A Simple Affordable Open Flow Helium Cryostat for Area Detectors Diffractometers. A. Martin, A.A. Pinkerton, K. Kirschbaum and M. Hardie, Dept of Chemistry, University of Toledo, Toledo, OH, 43606, USA.

A new generation of area detectors has reduced the time for a data collection on a typical crystal to a matter of hours. This has made an open flow He cryostat far more economically viable. The main advantages of such a system, over the more conventional closed system, are the absence of window materials, eliminating absorption errors, the absence of a heavy device attached to the goniostat and the associated motor wear, as well as the ability to observe the crystal directly. This is not the first open flow cryostat to use liquid helium as the cryogen, at least two others have been documented. However, both of these systems were custom built, and such devices, while showing the basic idea is sound are hardly likely to become common. The present cryostat is capable of delivering a 10K stream of He to the crystal. It been developed using off the shelf components based on a commercial ESR cryostat. The modifications are simple but crucial. Frozen air build up is prevented using the transfer line helium back flow and a heated nozzle, similar to some nitrogen systems. The system has run for over 30 hours at under 30K with no frost build up. The total cost of the complete setup is less than $20,000 making it very affordable. A data set for oxalic acid will be presented to demonstrate the effectiveness of the system.