A hydrogen pellet injector by a droplet-method has been constructed and studied, in order to realize a hydrogen-isotope pellet injector for refueling into nuclear fusion reactors, which can inject pellets into plasma repetitively. Preliminary experiments with oxygen gas, instead of hydrogen gas, has been systematically carried out. Assuming the liquid concerned as viscous fluid, theoretical predictions about droplet-diameter, its ejected velocity and optimum frequency of ejecting-nozzle vibration for stable droplet production has been made, and it is found that theoretical results are in good agreement with experimental ones. It is found that the stable droplet train can be obtained when the value of Reynolds number is in the range of 1, 100-1, 300. In the hydrogen experiments based upon the oxygen results, the production of a stable hydrogen liquid-droplet train, their self-solidification and transfer into a vacuum space through an orifice (with the diameter of 1mm) have been successfully realized, by maintaining the gas pressure around the droplets at 45-50 Torr.
