Proceedings of the Korea Institute of Applied Superconductivity and Cryogenics Conference (한국초전도저온공학회:학술대회논문집)
The Korean Society of Superconductivity and Cryogenics (KSSC)
- 기타
Domain
- Physics > Condensed Matter Physics
1999.02a
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The recent progress in the new cooling technology for superconducting systems without liquid cryogens is briefly presented. In these conduction-cooled systems, the super-conducting magnets are cooled by a direct contact with closed-cycle cryocoolers and only electricity is supplied to maintain the cryogenic temperatures. It is reported that at least 20 conduction-cooled (low Tc or high Tc) super- conducting systems have been constructed, tested, or commercially used worldwide. Some of the significant design issues are discussed in comparison with the conventional liquid-helium cooled systems.
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The grain morphology, the changes in morphology and Jc with the thermo-mechanical treatment (TMT) history, the field dependence of Jc and the nature of intergranular bonding were studied in
$T_{10.8}$ $Pb_{.2}$ $Bi_{0.2}$ $Sr_{1.8}$ $Ba_{0.2}$ $Ca_{2.2}$ $Cu_{3}$ $O_{z}$ /Ag tapes. As a result, incorporation of intermediate rolling during the final heat-treatment resulted in of plate-like TI-1223 grains, and thus enhanced Jc. Jc's near 2.5$\times$ 104 A/cm2 at 77 K and 0 T were obtained in just rolled tapes with an excellent reproducibility. The high Jc's seem to grain-connectivity easy recovery of excellent grain-connectivity during final heat-treatment after inter -mediate rolling, probably due to retarded T1 evaporation and excessive Ca content in the present composition. The strong field dependence of Jc even in low fields, however, indicated that there still existed significant weak-links and the degree of directional grain-alignment was far from the desired one. The intergranular binding in the tapes seemed to be mainly dominated by SIS junctions. -
For large scale applications of high temperature superconductor(HTS) such as transmission cables, motors and generators, long length of flexible HTS conductors is required. Currently, HTS tape that is capable of being fabricated in long length by industrial processes is the Bi-2223 HTS tape. In this study, we fabricated 19 filamentary Bi-2223(
$Bi_{1.8}$ $Pb_{0.4}$ $Sr_{2}$ $Ca_{2}$ $Cu_{3}$ $O_{10+X}$ ) HTS tape with 100m length by PIT(Powder In Tube) process. Critical current(Ic) of this long length tape was measured 18.5 A at 77 K, self field and short sample Ic is 32.5 A at the same condition. Critical current of 100m length tape was decreased by about 1/3 compared to that of short tape. This was mainly resulted from the increase of non homogeneity in oxide layer. -
Four designed
$Nb_{3}$ Sn superconductors have been fabricated in order to investigate the effect of pre-heat treatment for internal tin process. 3 types of sub-elements and 2 types of Sn reservers were fabricated. Diffusion of Sn is better in the strand divided Sn equally than in the strand had one large Sn reserver during pre heat-treatment. -
The effects of joining process such as contact method, shape of joined area and pressure on the properties of Bi-2223 superconducting tape have been optimized. In the process tapes were etched to expose the superconductor core in the shape of 'ㅁ' and 'ㄷ'. The exposed cores of the two tapes were brought into contact, uniaxially pressed and sintered. Subsequently, the current capacity of the joined tape was measured as a function of uniaxial pressure. It was observed that the current capacity was significantly dependent on uniaxial pressure. The joined tape, fabricated with a pressure of 1,600 MPa, showed the highest value of current capacity(90%) of highest value of current capacity is resulted from improvements in core density, contacting area and grain alignment, etc. In addition the effect of processing variables on microstructural evolution and mechanical property of joined tape will be presented.
