This was an extension of the MCKESR (Magnetically Confined Kinetic Energy Storage Ring) concept Hull was exploring at ANL. The idea here is a ring-shaped flywheel where the centripetal force is supplied by magnetic forces rather than strength of the rotating ring. The advantage is that the stored energy per mass of ring + magnets scales linearly with radius, unlike in a conventional flywheel where (by the virial theorem) the ratio is limited by a constant factor proportional to the strength of the flywheel material divided by its density.
The original MCKESR concept had a ring-shaped conductor orbiting in a magnetic field, but a later concept had a chain of ferromagnetic objects being attracted magnetically. The latter was kept passively stable by alternating segments of magnets, one segment where the attraction was stable radially and unstable vertically, the next the opposite. If the ring was moving in the right speed range this would cause dynamic stability in both directions. This Alternating Gradient principle is used (via magnetic forces on moving charged particles) to focus beams in most modern particle accelerators.
The original MCKESR concept had a ring-shaped conductor orbiting in a magnetic field, but a later concept had a chain of ferromagnetic objects being attracted magnetically. The latter was kept passively stable by alternating segments of magnets, one segment where the attraction was stable radially and unstable vertically, the next the opposite. If the ring was moving in the right speed range this would cause dynamic stability in both directions. This Alternating Gradient principle is used (via magnetic forces on moving charged particles) to focus beams in most modern particle accelerators.
https://ieeexplore.ieee.org/document/4765896
https://digital.library.unt.edu/ark:/67531/metadc173309/