PERSISTENT CURRENTS IN SUPERFLUID HE-3

Measurements are reported of persistent currents in superfluid **3He-B and **3He-A. An ac gyroscope filled with 20 mu m powder and mounted into a rotating nuclear refrigerator was employed. In **3He-B, undiminished circulation was observed for 48 h; this implies an effective viscosity at least 12 orders of magnitude lower than in the normal fluid at the same temperature. At P less than 15 bar, the observed critical velocity is independent of temperature, but it is a weak function of pressure; v//c varies between 4 and 6 mm/sec. The response to rotation is hysteretic, with elastic potential flow at slow rotation and irreversible vortex flow at higher angular velocities.