. Schlutt, C.C. Hegna, E. Held A resistive MHD model is used to investigate pressure-induced magnetic islands in 3-D equilibria. We revisit previous island calculations while allowing for finite parallel heat transport, to derive an equation for equilibrium island width. We find that finite parallel heat transport can alter the impact of resistive interchange and bootstrap current contributions to magnetic island formation. However, Pfirsch-Schl\"uter currents driven by resonant components in $\frac{1}{B^{2}}$ are largely unaffected by transport processes. To make further progress, this problem is modeled using NIMROD. A vacuum equilibrium helical magnetic field is loaded into the geometry of a straight stellarator. The symmetry of the vacuum field with a dominant magnetic harmonic can be spoiled by adding small magnetic perturbations. These perturbations alter the magnetic spectrum, and potentially produce magnetic islands and regions of stochasticity. Numerical simulations will be performed that include the effect of a heating source and self-consistent anisotropic transport processes in a variety of magnetic configurations. The effect of finite parallel heat transport on the island formation and saturation processes will be examined. [Preview Abstract] |
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BP6.00075: Application of 3D Equilibrium Code to Calculation of Neoclassical Tearing Modes Daniel Raburn, Allan Reiman, Donald Monticello, Ravi Samtaney, Eric Fredrickson We have implemented a JFNK (Jacobian-free Newton-Krylov) method in PIES (the Princeton Iterative Equilibrium Solver), which solves for 3D MHD equilibria. The code uses numerous enhancements to traditional JFNK, including adaptive preconditioning and subspace restricted Levenberg-Marquardt backtracking. The code has also been modified to handle neoclassical effects and is being validated against neoclassical tearing mode data from the TFTR tokamak. [Preview Abstract] |
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BP6.00076: Investigation of gyrokinetic instabilities in stellarator geometry with the GS2 code J.A. Baumgaertel, W. Dorland, E. Belli, D.R. Mikkelsen, G.W. Hammett, M.A. Barnes The GS2 gyrokinetic turbulence code has been used to model microinstabilities in flux-tubes in non-axisymmetric geometries such as stellarators. The threshold for various microinstabilities is known to improve with negative magnetic shear and other magnetic field shaping effects. Stellarators can have natural negative magnetic shear, very large local magnetic shear, and have many additional shaping parameters that might be optimized regarding tokamak geometry. The extent to which it might be possible to optimize designs relative to gyrokinetic microinstabilities and turbulence is not yet known. Here we carry out some studies of growth rates and instability thresholds for a sample NCSX quasi-axisymmetric stellarator design. This work is supported by the DOE Fusion Energy Sciences Fellowship, CMPD, and DOE Grant \#DE-FC02-04ER54784. [Preview Abstract] |
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BP6.00077: Plasma Equilibrium in a Magnetic Field with Stochastic Field-Line Trajectories J.A. Krommes, A.H. Reiman The nature of plasma equilibrium in a magnetic field with stochastic field lines is examined, expanding upon the ideas first described by Reiman et~al.\footnote{A. Reiman et al, Nucl.\ Fusion \textbf{47}, 572--8 (2007).} The magnetic partial differential equation (PDE) that determines the equilibrium Pfirsch-Schl\"uter currents is treated as a passive stochastic PDE for $\mu \doteq j_\parallel/B$. Renormalization\footnote{J. A. Krommes, Phys.\ Reports \textbf {360}, 1--351.} leads to a stochastic Langevin equation for $\mu$ in which the resonances at the rational surfaces are broadened by the stochastic diffusion of the field lines; even weak radial diffusion can significantly affect the equilibrium, which need not be flattened in the stochastic region. Particular attention is paid to satisfying the periodicity constraints in toroidal configurations with sheared magnetic fields. A numerical scheme that couples the renormalized Langevin equation to Ampere's law is described. [Preview Abstract] |
