Electron-ion heating partition in imbalanced solar-wind turbulence

Abstract

A likely candidate mechanism to heat the solar corona and solar wind is low-frequency "Alfvénic" turbulence sourced by magnetic fluctuations near the solar surface. Depending on its properties, such turbulence can heat different species via different mechanisms, and the comparison of theoretical predictions to observed temperatures, wind speeds, anisotropies, and their variation with heliocentric radius provides a sensitive test of this physics. Here we explore the importance of normalized cross helicity, or imbalance, for controlling solar-wind heating, since it is a key parameter of magnetized turbulence and varies systematically with wind speed and radius. Based on a hybrid-kinetic simulation in which the forcing's imbalance decreases with time -- a crude model for a plasma parcel entrained in the outflowing wind -- we demonstrate how significant changes to the turbulence and heating result from the "helicity barrier" effect. Its dissolution at low imbalance causes its characteristic features -- strong perpendicular ion heating with a steep "transition-range" drop in electromagnetic fluctuation spectra -- to disappear, driving more energy into electrons and parallel ion heat, and halting the emission of ion-scale waves. These predictions seem to agree with a diverse array of solar-wind observations, offering to explain a variety of complex correlations and features within a single theoretical framework.

arXiv comment8 pages, 5 figures. Figure 4 updated from published version

References in corpus (19)

• Perpendicular Ion Heating by Low-Frequency Alfven-Wave Turbulence in the Solar Wind
• Astrophysical Gyrokinetics: Basic Equations and Linear Theory
• Thermal disequilibration of ions and electrons by collisionless plasma turbulence
• Spectral Slope Variation at Proton Scales from Fast to Slow Solar Wind
• Multi-Species Measurements of the Firehose and Mirror Instability Thresholds in the Solar Wind
• Hybrid-Kinetic Simulations of Ion Heating in Alfvénic Turbulence
• Measuring Collisionless Damping in Heliospheric Plasmas using Field-Particle Correlations
• Pegasus: A New Hybrid-Kinetic Particle-in-Cell Code for Astrophysical Plasma Dynamics
• Violation of the zeroth law of turbulence in space plasmas
• The In Situ Signature of Cyclotron Resonant Heating
• Anisotropy of Solar-Wind Turbulence in the Inner Heliosphere at Kinetic Scales: PSP Observations
• On stochastic heating and its phase-space signatures in low-$\beta$ kinetic turbulence
• Constraints on ion vs. electron heating by plasma turbulence at low beta
• Evolution of The Proton Velocity Distribution due to Stochastic Heating in the Near-Sun Solar Wind
• Quantifying the Energy Budget in the Solar Wind from 13.3-100 Solar Radii
• A Self-Consistent Marginally Stable State for Parallel Ion Cyclotron Waves
• Proton and electron temperatures in the solar wind and their correlations with the solar wind speed
• Magnetic helicity signature and its role in regulating magnetic energy spectra and proton temperatures in the solar wind
• Thermal energy budget of electrons in the inner heliosphere: Parker Solar Probe Observations

Cited by in corpus (7)

• Evidence for the helicity barrier from measurements of the turbulence transition range in the solar wind
• Modeling hot, anisotropic ion beams in the solar wind motivated by the Parker Solar Probe observations near perihelia
• A Unified Phenomenology of Ion Heating in Low-$\beta$ Plasmas: Test-Particle Simulations
• The effects of finite electron inertia on helicity-barrier-mediated turbulence
• AHKASH: a new Hybrid particle-in-cell code for simulations of astrophysical collisionless plasma
• Turbulent heating in collisionless low-beta plasmas: imbalance, Landau damping, and electron-ion energy partition
• Rugged magneto-hydrodynamic invariants in weakly collisional plasma turbulence: Two-dimensional hybrid simulation results