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A well oriented Bi-2212 superconductor thick films were fabricated by screen printing with a Cu-free Bi-Sr-Ca-Cu-O powder on a copper plate and heat-treating at 820-
$880^{\circ}C$ for several minute in low oxygen pressure or are. At minute in low oxygen pressure of air. At , the printing layer partially melted by reaction between the Cu-free precursor by reaction between the Cu-free$870^{\circ}C$ precursor and CuO of the oxidizing copper plate. It is believed that the solid phase is Bi : Sr : Ca : Cu = 2 : 2 : 0 : 1. It is likely that the Bi-2212 superconducting phase is formed at Bi-2212 superconducting phase is formed at Bi-free phase/liquid interface by nucleation and grows. -
Superconducting
$YBa_{2}$ $Cu_{3}$ $O_{7-x}$(YBCO) thin films were deposited on MgO(100) substrates using a hollow cathode discharge sputtering system. Influence of the sputtering conditions such as substrate temperature and discharge sputtering gas pressure on electrical and structural properties were investigated. It was found that YBCO thin films with zero resistance temperature higher than 85 K were obtained to the pressure 200 mToorr(Ar/O2=0.9), substrate temperature of $760^{\circ}C$ , and target-substrate distance of 10 mm during film deposition. Homogeneous large area YBCO films with 2 inch diameter were also sucessfully fabricated by this method. -
In this study, the fatigue test at room temperature and residual resistivity measurement test at 12K were carried out, respectively, using a 9 strand Cu-Ni/NbTi/Cu composite cable, in order to investigate how the fatigue damage effects on critical properties. Through the fatigue test of a 9 strand Cu-Ni/NbTi/Cu composite cable, a conventional S-N curve was obtained even though there existed a possibility of fretting among strands. From the resistivity measurement of a NbTi strand after fatigue tests, it was found that with increase of the repeated number the RRR increased slightly, and the trend became significant with increase in maximum value of the applied stress amplitude.
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An acoustic emission(AE) technique has been used to monitor and diagnose quenching phenomenon in racetrack shaped superconducting magnets at cryogenic environment of 4.2K. The ultimate goal is to ensure the safety and reliability of large superconducting magnet systems by being able to identity and locate the sources of quench in superconducting magnets. The characteristics of AE parameters have been analyzed by correlating with quench number, winding tension of superconducting coil and charge rate by transport current. It was found in this study stat there was good correlation between quench current and AE parameters. The source location of quenching in superconducting magnet was also discussed on the correlation between magnet voltage and AE energy.
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The characteristics of Nb3Sn strands shich will be used for the been investigated. The physics requirements for the KSTAR operation demands the two conditions, high non-Cu critical current density and low contradictory to each other. It is recent that superconductor manufacturers. IGC and Mitsubishi, have succeded in the production of the strand which satisfies the ITER HP-1 and HP-2 conditions at the same time. It has been determined that this type of strand, so-called HP-3, will be used for the KSTAR magnets and its properties, critical current density and hysteresis loss investigated by the several institutes are presented here. On the basis of the round robin tests for many strand samples under various optimized and the vendor will be seleted.
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The microstructure of Top Seed Milt-Processed
$YBa_{2}$ $Cu_{3}$ $O_{7-\delta}$ single crystal was studied. It was presumed that the segregation of Y211 is due to the difference of growth rates between a, b axis and c axis in crystal direction. Corn kernel lide structure which was grown by the diffusion of Y211 was observed. At the near corner of the seed crystal, the diagonal line on Y123 cry crystal is formed by the corn kernel like structure. -
The orientation mechanism of an amorphous
$Bi_{2}$ $Sr_{2}$ $Ca_{2 x}$ $Cd_{x}$ $Cu_{3}$ $O_{y}$ phase were studied by using the dilatometry. The amorphous$Bi_{2}$ $Sr_{2}$ $Ca_{2 x}$ $Cd_{x}$ $Cu_{3}$ $O_{y}$ samples brought about a volume shrinkage at the onset of the crystallization of a$Bi_{2}$ $Sr_{2}$ $CaCu_{2}$ $O_{6}$ phase around$400^{\circ}C$ . The random crystal growth of$Bi_{2}$ $Sr_{2}$ $CaCu_{2}$ $O_{8}$ phase around$800^{\circ}C$ . yielded a rapid volume expansion and after then samples shrinmed, accompanied with the crystal orientation. The$Bi_{2}$ $Sr_{2}$ $Ca_{2 x}$ $Cd_{x}$ $Cu_{3}$ $O_{y}$ (x=0.4) sample exhibited the best-oriented structure because the liquid phase formed seemed to have the lowest viscosity which would contributed to the easy collapse of the card-house structure. -
The crystallization mechanism of an amorphous
