  The Coronal Multi-channel Polarimeter (CoMP) obtains daily full-Sun
above-the-limb coronal observations in linear polarization, allowing for the
first time a diagnostic of the coronal magnetic field direction in quiescent
prominence cavities. We find that these cavities consistently possess a
characteristic "lagomorphic" signature in linear polarization indicating twist
or shear extending up into the cavity above the neutral line. We demonstrate
that such a signature may be explained by a magnetic flux-rope model, a
topology with implications for solar eruptions. We find corroborating evidence
for a flux rope structure in the pattern of concentric rings within cavities
seen in CoMP line-of-sight velocity.
