Bulletin of the American Physical Society
64th Annual Meeting of the APS Division of Plasma Physics
Volume 67, Number 15
Monday–Friday, October 17–21, 2022; Spokane, Washington
Session TO03: Fundamental Plasmas: Turbulence, Transport, and ShocksLive Streamed
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Chair: Forest Doss, LANL Room: Ballroom 100 C |
Thursday, October 20, 2022 9:30AM - 9:42AM |
TO03.00001: Fluctuations and Intermittent Transport in Single and Multiple Entangled Magnetized Plasma Pressure Filaments Richard D Sydora, Scott Karbashewski, Bart G Van Compernolle, Matthew J Poulos, Thomas Simala-Grant
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Thursday, October 20, 2022 9:42AM - 9:54AM |
TO03.00002: Anisotropic Energy Transfer and Conversion in Magnetized Compressible Turbulence Senbei Du, Hui Li, Zhaoming Gan, Xiangrong Fu We present a spatial filtering (or coarse graining) analysis on 3D magnetized magnetohydrodynamic (MHD) turbulence simulations. The anisotropic filtering allows us to analyze the energy flows perpendicular and parallel to the global mean magnetic field separately. The filtered compressible MHD formulas show transfer of kinetic and magnetic energies from large to small scales, as well as energy conversion between kinetic, magnetic, and thermal energy. We find notable anisotropy for the energy conversion between kinetic and magnetic energy when both velocity and magnetic fluctuations are injected at large scales. While the compressibility of driving force affects the partition of different channels of energy transfer and conversion, the global energy flow remains unchanged qualitatively. |
Thursday, October 20, 2022 9:54AM - 10:06AM |
TO03.00003: Gyrokinetic Simulations of Tearing Mode Evolution Towards Multi-Scale Interactions T. Jitsuk, A. Di Siena, M.J. Pueschel, P.W. Terry, F. Widmer, E. Poli The nonlinear evolution of global tearing modes (TMs) occurs in the reversed field pinch (RFP) and interacts with microturbulence, affecting fluctuation amplitudes and transport. Earlier work used an ad-hoc tearing-type perturbation to model the impact of TMs on microturbulence in local simulations with the gyrokinetic code GENE. Here, the global version of GENE is modified to allow a current-gradient drive by implementing a shifted Maxwellian into the background distribution of the Vlasov equation and coupling it with field equations based on the shifted Maxwellian to reproduce TMs self-consistently. The code is then benchmarked for different computational scenarios, including against the gyrokinetic PIC code ORB5. Various plasma parameters are scanned, including mass ratio, plasma beta, and collisionality. Linear growth rates are in good agreement, and scalings are consistent with theory. The code is then employed to study linear and nonlinear TMs of a non-reversed RFP discharge. Analysis of nonlinear TM saturation is presented. Interactions with trapped- electron modes, effects on zonal flows, and back-reactions on the TMs will be studied by adding small scales in saturation. |
Thursday, October 20, 2022 10:06AM - 10:18AM |
TO03.00004: Differential Cross-Field Ion Transport and Temperature Screening from a Thermodynamic Perspective Elijah J Kolmes, Ian E Ochs, Mikhail Mlodik, Nathaniel Fisch The cross-field accumulation of high-Z impurities follows obeys the same equilibrium condition across a surprisingly wide variety of systems. Information theory and thermodynamics provide a set of tools that makes it possible to explain this behavior in terms of a minimal set of requirements, without any need to solve to the system's equations of motion directly. For a system without temperature gradients, familiar results from impurity transport theory can be recovered by imposing an ambipolarity condition and calculating the system's maximum-entropy state [1]. For a system with temperature gradients, temperature-screening effects can be recovered in a generic linear-response theory by combining ambipolarity with certain symmetries of the transport matrix [2]. |
Thursday, October 20, 2022 10:18AM - 10:30AM |
TO03.00005: Mode coupling, energy transfer, and saturation models of Kelvin-Helmholtz-instability-driven turbulence Bindesh Tripathi, Adrian E Fraser, Paul W Terry, Ellen G Zweibel, M.J. Pueschel Turbulence driven by instability saturates, apart from decay by quasilinear flattening, in a way fundamentally different from the common assumption that all the unstable mode energy cascades to small scales. The difference arises from the nonlinearity that transfers unstable mode energy to the large-scale linearly stable modes, as is shown here for Kelvin-Helmholtz-instability-driven turbulence in both 2 and 3 dimensions. In addition to the traditional diagnostic of scale-interaction between flow and magnetic fields, nonlinear energy transfer between non-orthogonal eigenmodes of shear flow, for the first time, is computed. Examination of three-eigenmode interactions exposes two dominant channels of energy transfer between the unstable and stable modes, which are labeled jointly as discrete modes here. These discrete modes at different wavenumbers interact, channeling nearly 50% of nonlinear energy transfer to the stable modes; the other 40% is transferred when continuum (c) modes mediate three-wave process. A small percentage of total energy transfer is lost to small-scale cascade via c-c mode interactions. With these, a truncated set of equations capturing the dominant energy balance is derived and a solution using a statistical closure approximation is sought. |
