Field errors from screening currents in REBCO accelerator magnets

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 $10^{-4}$ 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 $10^{-4}$ at fields $10^{5}\ \text{to}\ 2 \times 10^{5}\,\mathrm{G}$, and predict their decay in time from flux-creep parameters of the tape.

Magnetic measurements of field harmonics and their time decay in a REBCO dipole insert, matched by a model using independently measured tape properties.