• 한국초전도ㆍ저온공학회논문지
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• 제8권1호
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• pp.59-64
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• 2006

A closed-loop cryogenic cooling system for high field magnets is presented. This design is motivated by our recent development of cooling system for 21 tesla Fourier Transform ion Cyclotron Resonance (FT-ICR) superconducting magnets without any replenishment of cryogen. The low temperature superconducting magnets are immersed in a subcooled 1.8 K bath, which is connected hydraulically to the 4.2 K reservoir through a narrow channel. Saturated liquid helium is cooled by Joule-Thomson heat exchanger and flows through the JT valve, isenthalpically dropping its pressure to approximately 1 6 kPa, corresponding saturation temperature of 1.8 K. Helium gas exhausted from pump is now recondensed by two-stage cryocooler located after vapor purify system. The amount of cryogenic Heat loads and required mass flow rate through closed-loop are estimated by a relevant heat transfer analysis, from which dimensions of JT heat exchanger and He II heat exchanger are determined. The detailed design of cryocooler heat exchanger for helium recondensing is performed. The effect of cryogenic loads, especially superfluid heat leak through the gap of weight load relief valve, on the dimensions of cryogenic system is also investigated.

• 한국초전도ㆍ저온공학회논문지
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• 제12권3호
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• pp.44-48
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• 2010

Acoustic emission (AE) signal from an HTS tape has a low signal to noise ratio, due to the large amount of noise caused by the boiling of the liquid cryogen or mechanical vibration from the cryo-cooler. In an attempt to improve the sensitivity of the AE sensor, $Pb(Zr_{0.54}Ti_{0.46})O_3$ + 0.2 wt% $Cr_2O_3$ + 1.0 wt.% $Nb_2O_5$ ceramics sintered at $1200^{\circ}C$ was synthesized. In addition, the resonance ($f_r$) and anti-resonance frequencies ($f_a$) were measured using the specimens with various thicknesses (1.0, 1.5, 2.0, 2.5 and 3.0 mm). According to the test results, large AE signals with high frequencies were obtained from the AE sensor fabricated using a piezoelectric disc with a thinner thickness.

• 한국초전도ㆍ저온공학회논문지
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• 제26권1호
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• pp.25-30
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• 2024

High-temperature superconducting rotors offer advantages in terms of output-to-weight ratio and efficiency compared to conventional phase conduction motors or generators. The rotor can be cooled by conduction cooling, which attaches a cryocooler, and by refrigerant circulation, which uses circulating liquid or gas neon, helium and hydrogen. Recent work has focused on environmental issues and on high-temperature superconducting motors cooled with liquid hydrogen that can be combined with fuel cells. However, to ensure smooth supply and return of the cryogenic cooling fluid, a cryogenic rotational coupling between the rotating and stationary parts is necessary. Additionally, the development of a sealing structure to minimize fluid leakage applicable to the coupling is essential. This study describes the design and performance evaluation of a non-contact sealing method, specifically a labyrinth seal, which avoids power loss and heat load caused by friction in contact sealing structures. The seal design incorporates a spiral flow path to reduce leakage using centrifugal force, and computational fluid dynamics (CFD) simulations were conducted to analyze the flow path and rotational speed. A performance evaluation device was configured and employed to evaluate the designed seal. The results of this study will be used to develop a cryogenic rotational coupling with supply and return flow paths for cryogenic applications.

• 한국초전도ㆍ저온공학회논문지
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• 제19권4호
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• pp.45-50
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• 2017

This paper presents a conceptual design and analysis for a 1-kW-class high-temperature superconducting rotating machine (HTSRM) rotor. The designed prototype is a small-scale integration system of a HTSRM and a HTS contactless rotary excitation device (CRED). Technically, CRED and HTSRM are connected in the same shaft, and it effectively charges the HTS coils of the rotor field winding by pumping fluxes via a non-contact method. HTS coils in rotor pole body and toroidal HTS wire in CRED rotor are cooled and operated by liquid nitrogen in cryogen tank located in inner-most of rotor. Therefore, it is crucial to securely maintain the thermal stability of cryogenic environment inside rotor. Especially, we critically consider not only on mechanical characteristics of the rotor but also on cryogenic thermal characteristics. In this paper, we conduct two main tasks covering optimizing a conceptual design and performing operational characteristics. First, rotor parameters are conceptually designed by analytical design codes. These parameters consider to mechanical and thermal performances such as mechanical strength, mechanical rigidity, and thermal heat losses of the rotor. Second, mechanical and thermal characteristics of rotor for 1-kW-class HTSRM are analyzed to verify the feasible operation conditions. Hence, three-dimensional finite element analysis (3D-FEA) method is used to perform these analyses in ANSYS-Workbench platform.

