CDMS begins cooldown of dilution fridge at Soudan

A Fermilab cryogenics team led by Rich Schmitt has been working hard for the past few months assembling the cryogenic system to be used in the Cryogenic Dark Matter Search (CDMS) in the Soudan Laboratory. The heart of the system is a dilution refrigerator which provides the cooling necessary to bring 42 germanium and silicon detectors to a temperature of .025 degrees above absolute zero. Eventually the hockey puck size detectors will be in an attempt to detect the dark matter, which is believed to be the major constituent of the mass in the universe. The team has also fabricated and assembled the Icebox, a very intricate cryostat which will contain the detectors and maintain them at the super cold operating temperatures of the experiment.

Recently the system was cooled down to 4 degrees Kelvin as a test in preparation for the cooldown to the milliKelvin temperature regime. The system was then brought back to room temperature for further leak checking and a final checkout by Mark Jackson, an engineer from Oxford Instruments, the British company which supplied the dilution refrigerator. Jackson will also help with the initial start up of the dilution unit, currently scheduled to begin on August 6.

The Fermilab team including Bruce Lambin, Bryan Johnson, Jeff Duncan, and Rodney Choate have been working at Soudan in tag team fashion since October 2000 preparing the Icebox and cryogenic system for its first cooldown. The work has required the patience and skill of Swiss watchmakers and the ability to work in a less than ideal environment 2300 feet below the surface of the earth. Rich, Bruce, and Bryan all bring extensive experience with Fermilab cryogenic systems to the project, a crucial factor in the successes so far.