Numerical model for collisions in the drift approximation that reproduces classical and neoclassical transport

A numerical method is described for including collisions in the drift approximation in a way that reproduces diffusion of the guiding center and of the drift orbit center. For untrapped particles, the method gives transport that agrees with classical values for mobility and diffusivity both parallel and perpendicular to the magnetic field. For trapped particles, the method correctly reproduces the neoclassical mobility and diffusivity. The model has been applied to the annular Penning trap in which a non-neutral plasma of electrons in a helical magnetic field makes collisions with neutral gas. The model shows that the transport makes a transition from neoclassical to classical values as the collision frequency goes from less than to greater than the axial bounce frequency.