Persistent-Current Experiments on SuperfluidHe3-BandHe3-A

Abstract

We have investigated persistent flow of superfluid ${}_{}{}^3{}_{}{}^{}\mathrm{He}$ with an ac gyroscope filled with 20-μm powder. In ${}_{}{}^3{}_{}{}^{}\mathrm{He}$-$B$, currents circulate undiminished for 48 h at least; this implies a viscosity 12 orders of magnitude lower than in the normal fluid. In ${}_{}{}^3{}_{}{}^{}\mathrm{He}$-$A$, the current does not persist. The observed critical velocity in ${}_{}{}^3{}_{}{}^{}\mathrm{He}$-$B$ at $P<~12$ bars is independent of temperature. At $P>\mathrm{}12\mathrm{}$ bars there are two regimes in the $B$ phase: For example, at 29.3 bars the ultimate critical velocities are 5.4 and 7.8 mm/s, respectively.