Bulletin of the American Physical Society
58th Annual Meeting of the APS Division of Plasma Physics
Volume 61, Number 18
Monday–Friday, October 31–November 4 2016; San Jose, California
Session CO8: Magneto-Inertial Fusion II |
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Chair: Chris Jennings, Sandia National Laboratories Room: 212 CD |
Monday, October 31, 2016 2:00PM - 2:12PM |
CO8.00001: Magnetizing NIF Sub-Scale Capsules For Reaching Ignition Using Laser Energy in the 1 MJ Range G. Zimmerman, D. Ho, J. Perkins, G. Kagan, G. Logan, J. Salmonson, M. Rhodes, D. Blackfield Fusion yield for ICF can be amplified by imposing a seed B-field around 50 T to confine alphas and to reduce electron heat conduction. Achieving 58 T in offline lab tests in sample hohlraum coils driven by a pulsed-power supply was demonstrated by Rhodes. Three topics are addressed. (1) The derivation of a 0D energy balance equation that including the effect of B-field. The ignition boundary obtained from this equation shows that a strong compressed B-field substantially reduces the minimum hotspot $\rho $R required for ignition by about 50{\%}. (2) The design of a near-term experimental demonstration of the effect of B-field on yield improvement based on our sub-scale gas-filled Symcap design for the NIF experiment (non-magnetized) that gave 1D yield and showed good symmetry. (3) The quest and design of magnetized sub-scale capsule with DT ice layer that gives robust ignition and requires only about 1 MJ of laser energy. Our baseline non-magnetized sub-scale design, with a seed field of 50T, gives a robust ignition with 1 MJ yield. [Preview Abstract] |
Monday, October 31, 2016 2:12PM - 2:24PM |
CO8.00002: Fusion Reactor and Break-Even Experiment Based on Stabilized Liner Compression of Plasma Peter Turchi, Sherry Frese, Michael Frese An optimum regime [1], known as magnetized-target or magneto-inertial fusion (MTF/MIF), requires magnetic fields at megagauss levels, which are attainable by use of dynamic conductors called liners. The stabilized liner compressor (SLC) provides the basis for controlled implosion and re-capture of the liner for reversible energy exchange between liner kinetic energy and the internal energy of a magnetized-plasma target. This exchange requires rotational stabilization of Rayleigh-Taylor modes on the inner surface of the liner and pneumatically driven free-pistons that eliminate such modes at the outer surface [1, 2]. We discuss the implications of the SLC approach for the power reactor, a breakeven experiment, and intermediate experiments to develop the plasma target. Features include the importance of pneumatic drive and the liner-blanket for economic feasibility of MTF/MIF. [1] P.J. Turchi, ``Imploding Liner Compression of Plasma: Concepts and Issues'', IEEE Trans. on Plasma Science, 36, 1, 52 (2008). [2] P.J. Turchi, et al, ``Review of the NRL Liner Implosion Program'', in Megagauss Physics and Technology, P.J. Turchi, ed., Plenum, NY (1980). P. 375. [Preview Abstract] |
Monday, October 31, 2016 2:24PM - 2:36PM |
CO8.00003: Progress in the Design of the Stabilized Liner Compressor for MTF/MIF Plasma Target Development Sherry Frese, Michael Frese, Peter Turchi, Don Gale The Stabilized Liner Compressor (SLC) seeks to extend concepts for repetitive, rotationally stabilized, liquid-metal liners driven by free-pistons [1] to much higher drive pressures (25 vs 5 kpsi) and faster implosion speeds (2000 vs 100 m/s) than previously demonstrated. Such extension is needed to enable experiments with magnetized-plasma targets presently offering sizes and lifetimes of 10's cm diam and 10's microsec. SLC represents the confluence of several difficult technologies, including pulsed high pressures, high-speed rotating machinery and alkali-metal (Na, NaK) handling. Solution of the two-dimensional, unsteady, compressible flow of a rotating liquid-metal liner requires advanced numerical techniques. We report the use of the 2-1/2 dimensional MHD code MACH2 to explore flow options, including magnetic flux compression, and to provide pulsed pressure distributions for mechanical design. [1] P.J. Turchi, et al, ``Review of the NRL Liner Implosion Program'', in Megagauss Physics and Technology, P.J. Turchi, ed., Plenum, NY (1980). P. 375. [Preview Abstract] |
