Field errors from screening currents in REBCO accelerator magnets
In plain words
Magnets wound from flat high-temperature superconducting tape carry circulating currents inside the tape that distort the guiding field and drift in time.
Precise statement
In REBCO coated-conductor coils (tape width $\sim 0.4\,\mathrm{cm}$), screening currents induced during field ramps produce field harmonics and slow drifts well above the $1e-4$ relative field quality needed for beam optics, and add mechanical stress. Determine whether conductor layout (striated tapes, round twisted-tape cables) and ramp protocols can reduce screening-current field errors below $1e-4$ at fields $1e5\ \text{to}\ 2e5\,\mathrm{G}$, and predict their decay in time from flux-creep parameters of the tape.
What would settle it
Magnetic measurements of field harmonics and their time decay in a REBCO dipole insert, matched by a model using independently measured tape properties.