Energy Distribution of Recycling Particles in Front of the Limiter and the Wall on the HT-7 Tokamak

The H_α(D_α) line shape in front of the limiter and the wall is measured by two sets of optical spectroscopy multi-channel analysers. The energy distribution is derived directly from the H_α(D_α) line shape, especially showing several molecular processes. The dissociative excitation of molecules is dominating when the local electron temperature is above 10 eV. The D_α line shape is also simulated by the Monte Carlo method, the result shows that the molecular dissociation contributes 57% neutral atoms, 53% emission intensity in front of the limiter, and 85\% neutral atoms, 82% emission intensity in front of the wall. The power loss from molecular dissociation is about 5.6 x 10⁴kW/m^-3 and the molecular dissociation is an important cooling mechanism at the plasma edge.