Bulletin of the American Physical Society
54th Annual Meeting of the APS Division of Plasma Physics
Volume 57, Number 12
Monday–Friday, October 29–November 2 2012; Providence, Rhode Island
Session CO5: Liners, Gas Discharges, Rayleigh-Taylor |
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Chair: Patrick Knapp, Sandia National Laboratories Room: 552AB |
Monday, October 29, 2012 2:00PM - 2:12PM |
CO5.00001: ABSTRACT WITHDRAWN |
Monday, October 29, 2012 2:12PM - 2:24PM |
CO5.00002: Metal Liner Implosions for Cylindrical Convergent Isentropic Compression of Deuterium and its Application to MAGLIF Marcus Weinwurm, Brian Appelbe, Jonathan Skidmore, Simon Bland, Jeremy Chittenden Isentropic Compression Experiments on pulsed power machines in the field of High Energy Density Physics have gained interest in recent years. We describe a method of isentropically compressing cryogenic Deuterium inside a metal liner. Pulse shaping was performed by solving Kidder's homogeneous isentropic compression for cylindrical geometry and extending it to an arbitrary Equation of State. The obtained pulse shape enables us to simulate a cylindrically convergent ramp wave, which quasi-isentropically compresses the Deuterium fill to densities much higher than achievable by using a standard pulse. The effect of Rayleigh-Taylor instabilities upon the peak density achieved is evaluated using the resistive magneto-hydrodynamics code Gorgon for a maximum current of 25 MA. Therefore, isentropic liner implosions are a promising technique for recreating the conditions present in the interiors of gas giants. We applied this technique to the High-Gain Magnetized Liner Inertial Fusion (MAGLIF) scheme [1]. There a metal liner is filled with DT gas surrounded by a layer of DT ice. We show how the current pulse can be shaped in order to isentropically compress the DT ice layer. By doing so, we keep the fuel at low temperature. This maximises the compression of the DT ice layer, and increases rho-r at stagnation. Burn wave propagation in the isentropically compressed fuel is compared to propagation in fuel compressed by a standard current pulse. \\[4pt] [1] S.A. Slutz and R. A. Vesey, Phys. Rev. Lett. 108, 025003 (2012) [Preview Abstract] |
Monday, October 29, 2012 2:24PM - 2:36PM |
CO5.00003: Cylindrical Effects on Magneto-Rayleigh-Taylor Instability Matthew Weis, Yue Ying Lau, Ronald Gilgenbach, Christopher Jennings, Mark Hess This paper concentrates on the effects of cylindrical geometry on the magneto-Rayleigh-Taylor instability (MRT), a major concern in the magnetized liner inertial fusion concept (MagLIF) [1]. Several issues are being studied, such as the Bell-Plesset effect [2], the effects of magnetic shear and feedthrough [3], and the nonzero MRT growth rate that remains (but was hardly noticed) in the k = m = 0 limit in Harris' seminal paper on a cylindrical liner [4], where k and m are respectively the azimuthal and axial wavenumber. We shall use simulation and direct integration of the eigenvalue equation to investigate the importance of the cylindrical geometry, which is particularly relevant in the final stage of compression in the MagLIF concept. \\[4pt] [1] S. A. Slutz, et. al, Phys. Plasmas 17, 056303 (2010). \\[0pt] [2] G. I. Bell, Los Alamos Scientific Laboratory, Report LA-1321 (1951); M. S. Plesset, J. Appl. Phys. 25, 96 (1954).\\[0pt] [3] P. Zhang et al., Phys. Plasmas 19, 200703 (2012); Y. Y. Lau et al., Phys. Rev. E 83, 006405 (2011). \\[0pt] [4] E. G. Harris, Phys. Fluids 5, 1057 (1962). [Preview Abstract] |
Monday, October 29, 2012 2:36PM - 2:48PM |
