Development of a flux compression power unit for millisecond ETC pulsed power applications

A flux compression power unit (FCPU) is being developed to generate tailored millisecond current pulses for electrothermochemical (ETC) gun applications. A propellant mixture is used to accelerate a conducting piston into the magnetic field region within a helical coil. An armature integral to the piston makes sliding contact with the coil through compliant brushes and provides continuous current flow between the coil and a center rod which acts as a return current path. Interaction between the armature and the magnetic field decelerates the piston and transfers the piston's kinetic energy to the magnetic field. The initial current and energy in the helical coil (provided by a "seed" capacitor bank) are thereby multiplied and delivered to a resistive load. Repetitive operation may be obtained by using the compressed magnetic field to stop the piston at the end of the useful compression stroke and return it to the starting position. FCPU point of departure design parameters for a proof-of-principle experiment include: 120 mm bore diameter, 75 cm coil length, 80 turns/m helical winding, 15 kA seed current (7.2 kJ initial energy), 3.5 kg piston initially accelerated to 300 m/s. Simulations predict a FCPU current multiplication of 40/spl times/, 95 kJ delivered to a fixed resistance load, and the stopping of the piston. The simulations include current diffusion and flux trapping. Initial experiments using solid propellants to accelerate the piston are reported.