Non-statistical populations of magnetic sublevels of hydrogen beam atoms in fusion plasmas

Emission of spectral lines from the excited states of neutral beam atoms in fusion plasmas is the basis of beam emission spectroscopy and motional Stark effect diagnostics. It is well known that the measured intensities of Stark multiplet lines between the n=3 and 2 excited states of hydrogen systematically deviate from the full statistical model. Here we study the Hα Stark component intensities using a newly developed collisional-radiative model that is based on the description of magnetic sublevels in a parabolic basis. Proton excitation cross-sections between the parabolic states are calculated in the Glauber (eikonal) approximation. The model incorporates various collisional processes between the hydrogen beam atoms and plasma particles (protons, impurity ions and electrons) as well as the radiative processes. The simulated line component ratios σ1/σ0, π2/π3 and π4/π3 are found to agree with the measured ratios from JET plasmas within the experimental uncertainties.