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Title: STOCHASTIC HEATING, DIFFERENTIAL FLOW, AND THE ALPHA-TO-PROTON TEMPERATURE RATIO IN THE SOLAR WIND

We extend previous theories of stochastic ion heating to account for the motion of ions along the magnetic field B . We derive an analytic expression for the temperature ratio T{sub i}/T{sub p} in the solar wind assuming that stochastic heating is the dominant ion heating mechanism, where T{sub i} is the perpendicular temperature of species i and T{sub p} is the perpendicular proton temperature. This expression describes how T{sub i}/T{sub p} depends upon U{sub i} and β{sub ∥p}, where U{sub i} is the average velocity along B of species i in the proton frame and β{sub ∥p} is the ratio of the parallel proton pressure to the magnetic pressure, which we take to be ∼< 1. We compare our model with previously published measurements of alpha particles and protons from the Wind spacecraft. We find that stochastic heating offers a promising explanation for the dependence of T{sub α}/T{sub p} on U{sub α} and β{sub ∥p} when the fractional cross helicity and Alfvén ratio at the proton-gyroradius scale have values that are broadly consistent with solar-wind measurements. We also predict how the temperatures of other ion species depend on their drift speeds.
Authors:
; ; ;  [1] ;  [2] ;  [3]
  1. Space Science Center and Department of Physics, University of New Hampshire, Durham, NH 03824 (United States)
  2. Astronomy Department and Theoretical Astrophysics Center, 601 Campbell Hall, The University of California, Berkeley, CA 94720 (United States)
  3. Harvard-Smithsonian Center for Astrophysics, Cambridge, MA 02138 (United States)
Publication Date:
OSTI Identifier:
22270729
Resource Type:
Journal Article
Resource Relation:
Journal Name: Astrophysical Journal; Journal Volume: 776; Journal Issue: 1; Other Information: Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
79 ASTROPHYSICS, COSMOLOGY AND ASTRONOMY; ALPHA PARTICLES; ASTRONOMY; ASTROPHYSICS; COMPARATIVE EVALUATIONS; HEATING; HELICITY; ION TEMPERATURE; MAGNETIC FIELDS; PLASMA; PROTON TEMPERATURE; SOLAR WIND; STOCHASTIC PROCESSES; SUN; TURBULENCE; VELOCITY