Global Drift Wave Map Test Particle Simulations of Enhanced Confinement

Global drift wave map equations allow the integration of particle orbits on the long time scale needed to describe transport. Ensembles of test particles are used to simulate the L-mode/RS/ERS plasmas in TFTR, and the pellet injected OS plasma in JET. For the simulation, we adopt the result from neoclassical calculation of the radial electric field E_r and the Taylor et al. model for the drift wave fluctuations which takes into account the change of mode structures by E_r. The simulations give steady state particle density profile and two different measures of the global diffusivities: (1) time average of running diffusivity and (2) diffusivity from the mean exit time. The simulations show that for either weak or reversed magnetic shear and highly sheared E_r particle transport barriers are established. In the presence of the transport barrier, it is shown that there is, in general, a difference between two global measures of diffusivity. The difference is explained by a simple model of the transport barrier.