In space, a replacement must be found for gravtty to phystcally control and, m certain =nstances, contain cryogemc hqulds A programme has been started at the Jet Propulston Laboratory to study the use of electr0c field generated forces to estabhsh the requtred onentmg effects We present measurements whtch show that 0t ts posstble to apply strong enough electric fields to a hquld/vapour interface of 4He to obtain an onentmg force comparable to gravtty Our measurements span the temperature range 1 7-4 2 K and demonstrate the apphcabd~ty of Pashen's law for maximum attainable field before breakdown occurs Some advantages of the electnc field separator as opposed to passwe surface tens=on dewces are ident=fled
Keywords helium, phase separators, space cryogenics
When an electric field is applied to part of a dielectric llqmd, such as hquld 4He, &pole moments are induced in the 4He atoms exposed to the field The resulting interaction between the electric field and the dipole moments then produce a force that will tend to move some of the 4He from the low field region into the high field region 1 In this Paper we describe measurements to determine how strong the electric forces can be on a hquld/vapour interface in 4He Our measurements are carried out both at 4 2 K and at temperatures below the superfluld transition We find that we can easily produce orienting forces comparable to gravity at 4 2 K, but at a temperature of 1 9 K electrical breakdown occurs in the vapour when a force exceeding ~ 0 2 g is reached
We also present data showing that it is possible to control the thickness of a moving superflmd 4He film by means of an applied electric field These measurements are complicated in that we do not know the actual critical velocity of the moving film Preliminary reports on this research have been published elsewhere 2
Interface movement and breakdown studies
Expertmental detatls
The helium cryostat used in these measurements has two 2 5 cm diameter windows to provide visual access into the experimental region The hquld nitrogen jacket ends above the windows, therefore no nitrogen bubbles interfere with viewing the sample of 4He The experimental cell