• Progress in Superconductivity and Cryogenics
• /
• v.11 no.1
• /
• pp.16-19
• /
• 2009

Recently, for improvement of the magnetic field of high temperature superconductor (HTS) apparatus, many studies investigating on operating in the range of $20{\sim}65K$ with liquid helium or the conducting method using cryocooler is actively reviewed. Also, the cooling method using solid nitrogen as cryogen is being suggested. Since the nitrogen has very large specific heat in solid state, it is expected that it can enable long time operation without a continuous supply of cooling energy. However, there is still insufficient data on the characteristics of solid nitrogen such as thermodynamic properties and liquid-solid phase change. Especially, there was almost no study done on the electrical insulation properties of solid nitrogen so far. In this study, solid nitrogen to find the electrical characteristics was made by using cryocooler and cryostat, and investigated the flashover discharge and breakdown. The results of this study will be useful as a basic data for electrical insulation design of the HTS system using solid nitrogen as cryogen.

• Progress in Superconductivity and Cryogenics
• /
• v.26 no.1
• /
• pp.25-30
• /
• 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.

• Nuclear Engineering and Technology
• /
• v.37 no.5
• /
• pp.401-422
• /
• 2005

We review here research and development progress achieved in US Plasma Chamber technology roughly over the last decade. In particular, we focus on two major programs carried out in the US: the APEX project (1998-2003) and the US ITER TBM activities (2003-present). The APEX project grew out of the US fusion program emphasis in the late 1990s on more fundamental science and innovation. APEX was commissioned to investigate novel technology concepts for achieving high power density and high temperature reactor coolants. In particular, the idea of liquid walls and the related research is described here, with some detailed examples of liquid metal and molten salt magnetohydrodynamic and free surface effects on flow control and heat transfer. The ongoing US ITER Test Blanket Module (TBM) program is also described, where the current first wall/blanket concepts being considered are the dual coolant lead lithium concept and the solid breeder helium cooled concepts, both using ferritic steel structures. The research described for these concepts includes both thermofluid MHD issues for the liquid metal coolant in the DCLL, and thermomechanical issues for ceramic breeder packed pebble beds in the solid breeder concept. Finally, future directions for ongoing research in these areas are described.

• Corrosion Science and Technology
• /
• v.15 no.3
• /
• pp.113-119
• /
• 2016

Corrosion science faces new challenges in various nuclear environments. Three main areas may be identified where increases of knowledge and understanding have been done and are still needed to face the technical needs: (i) the extension of the service time of nuclear power plants from 40 years, as initially planned, to 60 years and probably more as expected now, (ii) the prediction of long term behaviour of metallic materials in nuclear waste disposal where the corrosion processes have to be predicted over large periods of time, some thousands years and more, (iii) the choice of materials for use at very high temperatures as expected in Generation IV power plants in environments like gas (helium), supercritical water, liquid metals or salts. Service time extension, deep geological waste repositories and high temperature reactors sustain researches and developments to model corrosion phenomena at various scales, from atoms to components.

• Proceedings of the Korea Institute of Applied Superconductivity and Cryogenics Conference
• /
• 2002.02a
• /
• pp.378-381
• /
• 2002

The helium liquefier was installed for 7.5 T superconducting wiggler, which is a source of synchrotron radiation, in Pohang Accelerator Laboratory (PAL) in 1995. It is MODEL 1410 fabricated by LINDE (old PSI America) of which capacity is about 17 liter per hour in normal mode and 47 liter per hour with liquid nitrogen pre-cooling. In addition to SC wiggler, we are anticipating that some devices related to electron accelerator are to be upgraded with superconducting application in order to improve the quality of photon beam.

