Applications of spectroscopic methods to the characterization of the ablation clouds of pellets in magnetic fusion devices

In the field of magnetic fusion research, pellet injection is considered as a major technique for deep plasma fuelling and plasma control by mitigation of edge instabilities. Pellet injection is planned for ITER as the primary core fuelling system. For such major purposes, pellets made of hydrogen or its isotopes are used. In addition, some other purposes are achievable using pellets made from other materials like carbon, aluminium, molybdenum, titanium and so on. In the Large Helical Device (LHD), pellets are used to characterize the transport of impurities. Investigating the ablation clouds of different pellets injected in LHD using spectroscopic measurements may allow to improve our understanding of the physics of the ablation of pellets injected in magnetic fusion devices. A spectroscopic technique based on the emission line intensities and broadening has been previously applied to carbon pellets before its generalization to other pellets. In this paper we illustrate this technique for the case of aluminium pellets. Using data from LHD, it has been shown that line intensities can bring valiant information allowing the characterization of the cloud surrounding the pellet core inside the plasma. For carbon pellets it was mandatory to take into account of radiation absorption effects on some lines. The data investigated here were obtained from LHD where different pellets were injected in the device in the aim of realizing high ion temperature plasmas