The effect of collision frequency on neoclassical polarisation current

We have determined the expression for the neoclassical polarisation current in the collisional limit (v_ii/eεω), using the drift kinetic theory. The result is in agreement with the fluid calculation of Ref.[6], when the collision operator in Ref.[5] is used. Using the same collision operator, the bootstrap current perturbation in Ref.[2] has been reviewed. The result is in better agreement with the standard expression for J_bs, but scaled by 〈∂h/∂_χ〉Ω, as expected. The collisional effects in the dissipation layer has been considered. In the low collision frequency limit, the contribution to the parallel current perturbation from the dissipation layer is found to scale as √ν_ii/εω, with an additional weak logarithmic variation √εω/ν_ii. Consequently, in the low collision frequency limit, the critical island width wc is found to scale as ι√ν_ii/εω. Work is in progress to determine the collision frequency dependency of w_c for an arbitrary value of √ν_ii/εω.