An open flow helium cryostat for synchrotron X-ray diffraction experiments

Open flow Helium cryostats, directly blowing a stream of cold gas over the sample, remain an attractive alternative to closed cryostats in a number of cases despite the high Helium cost and often unstable and difficult operation including the growth of ice crystals on the sample: they offer open access to the sample which may be rotated over large angles allowing for large diffraction angles and simultaneous visible optical access for spectroscopy techniques. We have designed and built a new open flow Helium cryostat, making use of the paraphernalia of a commercial cryostat as much as possible. The cryostat has a temperature range from 4.5 up to 100 Kelvin for a liquid Helium consumption of around 2 l/hr when cycled between 5 K and 50 K at constant flow. The use of the new cryostat allows data collection and structure determination below 10 K; at these temperatures it is possible to trap reaction intermediates in proteins in a frozen state, previously only identified spectroscopically. We have successfully carried out X-ray diffraction data collection of murine neuroglobin at 10 K.