Dynamics and Interplay of L-H-L Transitions and ITB Events in Reversed Shear Plasmas with Internal Barriers in JT-60U
Sergei V. Neudatchin1 , Tomonori Takizuka, Hiroshi Shirai, Takaaki Fujita, Akihiko Isayama, Yutaka Kamada, Yoshihiko Koide, Takahiro Suzuki and Satoshi Takeji
Japan Atomic Energy Research Institute, Ibaraki 311-0193, Japan
1) Permanent affiliation: RRC 'Kurchatov Institute', Moscow, Russia
Abstract.
Abrupt in time (correlated within a few ms with L-H and H-L transitions) and wide in space (from the edge up to ~0.3 of minor radius in the extreme case) variations of electron heat diffusivity δχe were found in reversed shear (RS) JT-60U tokamak plasmas with internal transport barrier (ITB) at various profiles of safety factor q . The δχe profile follows the position of q minimum (qmin) and penetrates into the RS region deeper for the weak ITB than for the strong one, suggesting the presence of 'global' edge-core connection throughout qmin in a ms timescale at L-H and H-L confinement bifurcations. The δχe value at the position of qmin is small for the strong ITB ( ~0.05 m2 s-1 ) and increases by an order of magnitude for the weak ITB. The ITB event is another non-local transport bifurcation (improvement or degradation) inside and around ITB. The case of strong ITB formation in H-mode via a series of ITB events in ELM-induced L-mode is described. ITB event degradation in the positive shear zone causes L-H transition.