Advanced Diagnostics of particle transport by using tracer-encapsulated pellet Injection

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A method using a flexible tracer-encapsulated solid pellet (TESPEL) has been developed for transport study on the Large Helical Device (LHD). The method has flexibility in the selection both of size of the pellet and of the tracer material. The size of the outer layer made of polystyrene can be changed from 300 \JLTO. to 900 \Lia in diameter. This contributes to the wide selection of the deposition location of the tracer particles in the plasma. The flexibility in the selection of the tracer material contributes to the appropriate selection of the atoms according to the plasma parameters such as Te in the concerned plasma. The amount of the tracer particles (typical number is 1017 particles) can be changed easily by more than a factor of 50. TESPEL consists of polystyrene as an outer part and another material as an inner core. At first, it was confirmed at the CHS that the tracer of lithium was deposited locally in the plasma. Moreover, the behavior of the tracer particles was observed clearly by charge exchange recombination spectroscopy using a heating neutral beam. TESPEL was also injected into the LHD. In this case, the Ka line and the other spectra in the vacuum ultra violet region of titanium were observed without necessity of a neutral beam. Those multi-chord data with temporal resolution of about 20 ms were compared with the impurity transport simulation with the codes such as MIST and STRAHL. Thus, the particle diffusion coefficient and the inward pinch velocity were obtained for various plasmas. Those results have shown that this method is promising.