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 YM10: Mini-Conference: Mixing in Fusion Plasmas III |
Hide Abstracts |
Chair: Daniel S. Clark, Lawrence Livermore National Laboratory Room: Governor's Square 17 |
Friday, November 15, 2013 9:30AM - 9:58AM |
YM10.00001: Hydrodynamic instability experiments in ICF, materials science, and astrophysics Bruce A. Remington We have been developing high energy density (HED) experiments on high power inertial confinement fusion (ICF) lasers over the past two decades that span (1) the radiative hydrodynamics of ICF capsule physics; (2) the high pressure, high strain rate, solid-state dynamics relevant to novel concepts for ICF and hypervelocity impacts in space and on Earth; and (3) the shock driven turbulence of exploding stars (supernovae). These different regimes are separated by many orders of magnitude in length, time, and temperature, yet there are common threads that run through all of these phenomena, such as the occurrence of hydrodynamic instabilities. Examples from each of these three seemingly very disparate regimes are given, and the common theme of hydrodynamic instability evolution is explored. [Preview Abstract] |
Friday, November 15, 2013 9:58AM - 10:17AM |
YM10.00002: Favorable effects of turbulent plasma mixing on the performance of innovative tokamak divertors D.D. Ryutov, R.H. Cohen, T.D. Rognlien, M.V. Umansky The problem of reducing the heat load on plasma-facing components is one of the most demanding issues for MFE devices. The general approach to the solution of this problem is the use of a specially configured poloidal magnetic field, so called magnetic divertors. In recent years, novel divertors possessing the 2-nd and 3-rd order nulls of the poloidal field (PF) have been proposed. They are called a ``snowflake'' (SF) [1] and a ``cloverleaf'' (CL) [2] divertor, respectively, due to characteristic shape of the magnetic separatrix. Among several beneficial features of such divertors is an effect of strong turbulent plasma mixing that is intrinsic to the zone of weak PF near the null-point [3]. The turbulence spreads the heat flux between multiple divertor exhaust channels and increases the heat flux width within each channel. Among physical processes affecting the onset of convection the curvature-driven mode of axisymmetric rolls is most prominent. The effect is quite significant for the SF and is even stronger for the CL divertor. Projections to future ITER-scale facilities are discussed.\\[4pt] [1] D.D. Ryutov. Phys. Plas., 14, 064502 (2007);\\[0pt] [2] D.D. Ryutov, M.V. Umansky. Phys. Plas., Submitted, June 2013;\\[0pt] [3] D.D. Ryutov, R.H. Cohen, T.D. Rognlien, M.V. Umansky. PPCF, 54, 124050 (2012). [Preview Abstract] |
Friday, November 15, 2013 10:17AM - 10:36AM |
YM10.00003: Shock-induced perturbation evolution in planar laser targets Y. Aglitskiy, M. Karasik, A.L. Velikovich, V. Serlin, J.L. Weaver, T.J. Kessler, A.J. Schmitt, S.P. Obenschain, N. Metzler, J. Oh Experimental studies of hydrodynamic perturbation evolution triggered by a laser-driven shock wave in a planar target done on the KrF Nike laser facility are reported. The targets were made of solid plastic and/or plastic foam with single mode sinusoidal perturbation on the front or back surface or plastic/foam interface. Two specific cases are discussed. When a planar solid plastic target rippled at the front side is irradiated with a 350 ps long laser pulse, ablative Richtmyer-Meshkov (RM) oscillation of its areal mass modulation amplitude is detected while the laser is on, followed by observed strong oscillations of the areal mass in the unsupported shock flow after the laser pulse ends. When the target is rippled at the rear side, the nature of the perturbation evolution after the shock breakout is determined by the strength of the laser-driven shock wave. At pressure below 1 Mbar shock interaction with rear-surface ripples produces planar collimated jets manifesting the development of a classical RM instability in a weakly compressible shocked fluid. At shock pressure $\sim$ 8 Mbar sufficient for vaporizing the shocked target material we observed instead the strong areal mass oscillations characteristic of a rippled centered rarefaction wave. [Preview Abstract] |
Friday, November 15, 2013 10:36AM - 10:55AM |
