Critical current ofHe3-Ain narrow channels

The critical current $J_c$ of superfluid ${}_{}{}^3{}_{}{}^{}\mathrm{He}$-$A$ in 0.8-μm-diam channels has been measured by the observation of the pressure difference along the channels versus the mass current. During warming $J_c$ was found to decrease by about 30% at $T_{\mathrm{BA}}\left(\mathrm{cyl}\right)$ and by another 30% at $T_{\mathrm{BA}}$; $T_{\mathrm{BA}}\left(\mathrm{cyl}\right)$ is the reduced $B\to A$ transition temperature in the narrow flow channels, with $\frac{T_{\mathrm{BA}}\left(\mathrm{cyl}\right)}{T_{\mathrm{BA}}}=0.92\mathrm{}$ at 27.4 bars. Above $T_{\mathrm{BA}}$ a second dissipative mechanism was observed at lower currents. These features are believed to be associated with the ends of the channels.