Modeling of an ablation-free electrothermal plasma pellet accelerator

Electromagnetic and electrothermal launch devices can provide high acceleration and inject pellets with speeds in excess of 3 km/s for masses up to 3gm. However, the ablation of the bore adds impurities to the plasma. An ablation-free electrothermal pellet accelerator is a concept that utilizes an ablation-free capillary discharge in which a quartz capillary is coated with a nanocrystalline diamond film (NCD). The ablationfree capillary connects to an extension tube, which is also an ablation-free quartz tube coated with NCD that serves as the acceleration barrel. An ablation-free capillary discharge computer code has been developed to model plasma flow and acceleration of pellets for fusion fueling in magnetic fusion reactors. The code incorporates ideal and non-ideal conductivity models and has a set of governing equations for the capillary, the acceleration tube, and the pellet. The capillary generates the plasma from hydrogen/deuterium gas when the discharge current flows through the capillary. The pellet starts moving in the extension tube when the pressure of the plasma flow from the capillary reaches the release limit. The code results show an exit velocity of 2.7 km/s for a 20 mg deuterium pellet when using a capillary and barrel each 9 cm long where the source and barrel diameters are 0.4cm and 0.6cm, respectively, with a discharge current of 20 kA over a 300 μs pulse length. An increase in the length of both the capillary and the barrel to 12 cm increases the pellet exit velocity to 2.9 km/s, and a further increase to 18 cm results in a 3.15 km/s pellet exit velocity. Increasing the barrel length to 36 cm, while keeping the source length at 18 cm, results in an increase in the pellet velocity to 3.32 km/s. The pellet starts moving at 35 μs, reaches 3.32 km/s in 100 μs, and maintains this velocity until exiting the acceleration tube.