Bulletin of the American Physical Society
61st Annual Meeting of the APS Division of Plasma Physics
Volume 64, Number 11
Monday–Friday, October 21–25, 2019; Fort Lauderdale, Florida
Session JM9: Mini-conference: Nonequilibrium Transport, Interfaces, and Mixing in Plasmas II |
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Chair: Walter Gekelman, UCLA Room: Grand C/E |
Tuesday, October 22, 2019 2:00PM - 2:25PM |
JM9.00001: Fluid instabilities and interfacial mixing in high energy density plasmas Snezhana Abarzhi Rayleigh-Taylor instability (RTI) and Rayleigh-Taylor (RT) mixing are common to occur in high energy density plasmas (HEDP) at astrophysical and at atomic scale. Examples include RTI quenching ignition in inertial confinement fusion, blast wave induced RT mixing in core-collapse supernova creating conditions for synthesis of heavy mass elements, and RTI governing material transformation in nano-electronics. By analyzing symmetries of RT dynamics in high energy density plasmas relevant conditions and by focusing on certain patterns of variable acceleration, we discover a special class of self-similar solutions and identify their scaling, correlations and spectra. We find that dynamics of RT mixing can vary from super-ballistic to subdiffusive depending on the acceleration and retain memory of deterministic conditions for any acceleration. These rich dynamic properties considerably impact the understanding and control of RT relevant phenomena in high energy density plasmas. Particularly, they reveal the new mechanism for energy accumulation and transport at small scales in supernova, via energy localization and trapping. [Preview Abstract] |
Tuesday, October 22, 2019 2:25PM - 2:50PM |
JM9.00002: Interfacial instabilities and turbulent plasma mixing in the lab and in geospace Mark Koepke, S.H. Nogami, V. Demidov, K. Gentle Lab and space examples of turbulent instability, growth, and mixing covering a rest-frame frequency range from zero-frequency to lower-hybrid frequency have been benchmarked by laboratory experiments and applied to interpretations of space observations, as reviewed here. Local and nonlocal models of shear-driven D'Angelo, Kelvin--Helmholtz, ion-cyclotron, and lower-hybrid modes guide the laboratory explorations and predict that ion-acoustic, drift, and ion-cyclotron wave turbulence is significantly modified by velocity shear. Experimental efforts to identify mechanism by which turbulent mixing is suppressed in toroidal confinement devices when a radial electric field is externally applied suggest that the interaction between velocity shear and turbulent fluctuations include linear and nonlinear coupling between fluctuations and flows, mode coupling with a stable or damped mode, and changes in phase relationship between density and potential fluctuations. [Preview Abstract] |
Tuesday, October 22, 2019 2:50PM - 3:15PM |
JM9.00003: Stirring Alfv\'{e}n waves with kink oscillations: perpendicular dissipation scales from long parallel wavelength modes Stephen Vincena Magnetic flux ropes and shear Alfv\'{e}n waves occur simultaneously in plasmas ranging from solar prominences, the solar wind, and the earth's magnetotail. If the flux ropes evolve to become unstable to the kink mode, interactions between the kink oscillations and the shear waves can arise, and may even lead to nonlinear phenomena. Experiments aimed at elucidating such interactions are performed in the Large Plasma Device at UCLA. Flux ropes are generated using a LaB$_{6}$ cathode discharge (with L=18 m and $0.01< \beta < 0.1$.) The flux rope (r=8cm) is embedded larger ($r=30$cm) ambient plasma produced by a second, BaO cathode. Shear Alfv\'{e}n waves, with azimuthal mode number, $m=-1$ are launched using an internal antenna. When the flux rope is driven kink unstable, $m=+1$ oscillations arise, and the shear wave develops sidebands separated by the kink frequency. The sidebands are shown to clearly satisfy three-wave azimuthal mode number matching, while modes with larger frequency separation from the driving Alfv\'{e}n wave show decreasing spatial scales approaching dissipation scales ($k_{r} \sim \rho_{s}^{-1}\sim\omega_{pe}/c \sim \rho_{i}^{-1}$). A broadening of the background power spectrum is also observed, and implications for sources in nature are discussed. [Preview Abstract] |
