A model for calculations of Charge eXchange Recombination (CXR) signals of impurity nuclei injected in a high-temperature plasma has been developed. The CXR signals for an Li tracer in Tracer Encapsulated Solid PELlet (TESPEL) experiments on LHD and CHS machines have been calculated. The difference of about two orders of magnitude found in the calculated signals is due to the difference both in the NBI neutral flux density and in the capture-radiation cross-sections, and explains the weak Li3+ CXR signals observed in the measurements on LHD.Calculations of the CXR signals for various injected impurities have been performed for LHD conditions. The operational range of TESPEL diagnostics in the visible spectral range on LHD has been determined. For Te = 1-2 keV (PNBI = 3 MW) and Ne = (2-5)×1013 cm-3, injection of F, Mg and Al as tracer materials ensures the largest CXR signals together with complete ionization times of the injected impurity which are much smaller than the impurity transport times.
Multiple-tracer TESPEL injection for studying impurity behaviour in a magnetically confined plasma