Simulation of nonquasilinear diffusion

The velocity diffusion coefficient for particles in a field of a large number of randomly phased electrostatic waves is calculated numerically by iterating a set of finite‐difference equations. For moderate values of Chirikov’s overlap parameter K, the diffusion is found to be significantly faster (up to a factor of 2.2 at K≊17) than suggested by quasilinear theory, which confirms recent findings by Cary et al. [Phys. Rev. Lett. 65, 3132 (1990)].