Bulletin of the American Physical Society
65th Annual Meeting of the APS Division of Plasma Physics
Monday–Friday, October 30–November 3 2023; Denver, Colorado
Session GM10: Mini-Conference: Magnetized Turbulence III |
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Chair: Lingling Zhao, The university of Alabama in Huntsville Room: Governor's Square 17 |
Tuesday, October 31, 2023 9:30AM - 9:46AM |
GM10.00001: Relativistic Kinetic Alfven Turbulence Stanislav A Boldyrev, Cristian S Vega, Vadim S Roytershteyn Turbulence in magnetized astrophysical plasmas (e.g., solar flares, pulsar-wind nebulae, active galactic nuclei jets), as well as plasmas produced in laboratory experiments (intense laser-matter interaction), may include regimes where the speeds of particle thermal motions or of plasma bulk fluctuations are comparable to the speed of light. At scales larger than the plasma micro scales (i.e., particle inertial scales), such turbulence resembles Kolmorogov-like magnetohydrodynamic turbulence. In this presentation, we discuss turbulence at sub-inertial scales, which is analogous to kinetic Alfven turbulence in a non-relativistic plasma. Such turbulence is thought to be responsible for sub-inertial energy cascade as well as particle heating and acceleration. |
Tuesday, October 31, 2023 9:46AM - 10:02AM |
GM10.00002: Magnetized Turbulence with Cosmic Rays and Radiative Cooling Roark S Habegger, Ka Wai Ho, Ka Ho Yuen, Ellen Zweibel
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Tuesday, October 31, 2023 10:02AM - 10:18AM |
GM10.00003: Effective Viscosity, Resistivity and Reynolds Number in Weakly Collisional Plasma Turbulence Yan Yang, Riddhi Bandyopadhyay, Tulasi Parashar, Vadim S Roytershteyn, Alexandros Chasapis, Sean Oughton, Michael A Shay, Francesco Pecora, William H Matthaeus Energy dissipation is an energy conversion process, but specifically emphasizes the transformation of energy into heat. Energy dissipation mechanism for weakly collisional or collisionless plasma is of principal importance for addressing long-standing puzzles like the acceleration of energetic particles and the heating of the solar corona and solar wind. When collisions are strong in a magnetized plasma, standard closures provide simple representations of dissipation in terms of coefficients of viscosity and resistivity. In the opposite limit of weak collisions, the analogous physical effects that lead to dissipation are present, but the simple approximations to describe them, the closures, are not available in general. Fortunately, there is growing evidence suggesting possible similarities of collisionless dissipation to well-studied collisional dissipation. We employ kinetic Particle-in-Cell simulations of proton-electron plasma as well as in-situ observations from the Magnetospheric Multiscale mission, to examine analogous viscous-like and resistive-like scaling in the weakly collisional regime. This intriguing finding allows not only extraction of collisional-like viscosity and resistivity, but also direct determination of effective Reynolds number (in the form of viscosity and resistivity). The effective Reynolds number, as a measure of the available bandwidth for turbulence to populate various scale, links macro turbulence properties with kinetic plasma properties in a novel way. |
Tuesday, October 31, 2023 10:18AM - 10:34AM |
GM10.00004: Temporal Properties of Compressible MHD Turbulence Hui Li, KaHo Yuen, Huirong Yan We will discuss recent results on 4D FFT analysis (temporal plus 3D spatial) of compressible MHD turbulence. Most fluctuation power is found to have nearly zero or very low frequencies with finite wavenumbers. They do not follow the dispersion surfaces of linearized MHD waves, though a very small fraction of the power is observed to fall within the expected dispersion relations for Alfven, Slow, and Fast modes. We present our interpretation of how to understand the temporal behavior in MHD turbulence. The temporal response of any particular wavenumber is shown to be a Lorentzian in frequency. Its profile peaks at the eigenfrequency of a given wave mode (Alfven, Fast, and Slow) but has very broad wings extending to both low and high frequencies. We quantify how the Lorentzian profiles can be used to explain the turbulence simulation results. Implications for understanding space and astrophysical turbulence will be discussed as well. |
Tuesday, October 31, 2023 10:34AM - 10:50AM |
GM10.00005: Do we have critical balance in compressible MHD turbulence? Ka Ho Yuen, Hui Li, Huirong Yan The concept of critical balance in MHD turbulence theory suggests that the ratio between the nonlinear and Alfvén wave propagation times, denoted as χ, is approximately equal to unity across scales, resulting in a scale-dependent anisotropy described by the Goldreich-Sridhar relation (kll~k⊥2/3). The validity of the critical balance postulate is crucial for explaining the underlying physical mechanisms behind various astrophysical and space phenomena. However, recent simulations and space observations reveal that the distribution of χ exhibits a broad wing and is not peaked at unity for all three MHD modes, which challenges the foundations of the Goldreich-Sridhar theory of MHD turbulence. Motivated by the prevalence of non-zero low-frequency fluctuations observed in compressible MHD turbulence, we analytically derive and numerically verify a new form of "generalized critical balance" that is applicable to all three MHD modes. In particular, the compressible modes exhibit distinct scale-independent anisotropic amplitudes, particularly in low β regime. We also discuss the implications of our findings for recent space and astrophysical observations. |
