A Review of Pellet Injector Technology: Brief History and Recent Key Developments

For the last 15 to 20 years, substantial advancement has been achieved globally in the field of pellet injector technology (PIT). Nuclear fusion is a method for producing high-energy neutrons, alpha particles, and an enormous amount of energy with the help of thermonuclear reaction of hydrogen isotopes. The way of producing this huge energy source is similar to that of the sun’s generated energy. This type of energy does not produce greenhouse gases or a high-level radioactive surplus. Solid hydrogen is used as a fuel in a fusion reactor in the form of pellets of different diameters and lengths. These pellets are produced by a pellet injector. In the sophisticated fueling system, these pellets are continuously produced with the help of a twin-screw extruder (TSE) and cooled by more than one cryocooler or liquid helium. Each pellet injection system has its pros and cons. We have identified different injection criteria for different types of injectors. Higher-density, continuous injection with high reliability is the major constraint of a future pellet injection system such as the Gifford-McMahon cryocooler-based TSE. In the past, limited innovative applications for PIT were established and used effectively in fusion experiments. At the present time, an innovative cryogenic-based extrusion system is being designed to meet the different injection criteria. This technical notepresents the progress of eminent activities, discusses some of the best models as developed by Fisher and Arumugam et al., and highlights recent progress. Gray areas such as non-Newtonian behavior of solid H₂ with thermodynamics analysis are also discussed as well as associated challenges with recent key developments in the field of PIT.