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Oct 13 – 18, 2014
Hotel Park Inn Pribaltiyskaya
Europe/Moscow timezone

Mechanism of Low-Intermediate-High Confinement Transitions in Tokamaks

Oct 18, 2014, 11:30 AM
20m
Blue 1-5 (Hotel Park Inn Pribaltiyskaya)

Blue 1-5

Hotel Park Inn Pribaltiyskaya

Saint Petersburg, Russian Federation

Speaker

Mr Jiaqi Dong (China)

Description

Understanding the physics mechanism of low-high (L-H) confinement transitions in toroidal plasmas is essential for ensuring heating power requirements for future fusion reactors. Early experiments show that plasma may enter an intermediate phase (I-phase) with limit cycle oscillations (LCOs) of plasma parameters and pass through a slow L-H transition if heating power is close to the H-mode threshold. The triggering mechanism and conditions for L-I and I-H transitions are foci in the H-mode physics studies. Two theoretical models of LCOs were proposed and shown consistent with recent experimental observations, respectively. Here, we first report a discovery of two types of LCOs (type-Y and type-J, respectively) on HL-2A tokamak, which provides an opportunity to advance our understanding of LCO physics, and then discuss the L-I-H transition triggering mechanisms and conditions. The dynamics of the two types of LCOs observed in the experiment are analyzed in detail. Two loops of zonal flow versus turbulence and turbulence versus pressure gradient are proposed for the two types of LCOs. The conditions for the observed I-H transitions are identified to be (1) the I-phase has type-J LCOs, (2) the plasma pressure gradient scale length L_pe is less than a critical value (1.7 cm, here) and the EXB flow shearing rate is higher than a critical value (10^6 s^-1, here), and (3) the growth rate of the diamagnetic drift flow \gamma_DD is equal to or higher than the ion-ion collision frequency \nu_ii. Detailed observations, revealing L-I-H transition mechanism, will be presented.
Country or International Organisation China
Paper Number EX/11-3

Primary author

Mr Jiaqi Dong (China)

Co-authors

Dr Deliang Yu (Southwestern Institute of Physics) Dr Huasheng XIE (Institute for Fusion Theory and Simulation, ZJU) Dr Jun Cheng (Southwestern Institute of Physics) Dr Kaijun Zhao (Sothwestern Institute of Physics) Prof. Kimitaka Itoh (NIFS) Mr Lin Nie (Southwestern Institute of Physics) Prof. Longwen YAN (Southwestern Institute of Physics) Prof. Qingwei Yang (Southwestern Institute of Physics) Prof. Sanae Itoh (Research Institute for Applied Mechanics, Kyushu University) Prof. Wenyu HONG (Southwestern Institute of Physics) Mr Wulu Zhong (Southwestern Institute of Physics) Prof. Xianming SONG (Southwestern Institute of Physics) Dr Xiaoquan JI (Southwestern Institute of Physics, Chengdu 610041 China) Prof. Xuantong Ding (Southwestern Institute of Physics) Prof. Xuru Duan (Southwestern Institute of Physics) Prof. Yong LIU (Southwestern Institute of Physics) Prof. Yong Xiao (Institute for Fusion Theory and Simulation) Dr Yuan Huang (Southwestern Institute of Physics) Mr Zhihui HUANG (Southwestern Institute of Physics) Dr Zhixiong He (Southwestern Institute of Physics) Dr xiaolan zou (CEA)

Presentation materials