Vibrational population of the ground state of H2 and D2 in the divertor of ASDEX Upgrade

Molecular hydrogen isotopes in the divertor region of fusion experiments may affect the divertor plasma via dissociation, ionization and recombination processes [1]. These processes depend on the vibrational population of the ground state of the molecules. The vibrational populations of D2 and H2 were investigated simultaneously at similar divertor plasma conditions, i.e., degree of detachment. The spectroscopic method [2] used, yields vibrational temperatures of 4000–6000 K in the outer divertor, depending on plasma parameters. The isotopes show tendencies, known from laboratory experiments [2], especially similar vibrational ground state populations up to v=4. As previously shown for pure hydrogen discharges [3], the interpretation of experimental data and plasma edge simulations (B2-EIRENE) needs a collisional-radiative (CR) model for H2. With respect to isotope investigations the measurements and parameter studies show that the transfer of the CR model to D2 needs an implementation of complete data sets, i.e., rate coefficients, or at least reliable scaling of the input data given.