关键词: plasma, diffusion coefficients, energy profile, atomic and molecular processes, simulation of D_α line shape

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 $1.5\times10^{19}$ to $3.0\times10^{19}$m$^{-3}$. The energy profile of the particles is derived directly from the $H_{\alpha}(D_{\alpha}$) 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 $D_{\alpha}$ 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 $6\times10^4$kW 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$$\cdot$s$^{-1}$ and the particle confinement time rises from 9 to 12ms.

Key words: plasma, diffusion coefficients, energy profile, atomic and molecular processes, simulation of $D_{\alpha}$ line shape