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Title: PERPENDICULAR ION HEATING BY REDUCED MAGNETOHYDRODYNAMIC TURBULENCE

Recent theoretical studies argue that the rate of stochastic ion heating in low-frequency Alfvén-wave turbulence is given by Q = c{sub 1}((δu){sup 3}/ρ)exp (– c{sub 2}/ε), where δu is the rms turbulent velocity at the scale of the ion gyroradius ρ, ε = δu/v{sub i}, v{sub i} is the perpendicular ion thermal speed, and c{sub 1} and c{sub 2} are dimensionless constants. We test this theoretical result by numerically simulating test particles interacting with strong reduced magnetohydrodynamic (RMHD) turbulence. The heating rates in our simulations are well fit by this formula. The best-fit values of c{sub 1} are ∼1. The best-fit values of c{sub 2} decrease (i.e., stochastic heating becomes more effective) as the Reynolds number and the number of grid points in the RMHD simulations increase. As an example, in a 1024{sup 2} × 256 RMHD simulation with a dissipation wavenumber of the order of the inverse ion gyroradius, we find c{sub 2} = 0.21. We show that stochastic heating is significantly stronger in strong RMHD turbulence than in a field of randomly phased Alfvén waves with the same power spectrum, because coherent structures in strong RMHD turbulence increase orbit stochasticity in the regions where ions are heated mostmore » strongly. We find that c{sub 1} increases by a factor of ∼3 while c{sub 2} changes very little as the ion thermal speed increases from values <« less
Authors:
; ;  [1] ;  [2]
  1. Space Science Center and Department of Physics, University of New Hampshire, Durham, NH (United States)
  2. Astronomy Department and Theoretical Astrophysics Center, 601 Campbell Hall, The University of California, Berkeley, CA 94720 (United States)
Publication Date:
OSTI Identifier:
22270774
Resource Type:
Journal Article
Resource Relation:
Journal Name: Astrophysical Journal; Journal Volume: 776; Journal Issue: 2; Other Information: Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
79 ASTROPHYSICS, COSMOLOGY AND ASTRONOMY; ALFVEN WAVES; ASTRONOMY; ASTROPHYSICS; COMPUTERIZED SIMULATION; HEATING RATE; IONS; MAGNETOHYDRODYNAMICS; PLASMA; RANDOMNESS; REYNOLDS NUMBER; SOLAR WIND; STOCHASTIC PROCESSES; SUN; TURBULENCE; VELOCITY