CO5.00004: Kr Z-Pinch Simulations Using Different Models for Radiation Transport J.L. Giuliani, J.W. Thornhill, A. Dasgupta, J.P. Apruzese, D.J. Ampleford, B. Jones In a Z pinch of moderate to high atomic number material, the radiation can control the dynamics of the plasma during stagnation on axis. In this work we study the power and yield from a Kr gas puff on the refurbished Z generator using the MACH2-TCRE simulation code in R-Z coupled to four different models for the radiation transport of bound-bound transitions within the probability-of-escape formalism: optically thin, strictly local, on-the-spot approximation, and non-local which includes absorption in distant zones. In the thin case the K-shell yield is about twice the 14 kJ yield seen for the non-local transport and the total peak power varies by an order of magnitude. Moreover the density, temperatures, and velocity vary significantly with the model employed. In particular, the thin approach leads to large velocity gradients at implosion not found with the non-local model. This result suggests that the reduced line opacity due to the inclusion of Doppler shifts could significantly affect the plasma dynamics and Kr K-shell emission. Consequently we extend the non-local transport model to a fifth one that is multi-frequency and can thereby, for the first time, account for Doppler shifts in an R-Z time-dependent simulation of a Z-pinch. [Preview Abstract] |
Monday, October 29, 2012 2:48PM - 3:00PM |
CO5.00005: Cylindrical Liner Z-pinch Experiments on the MAGPIE Generator Guy Burdiak, Sergey V. Lebedev, Adam J. Harvey-Thompson, George F. Swadling, Francisco Suzuki-Vidal, Jonathan Skidmore, Lee Suttle, Essa Khoory, Louisa Pickworth, Philip de Grouchy, Gareth N. Hall, Simon N. Bland, Marcus Weinwurm, Jeremy P. Chittenden Experimental data from gas-filled cylindrical liner z-pinch experiments is presented. The MAGPIE current (1.4 MA, 240 ns) is applied to a thin walled (80um) Al tube with a static gas-fill inside. The system is diagnosed axially using interferometry, optical streak photography and optical spectroscopy. We observe a series of cylindrically converging shock waves driven into the gas-fill from the inside liner surface. No bulk motion of the liner occurs. The timing of the shocks and their trajectories provide information on the shock launching mechanisms. This in turn allows a study of the response of the liner to the current pulse. Shock wave timing is compared to measurements of the liner resistance and optical images of the liner's outside surface. The system provides a useful, essentially 1D problem for testing MagLIF relevant MHD codes, particularly with regards to EOS, strength and resistivity models. This work may also be relevant to the study of shocks in astrophysical plasmas. The shocks launched into the gas radiatiate strongly; spatially resolved optical spectroscopy data and radial electron density profiles from interferometry images provide evidence for a radiative precursor ahead of the first shock. Instabilities are seen to develop in the downstream regions. [Preview Abstract] |
Monday, October 29, 2012 3:00PM - 3:12PM |
CO5.00006: Study of the Initiation Phase of Thick, Metallic Liners at 1MA Simon Bott, I.C. Blesener, C.L. Hoyt, P.A. Gourdain, J.B. Greenly, D.A. Hammer, B.R. Kusse, J.P. Chittenden, M. Weinwurm, M.E. Cuneo We present a study investigating the initiation of plasma in solid, metallic liners where the liner thickness is large compared to the collisionless skin depth. The current pulse on the 1 MA, 100ns COBRA generator is comparable to the early stages of the current pulse on the Z generator, and studies in the low current regime may highlight details of the liner initiation pertinent to the MagLIF fusion scheme [1]. We present optical emission data from aluminum liners using gated imaging and streak photography, which show a dependence of onset of emission with the size of a small power-feed gap introduced at the cathode. We also show measurements of the B-field inside the liner, using miniature Bdot probes, which show a dependence on the liner diameter and thickness. These data will be compared to magneto-hydrodynamic simulations. Sandia National Laboratories is a multi-program laboratory managed and operated by Sandia Corporation, a wholly owned subsidiary of Lockheed Martin Corporation, for the U.S. Department of Energy's National Nuclear Security Administration under contract DE-AC04-94AL85000. Work at Cornell University is supported by the NNSA-SSAA through Cooperative Agreement DE-FC03-02NA00057. \\[4pt] [1] Slutz et al, Phys Plasmas, 17, 056303 (2010) [Preview Abstract] |
