Development of a compact and continuous sub-millikelvin refrigerator

2018 Fiscal Year Final Research Report

• Project/Area Number: 15K13398
• Research Category: Grant-in-Aid for Challenging Exploratory Research
• Allocation Type: Multi-year Fund
• Research Field: General applied physics
• Research Institution: The University of Tokyo
• Principal Investigator: FUKUYAMA Hiroshi 東京大学, 大学院理学系研究科(理学部), 教授 (00181298)
• Co-Investigator(Kenkyū-buntansha): 村川 智 東京大学, 低温センター, 准教授 (90432004) ; 戸田 亮 東京大学, 低温センター, 技術職員 (20452203)
• Project Period (FY): 2015-04-01 – 2019-03-31
• Keywords: 磁気冷凍 / 断熱消磁冷凍 / 超低温 / 熱スイッチ / 熱接触 / 磁気シールド

Outline of Final Research Achievements

Through detailed thermal and magnetic simulations, we have shown that a newly-designed adiabatic demagnetization refrigerator can produce and hold continuously ultra-low temperatures as low as one thousandth of a degree above absolute zero. As a magnetic working material, we use PrNi5 in which an applied magnetic field is effectively enhanced at the location of Pr nuclei. Relatively low magnetic fields up to one Tesla are applied to PrNi5 by a compact shielded superconducting magnet. Two such cooling units are connected in series via two superconducting heat switches in between a dilution refrigerator, a precooling stage, and a sample. By demagnetizing and magnetizing the two units alternately and cyclically, the system can keep ultra-low temperatures continuously. We have developed these main parts and confirmed that their performances are as planned.

Free Research Field

低温物理学

Academic Significance and Societal Importance of the Research Achievements

絶対零度まで1/1000度の超低温環境を連続的に発生できる小型の新型冷凍機が実現できることを数値計算で示し、そのための主要な要素技術の開発に成功した。この冷凍機が最終的に完成すれば、物質の新現象や新機能を探る温度範囲を大きく拡げ、熱雑音を減らして観測機器の感度を著しく向上できるので、物質科学や宇宙・素粒子研究などさまざまな基礎研究の分野で新たな発見につながると期待される。本研究でその技術革新が大きく現実に近づいた。