  We investigate the motion of charged particles in a turbulent electrostatic
potential using guiding-center theory. By increasing the Larmor radius, the
dynamics exhibit close-to-ballistic transport properties. The transition from
diffusive to ballistic transport is analyzed using nonlinear dynamics. It is
found that twistless invariant tori in the guiding-center dynamics are
responsible for this transition, drastically affecting transport properties of
charged particles.
