Evaluation of Ion Temperature and Plasma Rotation at LHD from Charge-Exchange Spectra with Photon-Statistical Weighting

Abstract

A new diagnostic for LHD is presented, which utilizes active charge-exchange signals from Hydrogen (main ions) and Helium (impurity ions) to derive the radial ion-temperature and ion-velocity profiles as well as the H/He ratio profile. In a sensitivity study, different models for profile fitting and measurement uncertainties are compared, which leads to first results. This covers fitting with one Gauss function and two Gauss functions as well as the inclusion of read-out noise and photon noise. Full error propagation from the measured spectra to the resulting profiles is provided by utilizing Bayesian statistics in combination with a weighted least-squares fit and boundary conditions. Reliable and accurate results were achieved for the ion-temperature profiles, which are in good agreement with the well-proven Carbon diagnostic. Concerning the quality of the velocity profiles, no statement could be made. The H/He ratio measurements in contrary lead to accurate results. Calibration with the H/He ratio of passive emission near the plasma edge just before the end of the discharge allows calculating absolute values for Helium and Hydrogen density profiles.