YM10.00004: Instabilities in counterstreaming plasmas Hye-Sook Park We are performing high power laser experiments showing large, stable, reproducible electromagnetic field structures that arise in counter-streaming interpenetrating supersonic plasma flows in the laboratory. Self organization, whereby energy progressively transfers from smaller to larger scales in an inverse cascade, is widely observed in fluid flows, such as in the nonlinear evolution of multimode Rayleigh-Taylor and Kelvin-Helmholtz instabilities. There are many scenarios in astrophysics where self organization involving magnetic or electric fields in collisionless settings is observed. These surprising structures, predominantly oriented transverse to the primary flow direction, extend for much larger distances than the intrinsic plasma spatial scales, and persist for much longer than the plasma kinetic timescales. Their origin may be magnetic field advection from the recompression of the Biermann battery fields in the midplane. Understanding interactions of high velocity plasma flows is interests to the ICF and astrophysics. This paper will present experimental results and interpretation of these counterstreaming plasma experiments. [Preview Abstract] |
Friday, November 15, 2013 10:55AM - 11:14AM |
YM10.00005: Shear suppression of turbulent transport in a magnetized laboratory plasma Troy Carter, David Schaffner, Brett Friedman, Giovanni Rossi, Daniel Guice, Stephen Vincena The Large Plasma Device (LAPD) is 17m long, 60 cm diameter magnetized plasma column with typical plasma parameters: $n_e \sim 1 \times 10^{12}$ cm$^{-3}$, $T_e \sim 10$eV, and $B \sim 1$kG. Broadband, fully-developed turbulence is observed in the edge of the LAPD plasma along with spontaneously driven azimuthal flows. Azimuthal flow and flow shear is varied continuously via a biased limiter. Turbulent particle flux and radial correlation length are observed to decrease with increasing shear [1]. The decrease occurs with shearing rates which are comparable to the inverse turbulent autocorrelation time in the zero flow state. The control over edge flows and flow shear and extensive measurement capability in LAPD provides an opportunity to validate edge turbulence models. LAPD turbulence has been modeled using the 3D Braginskii fluid turbulence code BOUT++. Good qualitative and semi-quantitative agreement is found between BOUT++ simulations and LAPD experimental measurements [2]. Analysis of nonlinear BOUT++ simulations indicates that a nonlinear instability controls the saturated turbulent state. \\[4pt] [1] D.A. Schaffner, et al., Phys. Rev. Lett. 109, 135002 (2012)\\[0pt] [2] B. Friedman, et al., Phys. Plasmas 20, 055704 (2013) [Preview Abstract] |
Friday, November 15, 2013 11:14AM - 11:33AM |
YM10.00006: Asymmetric Diffusion of Magnetic Field Lines Andrey Beresnyak Charged particles in magnetized plasmas move preferentially along magnetic field lines. The perpendicular transport and mixing are suppressed in quiet, laminar plasmas. In turbulent plasmas, however, magnetic field lines are stochastic and this accounts for a big part of perpendicular transport. Magnetic field lines separate faster than diffusively in turbulent plasma, which is called superdiffusion. Furthermore, we discovered that this superdiffusion is, in general, asymmetric, so that the separation of field lines along the magnetic field direction is different from the separation in the opposite direction, if the symmetry of the flow is broken by the so-called imbalance or cross-helicity. The difference between forward and backward diffusion, however, is not directly due to imbalance, but a non-trivial consequence of both imbalance and non-reversibility of turbulence. The asymmetric diffusion perpendicular to the mean magnetic field entails a variety of new physical phenomena, such as the production of parallel particle streaming in the presence of perpendicular gradients. Such streaming and associated instabilities are important for particle transport in laboratory, space, and astrophysical plasmas. [Preview Abstract] |
Friday, November 15, 2013 11:33AM - 11:52AM |
