Magnet Energy Extraction and Dump

When a magnet must be de-energized fast, its stored energy is driven into external resistors along a fail-safe path that defaults to dumping on loss of control.

Getting the energy out safely

A high-field magnet stores a large amount of energy in its field. On a quench or overstress trip that energy must leave the magnet quickly and land somewhere safe — external dump resistors — rather than depositing in the fault. The extraction path is the actuator end of the quench and coil-stress reflexes, and it is engineered to fail toward dumping, not toward holding current.

def dump_time_constant(inductance_H, dump_resistance_ohm):
    return inductance_H / dump_resistance_ohm     # L/R decay

def peak_dump_voltage(current_A, dump_resistance_ohm):
    return current_A * dump_resistance_ohm        # must stay within insulation

# larger R -> faster dump but higher voltage: a bounded trade
tau = dump_time_constant(inductance_H=5.0, dump_resistance_ohm=0.5)  # 10 s
assert peak_dump_voltage(current_A=10_000, dump_resistance_ohm=0.5) < 6000

The dump-rate trade

A larger dump resistance extracts energy faster (shorter L/R time) but raises the peak voltage across the coil, which the insulation must survive. The dump resistance is sized to extract energy fast enough to protect the hot spot while keeping voltage within the insulation limit. This is a bounded, pre-computed trade, not a runtime decision.

• Fail-safe switch: the current path holds through a switch that opens (diverting to the dump) on loss of hold or power.
• Sized resistors: fast enough for the hot-spot budget, low enough voltage for the insulation.
• Distributed dumps for large magnets so no single resistor or node is a common-cause point.

The extraction path is engineered fail-safe from the switch outward: the current is held by an element that opens on loss of power, loss of hold, or an explicit trip, so any failure of the controlling logic diverts current into the dump rather than trapping it in the magnet. This inversion — where doing nothing means dumping, and holding requires active, healthy control — is what lets the extraction path sit behind the ML-independent failsafe and be trusted to act when everything upstream has gone dark.

Extraction is invoked by the quench protection chain and by plug-coil overstress protection, and it is a component of the fail-safe state for both machines. Its fail-safe-by-default behavior is what lets it sit behind the ML-independent failsafe.