Figure-8 inductive store for EM brushgun

The paper is based on the poster presented at IEEE Pulsed Power Conference 2015. To test EM brushgun prototype described in the associated paper [1], GEDI Lab built a massive inductive store of transformer type energized by a bank of ultracapacitors (UC bank). Its primary circuit is assembled of 28 jelly roll coils with small height-to-diameter ratio mounted in two adjacent stacks. The coils are energized by a sectioned UC bank in such a way that current has opposite directions in the left and right stacks. As illustrated below, the coils in the stacks are interleaved by 13 layers of common to both stacks secondary windings, each consisting of a dozen of individual “Figure-8” wire loops (just two are shown to avoid clutter), all connected in parallel to EM brushgun. In each stack, pairs of vertically adjacent primary coils are connected in series, forming 14 sections of the primary circuit energized by 14 dedicated sections of the UC bank. The paper explains the rationale behind this design, and discusses the operation of the entire circuit including, in addition to the inductive store and UC bank, EM brushgun and a set of mechanically synchronized opening/closing switches. Simulation of charging and discharging phases in the inductive store operation, accurately accounting for inductive coupling of all participating circuits, has shown that due to nearly ideal coupling between the primary and secondary circuits less than 0.1% of stored energy has to be dissipated in the switches during current commutation into secondary windings. The fraction of energy that cannot be outputted from the secondary to the brushgun because it is associated with the magnetic flux “trapped” between the windings belonging to different layers of the secondary circuit is much larger, but still does not exceed 10%. Additional resistive losses in the secondary depend on the launch duration and therefore cannot be characterized without the complete simulation of a particular launch event.