The design and performance of a twenty barrel hydrogen pellet injector for Alcator C-mod

A twenty barrel hydrogen pellet has been designed, built and tested for use on the Alcator C-Mod Tokamak at MIT. The design is the first to use a closed cycle helium refrigerator to cool the thermal system components and employs in-situ condensation of the fuel gas. The design of the pellet tracker a diagnostic for following the trajectory of the pellets in time is outlined. This paper discusses the design goals and engineering features of the injector as well as laboratory performance results. Tracker data obtained during injection experiments is also presented.