Electrostatic Manipulation of Level of Bulk Liquid for Studies of Saturated Superfluid 3He Films

For studies of saturated superfluid helium films, the level of bulk liquid is an important parameter to determine the thickness of the film. To change the level at low temperatures, a complicated system with a bellows and an extra fill line is usually needed. In this paper, we report a simple device to change the level using an electrostatic force. This level controller consists of a stack of 60 silver plates 0.1 mm in thickness, separated by a 0.1-mm-gap with each other. The application of a dc voltage V on every other plates pulls the dielectric liquid He-3 into the gaps, resulting in the drop of the bulk level. The level changes as expected by the balance between the electrostatic force and the gravity, and the decrease is as high as 0.27 mm at V = 200 V. The level controller is also used to detect the superfluid transition of the bulk liquid He-3 by the sudden reduction of the response time after V is varied.