Magnetic pumping as a source of particle heating and power-law distributions in the solar wind

Abstract

Based on the rate of expansion of the solar wind, the plasma should cool rapidly as a function of distance to the Sun. Observations show this is not the case. In this work, a magnetic pumping model is developed as a possible explanation for the heating and the generation of power-law distribution functions observed in the solar wind plasma. Most previous studies in this area focus on the role that the dissipation of turbulent energy on microscopic kinetic scales plays in the overall heating of the plasma. However, with magnetic pumping particles are energized by the largest scale turbulent fluctuations, thus bypassing the energy cascade. In contrast to other models, we include the pressure anisotropy term, providing a channel for the large scale fluctuations to heat the plasma directly. In this work a complete set of coupled differential equations describing the evolution, and energization, of the distribution function are derived, as well as an approximate closed form solution. Numerical simulations using the VPIC kinetic code are applied to verify the model's analytical predictions. The results of the model for realistic solar wind scenario are computed, where thermal streaming of particles are important for generating a phase shift between the magnetic perturbations and the pressure anisotropy. In turn, averaged over a pump cycle, the phase shift permits mechanical work to be converted directly to heat in the plasma. The results of this scenario show that magnetic pumping may account for a significant portion of the solar wind energization.

7 pages, 4 figures

References in corpus (3)

• Kinetic Simulations of Magnetized Turbulence in Astrophysical Plasmas
• Recent progress in astrophysical plasma turbulence from solar wind observations
• Multiscale nature of the dissipation range in gyrokinetic simulations of Alfvénic turbulence

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• Nonlinear aspects of stochastic particle acceleration
• The Role of Pressure Anisotropy in Cosmic Ray Hydrodynamics
• A Heating Mechanism via Magnetic Pumping in the Intracluster Medium
• Energy Repartition and Entropy Generation across the Earth's Bow Shock: MMS Observations
• Electron Re-acceleration via Ion Cyclotron Waves in the Intracluster Medium
• Parallel Velocity Mixing Yielding Enhanced Electron Heating During Magnetic Pumping
• The Heliospheric Ambipolar Potential Inferred from Sunward-Propagating Halo Electrons