$Bi_{2}$ $Sr_{2}$ $Ca_{2 x}$ $Cd_{x}$ $Cu_{3}$ $O_{y}$ phase were studied from the relations between crystallization and volume changes by dilatometry. Further, the effect of addition of CdO on the crystallization mechanism and superconductivity was discussed. The shrinkage of the amorphous$Bi_{2}$ $Sr_{2}$ $Ca_{2 x}$ $Cd_{x}$ $Cu_{3}$ $O_{y}$ occurred with the crystallization of$Bi_{2}$ $Sr_{2}$ Cu$O_{6}$ phase decrease with increasing CdO content with a minimum at x=0.4. Better superconductivity was obtained in the specimens formation less amount of the$Bi_{2}$ $Sr_{2}$ Cu$O_{6}$ phase during the crystallization process. -
AC losses per cycle properties at 77K have been investigated on the Ag sheathed Bi2223 wire through two kinds of measuring methods(transport method and magnetic method). In case of transport method, the absolute value of losses agree with the results of Norris theory(strip and ellipse). In case of 19-filamentary tape, AC transport losses almost agree with those of magnetic method. In case of 1-filamentary tape, However, AC losses of magnetic method is smaller than AC transport losses
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Dry winding is generally adopted in superconducting coils of an UPS system. In these kinds of coils a quench is often initiated by a disturbance such as wire motion that generates a highly localized normal zone in a superconducting wire. To fabricate the stable coils, stability of the superconducting wire should be touched. In this paper, a model for a transient stability analysis of the wire is suggested. The influence of a local disturbance, cooling, an external field and a stabilizer to superconductor ratio on the wire stability is investigated and discussed.
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The major deisng parameters that are considered in this paper are: 1) EMF according to width of field coil. 2) EMF according to magnetic shield length. Because of superconducting generator (SG) is actually and air cored machine with its rotor iron and stator iron teeth having been removed. In this case, the desing of the SG must be based on the 3D analysis of the magnetic field. This study presents an effective armature winding type with 3D FEM(Finite Element Method), and compares analyzed and measured results.
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During the fast current and field ramp up experiment with CICC (Cable-In-Conduit Conductor) non-insulated 3 strand superconducting magnet, the unbalanced current distribution associated with the loop current has been obtained directly from the shunt resistor voltage data. To explain the generation of the loop current during the current ramp up, the steady-state three strand loop current model was proposed. This model gives an explanation for the relation between the loop current and the relation between the loop current and the twist geometry of the strands. According to this model, the twist geometry of the strand has significant influence on the generation of the loop current especially in the large superconducting magnet.
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Superconductors are dissipative when exposed to time-varying magnetic fields. To analyze the AC characteristics of the superconductor, one usually needs to know magnetization curves of it. A good magnetization curves can be obtained only in a homogeneous magnetic field. In this paper, we report the fabrication and test results of a homogeneous magnet, which aims to give background magnetic fields for the superconductor.
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In this paper. We experimentally investigated the magnetic properties of YBCO bulk superconductor using AC magnetization method. The sample is 2.8cm wide in a diameter and 1.4cm long. We applied Ac magnetic field parallel to the direction of length of YBCO bulk. It is observed that YBCO bulk has the diamagnetic properties. AC loss calculation of YBCO bulk superconductor was performed by evaluating the total area of magnetization traces. As depends on the frequency and amplitude of the applied magnetic field.
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The purpose of this paper is to find the magnetic field distribution inside the motor in order to find out if the high-Tc superconducting tapes operate stably in actual motor operation. With this gola, magnetic field distribution in a detailed model of the actual motor was analyzed through F.E.M. (Finite Element Method). As a result, it has been proved that the high-Tc superconducting tapes can withstand 4 A of current with stability. 4 A was the amount of current needed to achieve 600 A ·turns which is required by the previous simulation aimed at developing this motor. Also, it has been observed that the flux damper reduces armature reactance during the motor operation and during load changes, helping the stable motor operation. But, it was observed that the flux damper generates loss by means of leakage flux and this decreases the output of the motor by about 5%.
