Preferential Perpendicular Heating of Coronal Hole Minor Ions by the Fermi Mechanism

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Preferential Perpendicular Heating of Coronal
Hole Minor Ions by the Fermi Mechanism
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• Phil Isenberg
• At the origin of the fast solar wind, near the
  base of coronal holes, minor ions are observed to
  be heated perpendicular to the magnetic field to
  temperatures far in excess of the protons there.
  This strong heating leads to preferential
  acceleration of these ions due to the mirror
  force, and the hotter, faster minor ions are seen
  in the in situ fast wind. We are constructing a
  computational kinetic model of this preferential
  heating which should yield the observed speeds
  and temperatures of solar wind minor ions and may
  provide valuable information on the specific
  physical mechanisms responsible for heating the
  open corona and generating the solar wind.
• This figure shows preliminary results from
  the first steps in this model, investigating the
  resonant cyclotron interaction between minor ions
  and parallel-propagating ion cyclotron waves. We
  display normalized distributions of O5 at four
  times from a numerical solution of quasilinear
  diffusion in velocity space. The initial state
  is an isotropic distribution with ? 103. The
  results show strong perpendicular heating which
  will continue as long as resonant waves are
  present. This behavior contrasts with that of
  protons under identical conditions, since protons
  will evolve only until they reach a state of
  marginal stability at which time this resonant
  absorption ceases, even if resonant wave power
  remains. Minor ions have no such marginally
  stable state, and their continual perpendicular
  heating is equivalent to second-order Fermi
  acceleration of these thermal particles. Further
  work will add the effects of coronal hole forces,
  following the evolution of a plasma parcel
  accelerating away from the Sun.