PITCH-ANGLE SCATTERING OF ENERGETIC CHARGED PARTICLES IN NEARLY CONSTANT MAGNITUDE MAGNETIC TURBULENCE

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 (sigma(2)(B)). For each combination of E-p and sigma(2)(B), 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 (b=root delta B-x(2)(z)+ delta B-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 (sigma(2)(Bx) + sigma(2)(By)), 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 D mu mu 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 mu.