MACE: A Compact Deployable, Lightweight Electric Energy Storage System with Multi-Megamp and Gigajoule Delivery Capability

Abstract

A new concept for the storage of large amounts of electric energy that can be delivered in milliseconds at multi megamp current levels, is described. The MACE (magnetic cable energy) uses a multi-turn superconducting cable loop to store the electric energy. The primary superconducting cable is very closely coupled inductively to a single-turn normal metal, non-superconducting, open circuited secondary loop that does not carry current during the storage phase. Upon demand, the secondary loop is connected to the load and the superconductor material in the MACE cable is driven into the normal, non- superconducting high resistance state by a very short, intense heating pulse. Virtually all, >98%, of the total ampere turns of current in the MACE superconducting loop then instantly transfers inductively to the normal metal loop. As an example, if the multi-turn superconducting, loop carries three million ampere turns of current [e.g., 300 turns of 10,000 ampere superconductor], the single-turn normal metal loop would then carry three million amperes. Depending on application, the output current can be designed to deliver whatever level is appropriate. For electric rail guns, output currents of several megamps are desirable. For Maglev launchers, a lower current at higher voltage using a multi-turn secondary loop, is desirable. The MACE cable would be transported as a compact coiled package on existing transport vehicles. At the operating site, it would be uncoiled and deployed as a loop, either directly at ground level, or in a protective enclosure. Large amounts of energy can be stored in MACE. For example, a 50 centimeter diameter MACE cable could carry six million ampere turns of current cable. Formed into a 10 meter diameter loop, it would store ~400 megajoules of electric energy. More than 95% of the stored energy could be delivered to an electric gun. The MACE-1 system uses the liquid helium cooled niobium-titanium superconductors that have been used for decades, while the MACE-2 system uses the recently developed liquid nitrogen cooled YBCO high temperature superconductor. Both systems appear practical, and can be cycled many times. The Nb-Ti superconductors in MACE-1 operate at higher current density, >105 A/cm2, but require more refrigeration. For both systems, the temperature rise in the superconductor during the delivery pulse is very small, ~20 K, and it is not damaged by the pulse. Illustrative designs are described.