## Abstract

We use a method developed by Roberts that optimizes the phase angles of an ensemble of plane waves with amplitudes determined from a Kolmogorov-like power spectrum, to construct magnetic field vector fluctuations having nearly constant magnitude and large variances in its components. This is a representation of the turbulent magnetic field consistent with that observed in the solar wind. Charged-particle pitch-angle diffusion coefficients are determined by integrating the equations of motion for a large number of charged particles moving under the influence of forces from our predefined magnetic field. We tested different cases by varying the kinetic energy of the particles (E _{p}) and the turbulent magnetic field variance (σ_{B} ^{2}). For each combination of E _{p}and , we tested three different models: (1) the so-called "slab" model, where the turbulent magnetic field depends on only one spatial coordinate and has significant fluctuations in its magnitude (√δB_{x} ^{2}(z)+δ _{y} ^{2}(z)+B_{0} ^{2}) (2) the slab model optimized with nearly constant magnitude b; and (3) the slab model turbulent magnetic field with nearly constant magnitude plus a "variance-conserving" adjustment. In the last case, this model attempts to conserve the variance of the turbulent components (σ_{By} ^{2}+σ_{Bx} ^{2}), which is found to decrease during the optimization with nearly constant magnitude. We found that there is little or no effect on the pitch-angle diffusion coefficient between models 1 and 2. However, the result from model 3 is significantly different. We also introduce a new method to accurately determine the pitch-angle diffusion coefficients as a function of μ.

Original language | English (US) |
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Article number | 16 |

Journal | Astrophysical Journal |

Volume | 827 |

Issue number | 1 |

DOIs | |

State | Published - Aug 10 2016 |

## Keywords

- diffusion
- magnetic fields
- solar wind
- turbulence

## ASJC Scopus subject areas

- Astronomy and Astrophysics
- Space and Planetary Science