Balmer-α spectroscopic study on hydrogen recycling and molecular effects in HT-7

When incidence on the plasma facing material in a fusion device, hydrogen and its isotopic ions and neutrals return by either reflection or desorption in the form of molecules or atoms, which collide with the main plasma. These recycling behaviors strongly influence the energy and particle transports in the edge plasmas. In previous HT-7 experiment, it was shown that Dα profile can be decomposed into two energy groups, a group of atoms in energy up to 10 eV and the other group of atoms in energy less than 1 eV. In this paper, we modeled the hydrogen and deuterium atom/molecular transport using DEGAS2 code. Emission of Balmer-α lines and its profile are in particular modeled and compared with the experiment. It was shown that the H2/D2 molecular dissociation into H(2s) or D(2s) plays important role and is the main contribution to the low component of the observed Balmer-α emission.