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(EXP1/02) H$\alpha$ Line Shape in Front of the Limiter in HT-6M Tokamak / Current Relaxation and its Roles in Improved Confinement

   
B. N. Wan , J. Li , J. Luo , J. K. Xie , Z. W. Wu  and HT-6M Group 
 
Institute of Plasma Physics, Chinese Academy of Science, P.O.Box 1126 Hefei, China 230031

Abstract
In this paper H$\alpha$ line shape in front of the limiter in HT-6M  tokamak is analyzed by multi-Gaussian fitting. The energy distribution of neutral hydrogen atoms reveals that H$\alpha$ radiation is contributed by Frank-Condon (FC) atoms, atoms reflected at the limiter surface and charge exchange. Dissociation of hydrogen molecules and reflection of particles at the limiter  surface are dominante in edge recycling. To lower particle reflection at the limiter surface is an important issue for controlling edge recycling . The measured profiles of neutral hydrogen atom density are reproduced by particle continue equation and a simplified one-dimension Monte-Carlo simulation code.

Abstract
Effective Low Hybrid wave Current Driving (LHCD) and improved confinement  in higher electron density have been attained in HT-6M tokamak by combining with Low Hybrid wave Heating (LHH). Experiments and code simulation show that off-axis plasma current is driven and sustained by LHW in higher electron density and relax at the time scale of resistive diffusion. Sustaining of improved confinement is strongly governed by current density profile and its relaxation. Relevant issues are also discussed.

     

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