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The study of HTS bulk in permanent magnet applications requires the calculation of forces acting on the bulk. Currents distribution in HTS Superconducting bulk is very important to determine this forces. We have made computer program to find this current distribution and this program is applied to some simple disc-shape HTS bulk being magnetised in a uniform field. The techniques for determination of currents are FEM analysis and iteration method.
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A small scale joint sample of Nb3Sn CICC was fabricated by sub-cable to sub-cable joining. This joint was produced by parallel insertion of one end of each sub-cable into the sub-cable space of the other side of cable, which can decrease the equivalent electrical resistance at the joint is expected to have average properties, dc resistance and ac losses, in view of the shapes of ITER type joint and strand to strand joint. The 3.8nOhm of dc resistance was measured in the range of 10-200A transport current. The normalized resistivity of the joint was about 6.7
$\mu}$ Ohm-$^mm{2}$ . Considering the normalized resistivity, the full scale joint prepared by sub-cable to sub-cable joining may have similar joint dc resistance with other conventional full scale joints with a shorter joining length. -
This paper deals with the quench characteristic analysis in high-Tc superconducting synchronous motor of five to six hundred watts capacity. First, the magnetic field distribution and ac losses of high-Tc superconducting motor with the additive flux damper circuit was derived and computer simulation was performed with the equivalent model using FEM. The simulation results show that the quench state lasts for about 0.3 seconds.
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Nowadays the high-Tc Superconducting Fault current Limiter (SFCL) is one of the superconducting devices which are very closed to commercialization. The most popular model of High-Tc SFCL is a magnetic shielding type. A superconductor of magnetic shielding type SFCL can be stable in the superconducting state, because there is no contact between the superconductor and the normal conductor. But this model needs large place to set up and in a fault condition, mechanical vibrations may happen to damage the superconductor or total device. In this paper, to solve these problems, the simplified model of magnetic shielding type SFCL was introduced.
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We have performed an EMTDC simulation for the current limiting effects of a superconducting fault current limiter (SFCL). The fault currents in the 154 kV transmission line between the Gaepo and Sungnam substations increased up to 54kA and 60kA during the line-to-line and three phase faults, respectively. The SFCL with 100
$\Omega$ of impedance after quench limited the currents to less than 17 kA within a half cycle. This limited current is well below the upper limit of a circuit breaker, suggesting that the impedance of the SFCL in the transmission line is sufficient. -
The normal zone propagation (NZP) velocity and V-I characteristics of two Bi-2223 pancake coils with different Ag/SC ratio were investigated by experiment. Non-uniformity of Ic and broad restive transition was oberserbed in two coils. The NZP velocity of azimuth direction is faster than radius direction, and the NZP velocity of coil with higher Ag/SC ratio is faster than another coil with lower Ag/SC ratio.
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The shield effects of the actively shielded superconducting magnet systems for MRI were investigated. The magnetic field was calculated by FEM considering the winding error and the homogeneity of the magnetic field at the 30cm DSV was presented. The 5 gauss stray field line was restricted within 5m form the magnet center.
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This paper is about a modified induction generator which has a free inner-rotor. The improved induction generator utilizes a free inner-rotor that has a superconducting magnet. This kind of generator has same approach when analyzing as an ordinary induction generator, but shows a little difference when expressing in designing and analyzing such the machines.
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A horizontal axle-type superconductor flywheel energy storage system has many great features such as extensibility and stability compared to the traditional vertical axle-type flywheel systems. In this paper, a prototype flywheel device with a horizontal axle is presented briefly, and the hybrid construction as an essential supplement in superconductor journal bearing design against the levitation drift is proposed.
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This paper presents the 2-D analysis of damper transient in superconducting of damper transient in superconducting synchronous generator(SCG) using finite element method. Efficient 2-D analysis model which compensates the leakage flux is proposed for the savign of computation time and memory capacity required in 3-D finite element analysis. The characteristics of damper transient in SCG and the prime role of damper also have been evaluated.
