Propagation of Pressure Waves in Compression System Prototype for Magnetized Target Fusion Reactor in General Fusion Inc.

Abstract

A scaled prototype of a magnetized target fusion compression system has been designed and built in General Fusion Inc. to test full-size pistons and their synchronization algorithms. In the current prototype, 14 pistons are mounted on the steel sphere with inner radius of 0.5 m (staggered rings of seven pistons above and below the equator) as shown in Fig. 1a. The interior of the sphere is filled with tangentially pumped molten lead (Pb) such that an evacuated cavity (vortex) is formed in the middle of the sphere (Fig. 1b). Each piston consists of two main parts: “hammer” piston and floating “anvil” piston. A 100 kg hammer piston (accelerated by compressed air to velocities up to 50 m/s) impacts the “floating” anvil that is in contact with the liquid lead. As a result of this impact, the pressure wave propagates through the anvil and reaches the interface between steel and liquid lead. Due to the close acoustic match between steel and lead, most of the pressure wave is transmitted into the liquid lead. Discrete pressure waves produced by the individual pistons merge into a converging pressure wave as they propagate toward the evacuated cavity. When a combined converging wave hits the lead-vacuum interface, it is almost entirely reflected because of the severe mismatch between the acoustic impedances. This interaction results in a rapid inward acceleration of the interface. In the final design of the reactor, a magnetized plasma target (trapped inside evacuated cavity) is compressed as the interface moves and accelerates inward. At the same time, a wave reflected from the interface puts the liquid into tension and initiates formation of cavitation regions in the liquid lead.