Performance of a Miniature, Closed-Cycle Dilution Refrigerator at Tilt Angles between 0 and 30 Degrees
Ryan Snodgrass, Joel Ullom, Scott Backhaus
Closed-cycle dilution refrigerators (DRs) recirculate 3He from the still via condensation on a cooled surface; condensate from the cooled surface drips down toward the mixing chamber via gravity. Compact versions of these DRs are being considered for astrophysics balloon missions, but it is uncertain if they can provide sufficient temperature stability and if they are able to operate when tilted. Here, we show that a closed-cycle DR from Chase Research Cryogenics can successfully cool to about 70 mK at tilt angles up to and including 30°. There is a persistent change in the temperature of the mixing chamber when tilted, but the variation is only ± 5 mK between 0° and 30°. However, we have also identified that tilting at some azimuthal angles can interrupt the cooling process at the mixing chamber, perhaps by the translation of the fluid interfaces within the DR. Interrupted cooling at the mixing chamber can be avoided by mounting the DR in the proper orientation relative to the tilt axis. We also show that 10 µK RMS temperature stability can be achieved at the mixing chamber while continuously tilting the DR at 6 °/h. This stability is only achieved over 89% duty cycle because of large, cyclical perturbations to temperature that originate in the DR's 3He-4He pre-cooler. Temperature perturbations to the 3He condenser are cascaded to every other component of the DR, likely by heat advection through the (unconstrained) concentrated and dilute liquid columns.
, Ullom, J.
and Backhaus, S.
Performance of a Miniature, Closed-Cycle Dilution Refrigerator at Tilt Angles between 0 and 30 Degrees, Cryocoolers 22, Bethlehem, PA, US, [online], https://tsapps.nist.gov/publication/get_pdf.cfm?pub_id=935116
(Accessed June 6, 2023)