Abstract
Operating 6,800 feet underground at the SNOLAB facility in Sudbury, Ontario, Canada, the dilution refrigerator-cooled SuperCDMS SNOLAB (Super Cryogenic Dark Matter Search at the Sudbury Neutrino Observatory Laboratory) experiment has been designed for maximum cryogenic up-time and remote operations. A key element in achieving these goals is a pair cold traps in the helium circulation stream of the dilution refrigerator; the first operating near liquid nitrogen temperatures and the second operating near liquid helium temperatures. Previous experience with the CDMS experiment, located underground at the Soudan Under-ground Laboratory, has given significant operational experience with dilution refrigerator cold traps and has solidified the demand of a system of dual cold traps. Unlike the CDMS-era system, the new SuperCDMS system will feature a cryocooler powered liquid nitrogen re-liquefying system (as opposed to regular under-ground re-filling of cold trap dewars using portable nitrogen dewars) and a cryogen-free 4 K cold trap, which eliminates the need for a bath of liquid helium.
Highlights
SuperCDMS SNOLAB is an experimental collaboration searching for dark matter using extremely sensitive germanium and silicon detectors cooled to milli-Kelvin temperatures
The SuperCDMS SNOLAB collaboration will modify the Leiden Cryogenics dilution refrigerator system based on previous extended-uptime dilution refrigerator operational experience gained during operational runs of the CDMS experiment, as described in [4] for example
Basic calculations were performed when sizing this system, which studied the variation of gas temperature and tube wall temperature with respect to length of tube between different heat sinking stages, so that the overall length of the 4 K cold trap tubing would suffice per the requirements of the overall SuperCDMS SNOLAB dilution refrigerator system
Summary
SuperCDMS SNOLAB is an experimental collaboration searching for dark matter using extremely sensitive germanium and silicon detectors cooled to milli-Kelvin temperatures. Performance parameters of the Leiden Cryogenics BC model LC-CF2500-Maglev-2PT dilution refrigerator used for the SuperCDMS SNOLAB experiment.
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