Quench Protection and Energy Dump
Once a quench is confirmed the magnet's stored energy must leave the coil fast enough to keep the hot spot below damaging temperature.
The hot-spot problem
When a normal zone forms, the local temperature rise depends on how much current keeps flowing through it and for how long. The integral of current density squared over time, often written as the MIITs (mega-amp-squared-seconds), maps to peak conductor temperature. Protection succeeds if it drives current down before that integral exceeds the design limit, commonly a few hundred kelvin peak.
External dump
The most common scheme opens a switch to insert a dump resistor in series with the coil. Stored energy then discharges into the resistor with time constant tau = L/R. A larger resistor empties the coil faster but raises the terminal voltage V = I R that the insulation must withstand, so the resistor is sized to balance dump speed against voltage limits.
Internal methods
For very large coils, external dump alone cannot protect the winding fast enough, so quench heaters or coupling-loss induced quench (CLIQ) deliberately drive the whole coil normal. Spreading the normal zone shares the dissipated energy across the full winding volume instead of one hot spot, lowering peak temperature at the price of intentionally warming the magnet.
- Confirm quench, then trip the breaker
- Insert dump resistor, discharge with tau = L/R
- Optionally fire heaters to spread the normal zone
- Log MIITs to verify the coil stayed within limits
System coordination
A magnet dump is disruptive: the plasma loses its confining field, so quench protection is wired into the plant interlock chain to command a safe plasma termination in parallel. Cryogenic control must absorb the boil-off, and diagnostics record the event for post-mortem. In the Hyperion design the toroidal-field structure carries the largest stored energy, so its dump path receives the most protection margin. All values here are design targets for a machine that is simulated, not built.
After a dump the coil is recooled and requalified before the next ramp; a protection event is never treated as routine.