Monday, October 31, 2016 2:36PM - 2:48PM |
CO8.00004: First Scaled-Down Integrated MagLIF Experiments on OMEGA J.R. Davies, D.H. Barnak, R. Betti, V.Yu. Glebov, J.P. Knauer, S.P. Regan Magnetized liner inertial fusion (MagLIF)\footnote{ S. A. Slutz \textit{et al}. Phys. Plasmas \textbf{17}, 056303 (2010).} is an inertial confinement fusion (ICF) scheme that relies on compression of a cylindrical, magnetized, preheated plasma to achieve fusion conditions with a lower implosion velocity and a lower convergence ratio than conventional ICF. MagLIF research to date has been centered on the Z pulsed-power machine at Sandia National Laboratories---the only facility capable of carrying out such experiments. A laser-driven version of MagLIF has now been implemented on the OMEGA laser at the Laboratory for Laser Energetics, using targets roughly ten times smaller in linear dimensions than Z targets. Laser-driven MagLIF on OMEGA will test the scaling of MagLIF and provide a higher shot rate with better diagnostic access than Z. Preliminary results from integrated MagLIF experiments on OMEGA will be presented for the first time. The information, data, or work presented herein was funded in part by the Advanced Research Projects Agency-Energy (ARPA-E), U.S. Department of Energy, under Award Number DE-AR0000568, and the Department of Energy National Nuclear Security Administration under Award Number DE-NA0001944. [Preview Abstract] |
Monday, October 31, 2016 2:48PM - 3:00PM |
CO8.00005: Developing a Pre-Heat Platform for MagLIF with Z-Beamlet Matthias Geissel, Adam J. Harvey-Thompson, T.J. Awe, D.E. Bliss, M.E. Glinsky, E.M. Campbell, M.R. Gomez, E. Harding, S.B. Hansen, C.A. Jennings, M.W. Kimmel, P.F. Knapp, S.M. Lewis, R.D. McBride, K. Peterson, M. Schollmeier, D.J. Scoglietti, A.B. Sefkow, J.E. Shores, D.B. Sinars, G.A. Rochau, S.A. Slutz, I.C. Smith, M.R. Weiss, J.L. Porter Sandia's Magnetized Liner Inertial Fusion Program has put one of the main objectives towards developing standard platform for a `preconditioned' target, providing a scenario that reproducibly delivers pre-heated fuel. \newline The majority of this effort has been done at the ``Pecos'' Target Area using Sandia's Z-Beamlet laser to provide the pre-heat energy, just like for fully integrated MagLIF experiments. The nature and magnitude of Laser-Plasma-Instabilities during this process are particularly important, since they can lead to less energy in the fuel (backscatter processes) or to energy deposition in less desirable areas (filamentation/scatter). We present results for Stimulated Brillouin Backscatter and forward scatter, and show the effect of the laser pulse shape to laser-entrance-hole transmission and blast wave propagation in the fuel. [Preview Abstract] |
Monday, October 31, 2016 3:00PM - 3:12PM |
CO8.00006: Laser propagation through full-scale, high-gain MagLIF gas pipes using the NIF Bradley Pollock, Adam Sefkow, Clement Goyon, David Strozzi, Shahab Khan, Mordy Rosen, Mike Campbell, Grant Logan, Kyle Peterson, John Moody The first relevant measurements of laser propagation through surrogate high-gain MagLIF gas pipe targets at full scale [1,2] have been performed at the NIF, using 30 kJ of laser drive from one quad in a 10 ns pulse at an intensity of 2e14 W/cm$^{\mathrm{2}}$. The unmagnetized pipe is filled with 1 atm of 99{\%}/1{\%} neopentane/Ar, and uses an entrance window of 0.75 um polyimide and an exit window of 0.3 um of Ta backed with 5 um of polyimide. Side-on x-ray emission from the plasma is imaged through the 100 um-thick epoxy wall onto a framing camera at four times during the drive, and is in excellent agreement with pre-shot HYDRA radiation-hydrodynamics modeling. X-ray emission from the Ta exit plane is imaged onto a streak camera to determine the timing and intensity of the laser burning through the pipe, and the Ar emission from the center of the pipe is spectrally- and temporally-resolved to determine the plasma electron temperature. Backscatter is measured throughout the laser drive, and is found to be of significance only when the laser reaches the Ta exit plane and produces SBS. These first results in unmagnetized surrogate gas fills are encouraging since they demonstrate sufficient laser energy absorption and low LPI losses within high-density long-scale-length plasmas for proposed high-gain MagLIF target designs. We will discuss plans to magnetize targets filled with high-density DT gas in future experiments.\newline [1] S. A. Slutz and R. A. Vesey, Phys. Rev. Lett. 108, 025003 (2012). [2] A. B. Sefkow, et. al., Phys. Plasmas 21, 072711 (2014). \textit{This work performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344.} \textit{Sandia is a multiprogram laboratory operated by Sandia Corporation, a Lockheed Martin Company, for the National Nuclear Security Administration under Contract No. DE-AC04-94AL85000.} [Preview Abstract] |
