Acceleration characteristics of spherical and nonspherical pellets by the LHD impurity pellet injector

Nozato, Hideaki; Morita, Shigeru; Goto, Motoshi; Ejiri, Akira; Takase, Yuichi
March 2003
Review of Scientific Instruments;Mar2003, Vol. 74 Issue 3, p2032
Academic Journal
An impurity pellet injector with three differential pumping systems has been developed to study the particle/impurity transport in combination with bremsstrahlung profile measurement in the Large Helical Device (LHD) plasma. For this purpose three different shaped pellets are tested; sphere, hemisphere, and cylinder. The characteristics of the pellets accelerated by pressurized helium gas were studied as a function of shape and mass of the pellets and He gas pressure. The velocity of the pellets was measured at two different positions using a He-Ne laser, two optical fibers, two lenses, and a slit with two narrow apertures. The delay time until the pellet begins to accelerate, and the effect of opening time of the vacuum valves for differential pumping on the amount of He gas leakage were also investigated. The difference in the velocities among the three different shaped pellets is discussed with the simple analytical model.


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