YM10.00007: Magnetic Flux Ropes, Reconnection and Chaotic Fields and Flows Walter Gekelman Many systems in nature become chaotic when a threshold is crossed. Magnetic Flux Ropes are no exception. Magnetic field lines and plasma flows can become chaotic during reconnection. The ropes which are formed in a magnetized background plasma are kink unstable, twist, writhe and collide as they kink. Three dimensional magnetic fields and flows are measured at thousands of time steps and up to 50,000 spatial locations. The field lines are computed by conditionally averaging the data; when chaos sets-in, many ``shots'' are rejected by the averaging processes. This results in what is most interesting but cannot be seen. Recently, mathematical tools have been developed to identify chaotic dynamics. Permutation entropy can be calculated from measured time series and used to calculate a position on a Jensen-Shannon complexity (C-H) plane$^{\mathrm{1}}$. The location of data points on this plane indicates if the magnetic fields are stochastic, or fall into regions of minimal or maximal complexity. Various chaotic dynamical models provide a proxy for the chaotic region in this plane. The behavior of the flux ropes falls in the region of the C-H plane where chaotic systems lie. The entropy and complexity change in space and time, which reflects the type of dynamics associated with the ropes. C-H plane identification process has also been used in the study of temperature filaments$^{\mathrm{2}}$ and can be applied to spacecraft, solar or fusion data. Other examples will be shown. $^{\mathrm{1}}$ O. Russo et al., Phys. Rev. Lett., 99, 154102 (2007),$^{\mathrm{2}}$ J. Maggs, G.Morales, Plasma Phys Contr. Fusion 55, 085015 (2013) [Preview Abstract] |
Friday, November 15, 2013 11:52AM - 12:11PM |
YM10.00008: Nonlinear motion of non-uniform current-vortex sheets in MHD Richtmyer-Meshkov instability Chihiro Matsuoka, Katsunobu Nishihara, Takayoshi Sano When a supernova explosion occurs, materials that composed the star scatter in a high speed with a strong shock wave. These scattered materials, called ``supernova remnants'' (SNR), expand into the space and finally become a source in order to create new solar systems. It is known that SNR have a strong magnetic field compared to the surrounding interstellar medium; however, there exist few models to explain this extraordinary magnetic amplification mechanism in SNR. Here, we consider the Richtmyer-Meshkov instability in magnetohydrodynamic flows (MHD-RMI) and construct a model in order to describe the magnetic amplification in SNR. Due to the existence of the density jump, the tangential component of the magnetic field between the interface is different; therefore, the interface in MHD-RMI becomes a (non-uniform) current-vortex sheet. In this study, we investigate motion of this current-vortex sheet using the vortex blob method. We show that the current induced on a vortex sheet leads to a strong amplification of the magnetic field when the Lorenz force term is sufficiently small, and present various interfacial profiles depending on the magnitude of the Atwood number and Lorenz force. [Preview Abstract] |
Friday, November 15, 2013 12:11PM - 12:30PM |
YM10.00009: Multi-Scale Nested Simulations of Plasma Instabilities: Turbulent Mixing and Lagrangian Dynamics in Ionospheric Plasma Flows Alex Mahalov Turbulent hydrodynamic mixing induced by the Rayleigh-Taylor (RT) instabilities occurs in settings as varied as exploding stars (supernovae), inertial confinement fusion (ICF), and macroscopic flows in fluid dynamics such as ionospheric plasmas Nested numerical simulations of ionospheric plasma density structures associated with nonlinear evolution of the Rayleigh-Taylor (RT) instability in Equatorial Spread F (ESF) are presented. The equation for the electric potential is solved at each time step with a multigrid method. For the limited area and nested simulations, the lateral boundary conditions are treated via implicit relaxation applied in buffer zones where the density of charged particles for each nest is relaxed to that obtained from the parent domain. The high resolution in targeted regions offered by the nested model was able to resolve secondary RT instabilities, and to improve the resolution of the primary RT bubble compared to the coarser large domain model. Our studies focus on the charge-neutral interactions and the statistics associated with stochastic Lagrangian motion. In particular, we examine the organizing mixing patterns for plasma flows due to polarized gravity wave excitations in the neutral field, using Lagrangian coherent structures (LCS). [Preview Abstract] |
Follow Us |
Engage
Become an APS Member |
My APS
Renew Membership |
Information for |
About APSThe American Physical Society (APS) is a non-profit membership organization working to advance the knowledge of physics. |
© 2024 American Physical Society
| All rights reserved | Terms of Use
| Contact Us
Headquarters
1 Physics Ellipse, College Park, MD 20740-3844
(301) 209-3200
Editorial Office
100 Motor Pkwy, Suite 110, Hauppauge, NY 11788
(631) 591-4000
Office of Public Affairs
529 14th St NW, Suite 1050, Washington, D.C. 20045-2001
(202) 662-8700