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Solar Physics

, 294:34 | Cite as

On the Power-Law Distribution of Pitch-Angle Scattering Times in Solar Wind Turbulence

  • Silvia PerriEmail author
  • Francesco Pucci
  • Francesco Malara
  • Gaetano Zimbardo
Article
Part of the following topical collections:
  1. Solar Wind at the Dawn of the Parker Solar Probe and Solar Orbiter Era

Abstract

The propagation of energetic particles in the solar wind depends in a sensitive way on the pitch-angle scattering of particles in the presence of magnetic turbulence. The well-known quasi-linear theory gives an expression for the pitch-angle scattering rate under the assumption of small turbulence levels, but both in the solar wind and in other astrophysical environments the turbulent magnetic field fluctuations can be large. Therefore, a reliable assessment of the pitch-angle scattering requires an investigation that goes beyond the quasi-linear theory. To this end, we employ a recently developed model of synthetic magnetic turbulence, which allows reproduction of a very long spectrum, while varying the turbulence level and the turbulence intermittency. Test particles representing protons with energies in the range \(70~\mbox{keV}\,\mbox{--}\,1~\mbox{MeV}\) are injected in the turbulence spectrum plus a background magnetic field, and the pitch-angle scattering rate is determined by following the individual particles. Using turbulence and intermittency levels comparable to those observed in the solar wind, we find a broad power-law distribution of pitch-angle scattering times, which encompasses the quasi-linear value but extends to values both much larger and much smaller. We find that the distribution of pitch-angle scattering times also depends on the intermittency level. This finding shows that a description of parallel transport based on a single value of the pitch-angle scattering time is not sufficient. These numerical results are compared with observations of the distribution of magnetic variances at the particle resonant scale, measured in the solar wind by the Ulysses spacecraft.

Keywords

Particle transport Magnetic turbulence 

Notes

Acknowledgement

The work by S. Perri has been supported by the Agenzia Spaziale Italiana under the contract ASI-INAF 2015-039-R.O “Missione M4 di ESA: Partecipazione Italiana alla fase di assessment della missione THOR”.

Disclosure of Potential Conflicts of Interest

The authors declare that they have no conflicts of interest.

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Copyright information

© Springer Nature B.V. 2019

Authors and Affiliations

  1. 1.Dipartimento di FisicaUniversità della CalabriaRendeItaly
  2. 2.Center for Mathematical Plasma Astrophysics, Department WiskundeKU LeuvenLeuvenBelgium

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