SIMULATION OF NONQUASILINEAR DIFFUSION

The velocity diffusion coefficient for particles in a field of a large number of randomly phased electrostatic waves is calculated numerical ly by iterating a set of finite-difference equations. For moderate val ues of Chirikov's overlap parameter K, the diffusion is found to be si gnificantly faster (up to a factor of 2.2 at K almost-equal-to 17) tha n suggested by quasilinear theory, which confirms recent findings by C ary et al. [Phys. Rev. Lett. 65, 3132 (1990)].