Hydrogen extruder concept for repetitive pellet injection

Plasma fueling by pellet injection is an important technological requirement of a tokamak machine. Based on the twin-screw extrusion principle design of a hydrogen extruder system has been carried out. It is aimed for the development of repetitive pellet injector system for Indian tokamaks SST-1 and Aditya-Upgrade. This extruder system will be initially used as an experimental system to attain a hydrogen extrusion throughput of ~ 400 mm³ /s. With a sufficient safety margin we are expecting pellet frequency of 10Hz and pellet size 3mm (L) x 3mm (D) in size. In the present design a counter rotating intermeshing twinscrew geometry with square thread is selected. Each screw will be having 28 mm root diameter, 4 mm screw cavity depth and 10 mm pitch with a screw helix angle of 6.5 degree. In the present work design of screw geometries, their support, thermal link with the cryocooler are discussed along with the thermal and structural analysis. A cuboid shaped chamber is designed to accommodate all the cooling stages and extruder elements. The design of subcomponents and extruder system as a whole is discussed here. (author)