Monday, October 31, 2016 3:12PM - 3:24PM |
CO8.00007: Direct measurement of magnetic flux compression on the Z pulsed-power accelerator R.D. McBride, D.E. Bliss, M.R. Martin, C.A. Jennings, D.C. Lamppa, D.H. Dolan, R.W. Lemke, D.C. Rovang, G.A. Rochau, M.E. Cuneo, D.B. Sinars, T.P. Intrator, T.E. Weber We report on the progress made to date for directly measuring magnetic flux compression on Z. Each experiment consisted of an initially solid aluminum liner (a cylindrical tube), which was imploded using Z's drive current (0--20 MA in 100 ns). The imploding liner compresses a 10--20-T axial seed field, $B_{z}$\textit{(0)}, supplied by an independently driven Helmholtz coil pair. Assuming perfect flux conservation, the axial field amplification should be well described by $B_{z}(t)=B_{z}$\textit{(0)\texttimes [R(0)/R(t)]}$^{2}$, where $R$ is the liner's inner surface radius. With perfect flux conservation, $B_{z}$ and \textit{dB}$_{z}$\textit{/dt} values exceeding 10$^{4}$ T and 10$^{12}$ T/s, respectively, are expected. These large values, the diminishing liner volume, and the harsh environment on Z, make it particularly challenging to measure these fields directly. We report on our latest efforts to do so using a fiber-optic-based Faraday rotation diagnostic, where the magneto-active portion of the sensor is made from terbium-doped optical fiber. We have now used this diagnostic to measure a flux-compressed magnetic field to over 600 T prior to the imploding liner hitting the on-axis fiber housing. This project was funded in part by Sandia's LDRD program and US DOE-NNSA contract DE-AC04-94AL85000. [Preview Abstract] |
Monday, October 31, 2016 3:24PM - 3:36PM |
CO8.00008: Fuel magnetization without external field coils (AutoMag) Stephen Slutz, Christopher Jennings, Thomas Awe, Gabe Shipley, Derek Lamppa, Ryan McBride Magnetized Liner Inertial Fusion (MagLIF) has produced fusion--relevant plasma conditions on the Z accelerator where the fuel was magnetized using external field coils [S.A. Slutz et al. Phys. Plasmas 17, 056303 (2010); M.R. Gomez et al. Phys. Rev. Lett. \textbf{113}, 155003 (2014)]. We present a novel concept that does not need external field coils. This concept (AutoMag) magnetizes the fuel during the early part of the drive current by using a composite liner with helical conduction paths separated by insulating material. The drive is designed so the current rises slowly enough to avoid electrical breakdown of the insulators until a sufficiently strong magnetic field is established. Then the current rises more quickly, which causes the insulators to break down allowing the drive current to follow an axial path and implode the liner. Low inductance magnetically insulated power feeds can be used with AutoMag to increase the drive current without interfering with diagnostic access. [Preview Abstract] |
Monday, October 31, 2016 3:36PM - 3:48PM |
CO8.00009: Ion Acceleration in Megaampere Deuterium Gas-Puff Z-Pinch D, Klir, J. Cikhardt, B. Cikhardtova, J. Kravarik, P. Kubes, V. Munzar, K. Rezac, O. Sila, A. Shishlov, R. Cherdizov, F. Fursov, V. Kokshenev, B. Kovalchuk, N. Kurmaev, A. Labetsky, N. Ratakhin, G. Dudkin, V. Padalko, J. Krasa, K. Turek Acceleration of ions to high energies was observed in deuterium z-pinches already at the beginning of the fusion research in the 1950s. Even though the ion acceleration mechanism in z-pinches and dense plasma foci has been studied for decades, it is still a source of controversy which has not been resolved. Recently, the ion emission has been researched at a 3 MA current on the GIT-12 generator (IHCE in Tomsk). When an outer hollow cylindrical plasma shell was