Bulletin of the American Physical Society
55th Annual Meeting of the APS Division of Plasma Physics
Volume 58, Number 16
Monday–Friday, November 11–15, 2013; Denver, Colorado
Session UM10: Mini-Conference: Mixing in Fusion Plasmas II |
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Chair: Igor Kaganovich, Princeton Plasma Physics Laboratory Room: Governor's Square 17 |
Thursday, November 14, 2013 2:00PM - 2:28PM |
UM10.00001: On fundamentals of Rayleigh-Taylor instabilities and mixing Snezhana I. Abarzhi Rayleigh-Taylor instability (RTI) develops when fluids of different densities are accelerated against the density gradient; extensive inter-facial mixing of the fluids ensues with time. Rayleigh-Taylor (RT) mixing controls a variety of plasma processes in high and low energy density regimes, including supernova explosion, stellar convection, and light-material interaction. RT mixing is a central concern in achieving ignition in fusion plasmas due to the seeding of RTI by the drive and target imperfections. Traditionally, it was presumed that RTI leads to uncontrolled growth of small-scale imperfections, single-scale nonlinear dynamics, and extensive mixing that is similar to canonical turbulence. A need in alternative scenarios is suggested now by the success that was recently achieved on the sides of experiments in high energy density plasmas, large-scale numerical simulations, and rigorous analysis of RTI and RT mixing. We find that RT evolution is essentially multi-scale, and that the properties of RT mixing depart substantially from those of canonical turbulence. The accelerated self-similar RT mixing indeed exhibits more order thus opening new opportunities for its regularization and control in high energy density plasmas. [Preview Abstract] |
Thursday, November 14, 2013 2:28PM - 2:47PM |
UM10.00002: Overview of recent experiments on hydrodynamic instabilities at ablation front Alexis Casner Understanding and mitigating hydrodynamic instabilities is a key element for achieving ignition in Inertial Confinement Fusion (ICF). Cryogenic indirect-drive implosions on NIF have evidenced that the ablative Rayleigh-Taylor Instability (RTI) is the dominant driver of hot spot mix. This motivates in particular the switch to a more forgiving higher adiabat implosion design. After a recall of some results obtained in indirect drive (ID) on the OMEGA laser facility in the last decade, I will explain how the unique capabilities of the National Ignition Facility could be harnessed to accelerate planar samples over much larger distances and longer time periods than previously achieved. I will describe a fundamental science proposal which aims at achieving a highly nonlinear stage for the ablative RTI, a question also of crucial interest in astrophysics. The existence of a turbulent-like regime at ablation front is in fact not precluded and the late-time dynamics of single-mode RTI is a subject of theoretical investigations. On the other hand in direct drive (DD) ICF, laser intensity (and target surface) non uniformities seed the initial conditions of the ablative RTI. I will discuss DD planar experiments devoted to the study of laser imprint perturbations with special phase plates. As it is also the case in ID, simulations of the Richtmyer-Meshkov phase reversal during the shock transit phase is challenging, and of crucial interest because it sets the sign of the RTI growth factors. Future work will try to increase the accuracy of measurements when phase inversion is present, as well as to demonstrate advanced imprint mitigation using underdense foams. [Preview Abstract] |
Thursday, November 14, 2013 2:47PM - 3:06PM |
UM10.00003: Sensitivity of ignition designs to hydrodynamic instabilities Laurent Masse After a short overview of ignition designs we discuss the sensitivity of those designs to hydrodynamics instabilities and the different ways to control them. We discuss in particular the influence of the drive temperature and the different tradeoff leading to a robust design. We finally present an experimental platform [1] aimed to assess a part of the main features of hydrodynamic instabilities in the context of ignition capsules. \\[4pt] [1] A. Casner et al., ``Design and implementation plan for indirect-drive highly nonlinear ablative Rayleigh-Taylor instability experiments on the {N}ational {I}gnition {F}acility,'' Phys. Plasmas, 19, 082708, (2012). [Preview Abstract] |
Thursday, November 14, 2013 3:06PM - 3:25PM |
UM10.00004: Fusion Turbulence without a Toroidal Magnetic Field M.E. Mauel, J. Kesner Three decades since Surko and Slusher\footnote{Surko and Slusher, {\it Science} {\bf 221}, 817 (1983).}, fusion scientists have achieved tremendous progress understanding driven turbulence and turbulent transport in tokamaks. Nonlinear gyrokinetic theory provides a workable formalism for simulating gradient-driven turbulent transport, and recent validation studies in high-power reactor-relevant regimes show important areas of agreement. The new application of nonlinear gryokinetic theory to toroidal magnetic confinement without a toroidal magnetic field is an important opportunity to extend the reach of turbulence models used for magnetic fusion to different geometries, to higher beta plasmas ($\beta \sim 1$), and to plasma confined in magnetospheres. Magnetic geometry strongly influences turbulent mixing, and low-frequency fluctuations are enturely field-aligned for a toroidal plasma confinement by a purely poloidal field. Fusion turbulence without a toroidal field eliminates coupling between parallel streaming and perpendicular decorrelation, drives either a particle pinch or a thermal pinch\footnote{Kesner, {\it et al., Phys Plasmas} {\bf 18}, 050703 (2011).}, and exhibits 2D dynamics and the inverse energy cascade\footnote{Grierson, {\it et al., Phys Plasma} 16, 55892 (2009)} [Preview Abstract] |
