VOx Quench-Bypass Dump

When the precursor trips, a metal-oxide switching element commutates coil current into an external dump, removing stored magnetic energy from the winding.

Function

The dump element's job is to take current out of a threatened winding fast enough that Joule heating in the forming normal zone stays below the conductor's damage limit. Kronos uses a VOx (vanadium/metal-oxide) switching path biased so that, on a trip, it opens a low-impedance route from the coil into an external resistive dump bank, forcing the magnetic energy to dissipate outside the cold mass.

Energy accounting

The stored energy E = ½ L I² must go somewhere. If it stays in the coil it appears as local heating at the normal zone; if it is commutated to an external resistor R_d it dissipates there as the current decays with time constant τ = L / (R_d + R_normal). The design sizes R_d so τ is short enough to protect the conductor yet not so short that induced voltages exceed insulation limits.

Why a passive-biased element

Speed and independence drive the choice. The switching path is biased so that loss of control power, or a trip signal from the analog comparator, causes it to act — a fail-safe disposition. It does not wait for a command from any processor. This is what lets the whole chain, from ΔT precursor to dump, carry a zero-AI, zero-software guarantee.

• Latching: once tripped, stays tripped until a deliberate reset.
• Voltage-clamped: induced dump voltage held within insulation margin.
• Redundant: multiple channels so one element's failure does not defeat protection.
• Instrumented: L2 logs the event, but logging is not in the trip path.

Coordination with slower dumps

The fast bypass handles the initial commutation; a coordinated slow dump then brings the full magnet system to a safe state. On both the breeder toroidal/PF set and the burner plug magnets, the sequence is staged so the fastest element protects the local conductor and the system-level dump follows within its own bounded time.