In-situ calibration of charge exchange spectroscopy for spatially resolved measurements of helium-hydrogen density ratio in Wendelstein 7-X

Abstract

In-situ calibration of charge exchange spectroscopy for spatially resolved measurements of helium-hydrogen density ratio is described in this paper. The helium-hydrogen density ratio in the core plasma is derived from the intensity ratio of the active helium line HeII (468.6 nm) and hydrogen line HI (656.3 nm) due to the charge exchange recombination process between fully ionized ions and neutral beam. This system is calibrated by the helium-hydrogen density ratio evaluated from HeII (656.0 nm) and HI (656.3 nm) in the recombining phase at the end of the discharge. The helium-hydrogen density ratio at the plasma center derived from the calibrated charge exchange spectroscopy is compared with the influx ratio estimated from the passive spectroscopy.journal articl