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In recent years, there is a growing needs for large capacity underground power transmission lines with the increasing demand of electric power in the urban area, where various environmental limitations are imposed on the overhead transmission lines. But it is difficult to get the space for the underground power transmission cables because of complicated distributions of underground public facilties such as subway, water pipes, gas etc. As the superconducting power cables have the large power transmission capacity, the high power transmission capacity, the high power transmission density, and low loss characteristics in comparison with a conventional cable, it would be a solution to meet the increased power demand. In this paper, the results of the conceptual design and analysis of power system of HTS power transmission cable is described.
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This paper describes the design, code of a
$\mu$ SMES device that we developed. The 0.7MJ$\mu$ SMES coil was wound with high winding tension of about 14kbf/$mm^{2}$ in order to prevent wire motion from Lorentz force. This coil was charged up to a current of 1820A with a ramping rate of about 10A/s, where a quench occurred. This quench current is sbout 82% fo the coil critical current. -
전류의 손실 없이 MRI 마그네트의 연구전류 운전을 위한 영구전류스위치(Persistent Current Switch;PCS)를 설계 및 제작하여 그 특성을 측정하였다. 한국전기연구소의 Whole body MRI 마그네트로의 적용을 위해 설계되었으며, 또한 PCS 보빈을 기존의 FRP에 비해 열전도 특성과 기계적 강도가 우수한 알루미늄으로 제작하였다. Main 코일 1개와 Shim 코일 9개의 PCS에 대한 필요한 파라미터를 계산하여 제작하였다. PCS의 기본요구조건인 step 형태의 스위칭 특성과 각 PCS가 실온저항의 50%∼55%의 상전도 저항 특성을 보임을 확인하였다.
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For the first time in Korea, a 30kVA superconducting generator has been designed, developed and successfully tested recently. This is the forerunner of a 1MVA superconducting generator which is currently under development. The paper discusses the design, development and cooling experience of a superconducting rotor. This has 3 passages of the recovered Helium gas and a gas flow control system.
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A 30kVA superconducting generator has been designed, developed and successfully tested recently. The design is based on 2-dimensional electromagnetic field analysis. The rotor has been wound with superconducting wire of Nb-Ti alloy. The stator has the air-gap type armature windings. Open-circuit test, short-circuit test and lamp load test have been conducted. The details of design program, design, machinebuilding, test results and conclusions are given in this paper.
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In this paper, the inertance tube is modeled by the distributed impedance model. This model is verified by the analytical solutions for the long tube without the reservoir. In this model the distributed impedace effect of the inertance tube is included and mass flow rate and pressure distributions are calculated along the inertance tube for various inertance tube lengths. Mass flow rate at the inlet of the inertance tube is also calculated by this model and compared to the lumped impedance method. Mass flow rate by the distributed model shows quite different behaviors from the lumped model when the operating frequency is high and the length of the tube becomes large.
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Enthalpy transport in a pulse tube was investigated by two-dimensional analysis of mass, momentum and energy equations of the gas as well as energy conservation of the tube wall. The mean temperature of the gas and the tube wall was obtained directly by assuming that the outer surface of a pulse tube is adiabatic. Effects of operating frequency, tube wall thickness, velocity ratio and velocity phase angle between both ends of a pulse tube on net enthalpy flow were shown.
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$^{3}$ He melting curve thermometer is made, tested, and compared with Greywall scale. The experimental results show that we can identify the temperature within a few percentage. To improve the accuracy of our thermometer we need temperature fixed points like$^{3}$ He superfluid phase transition temperature. -
Thermodynamic cycle analysis has been performed for the power generation systems to utilize the cold energy of liquefied natural gas (LNG). Among many possible configurations of the cycle, the open Rankine cycle, the closed Rankine cycle, and the closed Brayton cycle are selecte for the analysis because of their practical importance. The power output per unit mass of LNG has been analytically calculated for various design parameters. The optimal conditions for the parameters to maximize the power output are presented and some of the design considerations are discussed.
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The exergy method is used for analysis and evaluation of the cryogenic nitrogen production process which is operated by expansion turbene and liquid nitrogen. The exergy loss and thermodynamic effeciency are calculated for the each process. Also the operating efficiency and the exergy distribution are examined for each unit of proces. The optimal conditions to minimize the exergy loss of nitrogen column are found that nitrogen recovery ratio is maximum and operating pressure is 5.0 kg/cm2g. The exergy method can be used to design a plant and to evaluate its process.
