The 24.42-Tesla Magnet System
A deep-dive on the Kronos magnet: a graded, demountable REBCO winding pack at 24.42 T peak — exactly the demonstrated single-coil field — defended by a strain clamp carried at the 24.6 T Mode-C-era stress basis.
- On-axis field
- B₀ = 6.37 T
- Peak conductor field
- 24.42 T at R_c = 1.50 m
- Strain margin
- 0.252% peak vs 0.40% limit (1.59×, per S47 at the 24.6 T stress basis)
- State of the art (2025)
- Tokamak Energy Demo3: 24.4 T single coil — matched
The magnet is the enabling technology of a compact high-field tokamak, and Kronos states its magnet claim precisely. The MetroVolt field is B₀ = 6.37 T on axis, rising to a 24.42 T peak conductor field on the inboard leg at Rc = 1.50 m — a peak-to-axis ratio of about 3.8, set by the ratified Mode-D basis (24 July 2026), which adopted the deposited S78 field lever at the build limit.
Where 24.42 T sits. As of 2025, CFS/MIT's toroidal-field model coil exceeded 20 T (single coil, 2021); Tokamak Energy's Demo3 single coil reached 24.4 T at 21 K; and its Demo4 full tokamak-configuration set (14 TF + 2 PF) reached 11.8 T with a 20 T target. The 24.42 T inboard leg therefore matches the demonstrated 24.4 T single-coil field — the remaining gap is full-system scale, not conductor field.
How it is defended. The graded, demountable REBCO winding pack runs at 0.252% peak strain against the 0.40% irreversible limit — a 1.59× margin, evaluated at the 24.6 T Mode-C-era stress basis that bounds the 24.42 T operating peak (simulation S47). "Graded" means the conductor is tuned layer by layer to the local field; "demountable" means the pack can be opened for maintenance. The G2 gate qualifies the full operating envelope.