Monday, October 29, 2012 3:12PM - 3:24PM |
CO5.00007: Dynamic Z-pinches for high-gradient, high-current acceleration V. Tang, A. Schmidt, J. Ellsworth, S. Falabella, B. Rusnak, G. Guethlein, G. Akana, E. Cook, S. Hawkins, D. Welch In this talk, we discuss planned experiments on acceleration of an injected ion beam in a Z-pinch plasma with MV/cm gradients and the first fully kinetic simulations of such beam-plasma systems. Multi-MeV, kilo-Ampere ion beams have been produced by 100 kJ class, centimeter scale, Dense Plasma Focus (DPF) Z-pinches. We have now demonstrated similar acceleration gradients in a 1 kJ DPF using a fast capacitive driver. Understanding the mechanisms behind these high gradients is essential for optimizing the device for unique compact accelerator applications. We have an RFQ accelerator producing a 4 MeV deuteron beam for probing the DPF plasma. Using this beam we can directly measure the gradients and demonstrate acceleration of an injected ion beam for the first time. Our fully kinetic particle-in-cell simulations have reproduced observed DPF ion beams. Direct comparisons between the experiment and simulations enhance our understanding of these plasmas and provide predictive design capability. These are the first steps to enabling a technologically simple, compact, high-current, plasma-based accelerator. [Preview Abstract] |
Monday, October 29, 2012 3:24PM - 3:36PM |
CO5.00008: Extreme degree of ionization in micro-capillary plasma columns heated by ultrafast current pulses Jorge Rocca, Jing Li, Gonzalo Avaria, Michael Grisham, Fernando Tomasel, Vyacheslav Shlyaptsev The efficient generation of dense large-scale plasma columns with very high degree of ionization and high homogeneity can enable fundamental plasma studies and a variety of promising applications. We demonstrate the generation of dense large-aspect-ratio plasmas columns with extremely high degree of ionization in micro-capillary channels heated by ultrafast discharge current pulses. Xenon plasma columns were ionized to the Co-like stage (Xe XXVIII) injecting 37 kA current pulses with 4 ns risetime into of 500 micrometer diameter, with lines from the Fe-like ion (Xe XXIX) also visible in the spectra. Sequences of time-resolved filtered pinhole images of the plasma column show a symmetric compression leading to 300: 1 aspect-ration plasma channels. The experimental results, that include ionization of Al impurities up to the H-like stage, support model simulations in showing that rapid ohmic heating of micro-capillary channels with relatively modest currents can generate very hot dense plasma columns which electron temperature could approach 1 KeV. [Preview Abstract] |
Monday, October 29, 2012 3:36PM - 3:48PM |
CO5.00009: Z-pinch research at the Chilean Nuclear Energy Commission: from basic research to portable devices for field applications Gonzalo Avaria, Jose Moreno, Cristian Pavez, Ariel Tarifeno-Saldivia, Marcelo Zambra, Leopoldo Soto Research in pinch discharges at the Chilean Nuclear Energy Commission includes: a) experimental studies in plasma dynamics, stability, X-ray and particles radiation, fusion mechanisms using gas embedded z-pinch, wire arrays and plasma foci; b) development of transportable and portable non radioactive sources based upon plasma focus devices for field applications; c) development and improvements of diagnostics suitable for the extreme conditions of this research. This work will present an overview of recent results in coupling studies of SPEED 2 generator (2.4MA achieved in 450ns) working in cylindrical wire array configuration, as well as the main conclusions from the scalability work in plasma focus devices from MJ to less than 1J. Ultimate results in a 2J portable PF device as non radioactive neutron source for field applications are presented. [Preview Abstract] |
