Resonant absorption of an Alfvén wave: Hybrid simulations

Details Resonant absorption of an Alfvén wave: Hybrid simulations Resonant absorption of an Alfvén wave: Hybrid simulations

Jul 2005

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2005jgra..11010s02v&link_type=abstract

Journal of Geophysical Research, Volume 110, Issue A10, CiteID A10S02

Physics

Plasma Physics

1

Solar Physics, Astrophysics, And Astronomy: Corona, Space Plasma Physics: Kinetic Waves And Instabilities, Space Plasma Physics: Parametric Processes, Space Plasma Physics: Wave/Particle Interactions (2483, 6984), Space Plasma Physics: Wave/Wave Interactions

Scientific paper

We examine the evolution of a planar Alfvén wave propagating along and across a pressure-balanced structure. The structure has mostly a magnetic field component perpendicular to a uniform background magnetic field B0 and gives an almost sinusoidal Alfvén speed gradient across B0. The Alfvén wave propagates both oblique to the structure and B0. A hybrid simulation code with particle protons and massless fluid electrons is used to follow evolution. The structure advects little with the wave so that the wave evolves mostly in accord with a fixed Alfvén speed gradient. The Alfvén wave undergoes resonant absorption wherein one set of resonant field lines loses wave energy to another set of resonant field lines by cross-field energy transport. We derive the timescale of the cross-field transfer and associate it with global modes. This feature of wave evolution occurs independently of ion kinetics. On resonant field lines, wave refraction generates ever smaller scales perpendicular to B0. When the perpendicular scales are of order 10 proton inertial lengths (10c/ωpi), a nonpropagating density fluctuation begins to grow to large amplitudes. The growth saturates by exciting highly oblique, compressive, and low-frequency waves which dissipate and heat protons. Protons are heated approximately by equal amounts along and across the local magnetic field. Heating continues until most of the resonantly absorbed Alfvén wave energy is exhausted. This process limits density fluctuations to scales across B0, which are greater than ~ c/ωpi. This process could play a role in the solar corona where a cutoff of density fluctuations at scales near and below c/ωpi is inferred from radio observations.

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