The plastic flow of solid ⁴He through a porous membrane

The flow velocity of solid ⁴He through a porous membrane frozen into a crystal has been measured in the temperature interval 0.1-1.8 K. A flat capacitor consisting of a metalized plastic porous membrane and a fixed electrode is applied and the gap in the capacitor is filled with examined helium. The flow of helium through the membrane pores is caused by a d.c. voltage applied to the capacitor plates. Above T∼1 K the velocity of solid ⁴He flow decreases with lowering temperature following the Arrhenius law with the activation energy of the process close to that of vacancies. At low temperatures the flow velocity is almost independent of temperature and the absolute value of the velocity V in this region is less than 10^-11 cm/s under the voltage 400 V.