A SIMPLE CONTINUOUS TRANSFER LIQUID HELIUM CRYOSTAT FOR AN ULTRA-HIGH VACUUM FIELD ION MICROSCOPE

A simple continuous transfer liquid helium cryostat for an ultra-high vacuum field ion microscope has been constructed. In this cryostat the liquid helium is continuously transferred from a conventional 30 or 50 1 storage vessel, employing a standard transfer line, to a small reservoir which is in direct contact with the field ion microscope specimen holder. The enthalpy of the outgoing cold helium gas is used to cool a copper radiation shield which surrounds both the specimen holder and the reservoir section of the cryostat. The economical operating temperature range of this cryostat is 8°K to room temperature with a temperature stability of better than ±0·1 degK over most of this temperature range. Details of construction and the operational characteristics are presented.