Cosmic-ray scattering in simulated interplanetary magnetic field fluctuations

We study the diffusion of cosmic rays in simulated interplanetary magnetic-field fluctuations using the Monte Carlo pitch-angle scattering technique of Jones, Kaiser, and Birmingham. Our calculations are based on the ''slab'' model, with transverse (x, y) field fluctuations (B') varying only along the average magnetic field direction (z). The rms variation of B' is one-half the average field for each of the independent transverse field components, and each fluctuating field component has a power spectrum p(k)=A/[1+(kL)/sup 1.5/], as observed in interplanetary space. The derived pitch-angle scattering coefficient is used to calculate the spatial diffusion coefficient applicable near Earth. There is significant scattering near the pitch-angle cosine μ=0. Our calculated parallel diffusion coefficient is within about 20]% of that predicted by quasi-linear theory, for particles with cyclotron radii r0.03=(en-dash1) times the field correlation length