Thursday, October 20, 2022 10:30AM - 10:42AM |
TO03.00006: Energy transfer across scales in laser-driven turbulence Hao Yin, Hussein Aluie, Jessica Shang We investigate the kinetic energy (KE) pathways in high-energy-density turbulence by applying the coarse graining approach to decompose scales. Using the FLASH code, we simulate a turbulent jet ablated from an aluminum cone target in both 2D and in 3D, following the configuration by Liao et al. [1]. The KE transfer across scales includes two processes: (i) deformation work, Π, which transfers energy due to multiscale velocity and determines the cascade in constant-density turbulence, and (ii) baropycnal work, Λ, which transfers energy due to pressure and density variations. We show that in both 2D and 3D, the strong shocks and high compressibility levels in our flows lead to a downscale transfer by deformation work, Π, and an upscale transfer by baropycnal work, Λ. However, marked differences between 2D and 3D become apparent when we restrict the analysis to the divergence-free part of the flow, where we find that Π transfers energy upscale in 2D, unlike in 3D. This contributes to the 2D turbulent jet to be more energetic at large scales and to travel faster relative to 3D. |
Thursday, October 20, 2022 10:42AM - 11:06AM |
TO03.00007: Collisional Multi-Ion Cross-Field Transport in Magnetized Plasma. Mikhail Mlodik, Elijah J Kolmes, Ian E Ochs, Nathaniel Fisch Impurity transport is important in a number of applications, including nuclear fusion and plasma mass filters. We find out that the presence of multiple ion species enables plasma to exhibit curious effects such as charge incompressibility, heat pump, and ion stratification when plasma is subjected to external forces or temperature gradient. [1,2] We show that the equilibrium state and the direction of impurity transport strongly depend on plasma magnetization, which is characterized by the ion Hall parameter. [3] Moreover, we find out that the Hall parameter of interest is the ratio of light ion gyrofrequency to collision frequency between light and heavy ion species. Finally, we show that multi-ion transport changes its nature in partially ionized plasma, where ions can be in different charge states. In particular, we find out that partially ionized plasma experiences much faster deconfinement than fully ionized plasma due to the fact that combined presence of cross-field transport, ionization, and recombination leads to net ion charge moving across magnetic field lines on ion-ion transport timescale as opposed to electron-ion transport timescale in the case of fully ionized plasma. |
Thursday, October 20, 2022 11:06AM - 11:18AM |
TO03.00008: On resonance three-wave interactions and strange attractor Sergei I Krasheninnikov, Alexey R Knyazev Nonlinear interactions of waves are important in different media. Specifically, resonant interactions in three- and four-wave clusters play a crucial role in the interaction of waves with disparate scales and in establishing the turbulence spectra in the inertial range of the wave vectors. |
Thursday, October 20, 2022 11:18AM - 11:30AM |
TO03.00009: Turbulent dynamics under two ideal invariants: dynamic phase alignment in plasmas and non-ionized fluids Lucio M Milanese, Nuno F Loureiro, Stanislav A Boldyrev, Maximilian Daschner Turbulent dynamics in the presence of two invariants, e.g., energy and kinetic helicity, is poorly understood in both plasmas and non-ionized fluids. We present results of numerical studies of turbulence in low-$\beta_e$ plasmas at scales below the electron skin depth and turbulence in non-ionized fluids governed by the Navier-Stokes equations. In both systems, the dynamics is dominated by the presence of energy and (generalized) kinetic helicity as two exact invariants. We show that, in the two systems, both invariants are subject to a forward cascade, and we demonstrate that this joint cascade is possible due to the existence of a strong dependence on scale of the Fourier phase alignment angle between, in low-$\beta_e$ plasmas, fluctuations of electric and magnetic potential and, in Navier-Stokes turbulence, fluctuations of velocity and vorticity [L. M. Milanese \textit{et al.}, ``Dynamic Phase Alignment in Inertial Alfv\'en Turbulence", Physical Review Letters, 2020]. This phenomenon, termed \textit{dynamic phase alignment}, thus acquires importance as a mechanism regulating the dynamics in the presence of two invariants, arising from their conservation in the joint direct cascade, regardless of the details of the physical interactions [L. M. Milanese \textit{et al.}, ``Dynamic Phase Alignment in Navier-Stokes Turbulence", Physical Review Letters, 2021]. |
Thursday, October 20, 2022 11:30AM - 11:42AM |
