Development of advanced compact railguns for injection of hypervelocity hydrogen pellets into magnetic fusion plasmas

We have designed, fabricated, and tested a number of compact railguns utilizing a variety of gun geometries, augmentation schemes, and state-of-the-art rail and insulator materials in order to develop an injector that can accelerate pellets of hydrogen isotopes to very high velocities (~10 km/s) continuously and at high repetition rates for refueling magnetically confined fusion plasmas. These advanced guns are designed to achieve two goals: to minimize or eliminate gunwall erosion and to produce the maximum possible pellet acceleration. These closely related goals assure long gun lifetimes. Using an advanced transaugmented compact gun with an acceleration length of only 45-cm, we have recently achieved hydrogen pellet velocities as high as 2.2 km/s with a time-averaged pellet acceleration of 4.7×10⁶ m/s ² at a modest rail current of 10 kA. This paper includes a brief overview of our railgun control and diagnostic systems and discusses recent results of our railgun experiments using both plexiglass and cryogenic hydrogen pellets