Screening Currents and Field Error
Wide REBCO tape carries induced screening currents that distort the magnetic field and must be managed for plasma control.
A side effect of flat tape
Because REBCO is a wide, flat conductor, changing fields induce screening currents that circulate within the tape width. These persist and produce a magnetization that adds an error to the intended field. In a precision device that shapes a negative-triangularity plasma, uncontrolled field error degrades control and can shift the equilibrium.
Why it matters here
The breeder holds a -0.30 triangularity shape that is less naturally stable than a conventional D. Field error from screening currents competes with the poloidal-field system's ability to hold that shape. The effect is time-dependent: it is largest during ramps and decays with a long time constant, so it couples plasma-control design to magnet design.
- Screening currents scale with tape width and field ramp rate.
- They produce a slowly decaying magnetization error.
- Narrower tape or striation reduces the effect at a manufacturing cost.
- Control algorithms must anticipate the error, not just react to it.
Mitigations
Options include striating or narrowing the conductor, controlling ramp rates, and modeling the magnetization so the control system compensates. The breeder treats field error as a design input to both the magnet and the control system rather than a nuisance discovered at commissioning.
Measurement and feedback
Because screening-current error decays slowly and depends on operating history, the breeder plans magnetic diagnostics that measure the actual field and feed the control system, so compensation is based on the real magnetization state rather than a static model. Diagnostics near the plasma must themselves survive the radiation environment, tying field-error management back to component design.
This page documents a design and simulation study, not a built machine. Construction begins Q2 2027; first-of-a-kind first tritium is targeted near 2030. Figures are computed, reproducible targets, not measurements.