Study of advanced railgun hydrogen pellet injectors for fusion reactor refueling

An advanced railgun system has been developed to assess its feasibility as a hypervelocity hydrogen pellet injector for magnetically confined plasmas. It consists of a pellet generator/gas gun assembly for freezing hydrogen pellets and injecting them into the railgun at velocities as high as 1.5 km/s. A plasma armature is formed by ionizing the low-Z propellant gas behind the pellet and firing the railgun. This fuseless operation prevents high-Z impurities from entering the reactor during pellet injection.The railgun system has several features that distinguish it from its predecessors, including: (1) a more compact, versatile pellet generator, (2) a new gas gun configuration that produces significantly higher pellet speeds, (3) a perforated coupling piece between the gas gun and railgun to prevent spurious arcing, and (4) ablation-resistant sidewalls, perforated sidewalls and transaugmentation to reduce inertial and viscous drag, the primary obstacles to achieving hypervelocity.A unique system of sophisticated controls and diagnostics has been assembled to operate the railgun system and assess its performance, including fully automated pellet freezing and gas gun operation, an automatic timing circuit that is immune to mistriggering caused by pellet fragmentation or electromagnetic interference, a streak camera, photostations, light gates, current trans formers, B-dot probes, laser interferometry and optical spectroscopy.Free-arc and hydrogen pellet experiments were conducted to evaluate various railgun designs. Transaugmented and simple railguns 1.2 and 2 m long were tested. The performances of railguns using Mullite, solid Lexan and perforated Lexan sidewalls were compared. The railgun theory of operation and anticipated losses are also examined. The theoretical predictions are found to be in good agreement with the experimental results.The advanced railgun system has set several world records for bare hydrogen pellet velocity, including a 3.3 km/s shot on the 2 m gun, thus demonstrating that railguns are viable candidates for high speed pellet injection.U of I OnlyETDs are only available to UIUC Users without author permissio