Anomalous Particle and Impurity Transport in JET and Implications for ITER
Results from an extensive database analysis of JET density profiles show that the density peaking factor ne0/<ne> in JET H-modes increases form near 1.2 at high collisionality to around 1.5 as the plasma collisionality decreases towards the values expected for ITER. This result confirms an earlier observation on AUG. The density peaking behaviour of L modes is remarkably different from that of H modes, scaling with overall plasma shear as (ne0/<ne> µli), independently of collisionality. H-mode density profiles show no shear dependence, except at the lowest collisionalities. No evidence for additional LTe, LTi, Te/Ti, b or r* dependences has been obtained. Carbon and neon impurity density profiles from Charge Exchange Spectroscopy are less peaked than electron density profiles and usually flat in H modes. The possibility of heavy impurity accumulation at ITER collisionalities remains an issue. The peaking of the electron density profiles, together with the flatness of the light impurity density profiles, are favourable for fusion performance if they can be extrapolated to ignited conditions. Peaked density profiles would help to recover the fusion performance loss resulting from a possible lower-than-expected density limit in ITER.