Dense plasma effects on atomic data and line emission of He I for divertor plasma conditions

Effects of collisions between autoionizing levels of helium on its dielectronic recombination rate coefficients are investigated for ionizing plasma conditions encountered in magnetic fusion devices. It is shown that the so-called density effects including collisions and level depression seriously affect dielectronic recombination rates and can alter the atomic/ionic fraction of helium which enters in several diagnostics employing population densities. On the other side, Stark broadening of the high members of the diffuse series of neutral helium is also examined for recombining plasma conditions relevant to divertor regions. It is shown that similarly to the Balmer lines of hydrogen isotopes, high-n helium lines can be used for electron temperature and density determination.