Return To: Session EX2 - Transport 1
Prev Page: (EX2/6) Core and Edge Confinement Studies with Different
Next Page: (EX2/D) Discussion of Session EX2

(EX2/7) Relation Among Potential, Fluctuation Change and L/H Transition in the JFT-2M Tokamak

Y. Miura¹⁾, T. Ido²⁾, K. Kamiya¹⁾, Y. Hamada²⁾ and JFT-2M Group^1)
 
1) Japan Atomic Energy Research Institute, Ibaraki, 311-0193, Japan
²⁾ National Institute for Fusion Science, Gifu, 509-5292 Japan

Abstract.  Potential and density/temperature fluctuation at L-H transition are measured by the heavy ion beam probe (HIBP) on JFT-2M. It has been observed that the time scale of potential change is as fast as 10-100 $\mu$s when the input power ( P_in) is larger than the L-H threshold power ( P_th). When P_in $\sim$ P_th , the confinement is improved gradually step by step with sawteeth crashes accompanied with the decrease of potential. After a few sawteeth crashes, potential drops rapidly to the level of the ELM-free H-mode. From the gradual change of the potential with assuming that dE_r/dr is a key to form and to sustain the transport barrier, the criterion of the dE_r/dr is less than (1.2±0.4)×10³kV/m². At an ELM just before H-L transition, the potential inside the separatrix also shows the rapid positive jump. The time scale of the positive jump and its recover to its negative value is about 40$\mu$sec and 150$\mu$sec, respectively. Before the H-L transition, the time between ELMs and/or dithering transition becomes shorter and the plasma finally goes back to L-mode.

Read the full paper in PDF format.