A 750 KJ Computer Controlled Sequentially-Fired Pulse Forming Network for a Helical Coil Electromagnetic Launcher

The design, simulation, and development of a sequentially-fired pulse forming network (SFPFN) to power a large bore helical coil electromagnetic launcher (HCEL) is presented and discussed. In principle, the HCEL will be able to accelerate a 750 gram mass to approximately 440 m/s. This investigation furthers the previous work of a medium-bore HCEL SFPFN. Improvements on the previous design include increasing total stored energy and peak current. The SFPFN power supply will integrate a real-time computer monitoring and control system to allow a single power supply to charge multiple capacitor modules, even though each module may be charged to a different voltage. Since the load is non-linear and accurate predictions of SFPFN performance are desired, a zeroth order HCEL model is included in the PSPICE simulation of the overall system. The PSPICE model predicts the output current pulse magnitude and shape, given the capacitor module charge voltages, the projectile mass, and related HCEL parameters such as resistive losses, bore length, and mutual inductance gradient. The PSPICE model also predicts projectile velocity and overall system efficiency. From the PSPICE simulations, the SFPFN will typically produce a relatively constant 20 kA current pulse for approximately 5 ms with a maximum charging voltage of 3000 V and an average load of 100 mOmega. With an HCEL inductance gradient of 145 muH/m and 750 gram projectile, the simulations predict a maximum projectile velocity of 440 m/s at 30.9% efficiency. Additional improvements to the SFPFN include a computer controlled Lab VIEW field programmable gate array (FPGA) to trigger the individual module firing intervals. The use of a computer controlled firing circuit also provides an opportunity to incorporate real-time SFPFN monitoring and feedback to select optimal firing times and durations while the projectile is being accelerated.