Monday, October 29, 2012 3:48PM - 4:00PM |
CO5.00010: Long-Implosion-Time Z-pinch Experiments with Deuterium Gas-Puffs on the GIT-12 Generator D. Klir, P. Kubes, K. Rezac, J. Cikhardt, J. Kravarik, A. Shishlov, A. Labetsky, F. Fursov, V. Kokshenev, B. Kovalchuk, N. Kurmaev, N. Ratakhin Experiments with deuterium triple shell gas-puffs have been carried out on the GIT-12 generator at the IHCE in Tomsk. Outer, middle, and inner nozzle diameters were 160 mm, 80 mm and 30 mm, respectively. The influence of the mass of deuterium shells on neutron emission times, neutron yields and neutron spectra was studied. The linear mass density of deuterium varied between 50 and 270~$\mu $g/cm. Gas puffs imploded onto the axis before the peak of a generator current at 700-1100 ns. The first neutron peak occurred during the stagnation. Most of the neutrons were emitted during the second neutron pulse after the development of instabilities. In lower mass gas puffs, neutron energies of up to 4.4 MeV gave the evidence of 1 MeV deuterons. The peak neutron yield from D(d,n)$^{3}$He reactions reached 3$\times $10$^{11}$ on a current level of 2.5 MA. Secondary DT neutrons were measured by BDS-10000 bubble detectors. An average neutron yield ratio Y$_{>10 MeV}$/Y$_{2.5 MeV}$ exceeded (6$\pm $3)$\times $10$^{-4}$. Ne-Ne-D$_{2}$ and Ne-D$_{2}$-D$_{2}$ gas puffs produced 3~times lower neutron yields but the first neutron pulse during the stagnation was nearly the same as with D$_{2}$-D$_{2}$-D$_{2}$ gas puffs. [Preview Abstract] |
Monday, October 29, 2012 4:00PM - 4:12PM |
CO5.00011: Improving Agreement between the Neutron Yield Scaling Model of Fast Z-pinches with Experimental Data Using the Time Derivative of the Current Brian Bures, Mahadevan Krishnan The Z-pinch community has accepted a power law scaling of the DD neutron yield with current (Y=aI$^{d})$ for decades. While the exponent, d, in the power law has received much of the attention in literature (3.5$<$d$<$5), the constant, a, relating the neutron yield and the current has received little attention. Yet once an exponent is selected, typically around 4, the experimental data are observed to show a standard deviation of 3000{\%} or more relative to the model prediction with a scalar value for a. We have revised the long standing scaling relationship by replacing this scalar constant with a linear function of the minimum in the time derivative of the current (Y=(bdI/dt+c)I$^{d})$. Our revised scaling relationship reduces the standard deviation in DD neutron yield to $\sim $100{\%} from 25,000{\%}, on Z-pinch machines with peak currents ranging from 60 kA to 18 MA. The improved correlation of measured yield on both I and dI/dt motivates an examination of microscopic dynamics in these pinches., The dI/dt term is related to the pinch voltage that in turn is the source term for the fast ion spectrum that drives beam-target fusion. [Preview Abstract] |
Monday, October 29, 2012 4:12PM - 4:24PM |
CO5.00012: New routes to higher fusion yields in a plasma focus device Eric Lerner, Aaron Blake, Derek Shannon, Fred Van Roessel, Ahmad Talaei, Kyle Lindheimer While fusion yield in plasma focus devices scales as I$^{4}$ to I$^{5}$ up to yields of approximately 1 joule with deuterium fuel, there has been an apparent plateau above that level. In experiments with FF-1, a mega-amp PF facility, we have found that going beyond this plateau requires elimination or extreme minimization of erosion of metals into the plasma sheath. Asymmetric erosion of electrode metals, common in such devices, has a large effect on the mass, velocity, viscosity and magnetization of the filaments, preventing symmetric compression of the dense plasmoid where fusion reactions take place. Such erosion tends to increase with higher currents, blocking higher yields. In addition, simulations have indicated that if the initiation points on the inner edge of the cathode are set too closely, filaments of current will collide chaotically, rather than emerging as isolated and identical structures, also impairing symmetrical compression. We have addressed these various obstacles in a set of experiments and report on results. [Preview Abstract] |
