Diffusion of ions in an electrostatic stochastic field and a space-dependent unperturbed magnetic field

We calculate the diffusion coefficients for ions moving in a prescribed electromagnetic field. The field is considered to be a superposition of an electrostatic stochastic field and a space-dependent and sheared magnetic field. We have considered as parameters involved in the calculation of the diffusion coefficients the shear ion Kubo number K_s^ion, the electrostatic Kubo number K, the parallel shear ion Kubo number K_zs^ion, and the parallel thermal ion Kubo number K_z ^ion. A geometrical parameter which is the measure of the product of the stochastic perpendicular correlation length and the gradient in the magnetic field strength (see definitions in the text) is found not to be important in our calculation. The results concerning the diffusion coefficients obtained in our model are in agreement with experimental data and with those corresponding to other models, and the neoclassical and anomalous values for the diffusion coefficients are obtained.