Study of particle behaviour at the edge in HT-7 tokamak |
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| Authors: | Xu Wei Wan Bao-Nian Zhou Qian Wu Zhen-Wei Mao Jiao-Shan and Li Jian-Gang |
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| Affiliation: | Institute of Plasma Physics, Chinese Academy of Sciences, Hefei 230031, China; Department of Physics, Guangzhou University, Guangzhou 510405, China |
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| Abstract: | The cross-field diffusion coefficient (D_⊥) at the edge in the HT-7 tokamak is close to the Bohm value when the line average electron density ranges from 1.5×10^{19} to 3.0×10^{19}m^{-3}. The energy profile of the particles is derived directly from the H_α(D_α) line shape; the dissociative excitation of molecules is dominating when the local electron temperature is above 10eV. By means of the Monte Carlo method the D_α line shape is also simulated. We find that the molecular dissociation contributes to 57% of neutral atoms and 53% of emission intensity in front of the limiter, and 85% of neutral atoms and 82% of emission intensity in front of the wall. The influence of atomic and molecular processes on the energy balance is discussed for the scrape-off layer (SOL), and the power loss from molecular dissociation is found to be 6×10^4kW at the SOL. The ion Bernstein wave (IBW) can effectively suppress the magnetohydrodynamic behaviour, the fluctuation levels and the turbulence; the D_⊥ in front of the limiter declines from 0.84 to 0.2m^2·s^{-1} and the particle confinement time rises from 9 to 12ms. |
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| Keywords: | plasma diffusion coefficients energy profile atomic and molecular processes simulation of D_α line shape |
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