Monday, October 29, 2012 4:24PM - 4:36PM |
CO5.00013: Magnetic Field Generation by the Nonlinear Rayleigh--Taylor Instability in Laser-Driven Planar Plastic Targets L. Gao, I.V. Igumenshchev, S.X. Hu, C. Stoeckl, D.H. Froula, P.M. Nilson, J.R. Davies, R. Betti, D.D. Meyerhofer, M.G. Haines Magnetic field generation during the nonlinear phase of the Rayleigh--Taylor (RT) instability in an ablatively driven plasma using ultrafast laser-driven proton radiography has been measured. Thin plastic foils were irradiated with $\sim $4-kJ, 2.5-ns laser pulses focused to an intensity of $\sim $10$^{14}$ W/cm$^{2}$ on the OMEGA EP Laser System. Target modulations were seeded by laser nonuniformities and amplified during target acceleration by the RT instability. The experimental data show the hydrodynamic evolution of the target and MG-level magnetic fields generated in the broken foil. The experimental data are in good agreement with predictions from 2-D magnetohydrodynamic simulations. This work was supported by the U.S. Department of Energy Office of Inertial Confinement Fusion under Cooperative Agreement No. DE-FC52-08NA28302. [Preview Abstract] |
Monday, October 29, 2012 4:36PM - 4:48PM |
CO5.00014: Experimental Reduction of Laser Imprinting and Rayleigh--Taylor Growth in Spherically Compressed, Medium-\textit{Z}--Doped Plastic Targets G. Fiksel, S.X. Hu, R. Epstein, V.N. Goncharov, D.D. Meyerhofer, T.C. Sangster, B. Yaakobi, M.J. Bonino, R.K. Jungquist, V.A. Smalyuk The effect of medium-$Z$ doping of plastic ablators on laser imprinting and Rayleigh-- Taylor (RT) instability growth was studied using spherical direct-drive implosions on the OMEGA Laser System. The targets were spherical plastic (CH) shells, with an outer diameter of 860~\textit{$\mu $}m and a thickness of 22 \textit{$\mu $}m, doped with a varied concentration of Si (4.3{\%} and 7.4{\%}) and Ge (3.9{\%}). The targets were imploded with 48 beams with a low-adiabat, triple-picket laser shape pulse with a peak intensity of 4 $\times $ 10$^{14}$ W/cm$^{2}$ and a pulse duration of 2.5 ns. The shells were x-ray radiographed through a 400-\textit{$\mu $}m opening in the side of the target. The results show that impurity doping strongly reduces the shell-density modulation and the instability growth rate. The amplitude of the initial imprint is reduced by a factor of 2.5$\pm $0.5 for CH[4.3{\%} Si] targets and a factor of 3$\pm $0.5 for CH[7.4{\%} Si] and CH[3.9{\%} Ge] targets. At the end of the acceleration phase, the reduction factor becomes 3$\pm $0.5 and 5$\pm $0.5, correspondingly. The RT instability growth rate in doped targets is reduced by a factor of 1.5 compared to undoped ones. Simulations using the 2-D radiation--hydrodynamics code \textit{DRACO} show good agreement with the measurements. This work was supported by the U.S. Department of Energy Office of Inertial Confinement Fusion under Cooperative Agreement No. DE-FC52-08NA28302. [Preview Abstract] |
Monday, October 29, 2012 4:48PM - 5:00PM |
CO5.00015: Measurements of modulation growth due to ablative Richtmyer-Meshkov instability using 2D laser-imprinted modulations David Martinez, V.A. Smalyuk, H.-S. Park, B. Remington, A. Casner, L. Masses, B. Delorme, I. Igumenschev, D. Shvarts, Y. Elbaz Unstable growth due to the ablative Richtmyer-Meshkov instability was studied on OMEGA at laser drive intensity of 5e13 W/cm$^{2}$ in a direct drive configuration with a planer CH$_{2}$ foil. Initial 2D modulations with spatial wavelengths of 30, 70, and 120 um were imprinted on targets by laser beams using special 2D phase plates. The evolution of modulations due to the ablative RM instability was measured with x-ray radiography. Measured modulation growth will be presented and compared with predictions of 2D simulations. [Preview Abstract] |
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