Plug Coil Engineering
Reaching 26.49 T means caging huge Lorentz forces, managing quench, and controlling screening currents in stacked REBCO tape.
Where the stress lives
The plug coil is the most mechanically loaded part of the machine. At 26.49 T the magnetic pressure on the winding is immense, and the coil must be built as a structural object first and an electrical one second. Radial and hoop stresses are reacted by a reinforcing structure that surrounds the REBCO winding pack.
Quench protection
A superconducting magnet stores large energy in its field. If a spot goes normal (quenches), that energy can dump into a small volume and damage the coil. High-temperature superconductors quench slowly and locally, which is both an advantage — more warning — and a challenge, since the normal zone spreads slowly and can overheat before detection. The design includes detection and a controlled energy-dump path to protect the conductor.
- Structural cage reacts field-squared Lorentz loads
- Quench detection and dump protect stored magnetic energy
- Screening currents in tape stacks distort the field and must be modeled
- Joints between tape lengths must be low-resistance and mechanically sound
Screening currents
When field changes, currents are induced within the width of each REBCO tape that persist and perturb the field profile. In a precision machine like a tandem mirror, where the mirror ratio and field shape set confinement, these screening-current field errors must be modeled and compensated. This is one reason the plug coil is treated as a coupled electromagnetic-structural design rather than a simple solenoid.
All of this is engineering-in-progress on a design-study machine. The coils are validated in simulation against REBCO test data; the 2032 test unit is where plug-coil behavior would first be proven at scale.