injected around an inner deuterium gas puff, a larger amount of current was assembled on the z-pinch axis at stagnation. After the disruptive development of m$=$0 necks, hydrogen ions were accelerated up to 40 MeV energies. Comprehensive diagnostics of multi-MeV protons and deuterons provided unique information about the ion acceleration in z-pinches. The better knowledge of the ion emission was used to increase the neutron yield above 10$^{\mathrm{13}}$. A large amount of experimental data from various ion diagnostic instruments is also useful for validation of numerical codes and verification of various hypotheses about the ion acceleration mechanism in z-pinches. [Preview Abstract] |
Monday, October 31, 2016 3:48PM - 4:00PM |
CO8.00010: Enhancing X-ray Output with a Gas-Puff Based Plama Opening Switch Joseph Engelbrecht, Nicholas Ouart, Niansheng Qi, Philip de Grouchy, Tatiana Shelkovenko, Sergei Pikuz, Jacob Banasek, William Potter, Lauren Ransohoff, Sophia Rocco, John Giuliani, David Hammer, Bruce Kusse This talk introduces an idea for employing a low density gas-puff implosion as a plasma opening switch to rapidly transfer a current pulse into a more inductive load. A gas-puff on axial wire configuration is used to investigate the promise of this opening switch as a means of increasing the x-ray yield from the wire. We demonstrate the development of this configuration into a tunable current switch, and present promising x-ray measurements which suggest that this switch merits further investigation into its potential usefulness in x-ray source applications. [Preview Abstract] |
Monday, October 31, 2016 4:00PM - 4:12PM |
CO8.00011: Transition from Beam-Target to Thermonuclear Fusion in High-Current Deuterium Z-Pinch Simulations Dustin Offermann, Dale Welch, Dave Rose, Carsten Thoma, Robert Clark, Chris Mostrom, Andrea Schmidt, Anthony Link Fusion yields from dense, \textit{Z}-pinch plasmas are known to scale with the drive current, which is favorable for many potential applications. Decades of experimental studies, however, show an unexplained drop in yield for currents above a few mega-ampere (MA). In this work, simulations of DD Z-Pinch plasmas have been performed in 1D and 2D for a constant pinch time and initial radius using the code L\textsc{SP}, and observations of a shift in scaling are presented. The results show that yields below 3 MA are enhanced relative to pure thermonuclear scaling by beamlike particles accelerated in the Rayleigh-Taylor induced electric fields, while yields above 3 MA are reduced because of energy lost by the instability and the inability of the beamlike ions to enter the pinch region. [Preview Abstract] |
Monday, October 31, 2016 4:12PM - 4:24PM |
CO8.00012: High-Energy Ion Acceleration Mechanisms in a Dense Plasma Focus Z-Pinch D.P. Higginson, A. Link, A. Schmidt, D. Welch The compression of a Z-pinch plasma, specifically in a dense plasma focus (DPF), is known to accelerate high-energy electrons, ions and, if using fusion-reactant ions (e.g. D, T), neutrons. The acceleration of particles is known to coincide with the peak constriction of the pinch, however, the exact physical mechanism responsible for the acceleration remains an area of debate and uncertainty. Recent work has suggested that this acceleration is linked to the growth of an m$=$0 (sausage) instability that evacuates a region of low-density, highly-magnetized plasma and creates a strong (\textgreater MV/cm) electric field. Using the fully kinetic particle-in-cell code LSP in 2D-3V, we simulate the compression of a 2 MA, 35 kV DPF plasma and investigate in detail the formation of the electric field. The electric field is found to be predominantly in the axial direction and driven via charge-separation effects related to the resistivity of the kinetic plasma. The strong electric and magnetic fields are shown to induce non-Maxwellian distributions in both the ions and electrons and lead to the acceleration of high-energy tails. We compare the results in the kinetic simulations to assumptions of magnetohydrodynamics (MHD). Prepared by LLNL under Contract DE-AC52-07NA27344. [Preview Abstract] |
Monday, October 31, 2016 4:24PM - 4:36PM |
