Liquid helium transfer using a mass-flow controller

An automated liquid helium transfer method using a mass-flow controller, by means of which an empty cryostat at room temperature can be filled with liquid helium without thermal shock, has been developed. Before liquid helium collection is initiated, mass flow is controlled to be constant. After the start of liquid helium collection, mass flow is controlled so that the differential pressure of the empty cryostat against the storage Dewar containing the liquid helium is of the proper value to overcome the height difference due to the transfer tube. A mass-flow controller, a vacuum pump, a differential pressure sensor, a liquid helium level sensor and a computer with suitable software are required to replace the conventional manual transfer by this method. (C) 1999 American Institute of Physics. [S0034- 6748(99)03310-9].