Observation of the low to high confinement transition in the large helical device

K Toi,K Ida,K Matsuoka,M Osakabe,Y Takeiri,S Sakakibara,J Miyazawa,K Nagaoka,K Narihara,S Takagi,K Kawahata,I Yamada,K Yoshinuma,N Ohyabu,Y Nagayama,S Inagaki,M Goto,S Morita,Y Oka,K Y Watanabe,K Ikeda,O Kaneko,S Masuzaki,S Ohdachi,F Watanabe,Lhd Experimental Group,A Komori,K Tanaka,H Yamada,N Nakajima,K Tsumori,T Morisaki,T Tokuzawa,Satoru Yamamoto

doi:10.1063/1.1843122

Abstract

The low to high confinement transition has been observed on the large helical device [A. Iiyoshi, A. Komori, A. Ejiri et al., Nucl. Fusion 39, 1245 (1999)], exhibiting rapid increase in edge electron density with sharp depression of Hα emission. The transition occurs in low toroidal field (Bt=0.5–0.75T) discharges and are heated by high power neutral beam injection. The plasma thus has a relatively high value (∼1.5%) of the volume averaged β value. The electron temperature and density profiles have steep gradients at the edge region which has high magnetic shear but is at a magnetic hill. Formation of the edge transport barrier leads to enhanced activities of the interchange type of modes with m=2∕n=3 (m,n are the poloidal and toroidal mode numbers) in the edge region. At present, these magnetohydrodynamic activities limit the rise of the stored energy; the resultant increment of the stored energy remains modest.

Highlights

Observation of the low to high confinement transition in the large helical device journal or publication title volume number page range year
The low to high confinement transition has been observed on the large helical device 关A
The transition occurs in low toroidal field 共Bt

Summary

Introduction

Observation of the low to high confinement transition in the large helical device journal or publication title volume number page range year. The low to high confinement transition has been observed on the large helical device 关A. The electron temperature and density profiles have steep gradients at the edge region which has high magnetic shear but is at a magnetic hill.

Results

Conclusion