Speaker
Mr
Gunyoung Park
(Republic of Korea)
Description
High confinement mode (H-mode) is essential as a baseline operating scenario in ITER. In order to develop a predictive model of the power threshold for access to H-mode in ITER, it is essential to understand first the underlying mechanism that triggers the transition. It is widely accepted that edge transport barrier (ETB) formation in H-mode is due to the suppression of turbulence by E x B flow shear. In several recent experiments, turbulence-driven flows were suggested as a trigger for the L→H transition. In this paper, a 3D fluid simulation model of the L→H transition is presented. Specifically, we report the results of 3D flux-driven simulations of resistive ballooning modes (RBM) turbulence with neoclassical flow damping effect in the edge of a tokamak. It is found that ETB forms naturally due to mean shear feedback through evolving pressure gradient once input power exceeds a threshold value. We show that (1) the transition to ETB is triggered by the turbulence-driven flow via a limit cycle oscillation (LCO) of turbulence intensity and E x B flow shear; (2) the correct transition criterion (threshold) is given by R_T > 1 (R_T: normalized Reynolds power defined as a ratio of the Reynolds power to the rate of energy input into the turbulence), instead of the conventional mean shear criterion, i.e., E x B flow shearing rate larger than linear growth rate; (3) neoclassical poloidal rotation damping effect significantly affects the transition process. A slow power ramp-down simulation is also performed to study H→L back transition and hysteresis phenomena. Detailed results will be presented.
| Country or International Organisation | Korea, Republic of |
|---|---|
| Paper Number | TH/8-1 |
Author
Mr
Gunyoung Park
(Republic of Korea)
Co-authors
Dr
Hogun Jhang
(National Fusion Research Institute)
Dr
Michael Leconte
(NFRI)
Prof.
Patrick H. Diamond
(NFRI, UCSD)
Dr
Sung Sik Kim
(National Fusion Research Institute)
Dr
Tongnyeol Rhee
(NFRI, Daejeon, South Korea)
Dr
Xueqiao Xu
(Lawrence Livermore National Laboratory)
