Bulletin of the American Physical Society
56th Annual Meeting of the APS Division of Plasma Physics
Volume 59, Number 15
Monday–Friday, October 27–31, 2014; New Orleans, Louisiana
Session GO4: Magnetized Liner Inertial Fusion |
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Chair: Wolfgang Theobald, University of Rochester Room: Salon E |
Tuesday, October 28, 2014 9:30AM - 9:42AM |
GO4.00001: First Experiments with Planar Wire Arrays on U Michigan's Linear Transformer Driver A.S. Safronova, V.L. Kantsyrev, M.E. Weller, I.K. Shrestha, V.V. Shlyaptseva, M.C. Cooper, M. Lorance, A. Stafford, S.G. Patel, A.M. Steiner, D.A. Yager-Elorriaga, N.M. Jordan, R.M. Gilgenbach For petawatt-class Z-pinch accelerators, a Linear Transformer Driver (LTD)-driven accelerator promises to be (at a given pinch current and implosion time) more efficient than the conventionally used Marx-driven accelerator. Because there exists almost no data on how wire arrays radiate on LTD-based machines in the USA, it is very important to perform radiation and plasma physics studies on this new type of generator. We report on the first outcome of the new partnership with University of Michigan (UM), which resulted in successful UNR-UM experiments on the low-impedance MAIZE generator with planar wire arrays (PWA). PWA is a novel wire array load that was introduced and tested in detail on high-impedance Zebra at UNR during the last years and found to be the most efficient radiator. Implosion of Al Double PWAs of different configurations were achieved on MAIZE, observed with a set of various diagnostics which include x-ray diode detectors, x-ray spectroscopy and imaging, and shadowgraphy. Al and Mg plasmas of more than 450 eV were studied in detail. [Preview Abstract] |
Tuesday, October 28, 2014 9:42AM - 9:54AM |
GO4.00002: Theory of formation of helical structures in a perfectly conducting, premagnetized Z-pinch liner Edmund Yu, Alexander Velikovich, Kyle Peterson The magnetized liner inertial fusion (MagLIF) concept [1] uses an azimuthal magnetic field to collapse a thick metallic liner containing preheated fusion fuel. A critical component of the concept is an axial magnetic field, permeating both the fuel and surrounding liner, which reduces the compression necessary to achieve fusion conditions. Recent experiments [2] demonstrate that a liner premagnetized with a 10 T axial field develops helical structures with a pitch significantly larger than an estimate of $B_z/B_\theta$ would suggest. The cause of the helical perturbations is still not understood. In this work, we present an analytic, linear theory in which we model the liner as a perfectly conducting metal, and study how bumps and divots on its surface redirect current flow, resulting in perturbations to $B$ as well as $j\times B$. We show that in the presence of axial and azimuthal magnetic field, the theory predicts divots will grow and deform at an angle determined by the magnetic field. We compare theoretical results with three dimensional, resistive MHD simulations.\\[4pt] [1] S. A. Slutz et al., Phys. Plasmas 17, 056303 (2010)\\[0pt] [2] T. J. Awe et al., Phys. Rev. Lett. 111, 235005 (2013) [Preview Abstract] |
Tuesday, October 28, 2014 9:54AM - 10:06AM |
GO4.00003: Magneto-Rayleigh-Taylor, Sausage And Kink Mode In Cylindrical Liners Y.Y. Lau, Peng Zhang, Matthew Weis, Ronald Gilgenbach, Mark Hess, Kyle Peterson This paper analyzes the coupling of magneto-Rayleigh-Taylor (MRT), sausage (azimuthal mode number m$=$0) and kink mode (m$=$1) in an imploding cylindrical liner, using ideal MHD. A uniform axial magnetic field of arbitrary value is included in each region: liner, its interior, and its exterior. The dispersion relation, the feedthrough factor, and the temporal evolution of perturbations were solved exactly, for arbitrary values of g ($=$ gravity), k ($=$ axial wavenumber), m, aspect ratio, and equilibrium quantities in each region. For small k, a positive g (inward radial acceleration in the lab frame) tends to stabilize the sausage mode, but destabilize the kink mode. For large k, a positive g destabilizes both the kink and sausage mode. This analysis might shed lights into some puzzling features in Harris' classic paper [1], and in the recent cylindrical liner experiments [2] on MRT. \\[4pt] [1] E. G. Harris, Phys. Fluids 5, 1057 (1962).\\[0pt] [2] T. J. Awe, et al., PRL 111, 235005 (2013); PoP 21, 056303 (2014). [Preview Abstract] |
