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We developed a new diagnostic system of the hydrogen ice pellets for fueling into plasma devices. The system consists of three parts. They are: a light gate system, a microwave mass detector, and a shadowgraph system. This system provides the pellet velocity, mass and shape, simultaneously. In particular, by using multiple mirror system, the light gate system can achieve high detective probability with high signal to noise ratio for submillimeter pellets. At the results of the bench tests carried out on GAMMA 10 and the Large Helical Device, the light gate system completely detected the pellets used in the bench tests and the pellet velocity was estimated by using this system. Similarly, the shadowgraph system was available for the pellet. The microwave mass detector was found to be applicable. These results show the capability of simultaneous measurement of the pellet parameters using this diagnostic system. [ABSTRACT FROM AUTHOR]

A 20 barrel solid hydrogen pellet injector, which is able to inject 20 cylindrical pellets with a diameter and length of between 3.0 and 3.8 mm at the velocity of 1200 m/s, has been developed for the purpose of direct core fueling in LHD (Large Helical Device). The in situ pipe gun concept with the use of compact cryo-coolers enables stable operation as a fundamental facility in plasma experiments. The combination of the two types of pellet injection timing control modes, i.e., pre-programing mode and real-time control mode, allows the build-up and sustainment of high density plasma around the density limit. The pellet injector has demonstrated stable operation characteristics during the past three years of LHD experiments.