CO8.00013: The Effect of Driver Rise-Time on Pinch Current and its Impact on Plasma Focus Performance and Neutron Yield Jason Sears, Andrea Schmidt, Anthony Link, Dale Welch Experiments have suggested that dense plasma focus (DPF) neutron yield increases with faster drivers [Decker NIMP 1986]. Using the particle-in-cell code LSP [Schmidt PRL 2012], we reproduce this trend in a kJ DPF [Ellsworth 2014], and demonstrate how driver rise time is coupled to neutron output. We implement a 2-D model of the plasma focus including self-consistent circuit-driven boundary conditions. Driver capacitance and voltage are varied to modify the current rise time, and anode length is adjusted so that run-in coincides with the peak current. We observe during run down that magnetohydrodynamic (MHD) instabilities of the sheath shed blobs of plasma that remain in the inter-electrode gap during run in. This trailing plasma later acts as a low-inductance restrike path that shunts current from the pinch during maximum compression. While the MHD growth rate increases slightly with driver speed, the shorter anode of the fast driver allows fewer e-foldings and hence reduces the trailing mass between electrodes. As a result, the fast driver postpones parasitic restrikes and maintains peak current through the pinch during maximum compression. The fast driver pinch therefore achieves best simultaneity between its ion beam and peak target density, which maximizes neutron production. [Preview Abstract] |
Monday, October 31, 2016 4:36PM - 4:48PM |
CO8.00014: Axial characterization of particle beams emitted by conical wire array Z-pinches Gonzalo Munoz-Cordovez, Felipe Veloso, Vicente Valenzuela-Villaseca, Milenko Vescovi, Mario Favre, Edmund Wyndham The dynamics of the plasma and the emission of particle beams from tungsten conical wire arrays are experimentally studied in the Llampudken generator (400 kA in 300 ns) [1]. Particles are detected axially using biased Faraday cups and silicon substrates located at tens of centimeters above the array at different heights. Several ion pulses with kinetic energy \textasciitilde 90 eV preceded by an electron beam are measured using time of flight (ToF), whereas the deposition of tungsten on silicon substrates is observed. In addition, ToF indicates that the emission of the beam occurs during the formation of the precursor (i.e., during the implosion of the array) observed by time-resolved laser probing and XUV imaging. The results might indicate that outflows from conical wire arrays propagate much further away than the observations made after laser and XUV images from conical arrays suggesting densities below the detection limits of these diagnostics. [1] H. Chuaqui, et al. Laser Part. Beams 15, 241-248 (1997) [Preview Abstract] |
Monday, October 31, 2016 4:48PM - 5:00PM |
CO8.00015: Mixed and Uniform Double Planar Wire Arrays on University of Michigan's Linear Transformer Driver. A.S. Safronova, V.L. Kantsyrev, I.K. Shrestha, V.V. Shlyaptseva, M.T. Schmidt-Petersen, C.J. Butcher, E.E. Petkov, A. Stafford, M.C. Cooper, A.M. Steiner, D.A. Yager-Elorriaga, N.M. Jordan, R.M. Gilgenbach Uniform Double Planar Wire Arrays (DPWA), which consist of two parallel planes of wires of the same material, have previously demonstrated high radiation efficiency, compact size, and usefulness for various applications in experiments on a University-scale high impedance Z-pinch generator. We have already reported on the outcome of the first experiments with uniform Al DPWAs on the University of Michigan's low-impedance Linear Transformer Driver (LTD) MAIZE generator [A.S. Safronova \textit{et al}, IEEE Trans. Plasma Sci. 44, 432 (2016)]. Here we present the most recent results on the experiments with both uniform (Al wires) and mixed (one plane from Al and another plane from stainless steel or copper wires) DPWAs produced using a diagnostic set similar to the first campaign, including: filtered X-ray diodes, X-ray spectrographs and pinhole cameras, but with a new four frame shadowgraphy system with 2-ns, 532 nm frequency doubled Nd:YAG laser that was further upgraded to a twelve frame shadowgraphy system. Application of different wire planes and much longer period of time observed by the shadowgraphy led to the new results about wire array implosions on the LTD device. [Preview Abstract] |
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