Tuesday, October 28, 2014 10:06AM - 10:18AM |
GO4.00004: 2D HYDRA Calculations of Magneto-Rayleigh-Taylor Growth and Feedthrough in Cylindrical Liners Matthew Weis, Peng Zhang, Y.Y. Lau, Ronald Gilgenbach, Kyle Peterson, Mark Hess Cylindrical liner implosions are susceptible to the magneto-Rayleigh-Taylor instability (MRT), along with the azimuthal current-carrying modes (sausage, kink, etc). ``Feedthrough'' of these instabilities has a strong influence on the integrity of the liner/fuel interface in the magnetized liner inertial fusion concept (MagLIF) [1]. The linearized ideal MHD equations can be solved to quantify these effects, including the presence of an effective gravity and an axial magnetic field. We investigate the potential of this field to mitigate feedthrough, due to MRT growth from various initial surface finishes (seeded, rough), throughout the implosion using our analytic results and the LLNL code, HYDRA. We will present both low and high convergence cases. Lastly, we illustrate the effect shock compression can have on feedthrough in seeded liners for various fill gases (cold and pre-heated) and magnetic field configurations. \\[4pt] [1] S. A. Slutz, et. al, Phys. Plasmas 17, 056303 (2010). [Preview Abstract] |
Tuesday, October 28, 2014 10:18AM - 10:30AM |
GO4.00005: Comparison between initial Magnetized Liner Inertial Fusion experiments and integrated simulations A.B. Sefkow, M.R. Gomez, M. Geissel, K.D. Hahn, S.B. Hansen, E.C. Harding, K.J. Peterson, S.A. Slutz, J.M. Koning, M.M. Marinak The Magnetized Liner Inertial Fusion (MagLIF) approach to ICF has obtained thermonuclear fusion yields using the Z facility. Integrated magnetohydrodynamic simulations provided the design for the first neutron-producing experiments using capabilities that presently exist, and the initial experiments measured stagnation radii $r_{stag}$$<$75 $\mu$m, temperatures around 3 keV, and isotropic neutron yields up to $Y_n^{DD}$=2$\times$10$^{12}$ from imploded liners reaching peak velocities around 70 km/s over an implosion time of about 60 ns. We present comparisons between the experimental observables and post-shot degraded integrated simulations. [Preview Abstract] |
Tuesday, October 28, 2014 10:30AM - 10:42AM |
GO4.00006: ABSTRACT WITHDRAWN |
Tuesday, October 28, 2014 10:42AM - 10:54AM |
GO4.00007: Laser heating challenges of high yield MagLIF targets Stephen Slutz, Adam Sefkow, Roger Vesey The MagLIF (Magnetized Liner Inertial Fusion) concept is predicted by numerical simulation to produce fusion yields of about 100 kJ, when driven by 25 MA from the existing Z accelerator [S.A. Slutz et al Phys. Plasmas 17, 056303, 2010] and much higher yields with future accelerators delivering higher currents [Slutz and Vesey PRL 108, 025003, 2012]. The fuel must be heated before compression to obtain significant fusion yields due to the relatively slow implosion velocities ($\sim$ 100 km/s) of magnetically driven liners. Lasers provide a convenient means to accomplish this pre-compressional heating of the fusion fuel, but there are challenges. The laser must penetrate a foil covering the laser entrance hole and deposit 20-30 kJ within the $\sim$ 1 cm length of the liner in fuel at 6-12 mg/cc. Such high densities could result in beam scattering due to refraction and laser plasma interactions. Numerical simulations of the laser heating process are presented, which indicate that energies as high as 30 kJ could be deposited in the fuel by using two laser pulses of different wavelengths. Simulations of this process will be presented as well of results for a MagLIF design for a potential new machine delivering 50 MA of current. [Preview Abstract] |
