Non-diffusive Momentum Transport in JET H-mode Regimes: Modelling and Experiment
A broad survey of the experimental database of neutral beam heated baseline H-modes and hybrid scenarios in the JET tokamak has established the ubiquity of non-diffusive momentum transport mechanisms in rotating plasmas. As a result of their presence, the normalised angular frequency gradient Rw/w is higher than expected from momentum diffusion alone, by about unity in the core (r/a~0.3), rising to near 5 close to the edge, where its contribution to the total gradient is comparable to the gradient associated with the diffusive flux. The experimental plasma parameters have been used as input for an extensive set of linear gyrokinetic simulations using GKW. The magnitude and parameter dependencies of the non-diffusive contribution to the gradient are consistent with a theoretically expected pinch, which has its origin in the vertical particle drift resulting from the Coriolis force. Linear gyrokinetic calculations of the pinch number RV/cf and the Prandtl number cf/ci, are in fair agreement with the experimental observations, with similar dependencies on R/Ln, q and e = r/R for the convective part. However, the predicted non-diffusive transport is about 30% lower, on average, than the one inferred from observation. A second round of linear gyrokinetic simulations, with more realistic assumptions, has been initiated to clarify whether the difference may be attributed to residual stresses.