Propagation of thermal excitations in a cluster of vortices in superfluid 3He-B

We describe the first measurement on Andreev scattering of thermal excitations from a vortex configuration with known density, spatial extent, and orientations in He-3-B superfluid. The heat flow from a blackbody radiator in equilibrium rotation at constant angular velocity is measured with two quartz tuning fork oscillators. One oscillator creates a controllable density of excitations at 0.2T(c) base temperature and the other records the thermal response. The results are compared to numerical calculations of ballistic propagation of thermal quasiparticles through a cluster of rectilinear vortices. We find good agreement which supports the current understanding of Andreev reflection.