In fusion plasma, the behaviour of impurities is important. In order to study the behaviour of impurities spectroscopic measurement is necessary. We are now studying EUV spectra from Large Helical Device (LHD) to study the behaviour of impurities. We present here the three kinds of EUV spectra measured from LHD.

In order to analyse the observed spectra, we need atomic data. We use collisional radiative models of different ions to estimate the line intensities. To construct a collisional radiative model we need a lot of atomic data between excited states. Model and atomic data are coupled. To derive correct answers from a model we need reliable atomic data.