Dresden 2006 – scientific programme
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TT: Tiefe Temperaturen
TT 23: Solids At Low Temperature: Cryogenics
TT 23.3: Talk
Wednesday, March 29, 2006, 15:15–15:30, HSZ 02
Modified Closed Cycle Refrigerator for Neutron Diffraction Study at Temperatures around and below 1 K — •Bastian Klemke and Michael Meißner — BENSC, Hahn-Meitner Institut Berlin
A Joule-Thomson (J/T) Helium gas expansion stage has been designed to operate as a third stage attached to the second stage of a closed cycle refrigerator. Room temperature Helium gas (injection pressure p = 1...10 bar) is cooled by heat exchangers mounted to the cold heads of the first and the second stage, respectively. Inside the J/T unit the Helium gas is liquefied and simultaneously evaporated by an external rotary pump via an attached pumping tube. Using 4He-gas results in a base temperature of 1.3 K and in a precise temperature regulation up to 50 K. Operation with 4He-gas proved to be very simple and reliable as no gas handling system is needed. For closed loop circulation with 3He-gas we set up a small gas handling system which operates with the same J/T unit. Base temperatures down to 0.6 K have been observed stable over long times and easy temperature regulation has been achieved, too. Because in neutron and x-ray scattering experiments sample change and cooling time from 300 K are an important issue, the J/T unit and heat exchangers have small thermal masses. Due to these construction details our present design can be operated in HUBER 5020 Euler cradles in all goniometer orientations.