The cometary plasma in the magnetic barrier just outside the diamagnetic cavity which surrounds the nucleus of comet Halley is virtually stagnant. The outflowing neutral gas exerts an outward ion-neutral drag force on this plasma, which balances the inward magnetic pressure gradient force in the vicinity of the contact surface. The cometary ions are frictionally heated due to the relative motion of the ion and neutral gases. The ion flow velocity must have a few km/s non-radial component in order to explain the ion temperatures measured by the ion mass spectrometer on Giotto. ¿ 1987 American Geophysical Union