• The Transactions of the Korean Institute of Electrical Engineers C
• /
• v.49 no.4
• /
• pp.219-225
• /
• 2000

In this paper, we report the experimental setup and characterization of experimental results for the HTS antenna. The constructions of experimental setup must be fabricated, cautiously. We constructed the cryostat made of 3 stages which consists of radome, vacuum stage and helium refrigerator for the HTS antenna. The HTS antenna was mounted to cryostat and various characteristics were measured at room temperature and liquid nitrogen temperature, 77 K. Also the results for the HTS antenna and the gold antenna were compared in terms of reflection coefficient, E-plane and H-plane radiation pattern, input impedance, SWR and efficiency. It appeared that the HTS antenna was superior to gold counterpart over the all characteristics.

• Proceedings of the KIEE Conference
• /
• 1992.07b
• /
• pp.850-853
• /
• 1992

A cryogenic electron cyclotron resonance plasma etching system has been built to study wafer-temperature in the silicon etching characteristics. The wafer temperature was controlled from -150 to +30 $^{\circ}C$ during etching using the liquid nitrogen cooled helium gas. Although silicon was etched isotropically in $SF_6$ plasma at room temperatures, we found that it is possible to suppress the etch undercut in Si by reducing a substrate temperature without side wall passivation. In addition, the selectivity of silicon to photoresist was improved considerably at a low wafer temperature. Etch rates, anisotropy and selectivity to photo resist are measured as a function of the wafer temperature in the region of -125 $\sim$ 25$^{\circ}C$ and rf bias power of 20W $\sim$ 80W.

• Journal of the Korean Magnetic Resonance Society
• /
• v.21 no.4
• /
• pp.114-118
• /
• 2017

Here, I report solid state Dynamic Nuclear Polarization (DNP) of $^1H$ nuclear spins at 0.3 T and 4.2 K. The DNP polarizer was developed based on a commercial X-band Electron Spin Resonance (ESR) modified for DNP, in combination with a NMR console and a liquid-Helium cryostat. By detuning magnetic field, DNP spectrum was measured to find the optimal condition. At +3 mT detuned from on-resonance field, $^1H$ NMR signal of 60:40 glycerol/water frozen solution doped with 20 mM perdeuterated-Tempone was amplified 43 times. The $^1H$ spin polarization obtained at 4.2 K is over 3100 times higher than that at 300 K. The width of the DNP spectrum, which is five times broader than ESR spectrum, is inconsistent with solid effect or thermal mixing, and presumably suggests a different DNP mechanism.

• Proceedings of the KIEE Conference
• /
• 2001.07b
• /
• pp.574-576
• /
• 2001

This paper deals with High Temperature Superconducting (HTS) Motor, which have two characteristics: the HTS magnet with iron plates as field coil, and the solid nitrogen $(SN_2)$ as a cryogen. The HTS magnet has iron plates to achieve the maximum current-carrying capacity and the simple shape that can easily be wound and jointed. The HTS magnet with iron plates, magnet optimized current distribution, and initial magnet are presented through 3 Dimensional Finite Element Analysis (3D FEA), manufacturing and testing these magnets. And, it is employed $SN_2$ for keep the operating temperature of HTS synchronous motor. To make the liquid nitrogen $(LN_2)$ of $SN_2$, Gas helium (GHe) passes into the heat exchanger and cools its own temperature. Two types of heat exchangers are designed and manufactured to make the $SN_2$, and each of the temperature characteristics is compared.

• Progress in Superconductivity and Cryogenics
• /
• v.2 no.1
• /
• pp.7-13
• /
• 2000

A rotating cryogenic system was designed similar to the cooling system for the rotor of a superconducting generator. The experimental rotor has an inner vessel which simulates the winding space of an actual superconducting rotor, and a torque tube of comparable design. This paper describes the evaluation of the total heat leak into the inner vessel that leads to the study of the heat transfer characteristic of the rotating cryogenic system. To examine the insulation performance of the experimental rotor. temperature was measured at each part of the system at various rotaing speeds from 0 rpm to 600 rpm. Total heat leak into the inner vessel was calculated by measuring the boil-off rate of liquid helium. Conduction heat leak to the inner vessel was obtained by the vent tube, and radiation heat leak was calculated by subtracting the conduction heat lent from the total heat leak. There seemed to be no rotaional dependency of total heat leak at least up 600 rpm.