Tuesday, October 28, 2014 10:54AM - 11:06AM |
GO4.00008: Development of azimuthally correlated instabilities for MagLIF seeded by electro-thermal and material strength effects James Pecover, Marcus Weinwurm, Jeremy Chittenden Magnetized liner inertial fusion (MagLIF) is a promising route to controlled thermonuclear fusion. The concept involves magnetically imploding a metal liner; a key limitation of such systems is the magneto-Rayleigh-Taylor (MRT) instability. MagLIF relevant liner implosions carried out at Sandia showed high amplitude MRT growth. 3D simulations with our MHD code Gorgon have shown that azimuthal correlation required to explain this can be contributed to by early time effects the electro-thermal instability (ETI) and an ``electro-choric instability'' (ECI). Shear forces can damp short wavelength perturbations while the liner remains solid, potentially setting axial wavelengths for the ETI and ECI. We can now model shear stresses in solids with Gorgon using a Johnson-Cook strength model and a bulk modulus calculated from the FEOS equation of state. Gorgon results with the strength model are compared to results from the shock hydrodynamics code iSALE. Results for liners show elongation of perturbations at the outer edge relative to the case without strength. We present results showing the model applied to liner implosions with axial magnetic fields of 0T and 10T. [Preview Abstract] |
Tuesday, October 28, 2014 11:06AM - 11:18AM |
GO4.00009: Magneto-acoustic waves driven by self-generated magnetic field: relevance to helical structures in MagLIF experiments Jonathan Davies, Daniel Barnak, Riccardo Betti, Adam Carreon, Po-Yu Chang, Gennady Fiksel The observation of coherent helical structures in liner implosions on Z when an axial magnetic field more than 100 times smaller than the azimuthal field is added has yet to be adequately explained [1]. The results have been reproduced in a 3D MHD code by initializing helices on the outer surface, but this produces helices independently of the axial magnetic field [1]. We present the hypothesis that helices are seeded by self-generated magnetic field, which adds a driving term to the dispersion relation for magneto-acoustic waves when there is a temperature gradient perpendicular to the fluid motion. The key feature of this instability is that it is stable when magnetic pressure exceeds a fraction of the thermal pressure, therefore, instability driven by the helical field resulting from the combination of the initial axial field and the growing azimuthal field will stabilize before the net field has a small pitch angle and before the implosion starts, seeding helices on the surface. This work was supported by the Department of Energy National Nuclear Security Administration, Award Number DE-NA0001944, and the Fusion Science Center supported by the Office of Fusion Energy Sciences, Number DE-FG02-04ER54786.\\[4pt] [1] T. J. Awe {\it et al.} 2014 Phys. Plasmas {\bf 21} 056303 [Preview Abstract] |
Tuesday, October 28, 2014 11:18AM - 11:30AM |
GO4.00010: Point Design of Scaled-Down Magnetized Liner Inertial Fusion on OMEGA P.-Y. Chang, J.R. Davies, D.H. Barnak, G. Fiksel, R. Betti, A. Harvey-Thompson, D. Sinars Significant yield enhancement in cylindrical liner implosions using the Z machine at Sandia was observed when the deuterium fuel was laser heated and magnetized prior to compression.\footnote{M. R. Gomez\textit{ et al.}, ``Experimental Demonstration of Fusion-Relevant Conditions in Magnetized Liner Inertial Fusion,'' submitted to Physical Review Letters.