ICE-PISTON Preload Control

L1 sequences the cryogenic ICE-PISTON cycle that preloads the high-field magnets, keeping REBCO strain inside its envelope through cooldown and energization.

What the ICE-PISTON does

High-field REBCO magnets must be mechanically preloaded so that Lorentz forces during energization do not drive conductor motion or exceed the irreversible strain limit. Kronos's ICE-PISTON is a cryogenic preload mechanism that applies and maintains this clamping force as the magnet cools and charges. L1 controls its sequence deterministically and verifies it against strain feedback.

The sequence

Preload is not a single step. As the cold mass contracts during cooldown, the preload set-point tracks a schedule; as current ramps to the operating field, Lorentz load rises and the mechanism holds the structure in compression. L1 executes this as a state machine with interlocks: each phase transition requires strain, temperature, and force to be within window before the next phase is allowed.

• Cooldown: preload tracks thermal contraction of the winding pack.
• Energization: preload maintained against rising Lorentz load.
• Steady field: strain held inside the REBCO envelope.
• Fault: controlled release path coordinated with the quench dump.

Coupling to protection

Preload and quench protection are linked. Loss of preload can allow conductor motion, which can seed a quench; a quench dump changes the force state, which the preload control must accommodate. L1 therefore runs the ICE-PISTON loop and the quench logic on the same clock domain so their interactions are deterministic, not racy.

Both machines

The principle applies to the breeder's toroidal and PF magnets and to the burner's 26.49 T plug and 17 T throat magnets, where the higher field makes preload margin even tighter. In every case the goal is the same: keep the REBCO within its strain envelope across all thermal and electromagnetic states, verified in real time.