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Title: A PARALLEL-PROPAGATING ALFVENIC ION-BEAM INSTABILITY IN THE HIGH-BETA SOLAR WIND

Abstract

We investigate the conditions under which parallel-propagating Alfven/ion-cyclotron waves are driven unstable by an isotropic (T{sub {alpha}} = T{sub Parallel-To {alpha}}) population of alpha particles drifting parallel to the magnetic field at an average speed U{sub {alpha}} with respect to the protons. We derive an approximate analytic condition for the minimum value of U{sub {alpha}} needed to excite this instability and refine this result using numerical solutions to the hot-plasma dispersion relation. When the alpha-particle number density is {approx_equal} 5% of the proton number density and the two species have similar thermal speeds, the instability requires that {beta}{sub p} {approx}> 1, where {beta}{sub p} is the ratio of the proton pressure to the magnetic pressure. For 1 {approx}< {beta}{sub p} {approx}< 12, the minimum U{sub {alpha}} needed to excite this instability ranges from 0.7v{sub A} to 0.9v{sub A}, where v{sub A} is the Alfven speed. This threshold is smaller than the threshold of {approx_equal} 1.2v{sub A} for the parallel magnetosonic instability, which was previously thought to have the lowest threshold of the alpha-particle beam instabilities at {beta}{sub p} {approx}> 0.5. We discuss the role of the parallel Alfvenic drift instability for the evolution of the alpha-particle drift speed in themore » solar wind. We also analyze measurements from the Wind spacecraft's Faraday cups and show that the U{sub {alpha}} values measured in solar-wind streams with T{sub {alpha}} Almost-Equal-To T{sub Parallel-To {alpha}} are approximately bounded from above by the threshold of the parallel Alfvenic instability.« less

Authors:
; ;  [1]
  1. Space Science Center, University of New Hampshire, Durham, NH 03824 (United States)
Publication Date:
OSTI Identifier:
22140317
Resource Type:
Journal Article
Journal Name:
Astrophysical Journal
Additional Journal Information:
Journal Volume: 773; Journal Issue: 1; Other Information: Country of input: International Atomic Energy Agency (IAEA); Journal ID: ISSN 0004-637X
Country of Publication:
United States
Language:
English
Subject:
71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSICS; 79 ASTROPHYSICS, COSMOLOGY AND ASTRONOMY; ALFVEN WAVES; ALPHA PARTICLES; APPROXIMATIONS; BEAMS; DENSITY; DISPERSION RELATIONS; DRIFT INSTABILITY; EVOLUTION; FARADAY CUPS; HIGH-BETA PLASMA; HOT PLASMA; MAGNETIC FIELDS; NUMERICAL SOLUTION; PROTONS; SOLAR WIND; STREAMS; TURBULENCE; WAVE PROPAGATION

Citation Formats

Verscharen, Daniel, Bourouaine, Sofiane, Chandran, Benjamin D. G., and Maruca, Bennett A., E-mail: daniel.verscharen@unh.edu, E-mail: s.bourouaine@unh.edu, E-mail: benjamin.chandran@unh.edu, E-mail: bmaruca@ssl.berkeley.edu. A PARALLEL-PROPAGATING ALFVENIC ION-BEAM INSTABILITY IN THE HIGH-BETA SOLAR WIND. United States: N. p., 2013. Web. doi:10.1088/0004-637X/773/1/8.
Verscharen, Daniel, Bourouaine, Sofiane, Chandran, Benjamin D. G., & Maruca, Bennett A., E-mail: daniel.verscharen@unh.edu, E-mail: s.bourouaine@unh.edu, E-mail: benjamin.chandran@unh.edu, E-mail: bmaruca@ssl.berkeley.edu. A PARALLEL-PROPAGATING ALFVENIC ION-BEAM INSTABILITY IN THE HIGH-BETA SOLAR WIND. United States. https://doi.org/10.1088/0004-637X/773/1/8
Verscharen, Daniel, Bourouaine, Sofiane, Chandran, Benjamin D. G., and Maruca, Bennett A., E-mail: daniel.verscharen@unh.edu, E-mail: s.bourouaine@unh.edu, E-mail: benjamin.chandran@unh.edu, E-mail: bmaruca@ssl.berkeley.edu. 2013. "A PARALLEL-PROPAGATING ALFVENIC ION-BEAM INSTABILITY IN THE HIGH-BETA SOLAR WIND". United States. https://doi.org/10.1088/0004-637X/773/1/8.
@article{osti_22140317,
title = {A PARALLEL-PROPAGATING ALFVENIC ION-BEAM INSTABILITY IN THE HIGH-BETA SOLAR WIND},
author = {Verscharen, Daniel and Bourouaine, Sofiane and Chandran, Benjamin D. G. and Maruca, Bennett A., E-mail: daniel.verscharen@unh.edu, E-mail: s.bourouaine@unh.edu, E-mail: benjamin.chandran@unh.edu, E-mail: bmaruca@ssl.berkeley.edu},
abstractNote = {We investigate the conditions under which parallel-propagating Alfven/ion-cyclotron waves are driven unstable by an isotropic (T{sub {alpha}} = T{sub Parallel-To {alpha}}) population of alpha particles drifting parallel to the magnetic field at an average speed U{sub {alpha}} with respect to the protons. We derive an approximate analytic condition for the minimum value of U{sub {alpha}} needed to excite this instability and refine this result using numerical solutions to the hot-plasma dispersion relation. When the alpha-particle number density is {approx_equal} 5% of the proton number density and the two species have similar thermal speeds, the instability requires that {beta}{sub p} {approx}> 1, where {beta}{sub p} is the ratio of the proton pressure to the magnetic pressure. For 1 {approx}< {beta}{sub p} {approx}< 12, the minimum U{sub {alpha}} needed to excite this instability ranges from 0.7v{sub A} to 0.9v{sub A}, where v{sub A} is the Alfven speed. This threshold is smaller than the threshold of {approx_equal} 1.2v{sub A} for the parallel magnetosonic instability, which was previously thought to have the lowest threshold of the alpha-particle beam instabilities at {beta}{sub p} {approx}> 0.5. We discuss the role of the parallel Alfvenic drift instability for the evolution of the alpha-particle drift speed in the solar wind. We also analyze measurements from the Wind spacecraft's Faraday cups and show that the U{sub {alpha}} values measured in solar-wind streams with T{sub {alpha}} Almost-Equal-To T{sub Parallel-To {alpha}} are approximately bounded from above by the threshold of the parallel Alfvenic instability.},
doi = {10.1088/0004-637X/773/1/8},
url = {https://www.osti.gov/biblio/22140317}, journal = {Astrophysical Journal},
issn = {0004-637X},
number = 1,
volume = 773,
place = {United States},
year = {Sat Aug 10 00:00:00 EDT 2013},
month = {Sat Aug 10 00:00:00 EDT 2013}
}