High-speed multishot pellet injector prototype for the Frascati Tokamak Upgrade

The Frascati Tokamak Upgrade (FTU) may require multiple high-speed pellet injection in order to achieve quasi-steady-state conditions. A research and development program was thus being pursued at ENEA Frascati, aimed at developing a multishot two-stage pellet injector (MPI), featuring eight “pipe gun” barrels and eight small two-stage pneumatic guns. According to FTU requirements, the final goal is to simultaneously produce up to eight D2 pellets, and then deliver them during a plasma pulse (1 s) with any time schedule, at speeds in the 1–2.5 km/s range. A prototype was constructed and tested to demonstrate the feasibility of the concept, and optimize pellet formation and firing sequences. This laboratory facility was automatically operated by means of a programmable logic controller (PLC), and had a full eight-shot capability. However, it was equipped as a first approach with only four two-stage guns. In this article we will describe in detail the guidelines of the MPI prototype design, which were strong...