• 한국초전도ㆍ저온공학회논문지
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• 제18권1호
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• pp.41-45
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• 2016

The technology of supplying the electric power by wireless power transfer (WPT) is expected for the next generation power feeding system since it can supply the power to portable devices without any connectors through large air gap. As such a technology based on strongly coupled electromagnetic resonators is possible to deliver the large power and recharge them seamlessly; it has been considered as a noble option to wireless power charging system in the various power applications. Recently, various HTS wires have now been manufactured for demonstrations of transmission cables, motors, MAGLEV, and other electrical power components. However, since the HTS magnets have a lower index n value intrinsically, they are required to be charged from external power system through leads or internal power system. The portable area is limited as well as the cryogen system is bulkier. Thus, we proposed a novel design of wireless power charging system for superconducting HTS magnet (WPC4SM) based on resonance coupling method. As the novel system makes possible a wireless power charging using copper resonance coupled coils, it enables to portable charging conveniently in the superconducting applications. This paper presented the conceptual design and operating characteristics of WPC4SM using different shapes' copper resonance coil. The proposed system consists of four components; RF generator of 370 kHz, copper resonance coupling coils, impedance matching (IM) subsystem and HTS magnet including rectifier system.

• Tuberculosis and Respiratory Diseases
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• 제68권1호
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• pp.6-9
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• 2010

Background: The efficacious use of interventional bronchoscope for patients with central airway obstruction due to malignant or benign lesions has been proven. Among many therapeutic bronchoscopic procedures, endobronchial cryotherapy is an established recanalization method for the obstruction of the respiratory tract. Recently, the use of this procedure has been increasing in Korea. However, limited data are available in the literature regarding its efficacy in Korea. Methods: Thirty patients, who had been treated with a flexible cryoprobe for cryotherapy were enrolled; clinical characteristics and treatment outcomes were analyzed. The patients had been treated with the technique using nitrous oxide as a cryogen under local anesthesia. Objective outcomes were 3 different degrees of therapeutic success by use of follow-up bronchoscopic findings as follows: successful, partially successful, and unsuccessful response. Subjective outcomes were evaluated as an improvement in symptoms. Results: The mean age of enrolled patients was $59{\pm}11$ years and there was a male (22/30) dominance. Twenty-three patients had malignant tumor and 7 patients had benign lesions with central airway obstruction. Successful recanalization was achieved in 11 (37%) patients, and partially successful response was achieved in 15 (50%) patients. Dyspnea was improved in 84.2% (16/19) of patients. At least one respiratory symptom was resolved in 91.3% (21/23) patients. Seven patients (23.3%) needed additional bronchoscopic electrocautery because of the bleeding as a complication of cryotherapy. Conclusion: Endobronchial cryotherapy is an effective and less expensive procedure for the management of central airway obstruction. However, the procedure should be performed under the preparing for an emergency situation, such as massive bleeding.

• 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.

• Tuberculosis and Respiratory Diseases
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• 제64권4호
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• pp.272-277
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• 2008

연구배경: 중심성 기도폐쇄를 동반하는 진행성 폐암환자에서 기도폐쇄를 호전시키기 위해 다양한 중재적 시술 Tuberculosis and Respiratory Diseases Vol. 64. No. 4, Apr. 2008277방법들이 시도되고 있으며, 이러한 시술방법 중 최근 굴절성 cryoprobe를 이용한 냉동치료가 국내에서도 시도되고 있다. 방법: 냉동치료 기계는 cryomachine과 cryoprobe로 구성되며, 냉매로는 아산화질소(N2O)를 사용하였다. 굴곡경 기관지내시경의 working chanel을 통해 굴절성 cryoprobe를 악성종양의 중심에 위치한 후 급속 냉동($-89^{\circ}C$)하여 악성 종양 조직을 냉동 시킨 후 stalk을 puling하여 제거하거나 급속 냉동과 해동 과정을 반복하였다. 결과: 중심성 기도폐쇄가 발생한 진행성 폐암 환자 4명에게 냉동치료를 시술하였다. 3명의 환자에서 성공적으로 기도폐쇄를 유발하는 종양을 제거하였으며, 그 후 호흡곤란 및 무기폐 소견이 호전되었다. 1명의 환자에서 기관지 천공으로 인한 종격동 기종이 발생하였으며 또 다른 환자에서 냉동치료 도중 대량 출혈이 발생하였으나 응급 조치 후 다시 회복되었다.