Year: 2021
Type: article
Abstract: In Navier-Stokes turbulence, energy and helicity injected at large scales are subject to a joint direct cascade, with both quantities exhibiting a spectral scaling $\ensuremath{\propto}{k}^{\ensuremath{-}5/3}$. We demonstrate via direct numerical simulations that the two cascades are compatible due to the existence of a strong scale-dependent phase alignment between velocity and vorticity fluctuations, with the phase alignment angle scaling as $\mathrm{cos}{\ensuremath{\alpha}}_{k}\ensuremath{\propto}{k}^{\ensuremath{-}1}$.
Source: Physical Review Letters
Language: English
Subfield: Computational Mechanics
Field: Engineering
Domain: Physical Sciences
Open Access status: green
Funders: National Science Foundation, U.S. Department of Energy, National Aeronautics and Space Administration, Massachusetts Institute of Technology, National Energy Research Scientific Computing Center, Massachusetts Green High Performance Computing Center, Nuclear Safety and Security Commission, Office of Science
Awards: G122673668, G1286236842, CAREER: Magnetogenesis Revisited: The First Self-consistent Plasma Dynamo, G1632040200, G1677143136, G1863003419, Self-Similar Theory of Electron Thermal Conduction in a Weakly Collisional Plasma, G3083819904, Electron Distribution in the Solar Wind from the Sun to the Earth, THE WISCONSIN PLASMA PHYSICS LABORATORY: A USER FACILITY FOR FRONTIER PLASMA SCIENCE, G419881185, G42916606, G4501827968, MEASUREMENTS OF THE ELECTRON VELOCITY DISTRIBUTION FUNCTION (EVDF) IN THE SOLAR WIND ROUTINELY DETECT A NARROW MAGNETIC-FIELDALIGNED POPULATION OF SUPRATHERMAL ELECTRONS TERMED THE "STRAHL." DUE TO ITS HIGH ENERGY AND STRONG ANISOTROPY THE STRAHL PROVIDES A SIGNIFICANT CONTRIBUTION TO THE FIELD-PARALLEL HEAT TRANSPORT IT TAKES PART IN THE GLOBAL ENERGY BALANCE IN STEADY STATE AND MAY DRIVE KINETIC INSTABILITIES AND TURBULENCE IN A PLASMA. THE FULL KINETIC DESCRIPTION OF THE ELECTRON DISTRIBUTION FUNCTION IN A WEAKLY COLLISIONAL AND EXPANDING SOLAR WIND PLASMA IS EXTREMELY COMPLICATED. CURRENTLY THERE IS NO CONSENSUS ON WHAT PROCESSES ARE MOST RELEVANT FOR THE FORMATION AND THE STRUCTURE OF THE STRAHL. THE ROBUST PRESENCE OF THE STRAHL IN THE MEASUREMENTS HOWEVER INDICATE THAT ITS PHYSICS IS GOVERNED BY SOME UNIVERSAL PROCESSES. THE STUDIES BY THE INVESTIGATORS GROUPS [BALE ET AL ASTROPHYS. J. LETT. 769 L22 (2013); HORAITES ET AL PHYS. REV. LETT 114 245003 (2015)] SHED LIGHT ON SUCH UNIVERSALITY PUTTING FORWARD A NOVEL SUGGESTION THAT THE SHAPE OF THE ELECTRON DISTRIBUTION FUNCTION VARIES IN A SELFSIMILAR FASHION UNDER THE PROPER RESCALING OF THE ELECTRON VELOCITY DENSITY TEMPERATURE AND THE MAGNETIC FIELD WITH THE DISTANCE ALONG THE MAGNETIC FLUX TUBE. THE GOAL OF THE PROJECT IS THE OBSERVATIONAL STUDY OF THE SCALING AND STRUCTURE OF THE SOLAR WIND ELECTRON DISTRIBUTION. TO UNCOVER THE SCALING RELATIONS WE WILL ANALYZE THE SOLAR WIND DATA WHERE THE NARROW ANISOTROPIC STRAHL IS MOST PROMINENT AND BEST DISTINGUISHED FROM THE CORE AND HALO COMPONENTS. SINCE THE ELECTRON COLLISION FREQUENCY SCALES AS NT^{-3/2} WHERE T AND N ARE THE ELECTRON TEMPERATURE AND DENSITY THE REGIONS OF LOWER ELECTRON DENSITY ARE GOOD CANDIDATES FOR OUR ANALYSIS. ANOTHER FACTOR THAT AFFECTS THE ELECTRON BEAM COLLIMATION IS THE LAW OF SPATIAL EXPANSION OF A MAGNETIC FLUX TUBE. THIS BRINGS ATTENTION TO THE PLASMA EMANATING FROM CORONAL HOLES CORRESPONDING TO FAST SOLAR WIND AND/OR SOLAR WIND INTERVALS ASSOCIATED WITH CORONAL MASS EJECTIONS. WE WILL SEARCH AND ANALYZE THE DATA SETS CORRESPONDING TO THE REGIONS OF LOW ELECTRON DENSITY AND STRONG MAGNETIC FIELD. THE MEASUREMENTS OF THE EVDF AND COMPARISON OF ITS STRUCTURE WITH THE RECENTLY DEVELOPED THEORY WILL BE CRUCIAL FOR INTERPRETING THE PHYSICS GOVERNING THE FORMATION OF THE ELECTRON VDF. THEY WILL HELP TO ELUCIDATE THE PROCESSES RESPONSIBLE FOR THE STRALH STRUCTURE (COULOMB COLLISIONS MIRROR EFFECTS INTERACTION WITH KINETIC-SCALE TURBULENCE). IN THE PROPOSED PROJECT WE WILL ANALYZE THE SOLAR WIND DATA FROM WIND (3DP) HELIOS (E1 PLASMA EXPERIMENT) AND ULYSSES SPACECRAFT (SWOOPS) AS TO MAXIMIZE THE AVAILABLE RANGE OF THE COVERED HELIOSPHERIC DISTANCES. THE PROJECT WILL SUPPORT THE WORK OF THE GRADUATE STUDENT AT THE UNIVERSITY OF WISCONSIN-MADISON AND THE COLLABORATION BETWEEN THE UW-MADISON AND THE SPACE SCIENCES LABORATORY UC-BERKELEY. THE PROJECT BELONGS TO THE SUBDISCIPLINE HELIOSPHERE AND IT ADDRESSES THE HELIOSPHERIC PLASMA PROCESSES. AS THE ELECTRON HEAT CONDUCTION IS A FUNDAMENTAL PROCESS IN OTHER ASTROPHYSICAL SYSTEMS (INTERSTELLAR MEDIUM GALAXY CLUSTERS) THE PROJECT ALSO RESPONDS TO THE DECADAL SURVEY BROAD SCIENCE GOAL OF DISCOVERING AND CHARACTERIZING FUNDAMENTAL PROCESSES THAT OCCUR BOTH WITHIN THE HELIOSPHERE AND THROUGHOUT THE UNIVERSE., G498139845, G5076365615, G6671297155, THEORETICAL RESEARCH IN ADVANCED PHYSICS AND TECHNOLOGY, G969889393
OpenAlex ID: W3159171234