Development of a batch extruder for the testing of the EU-DEMO pellet puncher

Pellet injection technology is a proven, leading technology for fuelling and controlling the plasma density of magnetically confined fusion devices. Fuelling pellets are small in diameter and length, so when injected into the plasma, they don’t cause strong density modulation. In return, the injection frequency is quite fast, in the range of 10–20 Hz and quasi-continuous operation is required. Fuelling pellet injection systems consist of three main components: an ice extruder, a pellet cutter, and an accelerator. At the outlet of the extruder, a solid hydrogen rod is produced, which is cut to predefined lengths by a puncher mechanism. The pellets are then launched by gas propulsion or a centrifuge. In the Fusion Plasma Physics Department of the HUN-REN Centre for Energy Research (EK-CER), a new pellet puncher for EU-DEMO was developed (based on KIT design), along with a hydrogen batch extruder that would be used to test the pellet puncher in operation. The extruder is installed in our custom-made large flexible cryostat (LFC) and is cooled by a Sumitomo two-stage cryocooler. During the extrusion process, temperatures at multiple points, extrusion force, and piston position are all measured. This paper details the development of the EK-CER batch extruder, which was designed for the testing of the EU-DEMO Pellet Puncher. Mechanical design, thermal analyses, measurement results and planned future modification are presented.