A magnet coil carrying current I stores energy E = ½LI² in its field. If a small spot loses superconductivity (a quench), that spot becomes resistive, dissipates I²R as heat, and the heat conducts to neighbouring turns — pushing them normal too. The boundary of this normal zone spreads outward at the adiabatic propagation velocity:
v_NZP ≈ (J / C) · √( ρₙ·k / (T_c − T_op) )
where J is current density, ρₙ the normal-state resistivity, k the thermal conductivity, C the volumetric heat capacity, and T_c − T_op the margin to the critical temperature. The growing normal zone's resistance R_n(t) = ρₙ·ℓ(t)/A produces a real, measurable terminal voltage V = I·R_n — this is exactly what a real quench-detection system watches for.
Once V crosses the detection threshold, the protection circuit opens the magnet breaker and forces the current through an external dump resistor R_d, so the circuit obeys L·dI/dt = −I·(R_n + R_d) and the stored energy is extracted quickly and safely outside the cryostat instead of cooking the coil.
Meanwhile the hottest point (the original seed) has been resistive the longest and heats adiabatically: C(T)·dT/dt = J(t)²·ρₙ. Since heat capacity grows with temperature at cryogenic conditions, the hotspot's rate of rise self-decelerates — but if detection is too slow, or protection is disabled, the current keeps flowing through a small resistive spot for far longer, and the hotspot temperature can run away toward damage. Real accelerator and MRI magnets are sized so this "MIITs" integral (∫J²dt) never exceeds the conductor's safe limit — the same trade-off this simulator makes tunable.
- Operating current — sets the stored energy and the current density that drives both the propagation speed and the heating rate.
- Detection threshold — a lower value trips the dump resistor sooner, protecting the coil at the cost of nuisance-tripping on small signals.
- Dump resistor — a larger R_d discharges the field faster (shorter L/R time constant) but produces a higher peak terminal voltage across the coil.
- Protection disabled — shows what happens without a dump path: the normal zone alone must absorb the full discharge, and the hotspot runs far hotter.