Performance of Adiabatic Melting as a Method to Pursue the Lowest Possible Temperature in 3He and 3He – 4He Mixture at the 4He Crystallization Pressure

T. S. Riekki*, A. P. Sebedash, J. T. Tuoriniemi

*Corresponding author for this work

Research output: Contribution to journalArticleScientificpeer-review

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We studied a novel cooling method, in which 3He and 4He are mixed at the 4He crystallization pressure at temperatures below 0.5mK. We describe the experimental setup in detail and present an analysis of its performance under varying isotope contents, temperatures, and operational modes. Further, we developed a computational model of the system, which was required to determine the lowest temperatures obtained, since our mechanical oscillator thermometers already became insensitive at the low end of the temperature range, extending down to (90±20)μK≈Tc(29±5) (Tc of pure 3He). We did not observe any indication of superfluidity of the 3He component in the isotope mixture. The performance of the setup was limited by the background heat leak of the order of 30pW at low melting rates, and by the heat leak caused by the flow of 4He in the superleak line at high melting rates up to 500μmol/s. The optimal mixing rate between 3He and 4He , with the heat leak taken into account, was found to be about 100.150μmol/s. We suggest improvements to the experimental design to reduce the ultimate achievable temperature further.

Original languageEnglish
Pages (from-to)1230-1267
Number of pages38
JournalJournal of Low Temperature Physics
Issue number5-6
Early online date1 Jan 2020
Publication statusPublished - Jun 2020
MoE publication typeA1 Journal article-refereed


  • Adiabatic melting
  • Helium-3
  • Helium-3–Helium-4 mixture
  • Helium-4
  • Kapitza resistance


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