Tuesday, October 22, 2019 3:15PM - 3:35PM |
JM9.00004: Formation of coherent structures in turbulent collisionless interaction of electron and ion streams Igor Kaganovich We have studied several two-stream plasma devices where kinetic effects determine plasma self-organization: neutralization of ion beams and electron cloud effects in accelerators, ExB discharges, current ramp-up in tokamaks. In all three cases we observed a formation of turbulent state with embedded coherent structures. The excitation and propagation of electrostatic solitary waves (ESWs) are observed in two-dimensional particle-in-cell simulations of ion beam neutralization by electron injection by a filament. Electrons from the filament are attracted by positive ions and bounce inside the ion beam pulse. Bouncing back and forth electron streams start to mix, creating two-stream instability. The instability saturates with the formation of ESWs [1]. We have also preformed studies of rotating spoke in a Penning discharge [2]. Transport in spoke is turbulent due to well-developed small scale fluctuations. However, structure itself rotates coherently with a well defined frequency. We have also simulated tokamak start-up stage. Simulation results show development of ion acoustic turbulence with ion holes structures embedded [3]. [1] C. Lan and I. D. Kaganovich, Phys. Plasmas 26, 050704 (2019). [2] A. T. Powis, et al., Phys. Plasmas 25, 072110 (2018). [3]. A. Khrabrov, J. Chen, I. D. Kaganovich, this proceedings (2019). [Preview Abstract] |
Tuesday, October 22, 2019 3:35PM - 3:55PM |
JM9.00005: Nonlinear Simulations of Energetic Particle Effects in Fusion Plasmas. Elena Belova Neutral beam injection is an effective way to heat and sustain plasma in a variety of magnetic confinement concepts. The presence of energetic beam ions can significantly modify both the equilibrium and stability properties of such plasmas, particularly when the injection velocity of the fast ions is larger than the Alfve\textasciiacute n velocity. Possibility of resonant excitation of background plasma eigenmodes and a large Larmor radius of the energetic ions necessitates their kinetic description. Different hybrid MHD/kinetic models introduced to self-consistently couple the bulk fluid plasma with energetic particles are discussed. Results of 3D nonlinear simulations are presented demonstrating that beam-driven modes can significantly modify the transport properties of the background plasma, and channel the energy of the beam ions from the injection region to the location of the resonant mode conversion at the edge of the beam density profile. Unstable eigenmode can cause changes in beam ion distribution, creating an energetic tail and reducing the population of mid-range particles. [Preview Abstract] |
Tuesday, October 22, 2019 3:55PM - 4:15PM |
JM9.00006: Effect of magnetic field to improve energy deposition of relativistic electrons F.N. Beg, D. Kawahito, M. Dozières, P. Forestier-Colleoni, C. McGuffey, S. Hansen, M. Bailly-Grandvaux, K. Bhutwala, M. Wei, C. Krauland, P. Gourdain, J. Davies, K. Matsuo, S. Fujioka, M. Campbell, J. Peebles, J. Santos, D. Batani, S. Zhang A systematic study of relativistic electrons' propagation and energy deposition in a pre-assembled cylindrical plasma under controlled conditions of density and temperature with and without external magnetic field, has been carried out. Understanding the role of magnetic field in relativistic electrons' transport is important for several applications including fast ignition inertial confinement fusion. The OMEGA-60 laser with 36 beams (0.3 TW/beam, 1.5 ns square pulse) was used to compress a CH cylinder filled with Cl-doped CH foam to reach density of about 8 g/cm$^{\mathrm{3}}$ with an initial density of 0.1 g/cm$^{\mathrm{3}}$. OMEGA EP (1 kJ, 10 ps) produced a relativistic electron beam for transport studies. Modeling shows that both the rapidly growing self-generated and compressed external magnetic fields significantly improved the energy coupling to the compressed plasmas, in agreement with experiment. [Preview Abstract] |
