Role of low order rational q values on the ITB-events in JT-60U plasmas

The formation of internal transport barriers (ITBs) near q=2,3 surfaces in normal (NrS) or optimized shear discharges of JT-60U and JET is well known. In reverse shear (RS) JT-60U plasmas, the role of q minimum (qmin) equal to 3, 5, 3, 2, 5, 2 is not obvious for ITB formation. ITB-events (non-local confinement bifurcations inside and around ITB in a ms timescale) are found in various JT-60U NrS and RS plasmas. Under sufficient power, ITB-events are seen at rational and not rational values of qmin. The space-time evolution of Te and Ti is similar even being strongly varied in space and time, suggesting same mechanism(s) of Te and Ti transport. The temporal formation of strong ITB in H-mode under passing of qmin=3 (after periodical improvements and degradations via ITB-events with 8ms period) in RS mode with Pnbi=8MW is presented. Under smaller power, ITB-events are observed only at rational values of qmin. In a weak RS shot with Pnbi=4MW, abrupt rise of Te is seen at qmin=3.5, while more cases of Ti rise are observed. The difference of the Te and Ti evolution seen regularly under the low power, suggests decoupling of Te and Ti transport. (author)