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Vacuum insulated pipes (VIP) are one of the important equipments for cryogenic fluids' transfer. Flange type of VIP, which can easily be installed at the site, uses a set of male and female bayonet with very small gap between them. In order to prevent leakage of liquid from inner pipe to bayonet. Teflon or Kel-F is located outside both the inner pipe of male and the guide of female. Even though liquid may leak at room temperature, it cannot leak at cryogenic temperature since Teflon shrinks much more than pipes and adheres closely to the inner pipe and guide. Teflon seal method has the advantage of easy fabrication, low cost and effective sealing compared to the conventional method.
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Cold Neutron Source(CNS) facility comprises moderator circulation system, helium cooling system, neutron guide and auxiliary sistems. To increase the amount of cold neutron, the thermal neutron should pass cold moderator at cryogenic temperature. As cold moderator in Hanaro, the liquid hydrogen or liquid deuterium will be used and the temperature in operation will be used and the temperature in operation will be maintained to be
$250^{\circ}C$ below zero. To maintain the moderator at this cryogenic temperature. He refrigerator is used to cool it down in thermosiphon having natural circulation. As a part of the conceptual design of Hanaro CNS, study on the characteristics of moderators, design of moderator chanmber and cooling method were done through the collaboration of Korea Atomic Energy Research Institute and Petersburg Nuclear Physics Institute. During the collaboration, a program for the design of moderator cooling system design concept through the parametric study using this program. In the parametric study, the effect of the moderator type on the design parameters was investigated. Also, the requirements on the performance test for the cooling system, which will be made before the basic design, were investigated. -
Very simple continuous level meter with capacitive transducer for cryogenic liquid is fabricated and tested with liquid nitrogen. The principle of the level meter operation is presented.
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KSTAR cryostat is a large vacuum vessel that provides the necessary thermal barrier between the ambient temperature test cell and the liquid helium cooled magnets. In this work, the structural analyses for the cryostat under the normal operation condition were performed. As a result, it turns out that the vessel would be safe when it is exposed to normal operation loads, such as system weight, vacuum pressure, and plasma vertical disruption load. And, the preliminary result on the modal analysis is presented.
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An experimental study was carried out to improve the cooling capacity and performance of the pulse tube refrigerator. Three buffer pulse tube refrigerator was designed and fabricated, and the experimental apparatus was constructed. This paper presents operating process of three buffer pulse tube refrigerator and results obtained with the performance test. The cooldown characteristics and load characteristics are described. The lowest temperature measured in three pulse tube refrigerator was 88K and the cooling capacity at the optimum operating condition was 27W at 120K.
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Thermodynamic cycle analysis has been performed to maximize the liquid amount for two hydrogen liquefaction systems using two-stage GM(Gifford-McMahon) refrigerator. the optimal operating conditions have been analytically sought with real properties of normal hydrogen for the two-stage GM direct contact system and the two-stage GM precooled L-H (Linde-Hampson) system. In the precooled system, there existed optimal values for compressed mass flow and compressed pressure to maximize the liquefied mass. It was recommended to use a cryocooler, which had a large precooling capacity between 70 and 100K.
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An optimal cooling method for HTS(high Tc superconductor) current leads has been analytically sought to minimize the required refrigerator power. The binary current lead is a series combination of a normal metal conductor at the warmer part and an HTS at the colder part. The lead is cooled by direct contacts with a two-stage cryocooler at the joint and at the cold end. It is clearly proven that there exists unique optimal values for the joint temperature and the current density to minimize the refrigerator power per unit current. the actual power input to the cryocooler in the optimal conditions is compared with its thermodynamic limit, and some significant issues in practical design are presented with a useful graphical method.
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This paper presents operating process of the Stirling cryocooler and results obtained with the performance test for Signal Usfa UP 7075 Stirling cryocooler. An experimental study was carried out to develop the more reliable Stirling cryocooler. The cooldown characteristics and load characteristics are described. The lowest temperature measured in the Stirling cryocooler wa 62.5K and the cooling capacity at the optimum operating condition was 0.4W at 77K. At that time, carnot COP was 0.024.