Confinement degradation by Alfven-eigenmode induced fast-ion transport in steady-state scenario discharges

Analysis of neutron and fast-ion D-alpha data from the DIII-D tokamak shows that Alfven eigenmode activity degrades fast-ion confinement in many high beta(N), high q(min), steady-state scenario discharges. (beta(N) is the normalized plasma pressure and q(min) is the minimum value of the plasma safety factor.) Fast-ion diagnostics that are sensitive to the co-passing population exhibit the largest reduction relative to classical predictions. The increased fast-ion transport in discharges with strong AE activity accounts for the previously observed reduction in global confinement with increasing q(min); however, not all high q(min) discharges show appreciable degradation. Two relatively simple empirical quantities provide convenient monitors of these effects: (1) an 'AE amplitude' signal based on interferometer measurements and (2) the ratio of the neutron rate to a zero-dimensional classical prediction.