Hoop Stress

The outward tension in a magnet coil from its own Lorentz forces.

Like pressure in a pipe, the Lorentz forces in a magnet create hoop stress that tries to expand the coil. Containing it drives the choice of high-strength structural alloys and sets the fatigue limit.

Like pressure in a pipe, the Lorentz forces in a magnet create hoop stress that tries to expand the coil, and containing it drives the choice of high-strength cryogenic alloys and a robust case. Bore-resolved stress analysis shows the static case is sound; the cyclic version of this stress is the binding magnet gate.