Diagnostics of the high-speed single-pellet injector for the Frascati Tokamak Upgrade

A diagnostic apparatus has been designed and tested, giving mass and speed measurements and in-flight pictures of the solid D₂ pellets for the high-speed (up to 3.3 km/s) single-pellet injector (SPIN) to be installed on the Frascati Tokamak Upgrade, (FTU), in order to completely characterize each of the launched pellets. A detailed description of the apparatus and of experimental results obtained with a prototype injector is given. From the point of view of speed determination, the system gives reliable results. Some problems have been detected on the volume (mass) determination, because the inner surfaces of the cavities have not been accurately treated for vacuum since they are prototypes. A new set of cavities is under construction and the whole setup will be improved according to what the experience with the prototypes suggests. Good-quality in-flight pictures of the pellets are reliably obtained by means of a video recording apparatus and a 20-ns pulsed flash lamp