Tuesday, October 31, 2023 10:50AM - 11:06AM |
GM10.00006: Ion and Electron Acceleration in Low-Beta Plasma Turbulence Luca Comisso During this talk, we will discuss how turbulence efficiently accelerates particles in highly magnetized (low-beta) plasmas. We will show that magnetized turbulence accelerates ions and electrons into nonthermal energy distributions with power-law ranges. We find that the ion spectrum is harder than the electron spectrum, and both distributions become harder for lower beta values. We also find that the energization of electrons is accompanied by a significant energy-dependent pitch-angle anisotropy, with most electrons moving parallel to the local magnetic field, while ions remain roughly isotropic. We will show that particle injection from the thermal pool occurs in regions of high current density associated with magnetic reconnection, while scattering off larger scale turbulence fluctuations drives acceleration to higher energies. We will discuss the implications of these findings for understanding the origin of nonthermal particles in space and astrophysical plasmas. |
Tuesday, October 31, 2023 11:06AM - 11:22AM |
GM10.00007: Effects of Finite Frequency in Turbulence Spectral Observations Lingling Zhao, Gary P Zank, Hui Li In situ observations of turbulence spectrum in space plasmas are usually interpreted as wavenumber spectrum, assuming that the fluctuation frequency is negligible in the plasma flow frame. It is conventional that turbulence is described by the power spectrum in wavenumber space. However, recent progress in magnetized plasma turbulence has recognized the importance of the finite-frequency effects. We explore the effects of nonzero frequency on turbulence spectral observations. The finite frequency can be caused by either propagating waves such as the Alfven waves or the nonlinear broadening of non-propagating structures. The results may have an impact on the interpretation of recent Parker Solar Probe data. |
Tuesday, October 31, 2023 11:22AM - 11:38AM |
GM10.00008: Analytical solutions of turbulence energy in the turbulence transport models Bingbing Wang, Gary P Zank, Laxman Adhikari Turbulence plays vital roles in many processes in the heliosphere, such as the acceleration of solar wind, the heating of pickup ions, and the scattering of energetic charged particles. However due to the very limited observations for different time and space, we need to seek the turbulence transport model to obtain the turbulent quantities in the heliosphere. Zank et al. (2017) developed very complex models, while Wang et al. (2022) showed that the turbulence energy equation has a simple form that resembles the well-known WKB transport equation. Based on the turbulence energy equation, we derive some analytical solutions for turbulence energy by parameterizing some other turbulent quantities and adopting a simple geometry. The analytical solutions provide more transparent insights on the evolution of turbulence and are easy to be applied in other problems. |
Tuesday, October 31, 2023 11:38AM - 11:54AM |
GM10.00009: MHD turbulence in the very local interstellar medium and the IBEX ribbon Siyao Xu, Hui Li We investigate the role of the magnetohydrodynamic (MHD) turbulence measured by Voyager in the very local interstellar medium (VLISM) in modeling the Interstellar Boundary Explorer ({it IBEX}) ribbon. We demonstrate that the mirroring by compressible modes of MHD turbulence dominates over that by the mean magnetic field. Based on the new mirror diffusion mechanism identified by Lazarian & Xu 2021 for particles with large pitch angles in MHD turbulence, we find that the mirror diffusion can efficiently confine pickup ions and cause their enhanced intensity. The ribbon width is determined by both the range of pitch angles for effective turbulent mirroring and the field line wandering induced by Alfv'{e}nic modes. The field line wandering also affects the coherence of the ribbon structure across the sky. By extrapolating the magnetic energy spectrum measured by Voyager, we find that the injection scale of the turbulence in the VLISM is less than $sim 500$ au for the ribbon structure to be coherent. |
Tuesday, October 31, 2023 11:54AM - 12:10PM |
GM10.00010: Parallel helicity and coherent structure in rotating magnetized plasmas John V Shebalin The ideal invariants of MHD turbulence are energy, magnetic helicity and cross helicity. If the system is rotating, cross helicity is no longer an invariant; if there is a mean magnetic field present, the magnetic helicity is no longer invariant; if both rotation and mean field occur, neither cross helicity nor magnetic helicity are invariant. However, if they are aligned there is a new invariant, the parallel helicity, which is a linear combination of cross and magnetic helicity. Thus, in a plasma that is rotating around the mean field direction, there are two ideal invariants, energy and parallel helicity, and a statistical mechanics can be based on these. In this case, we can predict that the largest-scale modes have much more energy than any other mode and show that the energetic, largest-scale modes form a coherent structure. We will discuss theoretical and computational results leading up to these conclusions and also discuss the applicability to real (dissipative and forced) MHD turbulence. |
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