Ensemble Simulations of Proton Heating in the Solar Wind via Turbulence and Ion Cyclotron Resonance

Abstract

Protons in the solar corona and heliosphere exhibit anisotropic velocity distributions, violation of magnetic moment conservation, and a general lack of thermal equilibrium with the other particle species. There is no agreement about the identity of the physical processes that energize non-Maxwellian protons in the solar wind, but a traditional favorite has been the dissipation of ion cyclotron resonant Alfven waves. This paper presents kinetic models of how ion cyclotron waves heat protons on their journey from the corona to interplanetary space. It also derives a wide range of new solutions for the relevant dispersion relations, marginal stability boundaries, and nonresonant velocity-space diffusion rates. A phenomenological model containing both cyclotron damping and turbulent cascade is constructed to explain the suppression of proton heating at low alpha-proton differential flow speeds. These effects are implemented in a large-scale model of proton thermal evolution from the corona to 1 AU. A Monte Carlo ensemble of realistic wind speeds, densities, magnetic field strengths, and heating rates produces a filled region of parameter space (in a plane described by the parallel plasma beta and the proton temperature anisotropy ratio) similar to what is measured. The high-beta edges of this filled region are governed by plasma instabilities and strong heating rates. The low-beta edges correspond to weaker proton heating and a range of relative contributions from cyclotron resonance. On balance, the models are consistent with other studies that find only a small fraction of the turbulent power spectrum needs to consist of ion cyclotron waves.

Accepted for publication in the Astrophysical Journal Supplement Series. 26 pages (emulateapj style), 18 figures

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• Origins of the Ambient Solar Wind: Implications for Space Weather
• Ion Scale Electromagnetic Waves in the Inner Heliosphere
• Hybrid-Kinetic Simulations of Ion Heating in Alfvénic Turbulence
• The In Situ Signature of Cyclotron Resonant Heating
• On stochastic heating and its phase-space signatures in low-$\beta$ kinetic turbulence
• Observations of heating along intermittent structures in the inner heliosphere from PSP data
• MHD-kinetic transition in imbalanced Alfvénic turbulence
• The role of parametric instabilities in turbulence generation and proton heating: Hybrid simulations of parallel propagating Alfvén waves
• Preferential Heating and Acceleration of Heavy Ions in Impulsive Solar Flares
• Magnetic helicity signature and its role in regulating magnetic energy spectra and proton temperatures in the solar wind
• Dependence of ion temperatures on alpha-proton differential flow vector and heating mechanisms in the solar wind
• Fully Kinetic Simulations of Proton-Beam-Driven Instabilities from Parker Solar Probe Observations
• Resonant whistler-electron interactions: MMS observations vs. test-particle simulation
• Quasilinear Consequences of Turbulent Ion Heating by Magnetic Moment Breaking
• Design and Optimization of a High-Time-Resolution Magnetic Plasma Analyzer (MPA)