SUPERFLUID AVALANCHES

Avalanches are seen in the invasion percolation region of an adsorptio n/desorption isotherm for superfluid He-4 on a Nuclepore filter. A the ory of these avalanches combines elements from the geometry of the por e space of Nuclepore and elements from the dynamics of superfluid film s. The geometry of Nuclepore filters is studied and the percolation pr operties of these systems are assessed. The percolation threshold is f ound to be characterized by the average coordination number of the pol es. A model of the coupled pore space/superfluid system is introduced. This model is studied numerically and is shown to lead to self-quench ed avalanches that share many qualitative properties with the avalanch es seen in experiment.