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BP6.00078: Current-driven instability studies on the Compact Toroidal Hybrid (CTH) torsatron S. Knowlton, G. Hartwell, J. Hanson, M. Cianciosa, J. Peterson, B.A. Stevenson, G. Carson Ohmic currents are driven in ECRH plasmas in CTH (R$_{0}$ = 0.75 m, a = 0.2 m, B = 0.64 T, n$_{e} \quad \le $ 10$^{19}$ m$^{-3})$ to explore the resistance of stellarator plasmas to major disruptions with varying levels of vacuum rotational transform. While complete disruptions have not yet been observed, instabilities associated with rational values of the net rotational transform are noted. Also, rapid current and density decreases are observed that are possibly associated with double-valued rotational transform values as the current profile evolves. Efforts are ongoing to interpret these current-driven equilibria with magnetic and SXR diagnostics coupled to the V3FIT 3-D equilibrium reconstruction code. [Preview Abstract] |
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BP6.00079: Soft X-Ray Diagnostics on the Compact Toroidal Hybrid (CTH) Experiment G. Hartwell, S. Knowlton, J. Peterson, B.A. Stevenson, J. Hanson, G. Carson Soft X-Ray (SXR) systems are used on the CTH experiment for tomographic reconstruction of the emissivity profile and electron temperature measurement. The emissivities from the multi-chord arrays will also be incorporated into reconstruction of the 3-D flux surfaces of the CTH stellarator plasma. SXR tomography is performed with 3 cameras, each consisting of a 20-channel AXUV-20EL photo-diode array filtered with 500nm Al-foil in a poloidal cross-section. The SXR electron temperature diagnostic is a single chord system viewing the plasma simultaneously in 3 energy bands discriminated with filters of different thicknesses. Ratios of the photo-diode signals are used to infer the maximum electron temperature along the chord, subject to issues of impurity lines. Lastly, a vertically-viewing, 20-chord SXR system has been installed and will be used to infer the Shafranov shift of the plasma. A description of the SXR tomography cameras, the tomographic reconstruction technique, and results will be presented. [Preview Abstract] |
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BP6.00080: Magnetic diagnostics and plans for polarimetry on the Compact Toroidal Hybrid torsatron B.A. Stevenson, G. Hartwell, S. Knowlton, J. Hanson Plasma equilibria with significant levels of toroidal plasma current are investigated on the Compact Toroidal Hybrid (CTH) to assess the nature of current-driven instabilities in stellarators. Reconstruction of current-driven equilibria is being undertaken with the new V3FIT 3D magnetic equilibrium reconstruction code. Magnetic diagnostics for reconstruction include single and multi-part Rogowski coils, B-dot probes, and a diamagnetic loop. A 1-mm polarimeter / interferometer system for current profile measurements is also being investigated. Modeling results for the polarimeter diagnostic will be shown. These simulations show that the required frequency range needed to maximize the polarimetric phase shift while minimizing refractive effects in CTH plasmas is near 220 GHz. Initial reconstruction results using V3FIT will be shown using data from the internal and external Rogowski coil sets. [Preview Abstract] |
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BP6.00081: Modifications of the edge electric field in the Compact Toroidal Hybrid torsatron with the use of a biased limiter M. Cianciosa, E. Thomas, B.A. Stevenson, G. Hartwell, S. Knowlton Sheared flows arising from spatially inhomogeneous, transverse electric fields are of interest in space, laboratory and fusion plasmas. In toroidal fusion plasmas, these flows are often associated with enhanced stability regimes. This presentation reports on recent experiments performed on the Compact Toroidal Hybrid (CTH) device (R = 0.75 m, a $\sim $ 0.2 m , B $\le $ 0.7, $n_e \quad \le \quad 10^{19} \quad m^{-3})$ in which a biased limiter inserted into the edge of the plasma is used to modify the edge radial electric field. Probe measurements indicate an asymmetric plasma response depending upon the sign of the bias. Probe measurements are also compared with interferometer measurements, which confirm the asymmetric plasma response. [Preview Abstract] |
