PITCH-ANGLE DIFFUSION-COEFFICIENT IN AN EXTENDED QUASI-LINEAR THEORY

Using an extended quasi-linear theory that takes account of the distri bution of medium-scale background interplanetary magnetic field, we ca lculate the pitch angle diffusion coefficients of interplanetary energ etic ions, for a slab turbulence model consisting of a superposition o f parallel and antiparallel transverse R and L waves. Our results show that the background variation broadens the resonance function signifi cantly at pitch angles near 90 degrees, so that protons down to approx imate to 25 keV interact with hydromagnetic waves at all pitch angles, and the steepening of the magnetic field power spectrum in the dissip ation range does not result in a resonance gap or infinite scattering mean free path.