Ubiquity of non-diffusive momentum transport in JET H-modes

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 normalized angular frequency gradient R∇ω/ω 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 magnitude and parameter dependences 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/χphiv and the Prandtl number χphiv/χi are in good agreement with the experimental observations, with similar dependences on R/Ln, q and ε = r/R. A contribution due to residual stresses may also be present, but could not be identified with certainty.