Acceleration of Solid Hydrogen Pellet using Augmented Railgun for Magnetic Fusion Reactor Refueling

A 1.2-m long electromagnetic railgun with separate augmentation was designed, fabricated, and tested for the purpose of injecting hypervelocity hydrogen pellets into magnetic fusion devices for refueling. A compact configuration of two pairs of coaxial rails insulated by thin Kapton film was employed. Two pulse-forming networks were used to separately control the duration, amplitude, and overlap of the current pulses. Copper sulphate resistors were employed as impedance-matching resistors and bank short resistors. The magnetic field inside the gun bore was boosted by the high current on the augmentation rails, which in turn increased the J × B force without increasing the armature current, resulting in less ablation of the gun bore and pellet. Higher acceleration was achieved due to reduced inertial and viscous drag. Using a 1.2-m augmented railgun, hydrogen pellet velocities in excess of 2.5 km/s were achieved. Hydrogen pellet accelerations as high as 4.4×10⁶ m/s² were achieved at a railgun current of 13.5 kA while the acceleration obtained on a conventional railgun was 2.2×10⁶ m/s² at 14.1 kA. Computer simulations have been performed using the finite element code MSC/EMAS to analyze the current density, magnetic field, Lorentz force, and inductance gradient of the conventional and augmented railguns.