RESONANT INTERACTIONS BETWEEN PROTONS AND OBLIQUE ALFVEN/ION-CYCLOTRON WAVES IN THE SOLAR CORONA AND SOLAR FLARES

Journal Article · Sun Oct 10 04:00:00 EDT 2010 · Astrophysical Journal

DOI:https://doi.org/10.1088/0004-637X/722/1/710· OSTI ID:21464691

Chandran, Benjamin D. G.; Pongkitiwanichakul, Peera; Isenberg, Philip A; Lee, Martin A; Markovskii, Sergei A; Hollweg, Joseph V

We consider interactions between protons and Alfven/ion-cyclotron (A/IC) waves in collisionless low-{beta} plasmas in which the proton distribution function f is strongly modified by wave pitch-angle scattering. If the angle {theta} between the wave vector and background magnetic field is zero for all the waves, then strong scattering causes f to become approximately constant on surfaces of constant {eta}, where {eta} {approx_equal} v {sup 2}{sub perpendicular} + 1.5 v {sup 2/3}{sub A}|v{sub ||}|{sup 4/3}. Here, v{sub perpendicular} and v{sub ||} are the velocity components perpendicular and parallel to the background magnetic field, and v{sub A} is the Alfven speed. If f = f({eta}), then A/IC waves with {theta} = 0 are neither damped nor amplified by resonant interactions with protons. In this paper, we argue that if some mechanism generates high-frequency A/IC waves with a range of {theta} values, then wave-particle interactions initially cause the proton distribution function to become so anisotropic that the plasma becomes unstable to the growth of waves with {theta} = 0. The resulting amplification of {theta} = 0 waves leads to an angular distribution of A/IC waves that is sharply peaked around {theta} = 0 at the large wavenumbers at which A/IC waves resonate with protons. Scattering by this angular distribution of A/IC waves subsequently causes f to become approximately constant along surfaces of constant {eta}, which in turn causes oblique A/IC waves to be damped by protons. We calculate the proton and electron contributions to the damping rate analytically, assuming Maxwellian electrons and f = f({eta}). Because the plasma does not relax to a state in which proton damping of oblique A/IC waves ceases, oblique A/IC waves can be significantly more effective at heating protons than A/IC waves with {theta} = 0.

• OSTI ID: 21464691
• Journal Information: Astrophysical Journal, Journal Name: Astrophysical Journal Journal Issue: 1 Vol. 722; ISSN ASJOAB; ISSN 0004-637X
• Country of Publication: United States
• Language: English

Related Subjects

79 ASTRONOMY AND ASTROPHYSICS
ANGULAR DISTRIBUTION
ANISOTROPY
ATMOSPHERES
DISTRIBUTION
DISTRIBUTION FUNCTIONS
FUNCTIONS
INTERACTIONS
ION PLASMA WAVES
ION WAVES
MAGNETIC FIELDS
MAIN SEQUENCE STARS
PARTICLE INTERACTIONS
PLASMA
PLASMA WAVES
SOLAR ACTIVITY
SOLAR ATMOSPHERE
SOLAR CORONA
SOLAR FLARES
SOLAR WIND
STARS
STELLAR ACTIVITY
STELLAR ATMOSPHERES
STELLAR CORONAE
STELLAR FLARES
STELLAR WINDS
SUN