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BP6.00082: Three-Dimensional Equilibrium Reconstruction: V3FIT J.D. Hanson, S.F. Knowlton, S.P. Hirshman, E.A. Lazarus, L. Lao Equilibrium Reconstruction (ER) is an inverse problem, where the signals from experimental diagnostics are used to determine the parameters (current profile, pressure profile) which specify an MHD equilibrium. The V3FIT code is a tightly coupled ER code that uses VMEC (a three-dimensional MHD equilibrium code) to solve the forward problem. Results of a careful comparison with the axisymmetric ER code EFIT will be presented. We will also show results of reconstructions of the CTH toroidal hybrid experiment at Auburn University. [Preview Abstract] |
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BP6.00083: EBW Power Deposition and Fisch-Boozer Current Drive in the WEGA Stellarator Josef Preinhaelter, Heinrich Laqua, Jakub Urban, Linda Vahala, George Vahala We predict current drive following wave absorption of EBW in the WEGA stellarator. From the Fisch-Boozer mechanism, we estimate the driven current density from the power deposition into the individual harmonics and the direction of the resonant velocity. This driven current has been observed experimentally; but the experimental results are only in partial agreeing with the simulations. Simulations of the radial current profiles confirm the observed current reversal in some cases. These current reversals occur when there is a hot plasma component present with subsequent EBW absorption on the first and the second electron cyclotron harmonics. The reason for the strong absorption is a very pronounced change in the parallel component of the wave vector ($N_\parallel \sim 30)$.The generated RF current was mostly sensitive to the additional vertical magnetic field. Further work is needed to bring better agreement between our simulations and the experiments. [Preview Abstract] |
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BP6.00084: Study of Energetic Ion Driven Instability using Twin Heavy IonBeam Probe on Compact Helical System Shinsuke Ohshima, Akihide Fujisawa, Akihiro Shimizu, Haruhisa Nakano, Hiroaki Nishimura Energetic ion driven instabilities are concerned and extensively studied for the era of burning plasma in a number of tokamaks and stellarators since the instabilities can cause destabilization and degradation of the plasma performance and the resultant loss of energetic ions interacted with the instabilities can damage the vessel wall of the reactor. In Compact Helical System (CHS), we have investigated the energetic ion driven instabilities such as fishbone and Alfven modes, using twin heavy ion beam probes (HIBPs). Recently, we have succeeded in reconstructing the nonlinear evolution of the internal structure of CHS fishbone, an oscillatory state caused by the interaction between energetic ions and an MHD mode (m/n=2/1). In this presentation we mainly report the HIBP observations of CHS fishbone in terms of density and potential. The discovery of the zonal flow structure induced by the energetic ion loss during a cycle of CHS-fishbone is highlighted. [Preview Abstract] |
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BP6.00085: Equilibrium analysis of W7-AS high-beta plasmas M.C. Zarnstorff, A. Reiman, J. Geiger, A. Weller The equilibrium for W7-AS high-beta plasmas is reconstructed, fitting the magnetic diagnostic measurements and the Thomson-scattering pressure profile. Principal component analysis indicates that the available magnetic diagnostics are sensitive to two moments of the current profile and three moments of the pressure profile. The total plasma toroidal current is nulled using a feedback controlled ohmic current. The reconstructed equilibria show small local toroidal net-current, from the combindation of the ohmic, bootstrap and beam currents, which can reduce the central rotational transform by $\sim $0.1. Analysis of the free-boundary equilibria by PIES indicates that the magnetic field near the plasma edge becomes increasingly stochastic as beta increases. The achieved maximum beta-value in the configurations examined corresponds to a calculated loss of the outer $\sim $35{\%} of the minor radius to islands and stochastic fields. Thus, the beta-limit and its variation may be due to confinement degradation due to flux-surface break-up. The parametric variation of the calculated equilibrium properties will be presented. Extensions of this analysis to LHD will be discussed. [Preview Abstract] |
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