TO03.00010: On the Resilience of Staircase Structure in a Melting Vortex Crystal Flow Fredy R Ramirez, Patrick H Diamond A staircase profile of scalar concentration forms in a simple system of stationary, convective cells, set in a fixed array. In this setup, the interplay of two disparate time scales, the cell turn-over time and the diffusion time determines transport from cell-to-cell. This ratio is the Peclet number (Pe). For Pe>1, there is fast mixing within the cells and slow mixing across the boundaries of the cells. This disparity gives a simple example of staircase formation. Here we study the effects that a fixed global shear and some variability of the spatial pattern of turbulent mixing have on the staircase structure. First, we study the resilience of the staircase by imposing a spatially varying cross-profile shear flow and show that as shearing strength is increased, the staircase profile breaks down and total scalar confinement decreases. Next, we study the staircase structure at different evolutionary stages of a "melting" vortex crystal. The "vortex crystal" is simply the array of cells and "melting" is related to turbulence induced variability in the structure. The goal here is to examine how the staircase evolves as vortex scatter increases. The melting flow structure is created by slowly increasing the Reynolds number in the Navier-Stokes equation which includes a forcing and drag term, thus, scattering the vortex crystal. By injecting a scalar concentration into the crystal, we observe that the scalar forms a flamelet network pattern (i.e., scalar flows along and around vortices). On a global scale, this forms a web structure, thus, showing the scalar's path in the flow. By systematically varying the vortex crystal state (i.e., Reynolds number), one uncovers that the staircase structure is resilient and that the web is not destroyed though "holes" do appear. The relation between the web and staircase structures (i.e., mergers) is elucidated. |
Thursday, October 20, 2022 11:42AM - 11:54AM |
TO03.00011: Particle accceleration in relativistically hot plasmas Cristian S Vega, Stanislav A Boldyrev, Vadim S Roytershteyn In a weakly collisional plasma, particle interactions with turbulent fluctuations may lead to plasma heating. In recent numerical kinetic studies of relativistically hot plasmas, a power law tail was observed in the particle energy distribution function at ultra-relativistic energies (e.g., [1], [2]). In our previous work we proposed a phenomenological model of particle energization in which particles are magnetically trapped and accelerated in turbulent structures until they escape due to pitch angle scattering [3]. A formula for the power law observed in the particle energy pdf was derived and compared to the results of VPIC simulations. On this presentation we discuss this model and check it against a broader range of strengths of the background magnetic field relative to the magnetic fluctuations. |
Thursday, October 20, 2022 11:54AM - 12:06PM |
TO03.00012: A spectroscopic investigation of multi-ion-species plasma shock structures Ameer I Mohammed, Colin S Adams An experimental campaign aims to resolve the structure of shock layers formed during the stagnation of railgun-generated multi-ion-species plasma jets. Recently-published results indicate that these shock structures are collisional, with barodiffusion dominating the diffusive mass flux of light and heavy ions within the shock front. We report spatially-resolved spectroscopy measurements of ionization state and ion species number density within the ion shock layer, addressing their significance with regards to species separation and the role of ionization and non-LTE effects on shock formation and structure. We expect that these results will provide validation for computational models of plasma shocks present in astrophysical plasmas and inertial confinement fusion implosions. |
Thursday, October 20, 2022 12:06PM - 12:18PM |
TO03.00013: Ultrafast laser induced compression in aluminum Sophie E Parsons, Michael R Armstrong, Ross E Turner, Ka Ming Woo, Christian M Childs, Paulius Grivickas, Harry B Radousky, Javier E Garay, Farhat N Beg We report on theoretical and experimental studies of laser induced shock waves in aluminuminduced by a short pulse laser (100ps time scale regime). The main focus is to study the impact of tamper materials and sample geometries on the maximum pressures achievable using tabletop laser system, informing future laser induced shock experiments. We also investigated the hot electron penetration depth in the aluminum using arrival time data to provide a benchmark for the amount of material ablated during compression. Experimental results are used to better understand the underlying physics of laser induced compression in the ultrafast (100ps) time regime at intensities of ≈ 1010W/cm2. Simulations using a hydrocode are aimed to investigate the initial plasma formation in a sample. The simulation is compared to the experimental data with the corresponding sample and laser parameters to test the validity of the codes in the timescales of 100 ps. |
Thursday, October 20, 2022 12:18PM - 12:30PM |
TO03.00014: Collective Modes Associated with Rarefied Populations of Heavy Nuclei Bamandas Basu, Bruno Coppi Plasmas in which low density populations of heavier nuclei than those of the main population are a frequent occurrence [1] and an important case is that of ``impurities'' whose cyclotron frequencies, $Omega_I$, differ from that, $Omega_i$, of the main population. $Omega_I$, ``frequency'' modes are found to be sustained by the impurity density gradient. In the limit of ``short'' transverse wavelengths $k_{perp}^{2}d_{i}^{2}>1$ where $d_{i}={c}/{omega_{pi}}$ these modes are nearly electrostatic while in the relatively long wavelength limit $(k_{perp}^{2}d_{i}^{2}ll1)$ they involve significant magnetic field fluctuations [2]. The relevant transverse phase velocities are in the direction of the local impurity diamagnetic velocity and produce a transport of this population across the magnetic field. Growth rates are found which depend on pre-existing thermal energy transport processes for the same population such as those associated with the excitation of the lower frequency ``impurity drift modes'' introduced in Ref. [3].}\ |
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