Vibrational population of the ground state of H 2 and D 2 in the divertor of ASDEX Upgrade

Abstract

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 D 2 and H 2 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 H 2. With respect to isotope investigations the measurements and parameter studies show that the transfer of the CR model to D 2 needs an implementation of complete data sets, i.e., rate coefficients, or at least reliable scaling of the input data given.