Flow ofHe3-Bthrough Narrow Channels

The critical current $J_c$ of superfluid ${}_{}{}^3{}_{}{}^{}\mathrm{He}$-$B$ through 0.8-μm-diam channels has been measured. For small currents the pressure difference $\Delta P=0\mathrm{}$ along the flow channels within the resolution, implying small or zero dissipation. $\Delta P$ grows rapidly with increasing current above $J_c$; a clear transition to dissipative flow is thus observed. The temperature dependence of $J_c$ indicates that the superfluid density and the critical temperature are reduced inside the narrow flow channels.