Hydrogen Atom Velocities and Penetration Depths in Front of Graphite Surfaces in TEXTOR

On the tokamak TEXTOR hydrogen atom velocities and penetration depths have been determined both by active Lyman- and passive Balmer-line spectroscopy of atomic hydrogen in combination with molecular spectroscopy for a variety of surface temperatures and gas blow rates. These variations influence both the molecule to atom ratio and the local boundary plasma parameters, which in turn determine the Franck–Condon energies of the dissociated atoms. Most of the released atoms have thermal energies and reflect the temperature of the emitting surface. Molecules from these surfaces are selectively vibrationally excited and may dissociate with small energies because e.g. excitation can now take place into lower energies of the repulsive state 2p 3 Σ u . On the other hand this state can also give rise to high Franck–Condon energies for ground state molecules in a cold plasma.