Dependence of radial thermal diffusivity on parameters of toroidal plasma affected by resonant magnetic perturbations

We investigate how the neoclassical thermal diffusivity of an axisymmetric toroidal plasma is modified by the effect of resonant magnetic perturbations (RMPs), using a drift-kinetic simulation code for calculating the radial thermal diffusivity of ion in the perturbed region under an assumption of zero electric field. Here, the perturbed region is assumed to be generated on and near the resonance surfaces, and is wedged in between the regular closed magnetic surfaces. We find that the dependence of the radial thermal diffusivity on parameters of the toroidal plasma is represented as , where is the neoclassical thermal diffusivity and c0 is a positive coefficient. Here, ωb is the bounce frequency, νeff is the effective collision frequency, Δb is the banana width, 〈‖δBr‖2〉1/2 is the strength of the RMPs in the radial directions, and |Bt0| is the strength of the magnetic field on the magnetic axis. The value of is significantly reduced to in the simulations because of the drift motion affected by the Coulomb collision, as contrasted with predicted by the so-called field-line diffusion theory, where q is the safety factor, Rax is the major radius of the magnetic axis, and ϵt is the inverse aspect ratio.