Helium cooling units for X‐ and Q‐band ESR spectrometers

• Published in: Review of scientific instruments 1976-09, Vol.47 (9), p.1172-1177
• Main Authors: Cambell, S. J., Herbert, I. R., Warwick, C. B., Woodgate, J. M.
• Format: Article
• Language: English
• ISSN: 0034-6748; 1089-7623
• DOI: 10.1063/1.1134794

Two cooling units which have been designed for use with ESR spectrometers are described. A main aim of the designs has been to achieve good cryogenic performance consistent with a relatively simple mode of operation. Both units rely on the continuous flow of helium for their cooling with one unit operating in the range 1.8–300 K at X band and the other covering 4.8–300 K at Q band. The X‐band unit has easy top loading access and incorporates a helium reservoir of 0.13‐l capacity close to the sample region. This unit relies on two helium flow paths—one to supply the reservoir and the other to draw helium from the reservoir through the sample region. This feature allows sample temperatures of 1.8 K to be obtained and the base temperature to be achieved with a total liquid helium consumption of 1.6 l/h. The temperature stability was ±0.02 K in the liquid phase and ±0.08 K in the gas phase. In the Q‐band unit the sample is positioned on the end of the rotatable sample mount and conduction cooled through this mount. The sample is vacuum loaded, and for convenience of sample changing the sample vacuum is separate from the main vacuum. This unit has a helium consumption of 1.5 l/h at 10 K with an overall temperature stability of ±0.1 K.