Characterization of the deuterium recycling flux in front of a graphite surface in the TEXTOR tokamak

In the TEXTOR tokamak, experiments were performed to simultaneously determine the molecular, atomic and total particle flux of deuterium in front of a graphite limiter, the temperature of which can be controlled independently of the plasma conditions. With rising limiter temperatures, T-TL, but constant plasma conditions an increase in Balmer emission and a decrease in Fulcher-band emission were observed. This variation is associated with a change in the type of released species: molecules dominate at low temperatures (550 K < T-TL < 1100 K), whereas at temperatures T-TL >= 1100 K the direct atomic release starts to become important. The total number of deuterons remains constant for all temperatures. Since not all molecules dissociate into two potentially radiating atoms, it is necessary to take into account the ratio of atoms to molecules when deducing the total particle flux from the Balmer emission. We present a spectroscopic method which allows the determination of the atomic, molecular and total deuterium particle flux and which also gives effective conversion factors, (S/XB)(eff), to deduce the total deuterium flux from Balmer-alpha emission alone. Analysis of the spectroscopic data of both species can be performed to determine the rotational and vibrational populations for the molecules by means of Fulcher-alpha spectroscopy, and the penetration depth and energy for the atoms using Balmer spectroscopy. This further analysis gives additional information about the release mechanism, showing that both species, atoms and molecules, are released predominantly as thermalized particles.