Grant: Research Tools and Instruments

This proposal is for the purchase of a closed-cycle cryogenic cooler for a low-temperature flow cryostat for the Quantum Materials Spectroscopy Centre (QMSC) beamline led by Dr. Andrea Damascelli and located at the Canadian Light Source (CLS) in Saskatoon. The new cryogenic cooler will be used to convert a state-of-the-art liquid helium flow cryostat reserved for spin- and angle-resolved photoemission spectroscopy (Spin+ARPES) experiments for which consumed helium is not recovered to one that is essentially closed-cycled while maintaining high cooling power at the lowest temperatures. Today, low temperature experiments utilize two cooling approaches: the direct use of liquid helium in a flow cryostat or a closed-cycle refrigeration system designed for cryogenic temperatures. Each has unique benefits and drawbacks. A key problem with flow cryostats is the significant operating cost, particularly prohibitive for the CLS-QMSC whose typical users' program runs 24/7 for 10 month/year. Thus, using a conventional flow cryostat for the Spin+ARPES effort costs $100,000/year and consumes one of the earth's most precious non-renewable resources, releasing it into the atmosphere. Also, the helium dewar must be changed every 3-4 days requiring the system to be warmed up before it can be cooled again. This severely impacts the beamline uptime, a precious commodity to the academic and industrial users from around the world, each with limited allotted beamtime. Overall, this is extremely costly and inefficient. On the flip side, a typical closed cycle cryostat can be maintained at its lowest operational temperature almost indefinitely maximizing uptime operation, without the loss of helium. It will also have much lower cooling power at the sample location than a flow cryostat, which requires considerable design considerations to get to reasonably low temperatures. Our aim is to effectively convert the Spin+ARPES flow cryostat on the QMSC beamline into a closed cycle system with the 4K Stinger from ColdEdge Technologies, which has a demonstrated 0.9W of cooling power at 4K. It will allow us to reach and maintain a sample temperature of 6K for an unlimited time period, substantially increasing the QMSC beamline efficiency and uptime, and removing the prohibitive operational costs. Notably, this cooler seamlessly interfaces with our existing flow cryostat no redesign or hardware modifications needed and, unlike a conventional close-cycle system, is capable of reaching 3.0 K whenever necessary, by simply switching over to a liquid helium dewar and pumping on the exhaust side. For quantum materials and devices research, these seemingly “small” differences in base temperature are most significant. Thus, this system offers the best solution for CLS-QMSC national and international users' community, guaranteeing virtually endless operating times and very low base temperatures, while considerably decreasing the operational costs of the QMSC beamline at CLS.