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We present a new neoclassical transport model for large aspect ratio tokamakswhere the gradient scale lengths are of the size of the poloidal gyroradius.Previous work on neoclassical transport across transport barriers assumed largedensity and potential gradients but a small temperature gradient, or neglectedthe gradient of the mean parallel flow. Using large aspect ratio and lowcollisionality expansions, we relax these restrictive assumptions. We define anew set of variables based on conserved quantities, which simplifies the driftkinetic equation whilst keeping strong gradients, and derive equationsdescribing the transport of particles, parallel momentum and energy by ions inthe banana regime. The poloidally varying parts of density and electricpotential are included. Studying contributions from both passing and trappedparticles, we show that the resulting transport is dominated by trappedparticles. We find that a non-zero neoclassical particle flux requires parallelmomentum input which could be provided through interaction with turbulence orimpurities. We derive upper and lower bounds for the energy flux across atransport barrier in both temperature and density and present example profilesand fluxes.

Neoclassical transport in strong gradient regions of large aspect ratio tokamaks