Dr Gary Liu

In this seminar, I will present the vortex dynamics of hundreds of vortices in a span-down superfluid modelled by the Gross-Pitaevskii equation (GPE) and subjected to a span-down square-lattice pinning landscape, mimicking the inner crust of a neutron star. As the crust spins more slowly, superfluid angular momentum suddenly drops within a short time, and for the first time we find convincing spatial-temporal evidence of avalanching behaviour resulting from vortex depinning and collective motion for the first time. After glitches, vortices continue to depin and circulate around the vorticity void until the coarse-grained vortex density is about uniform. We also investigate the rotational lags of the superfluid with respect to the crust, which match the short-time vortex avalanche periods and present a preliminary statistical pattern of the avalanche sizes. In addition, in order to scale up our simulation, we then adapt the point-vortex model (PVM), and, surprisingly, though the  introduced dissipation in the GPE simulation is small, we found that a large mutual friction coefficient is needed to produce GPE-like results in the PVM simulation.