We have investigated a new approach to deriving a diffusion equation for charged particles in a static, random magnetic field. Our method incorporates essential effects of the magnetic fluctuations in the lowest order particle orbits. Significant corrections to the usual quasilinear diffusion coefficient for cosmic rays with pitch angles near 90° are a consequence. Monte Carlo results bear out the validity of our theory.

• Received 18 June 1973

DOI:https://doi.org/10.1103/PhysRevLett.31.485