Quiet Periods in Edge Turbulence Preceding the L-H Transition in NSTX

Zweben, S ; Hager, R ; Hallatschek, K ; Kaye, S M ; Munsat, T ; Poli, F M ; Roquemore, A L ; Sechrest, Y

关键词: SHEAR;    TURBULENCE;    VELOCITY H-Mode Plasma Confinement;    Turbulence;    Tokamaks;    NSTX;   

DOI  :  10.2172/981661
RP-ID  :  PPPL-4510
PID  :  OSTI ID: 981661
Others  :  TRN: US1004437

学科分类：原子、分子光学和等离子物理

美国|英语

来源: SciTech Connect

【 摘 要 】

This paper describes the first observations in NSTX of ???quiet periods??? in the edge turbulence preceding the L-H transition, as diagnosed by the GPI diagnostic near the outer midplane separatrix. During these quiet periods the GPI D?? light emission pattern was transiently similar to that seen during Hmode, i.e. with a relatively small fraction of the GPI light emission located outside the separatrix. These quiet periods had a frequency of ~3 kHz for at least 30 msec before the L-H transition, and were correlated with changes in the direction of the local poloidal velocity. The GPI turbulence images were also analyzed to obtain an estimate for the dimensionless poloidal shearing S =(dVp/dr)(Lr/Lp)??. The values of S were strongly modulated by the quiet periods, but not otherwise varying for at least 30 msec preceding the L-H transition. Since neither the quiet periods nor the shear flow increased significantly immediately preceding the L-H transition, neither of these appears to be the trigger for this transition, at least for these cases in NSTX.