quench
Catastrophic loss of superconductivity in the magnet. The superconducting wire transitions to normal resistance, energy stored in the magnetic field dumps into the wire as heat, and the helium cryogen boils off rapidly and vents through the quench pipe. Field strength drops to zero within seconds.
Why it matters to buyers: Never-happens-we-hope event but expensive when it does. Recovery cost is substantial — full cryogen refill plus weeks of downtime, with potential collateral damage to internal magnet joints from the thermal stress. A quench history on a refurb purchase is a meaningful disclosure; ask about it.
Why it matters to engineers: Emergency quench switch is a safety feature, not a service tool — operator discretion only. Ferromagnetic projectile is the most common real-world trigger; access-control discipline (Zone IV ferromagnetic screening) is the upstream prevention. Quench-pipe patency must be confirmed periodically — a blocked quench pipe in a ferromagnetic-event scenario is dangerous.
Decommissioning context
A controlled ramp-down preserves the magnet for resale; an uncontrolled quench typically destroys magnet resale value. See MRI decommissioning.