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RISS 인기검색어
- 검색키워드
- 저자 : Kabindra (검색결과 5 건)
- 무료
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- 유료
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Quench Analysis of a Multiwidth No-Insulation 7-T 78-mm REBCO Magnet
Bhattarai, Kabindra R.,Kwanglok Kim,Seokho Kim,SangGap Lee,Seungyong Hahn Institute of Electrical and Electronics Engineers 2017 IEEE transactions on applied superconductivity Vol.27 No.4
<P>Due to the self-protecting feature, no-insulation (NI) high-temperature superconductor magnets have been regarded as a reliable option to generate high fields, yet their intrinsic charging delay still remains a major drawback. To apply the NI technique for actual high-field user magnets, however, postquench transient behavior of such magnets need to be fully understood, particularly the electromagnetic interaction among magnetically coupled subcoils. Recent publications have shown successful simulations of the transient behavior of a single NI coil or a multicoil magnet using distributed network models. Even though these approaches are very accurate, they often require substantial computation time, especially when multiple iterations are required during design or analysis of an NI magnet having a large number of coils. This paper presents a simple circuit approach that may be effective for quench simulation of multicoil NI magnets. Each NI subcoil in a magnet is lumped into a single inductor with a resistor in series and a resistor in parallel. This approach has allowed us to simulate the whole magnet system within reasonable time without compromising the understanding of mutual interactions of all of the subcoils after quench, namely change in parameters such as voltage, current, and temperature with respect to time and coil to coil normal zone propagation in an electromagnetic manner. We verified the proposed approach by analyzing the quench process in a previously built 7 T, 78 mm all-REBCO NI magnet (by MIT), and by doing the first ever comparison between the simulated results with the data measured from actual experiment.</P>
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Design and performance estimation of a 35 T 40?mm no-insulation all-REBCO user magnet
Kim, Kwangmin,Bhattarai, Kabindra R,Jang, Jae Young,Hwang, Young Jin,Kim, Kwanglok,Yoon, Sangwon,Lee, SangGap,Hahn, Seungyong IOP 2017 Superconductor science & technology Vol.30 No.6
<P>This paper presents a design of a 35 T 40 mm winding diameter no-insulation?<I>standalone</I> magnet that consists of a stack of 52 double pancake (DP) coils wound with multi-width REBCO tapes. The inner and outer diameters and height of the magnet are 40 mm, 221.6 mm, and 628 mm, respectively. It is designed to generate 35 T at an operating current (<I>I</I> <SUB>op</SUB>) of 179.8 A in a bath of liquid helium at 4.2 K. All the DP coils will be ‘dry’ wound without epoxy, making turns within the DP coils to be essentially ‘self-supporting,’ which is effective to reduce the magnetic stress. To reduce the magnet charging time constant, the so-called ‘metallic cladding’ REBCO tapes will be adopted, where a 1–2 <I>μ</I>m thick stainless steel layer surrounds the tapes hermetically. With an average surface contact resistance (<I>R</I> <SUB>ct</SUB>) of 170 <img ALIGN='MIDDLE' ALT='$\mu {\rm{\Omega }}\,$' SRC='http://ej.iop.org/images/0953-2048/30/6/065008/sustaa6677ieqn1.gif'/> cm<SUP>−2</SUP>, experimentally obtained from a charging test of our recent 3 T 100 mm stainless steel cladding REBCO magnet, the charging time constant of the 35 T magnet was estimated to be 3.01 minutes, though the magnet will be energized substantially slower over a few hours to reduce ac loss and Joule heating from radial turn-to-turn leak currents. A preliminary post-quench analysis, based on our lumped equivalent circuit model, was performed; the total stored energy of 1.79 MJ (magnet inductance: 110.5 H) was expected to be discharged in approximately 1.28 seconds after a quench due to the fast electromagnetic quench propagation among the DP coils, while the peak hot spot temperature was estimated to rise to 94 K, acceptable for a safe quench of a REBCO magnet.</P>
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Seong H. Kim,Christopher M. Lee,Kabindra Kafle 한국화학공학회 2013 Korean Journal of Chemical Engineering Vol.30 No.12
Cellulose is among the most important and abundant biopolymers in biosphere. It is the main structural component of a vast number of plants that carries vital functions for plant growth. Cellulose-based materials have been used in a variety of human activities ranging from papers and fabrics to engineering applications including production of biofuels. However, our understanding of the cellulose structure in its native form is quite limited because the current experimental methods often require separation or purification processes and provide only partial information of the cellulose structure. This paper aims at providing a brief background of the cellulose structure and reviewing the basic principles, capabilities and limitations of the cellulose characterization methods that are widely used by engineers dealing with biomass. The analytical techniques covered in this paper include x-ray diffraction, nuclear magnetic resonance,and vibrational spectroscopy (infrared, Raman, and sum-frequency-generation). The scope of the paper is restricted to the application of these techniques to the structural analysis of cellulose.
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Quench behavior of a no-insulation coil wound with stainless steel cladding REBCO tape at 4.2 K
Kim, Kwanglok,Kim, Kwangmin,Bhattarai, Kabindra R,Radcliff, Kyle,Jang, Jae Young,Hwang, Young Jin,Lee, SangGap,Yoon, Sangwon,Hahn, Seungyong IOP 2017 Superconductor science & technology Vol.30 No.7
<P>A single pancake no-insulation (NI) coil was wound in a hermetic way with REBCO tape having a thin (1–2 <I>μ</I>m) cladding layer of stainless steel. With an electric heater embedded at the innermost turn of the coil, heater-induced quench tests were performed under a background field of 15 T in a bath of liquid helium at 4.2 K. Despite the large average contact surface resistance of 1.63 <img ALIGN='MIDDLE' ALT='${\rm{m}}{\rm{\Omega }}$' SRC='http://ej.iop.org/images/0953-2048/30/7/075001/sustaa6a8bieqn1.gif'/> cm<SUP>2</SUP> <img ALIGN='MIDDLE' ALT='$,\,\gt 20$' SRC='http://ej.iop.org/images/0953-2048/30/7/075001/sustaa6a8bieqn2.gif'/> times larger than those of pure NI coils, ‘thermal recovery’ was observed at a coil current density (<I>J</I> <SUB> <I>e</I> </SUB>) below 700 A mm<SUP>−2</SUP> mainly due to the local current sharing. The coil experienced nine consecutive ‘thermal runaway’ quenches at <I>J</I> <SUB> <I>e</I> </SUB> of 700–820 A mm<SUP>−2</SUP> (power supply limit), yet no discernible coil degradation or damage was observed. The results demonstrated that the stainless steel cladding REBCO tape may be effective at reducing the charging delay of high field NI REBCO magnets without sacrificing the self-protecting feature.</P>
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