Abstract
A variable temperature liquid helium cooling unit for use with ESR spectrometers is described. The unit is based on the continuous flow principle and the advantages of this method, particularly with regard to ESR experiments are explained. The unit is part of a complete cryogenic system which includes a flexible gas cooled helium transfer tube, a gas flow pump and controller and an automatic temperature controller. Sample temperatures between 3.7K and 300K can be obtained readily and the stability varies between +or-0.02K and +or-0.08K over this range. The total helium consumption of the system varies between 1.01 h-1 at 4.2K and 0.51 h-1 at 10K and decreases further with increased temperature. This compact cooling unit is well suited to other experiments with restrictive geometries.