• 한국초전도ㆍ저온공학회논문지
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• 제14권3호
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• pp.53-59
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• 2012

Adiabatic demagnetization refrigerator (ADR) for hydrogen re-liquefaction operating between 24 K and 20 K has been designed. $Dy_{0.9}Gd_{0.1}Ni_2$, whose Curie temperature is 24 K, is selected as a magnetic refrigerant. The magnetic refrigerant powder is sintered with oxygen-free high purity copper (OFHC) powder to enhance its effective thermal conductivity as well as to achieve relatively high frequency. A perforated plate heat exchanger (PPHE) operated with forced convection is utilized as a heat switch. The forced convection heat switch is expected to have fast response relative to a conventional gas-gap heat switch. A conduction-cooled high Tc superconducting (HTS) magnet is employed to apply external magnetic field variation on a magnetic refrigerant. $2^{nd}$ generation GdBCO coated conductor HTS tape with Kapton$^{(R)}$ insulation (SUNAM Inc.) will be utilized for the HTS magnet. The magnetization and demagnetization processes are to be achieved by the AC operation of the HTS magnet. The designed magnetic field and target ramp rate of the HTS magnet are over 4 T with 180 A and 0.4 T/s, respectively. AC loss distribution on HTS magnet is theoretically estimated.

• 한국초전도ㆍ저온공학회논문지
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• 제24권1호
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• pp.23-28
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• 2022

A sorption cooler, which utilizes helium-4 as a working fluid, was previously developed and tested in KAIST. The cooler consists of a sorption pump and a thermosyphon. The developed sorption cooler aims to pre-cool a certain amount of the magnetic refrigerant of an adiabatic demagnetization refrigerator (ADR) from 4.5 K to 2.5 K. To simulate the high heat capacitance of the magnetic refrigerant, liquid helium was utilized not only as a refrigerant for the sorption cooling but also as a thermal capacitor. The previous experiment, however, showed that the lowest temperature of 2.7 K which was slightly higher than the target temperature (2.5 K) was achieved due to the radiation heat leak. This excessive heat leak would not occur when the sorption cooler is completely integrated with the ADR. Thus, based on the experimentally obtained pumping speed, the prediction model for the sorption cooler is developed in this study. The presented model in this paper assumes the sorption cooler is integrated with the ADR and the heat leak is negligible. The model predicts the amount of the liquid helium and the required time for the sorption cooling process. Furthermore, it is confirmed that the performance of the sorption cooler is enhanced by reducing the volume of the thermosiphon. The detailed results and discussions are summarized.

• Journal of Radiation Protection and Research
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• 제38권3호
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• pp.132-137
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• 2013

기존에 많이 사용된 반도체 검출기의 분해능은 통계학적 이론으로 그 분해능의 한계가 따른다. 이러한 이유로 최근에 반도체 검출기가 갖는 에너지 분해능의 한계를 뛰어넘는 저온 검출기를 이용하여 다양한 방사성 핵종 분석을 시도하고 있다. 본 논문에서는 $2{\times}2{\times}0.05mm^3$ 크기 금막 흡수체에 입사하는 에너지 때문에 흡수체의 온도가 상승하는 원리를 이용해 $^{241}Am$ 알파 선원의 에너지를 측정하였다. 흡수체의 온도 변화 측정에는 자기양자센서인 Au:Er를 이용하였으며 이는 순수한 Au에 핵스핀이 0 인 $^{168}Er$을 수백 ppm을 첨가하여 얻은 상자성 합금이다. 알파 입자 흡수에 의한 미세한 온도증가를 측정하기 위해서 희석식 냉동기보다 작동이 편리한 무냉매 자기냉동기를 이용해 mK 온도 영역의 저온환경을 구성하였다. $^{241}Am$ 선원 측정 결과 5.5 MeV에서 6.8 keV의 FWHM의 에너지 고 분해능을 얻었다.