Using the radiation of hydrogen molecules for electron temperature diagnostics of divertor plasmas

The radiation of hydrogen molecules in the divertor of fusion experiments is proposed to be a sensitive diagnostic method for electron temperature (Te) in the range between 1 and 7 eV. A collisional-radiative (CR) model for H2 was used for the prediction of vibrational population in the ground state of the molecule, depending on electron temperature. In addition, the model was modified in order to enable diagnostics for deuterium. Applying the Franck-Condon principle and vibrationally resolved excitation rate coefficients the population was transferred into the upper state of the Fulcher transition (d3Πu-a3Σg+). On the other hand, the relative population in the excited state can be derived directly from the emission spectra of the diagonal Fulcher bands. Results of hydrogen discharges in ASDEX Upgrade will be presented, which show that the strong variation in Te during the discharge correlated with the degree of plasma detachment. The transferability for deuterium will be demonstrated by discussing results of deuterium discharges including hydrogen injections. Due to the spectroscopic technique, the derived Te represents the volume where the radiation of the molecules originates. (author)