The K18 Superconductor Energy Storage Kit is simple to understand.The fundamental property of superconductors is its complete lack of resistance to electrical current. This property can be exploited by using a ring (toroid) of superconductor material to store electrical power. Once the current is induced in the toroidal, its lack of resistance allows the induced current to flow forever. These permanent currents in a superconductor are called persistent currents. The current also produces a magnetic field around the superconductor, creating a powerful electromagnet.
A current is induced in the toroidal ring by passing a rare earth magnet through the opening of the toroidal. The toroidal may be momentarily removed from the liquid nitrogen to perform this operation, then quickly placed back into the liquid nitrogen.
The induced current can be detected by measuring the deflection of a compass needle held in close proximity to the superconducting toroidal.
The K18 kit's experimenter's guide provides equations and procedures for estimating the current in the superconductor based on the deflection of the compass needle.
While in theory the current in the toroidal should flow forever, because of flux creep and flux flow there is a small exponential decay of the stored electrical current. It has been estimated that in 1023 years the stored current will decrease to approximately 50% of its initial value.