} A higher initial temperature improves flux conservation and reduces the radial convergence required to achieve the final temperatures necessary for high neutron yield when heat flow is suppressed by the axial magnetic field. A scaled-down experiment with a 100-km/s implosion velocity using laser-driven implosions will be conducted on OMEGA. The implosion was simulated using the 1-D hydrocode \textit{LILAC} with the addition of resistive magnetohydrodynamic subroutines. For an initial D$_{2}$ temperature of 100 eV and an initial axial magnetic field of 15 T, the neutron-averaged ion temperature increases from 0.8 keV to more than 4 keV, and the neutron yield increases by $100\times$ compared to the case without the gas being heated and magnetized prior to compression. This material is based upon work supported by the Department of Energy National Nuclear Security Administration under Award Number DE-NA0001944 and the Office of Fusion Energy Sciences Number DE-FG02-04ER54786. [Preview Abstract] |
Tuesday, October 28, 2014 11:30AM - 11:42AM |
GO4.00011: Adaptive Beam Smoothing with Plasma-Pinholes for Laser-Entrance-Hole Transmission Studies Matthias Geissel, Lawrence E. Ruggles, Ian C. Smith, Jonathn E. Shores, C. Shane Speas, John L. Porter The concept of Magnetized Liner Inertial Fusion (MagLIF) requires the deposition of laser energy into a fuel-filled cylinder that is exposed to a magnetic field. To improve process, it is essential to optimize transmission through the foil covered laser entrance hole (LEH), which involves minimizing laser-plasma-instabilities (LPI). Laser beam smoothing is the most common approach to minimize LPI. It typically involves a Random-Phase-Plate (RPP) and smoothing by spectral dispersion (SSD). This approach can still cause LPI issues due to intensity ``hot-spots'' on a ps-time scale, and it inconveniently fixes the usable spot size. Changing laser spot sizes requires multiple dedicated RPPs. To study ideal spot sizes on a MagLIF LEH, the RPP/SSD approach gets cost prohibitive. As alternative, we use sacrificial thin foils (500 nm or less) at the laser focus, which instantly turn into a plasma-pinhole, acting as spatial filter. The smoothed laser spot size grows linearly with distance from best focus. We present experimental data for smoothing performance and resulting LEH transmission. [Preview Abstract] |
Tuesday, October 28, 2014 11:42AM - 11:54AM |
GO4.00012: ABSTRACT WITHDRAWN |
Tuesday, October 28, 2014 11:54AM - 12:06PM |
GO4.00013: Performance of the Plasma Focus with Monolithic Tungsten Electrodes Eric Lerner, Hamid Yousefi, Fred VanRoessel, Anthony Ellis, Ivana Karamitsos Fusion yield in plasma focus devices scales faster than I$^{4}$, where I is peak current, for I $\alt$ 1 MA, but then appears to plateau at around 1 joule for pure D fill gas. Recent experimental results with the FF-1 plasma focus and new calculations indicate that the cause of this plateau may be metal impurities in the plasma due to increased erosion of the electrodes at higher currents, causing asymmetries that reduce compression in the pinch. To reduce this impurity problem, we are installing in FF-1 monolithic tungsten electrodes, so that no electrical contacts will be inside the vacuum chamber, thus eliminating arcing and minimizing erosion. Tungsten electrodes will also reduce sputtering as compared with the copper electrodes previously used. We expect that this will greatly reduce impurities, preserve filament magnetization and increase density and thus fusion yield of plasmoids using pure D. In addition, we will be using pre-ionization of the fill gas to prevent erosion by runaway electrons when the current pulse is initiated. We will measure the impurity level through timing the speed of the rundown, and through optical spectroscopy, as well by measuring the actual amount of material eroded from the electrodes. Filamentation will be observed with a 4-frame ICCD camera. The dimensions of the plasmoid will be measured both in the optical and with an x-ray pinhole camera. We will report here on the result of initial experiments, including the effects of nitrogen-deuterium mixes, which we expect to further increase density. [Preview Abstract] |
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