In many astrophysical systems the low temperature of the plasma means that it is only partially ionized. In these systems, the motion of ions is frozen to that of the magnetic field, but neutral particles can only feel the magnetic field's Lorentz force indirectly through collisions with ions. This drift in the velocity between ionized and neutral species plays a key role in modifying important physical processes like magnetic reconnection, damping of magneto-hydrodynamic waves, transport of angular momenta in the formation and evolution of stars and disks, and heating in the solar chromosphere.
However, observations that detail the properties of the ion-neutral drift are lacking. We simultaneously observed spectra of the prominence in H I (H¥epsilon 397 nm) and Ca II (H 396 nm) using a high dispersion spectrograph of the Domeless Solar Telescope at Hida observatory, finding differences in Doppler-velocity of neutral hydrogen and calcium ions to be on almost three orders of magnitude larger than those theoretically predicted. Here we present observations of the decoupling of neutral hydrogen from calcium ions, and by extension the magnetic field, in a solar prominence as shown by the difference in their Doppler-velocities.