  With the excitation and demagnetization of a magnet for magnetic resonance
imaging in mind, we theoretically and numerically investigated electromagnetic
coupling--especially its dependence on the round core radius $R$--of
multifilament helically wound superconducting tapes under steady-state
conditions in a constantly ramped magnetic field. We found that even in a
rapidly ramped magnetic field, the electromagnetic coupling can be suppressed
by reducing $R$ to close to the tape width. We also clarified that the coupling
sweep rate at which the electromagnetic coupling starts scales as $R^{-2}$,
showing that the dependence on $R$ reflects the penetration of magnetic flux
from the edges of the tape. Even when the round core is as narrow as the tape
width, the behavior is considered to be similar to the electromagnetic response
of a flat tape rather than that of a tubular wire.
