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(EX/P2-06) Role of Low Order Rational q Values in the ITB-events in JT-60U Plasmas

S.V. Neudatchin1), T. Takizuka2) N. Hayashi2), H. Shirai2), T. Fujita2), A. Isayama2), Y. Kamada2), Y. Koide2), T. Suzuki2)
1) Nuclear Fusion Institute RRC Kurchatov Institute, Moscow, Russia
2 Japan Atomic Energy Researh Inst., Naka Fusion Research Est., Japan

Abstract.  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 evolution. ITB-events (non-local confinement bifurcations inside and around ITB in a ms timescale) are found in various JT-60U NrS and RS plasmas. (a) 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. The temporal creation of stronger ITB in H-mode (after periodical improvements and degradations via ITB-events with 8 ms period) under passing of qmin = 3 is presented ( Pnbi = 8 MW, 1.5 MA / 3.7 T). (b) Under smaller power, the influence of some rational qmin is seen clearly for ITB-events on Te. In 1.3 MA/3.7 T shot with very weak RS (Pnbi = 4 MW), abrupt rise of Te is seen at qmin = 3.5, while more cases of Ti rise are observed. (c) The possible role of MHD-activity as ITB-events trigger (ms time scale correlation in some NrS and RS cases) is under investigation.

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IAEA 2003