Super uid helicity and vortex reconnections

Vortex reconnections are considered to be an essential mechanism that sus-tains the chaotic state of a vortex tangle in turbulent helium II. In a pure turbulent super ow of helium II, super uid helicity is a topologically invari-ant quantity that counts the extent of linkage of closed vortex knots and loops. This implies that super uid helicity will not be conserved whenever vortex reconnections take place. However, I nd that, within the two- uid model, super uid helicity is a conserved quantity even when the restoring and drag forces (that arise due to the interaction of the super uid vortices with the normal uid) are taken into account. I brie y discuss the implications of this result