Charged-Particle Orbits in Sheared Magnetic Fields; Implications to Diffusion

Charged-particle motion across a sheared magnetic field and electrostatic wave is studied. Resonant-particle orbit widths are derived; two parametric dependences are found in the limits that the particle is near or far from the $k_{\parallel }=0\mathrm{}$ plane, with a smooth transition between the two. The orbit widths are used to calculate diffusion coefficients in tokamak-type configurations. These predictions are confirmed by test-particle computer simulations in ($x, y, v_x, v_y, v_z$) coordinates employing a Monte Carlo collision operator.