Thursday, November 14, 2013 3:25PM - 3:44PM |
UM10.00005: Self Organization Processes in Fusion Burning Plasmas* B. Coppi The presence of self-organization [1] in well confined plasmas was recognized originally [1] on the basis of the radial profiles of the thermal diffusion coefficients derived from relevant experiments. Thus the principle of ``profile consistency'' was proposed, and later, amply reconfirmed and applied to plasma pressure profiles. The radial profiles of the spontaneous rotation velocities investigated in recent years have required [2] the introduction of an inflow velocity, with a ``profile consistency'' feature, in the angular momentum transport equation. In experiments on plasmas close to ignition conditions self-organization should persist, given the variety of factors involved. Then it is justifiable to use transport model based on ``profile consistency,'' such as the so-called Coppi-Tang model [3], in order to simulate plasmas that Ignitor and ITER [3] should produce. *Sponsored in part by the US DOE.\\[4pt] [1] B. Coppi, Comments Pl. Phys. Cont. Fus. 5, 6: 261-270 (1980).\\[0pt] [2] B. Coppi, 18th IAEA Fusion Energy Conf. THP 1/17 (2000) and Nucl. Fus. 42, 1 (2002).\\[0pt] [3] T.A. Kasper, W.H. Meyer et al. Nucl. Fus. 51, 013001 (2011). [Preview Abstract] |
Thursday, November 14, 2013 3:44PM - 4:03PM |
UM10.00006: The growth of Richtmyer-Meshkov instability in magnetized plasma Takayoshi Sano, Katsunobu Nishihara, Chihiro Matsuoka, Tsuyoshi Inoue The Richtmyer-Meshkov instability (RMI) is of crucial importance in a variety of applications including astrophysical phenomena and laboratory experiments. The RMI occurs when an incident shock strikes a corrugated contact discontinuity separating two fluids with different densities. Inclusion of a magnetic field brings two important consequences into the RMI, which are the amplification of an ambient field and the suppression of the unstable motions. We demonstrated that the magnetic field can be amplified by the stretching motions at the interface associated with the RMI. We also investigated numerically the critical strength of a magnetic field required for the suppression of the RMI by using a two-dimensional single-mode analysis. For the cases of MHD parallel shocks, the RMI can be stabilized as a result of the extraction of vorticity from the interface. A useful formula describing a critical condition for MHD RMI has been introduced, and which is successfully confirmed by the direct numerical simulations. The critical field strength is found to be largely depending on the Mach number of the incident shock. If the shock is strong enough, even low-$\beta$ plasmas can be subject to the growth of the RMI. [Preview Abstract] |
Thursday, November 14, 2013 4:03PM - 4:22PM |
UM10.00007: ABSTRACT WITHDRAWN |
Thursday, November 14, 2013 4:22PM - 4:41PM |
UM10.00008: The effects of early time laser drive on NIF hydrodynamic growth J.L. Peterson, D.S. Clark, L.J. Suter, L.P. Masse Defects on inertial confinement fusion capsule surfaces can seed hydrodynamic instabilities, the growth of which can cause the mixing of fuel and ablator material and adversely affect capsule performance. Shocks and rarefactions during the early period of National Ignition Facility (NIF) implosions alter this mixing by determining whether perturbations will grow inward or outward at peak implosion velocity and final compression. In particular, the strength of the first shock, launched at the beginning of the laser pulse, plays an important role in determining Richtmyer-Meshkov (RM) oscillations on the ablation front. These surface oscillations can couple to the capsule interior through subsequent shocks before experiencing Rayleigh-Taylor (RT) growth. We compare radiation hydrodynamic simulations of NIF implosions to analytic theories of the ablative RM and RT instabilities to illustrate how early time laser strength can alter peak velocity growth. \\[4pt] This work was performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344. [Preview Abstract] |
Thursday, November 14, 2013 4:41PM - 5:00PM |
UM10.00009: Modeling Ignition Experiments and the Role of Mix on the National Ignition Facility Daniel Clark, Denise Hinkel, David Eder, Ogden Jones, Steven Haan, Bruce Hammel, Michael Marinak, Jose Milovich, Harry Robey, Jay Salmonson, Richard Town The National Ignition Campaign on the National Ignition Facility (NIF) was completed in September of 2012 with nearly three dozen cryogenic ignition experiments fired. While ignition was not achieved in these experiments, substantial progress was made towards that goal by achieving ignition relevant implosion velocities, high compressions, and high stagnation pressures. At present, larger than anticipated long-wavelength spatial asymmetries and possibly larger than expected instability growth are believed to have been responsible for preventing ignition. Furthermore, detailed 2-D simulations of ignition experiments showed significant discrepancies with measured implosion performance, especially in thermonuclear yield. This talk describes current efforts at improving our understanding of NIF implosion performance and the role mix and instabilities have played in determining that performance. The results of past 2-D simulations will be surveyed and efforts to improve their fidelity and agreement with experimental data will be described. Additionally, the results of 3-D simulations with resolution adequate to model the dominant unstable modes will be presented. While these large-scale simulations show closer agreement with experimental results, discrepancies nonetheless remain. In all cases, the importance of hydrodynamic instabilities and mix is evident and the need to control their growth to achieve ignition will be emphasized. [Preview Abstract] |
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