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

Abstract

INTRODUCTION A scaled prototype of the magnetized target fusion compression system has been designed and built in General Fusion Inc. to test full size pistons and algorithms of their synchronization. In the current prototype fourteen pistons are mounted on the steel sphere with inner radius of 0.5m (staggered rings of seven pistons above and below the equator) as shown in Figure 1a. Interior of the sphere is filled with tangentially pumped molten lead (Pb) such that 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 100kg 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 towards the evacuated cavity. When a combined converging wave hits the lead-plasma 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 a magnetized plasma target (trapped inside evacuated cavity) is compressed as the interface moves and accelerates inwards. At the same time a reflected from the interface rarefaction wave puts the liquid into tension and initiates formation of cavitation regions in the liquid lead. Compression efficiency of the system relies heavily on ability to engineer uniform collapse of