Stochastic particle acceleration in solar flares
ROSES ID: NNH06ZDA001N Selection Year: 2007
Program Element: Focused Science Topic
Principal Investigator: Benjamin Chandran
Affiliation(s): University of New Hampshire
Project Member(s):
Ng, Chung-Sang Co-I University of Alaska Fairbanks
Mason, Glenn M Collaborator JHU / APL
Summary:
The acceleration of particles to energies exceeding 50 MeV in solar
flares is a long-standing problem and one of the Focused Science
Topics of NASA's 2006 Living-With-a-Star (LWS) program. This proposal
addresses one of the leading theories for particle energization in
flares, namely stochastic particle acceleration. In this theory,
turbulent waves are excited in the flaring region by magnetic
reconnection and the ideal fluid motions that arise as the magnetic
field relaxes to a new configuration. The energy in these waves
undergoes a turbulent cascade to small scales, resulting in
high-frequency waves that accelerate particles to high energies
through resonant wave-particle interactions. If the power spectra of
these waves have the right properties, stochastic acceleration can
explain many of the observed features of flares, including the
acceleration time scales, the energy spectra of different particle
species, and the highly enhanced abundance of helium-3 relative to
helium-4 in the accelerated particle population. However, there is still
no predictive theory for the turbulent power spectra of waves on the
Alfven/ion-cyclotron and fast-magnetosonic/whistler branches of the
dispersion relation in flaring regions. The determination of these
power spectra is the most important unsolved problem for the
stochastic-acceleration model, and is the focus of this
proposal. Building on previous work by the PI and co-I, we will carry
out weak turbulence calculations and direct numerical simulations to
determine the power spectra of the above-mentioned waves for
solar-flare conditions. A notable feature of this turbulence research
is its extensive use of analytic theory in addition to numerical
simulations, which will lead to highly detailed quantitative results,
a theoretical framework that can be applied by other investigators,
and a clear physical picture of the energy cascade mechanisms. We
will use these power spectra to determine the acceleration times and
energy spectra of different particle species as a function of the
overall turbulence amplitude (i.e., the rms velocity at the largest scales)
using quasilinear theory to treat the particle-acceleration
process. We will then compare our results to x-ray, gamma-ray, and
in-situ particle measurements. By determining the power spectra of
the different wave modes in solar-flare conditions, our work will
provide key missing information that is essential for assessing the
importance of stochastic acceleration in solar flares, and for
determining the contribution of flare-accelerated particles
to large solar-energetic-particle (SEP) events observed at
Earth.
Publications:
Performance Year | Reference | Investigation Type | Actions |
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1 | Chandran, B., "Strong Anisotropic MHD Turbulence with Cross ...
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1 | Pongkitiwanichakul, Peera; Chandran, Benjamin D. G.; K...
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Presentations:
Performance Year | Reference | Actions |
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1 | Pongkitiwanichakul, P.; Chandran, B. D.; DeVore, C. R...
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1 | Pongkitiwanichakul, P.; Chandran, B. D.; (2012), Stochas...
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