Neutron star magnetic field decay: flux expulsion from the superconducting interior

The viscous force acting on a moving vortex in a proton type II superconductor has been calculated by application of Chambers' representation of the Boltzmann equation. Equilibrium between the buoyancy, Magnus and viscous forces defines a vortex drift velocity such that magnetic flux is expelled from the superconducting interior to the solid crust in less than 10 Myr, a time many orders of magnitude smaller than the previous consensus. Ohmic dissipation in the crust may then be the cause of the 5 Myr time constant seen in the decay of radio pulsar dipole moments. The longer time constant (≳ 103 Myr), for which some evidence exists, could be explained by a small central volume of a non-superconducting phase, such as a normal Fermi baryon liquid.