The Effect of Perimeter-Limited Superfluid 4He Fluid Flow on Avalanches in Nuclepore

Superfluid 4 He exhibits hysteretic behavior in the percolated nano-porous material Nuclepore during filling and draining of the pores due to capillary condensation, and one observes avalanches in the pore draining within a narrow range of chemical potential. We have previously demonstrated that the avalanches involve pores distributed across the entire sample, and that the avalanches are enabled by the superfluid film. We compare avalanches for Nuclepore that has a highly limited perimeter for 4 He film flow draining to avalanches for Nuclepore that has relatively unimpeded flow off the substrate. Time resolved measurements of the avalanche events show that the time duration of the individual avalanches is influenced by the time it takes for the fluid to leave the substrate.