Tuesday, October 22, 2019 4:15PM - 4:35PM |
JM9.00007: Non-diffusive asymmetric transport of energetic particles in fusion plasmas Diego Del-Castillo-Negrete, David Zarzoso Energetic particles (EP), i.e. particles with velocities much larger than the thermal speed, are ubiquitous in laboratory and astrophysical plasmas. In laboratory plasmas, the confinement of energetic alpha particles is critical for sustained controlled nuclear fusion. Here we present a study of EP transport in an oscillating radial electric field modeling energetic geodesic acoustic modes. Integration of the guiding-center equations reveals chaotic regions leading to particle losses consistent with those measured in experiments. The nature of the transport is analyzed in detail by focusing on the stochastic separatrix between passing and magnetically trapped orbits. We perform a statistical study of EP injected in the central region of the tokamak and show the existence of super-diffusive (i.e., faster than diffusion) asymmetric transport from the inner (counter-passing) to the outer (co-passing) regions. The particles' exit-time has a fractal dependence on the initial parallel velocity and magnetic moment, and the probability distribution function of displacement exhibits self-similar evolution with anomalous scaling and algebraic decay characteristic of non-Gaussian (Levy) statistics. The physics implications of the observed transport asymmetry are discussed. [Preview Abstract] |
Tuesday, October 22, 2019 4:35PM - 4:55PM |
JM9.00008: Vortex sheet dynamics with bulk point vortices in Richtmyer-Meshkov instability Chihiro Matsuoka Nonlinear interaction between bulk point vortices and the interface in the incompressible Richtmyer-Meshkov instability (RMI) is investigated theoretically and numerically. It is reported that when the vorticity of bulk vortices is small, the interface in RMI is stabilized by the existence of bulk vortices at least in the linear stage [Cobos-Campos and Wouchuk, PRE 93, 053111 (2016)]. In real physical systems, multi-shocks propagates through a multi-layer target for high-density fuel compression in ICF. When a shock wave crosses interfaces, RMI and reflected shocks or rarefaction waves occur at the interfaces. Defects in a target also cause the generation of point-like vortices in bulk when shocks pass through. The vorticity or strength of these defect-induced bulk vortices is not necessarily weak, and they can lead the system to a turbulent state by interacting the interface. Therefore, it is important to know the behavior of the interface or the vortex sheet coexisting with bulk vortices. In the present work, we present a mathematical model to describe the nonlinear interaction between bulk vortices and an interface and report the complicated interfacial shape and the loci of bulk point vortices numerically. [Preview Abstract] |
Tuesday, October 22, 2019 4:55PM - 5:15PM |
JM9.00009: Investigating shock-driven Richtmyer-Meshkov Rayleigh-Taylor ripple evolution before and after re-shock Sabrina R. Nagel, Channing M. Huntington, Ted Baumann, Jason D. Bender, Stephan A. MacLaren, Kumar S. Raman, Ping Wang, Ye K. Zhou Late-time Rayleigh-Taylor(RT)/Richtmyer-Meshkov(RM) instabilities in a planar geometry at high-energy-densities are investigated using a shock-tube containing a pre-machined interface between dense and light materials. The platform uses the NIF laser to indirectly drive a strong shock which turns the initially solid target into a plasma and the material boundary into a fluid interface with the imprinted initial condition. The interface evolves by action of the RT and RM instabilities, and the growth is imaged with backlit x-ray radiography. We present data from experiments using sinusoidal interface perturbations driven from the heavy to the light side. Late-time radiographic images show the initial conditions reaching the deeply nonlinear regime, and an evolution of fine structure consistent with a transition to turbulence. The evolution after re-shock, including a possible loss of initial conditions, and comparisons with post-shot numerical simulations are also discussed. [Preview Abstract] |
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