Diagnostic twin screw extruder for characterizing fusion fuel production

Fusion tokamaks require highly reliable fuel production systems to sustain reactions and continuously produce energy. For example, the ITER tokamak design specifies a control accuracy of 5 % for fueling. Counter rotating twin screw extrusion has a long history of success in the polymer industry and is theoretically the most reliable and efficient method for continuously producing hydrogenic fuel for fusion tokamaks. However, hydrogenic fuel solidifies at extremely low temperatures (in the range 10 -- 30 K) so extrusions are fundamentally different and initial prototypes have had problems with stalling and rapid expulsion. Polymer extrusion has benefited from specially designed extruder experiments for characterizing heat transfer and fluid flow. Data from these experimental machines has validated throughput models used to create characteristic curves for optimizing extruder performance. Currently there is no data to develop or validate throughput models for hydrogenic twin screw extrusion and no extruder experiment built for collecting such data. The only option for fusion scientists is to improve prototypes iteratively costing time and resources. The objective of this research is to design an experiment that produces fundamental data for characterizing hydrogenic twin screw extruders. The Diagnostic Twin Screw Extruder (DTSE) was designed specifically for characterization with a unique operating cycle and instrumentation including temperature sensors embedded in the screws. A full description of the DTSE design and operation is presented. Data has been collected from processing solid hydrogen, deuterium, and neon. Data analysis has shown heat transfer and fluid flow characteristics for reference when diagnosing extruder operation. Basic heat transfer predictions have been compared to experimental data to show how models can be developed using the DTSE. The DTSE enables fusion scientists to develop characteristic curves for designing reliable twin screw extruders for fueling ITER and other future tokamaks.