Abrupt in time and wide in space variations of heat diffusivity during ITB formation in JT-60U reverse shear discharges

摘要

New features of the space-time evolution of the internal transport barrier (ITB) were highlighted during recent JT-60U reverse shear (RS) experiments. An ITB evolution in RS plasmas is often a combination of the fast time-scale processes and the gradual ones. Fast time-scale processes are the common intrinsic features of JT-60U RS plasmas and are seen as the simultaneous (within a few milliseconds) rise and decay of electron temperature (T-e) on two zones separated by a region without variation of T-e. The region without variation of T-e is located near the position of the minimum safety factor profile (q(min)) for many fast processes. The present robust result is that the region of fast-time-scale improvements of electron heat diffusivity is wide in space (around 0.3 of the minor radius) and well extended to the zone of T-e decay. [References: 12]