For the study of plasma physics, the measurement of the ion temperature and plasma rotation velocity profiles are of fundamental importance in controlled fusion research, several diagnostics have been developed to measure this quantity. Among them, The Charge Exchange Spectroscopy(CES) has been used as a diagnostic tool for measuring the concentrations of impurity ions and studying impurity behaviors in fusion plasma. In general, The CES is applied to investigate spectral lines emanated from light impurities such as C, He, Ne, Be, etc. Although measurement of the properties of the main ion species (H or D) is of primary importance in fusion plasma, spectral lines from impurity have been preferred due to the complexities and difficulties on the analysis of the spectral lines from main ions. Practically, main ion temperature is assumed to be same with impurity temperature when the collision frequency between main ions and impurities with help enough but rotation velocity of main ion is expected to be the dissimilar with impurity rotation velocity. In addition, measurement of impurity has restrictions depending on what is the material of the Tokamak. Consequentially, direct measurement of main ion properties is still demanded since these approaches cannot be validated in some cases.
In 2012, 2013 KSTAR experimental campaign, the main ion spectral lines has been investigated under the framework of the development of main ion CES system. Also, in order to overcome difficulties in analyzing spectral information around deuterium and hydrogen lines at 656.1 nm and 656.3 nm from the main ions of high temperature plasma in KSTAR, a two-grating spectrometer system is built using two concave mirrors. The spectral resolution is achieved up to 0.03Å. Simulation work for predicting charge exchange spectral lines for hydrogen and deuterium in some cases has been don for assessing the requirement for the spectrometer for main ion CES. The measured active charge-exchange signal can be fitted with two-Gaussian functions by means of a nonlinear least-squares fitting.
