Relative drifts and temperature anisotropies of protons and $\alpha$ particles in the expanding solar wind -- 2.5D hybrid simulations

Abstract

We perform 2.5D hybrid simulations to investigate the origin and evolution of relative drift speeds between protons and $\alpha$ particles in the collisionless turbulent low-$\beta$ solar wind plasma. We study the generation of differential streaming by wave-particle interactions and absorption of turbulent wave spectra. Next we focus on the role of the relative drifts for the turbulent heating and acceleration of ions in the collisionless fast solar wind streams. The energy source is given by an initial broad-band spectrum of parallel propagating Alfvén-cyclotron waves, which co-exists with the plasma and is self-consistently coupled to the perpendicular ion bulk velocities. We include the effect of a gradual solar wind expansion, which cools and decelerates the minor ions. This paper for the first time considers the combined effect of self-consistently initialized dispersive turbulent Alfvénic spectra with differentially streaming protons and $\alpha$ particles in the expanding solar wind outflows within a 2.5D hybrid simulation study. In the non-expanding wind, we find a threshold value of the differential streaming $V_{\alpha p}=0.5V_{\mathrm{A}}$, for which the relative drift speed remains nearly steady. For ions, streaming below the threshold value, the waves act to increase the magnitude of the relative drift speed. Ions, which stream faster than the threshold value become subject to nonlinear streaming instability and as the system evolves their bulk velocities decrease. We find that the solar wind expansion strongly affects the relative drift speeds and significantly slows down both ion species for all values of the relative drift speeds considered in this study.

11 pages, 13 figures, submitted to A&A

References in corpus (2)

• Correlations between the proton temperature anisotropy and transverse high-frequency waves in the solar wind
• Ion Heating in Inhomogeneous Expanding Solar Wind Plasma: The Role of Parallel and Oblique Ion-Cyclotron Waves

Cited by in corpus (11)

• Differential kinetic dynamics and heating of ions in the turbulent solar wind
• Alpha-proton Differential Flow of the Young Solar Wind: Parker Solar Probe Observations
• Modeling ion beams, kinetic instabilities, and waves observed by the Parker Solar Probe near perihelia
• The impact of multi-fluid effects in the solar chromosphere on the ponderomotive force under LTE and NEQ ionization conditions
• The role of parametric instabilities in turbulence generation and proton heating: Hybrid simulations of parallel propagating Alfvén waves
• Parker Solar Probe Observations of High Plasma Beta Solar Wind from Streamer Belt
• Nonlinear Evolution of Ion Kinetic Instabilities in the Solar Wind
• Modeling hot, anisotropic ion beams in the solar wind motivated by the Parker Solar Probe observations near perihelia
• Evolution of an Alfvén Wave-Driven Proton Beam in the Expanding Solar Wind
• Particle acceleration by sub-proton cyclotron frequency spectrum of dispersive Alfven waves in inhomogeneous solar coronal plasmas
• Current sheets, plasmoids and flux ropes in the heliosphere. Part II: Theoretical aspects