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Design of HTS Modular Magnets for a 2.5 MJ Toroidal SMES: ReBCO vs. BSCCO
Seyeon Lee,Woo-Seok Kim,Sang-Ho Park,Ji-Kwang Lee,Chan Park,Joon-Han Bae,Ki-Chul Seong,Haigun Lee,Jong-Hoon Lee,Kyeongdal Choi,Songyop Hahn IEEE 2010 IEEE transactions on applied superconductivity Vol.20 No.3
<P>A 2.5 MJ HTS SMES is being developed as a national program in Korea. This paper presents design results of modular HTS magnets for the 2.5 MJ toroidal SMES. We considered a choice of BSCCO-2223 or ReBCO tapes as the conductors for the HTS magnets of the SMES. Operating temperature was decided to be 20 K which could be accomplished by conduction cooling with a couple of GM cryo-coolers. Key design factors may include minimization of total conductor requirement and low AC loss.</P>
Thermal Analysis of PCS for an HTS Pancake Coil in Persistent Current Mode
Woo-Seok Kim,Yungil Kim,Sang-Ho Park,Seyeon Lee,Ji-Kwang Lee,Chan Park,Bang-Wook Lee,Kyoung-Jun Kim,Haigun Lee,Hee-Gyoun Lee,Gye-Won Hong,Kyeongdal Choi IEEE 2010 IEEE transactions on applied superconductivity Vol.20 No.3
<P>It is well known that high temperature superconductors (HTS) are promising for a magnet application, but it has been almost impossible so far to apply them to the magnet in persistent current mode because of poor qualities of their superconducting joint at higher current as well as lower index values. In this paper, in order to get rid of the joints from an HTS superconducting magnet, a prototype HTS pancake coil using YBCO coated conductors by the technique of wind-and-flip pancake coil was made and will be tested later. This paper presents a design, fabrication, and thermal analysis of the prototype pancake coil. The coil will be cooled down around 20 K by conduction cooling using a GM cryocooler. The expected current drift rate for an MRI application has not been achieved, probably caused by large flux flow resistance of coated conductor at higher temperature, 77.3 K. A temperature dependency of temporal stability of the persistent current will be measured by monitoring the long-term drift of the magnetic field at different operating temperatures by Hall sensors.</P>
Lee, Jeyull,Kim, Junseong,Baek, Geonwoo,Choi, Yojong,Choi, Yoon Hyuck,Zhang, Zhan,Chung, Yoon Do,Kang, Hyoungku,Lee, Haigun,Lee, Sangjin,Ko, Tae Kuk IEEE 2018 IEEE transactions on applied superconductivity Vol.28 No.3
<P>High-temperature superconductors (HTSs) have a much larger thermal margin than low-temperature superconductors, owing to their high critical temperatures. This characteristic allows HTS magnets to tolerate extremely high heat loads that may arise from radiation. Therefore, research on the development of HTS quadrupole magnets is progressing widely. Quadrupole magnets are commonly used for focusing the transported beams of particles in accelerators. In order to focus the beam, the quadrupole magnet uses an iron yoke with a hyperbolic contour. However, the iron yoke induces nonlinear magnetic characteristics because of saturation. Therefore, an air-core HTS quadrupole magnet is proposed to improve the magnetic characteristics. In this paper, we design air-core and iron-core HTS quadrupole magnet models using a harmonic matching method. The field gradient and effective length of both magnets are 12.1 T/m and 550 mm, respectively. In order to verify the performances of the proposed air-core quadrupole magnet, the magnetic field gradient, field uniformity, and effective length are analyzed for operating currents ranging from 50 to 400 A.</P>
Lee, Jinhyung,Kim, Jong Cheol,Kim, Jongsik,Singh, Rajiv K.,Arjunan, Arul C.,Lee, Haigun Elsevier 2018 THIN SOLID FILMS - Vol.660 No.-
<P><B>Abstract</B></P> <P>The extent of subsurface damage on (0001) GaN wafers post different polishing treatments was quantified using depth-resolved cathodoluminescence spectroscopy (DRCLS). The band edge emission spectra were obtained from CLS with different electron energies, which manifested a significant non-radiative recombination resulted from polishing-induced subsurface damage. Cross-sectional transmission electron microscopy (XTEM) was also used to diagnose the extent of the subsurface damage layer. For the GaN polished with 1.00 and 0.25 μm diamonds abrasive, the extent of non-radiative subsurface damage is about 250 and 100 nm, corresponding to the calculated electron penetration depth at the accelerating voltage for the onset of band edge emission. In this study, the depth of subsurface damage estimated from CL spectra compared well with direct XTEM measurements in GaN substrate.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Subsurface polishing defects of bulk gallium nitride substrates have been studied. </LI> <LI> Estimated the subsurface damage depth. </LI> <LI> The subsurface damage defects are due to plastic deformation and are non-radiative. </LI> </UL> </P>
Jiho Lee,Tae Sung Lee,Oh Jun Kwon,Haigun Lee,Tae Kuk Ko IEEE 2014 IEEE transactions on applied superconductivity Vol.24 No.3
<P>This paper deals with the low-pass filtering characteristic of the axial magnetic field of no-insulation and partial-insulation high temperature superconducting (HTS) coils carrying a dc-biased ac current. Recently, the no-insulation winding technique has been issued as a key technique to enhance the performance of HTS coils in terms of the overall current density, thermal stability, and mechanical integrity. In this paper, to verify the effect of time-varying external distortion on no-insulation HTS coils, an experimental analysis is carried on three HTS coils-insulation, no-insulation, and partial-insulation coils. To simulate the environment in which time-varying external distortion influences the HTS coils, a dc-biased ac current is carried by the HTS coils. The axial magnetic fields of no-insulation, partial insulation, and insulation HTS coils are experimentally tested and analyzed. When the coils carry a dc-biased ac current, the no-insulation and partial-insulation coils have a tendency to attenuate the high-frequency components and to act as a low-pass filter on the axial magnetic field; however, the insulation coil does not attenuate the high-frequency components of the axial magnetic field. The analysis of the experimental results can be useful data for the adoption of no-insulation and partial-insulation windings in superconducting applications.</P>
Woo Seung Lee,Young Gun Park,Jinsub Kim,Seunghyun Song,Haeryong Jeon,Young-Gyun Kim,Haigun Lee,Tae Kuk Ko IEEE 2016 IEEE transactions on applied superconductivity Vol.26 No.4
<P>The field stability of a no-insulation and a turn-to-turn soldered high-temperature superconducting (HTS) magnet is analyzed under sinusoidal noise operation. The stability of the magnetic field is a critical factor for some applications such as nuclear magnetic resonance (NMR) spectrometer. The no-insulation and turn-to-turn soldered HTS magnets have intrinsic residual resistance which acts like a low-pass filter attached to the main magnet. The intrinsic low-pass filter can improve the time stability of the magnetic field by reducing ac noises generated by the power supply. In this paper, the improved field stability is analyzed with a no-insulation and a turn-to-turn soldered HTS magnet sample. The sample magnets are operated under sinusoidal power supply noise. Qualitative analysis is conducted by simulating the virtual NMR lineshapes based on the field mapping results obtained during sample magnet operation. Both the no-insulation and turn-to-turn soldered magnets demonstrated improved field stability, but the field stability in the turn-to-turn soldered case is greater.</P>
Design of HTS Magnets for a 2.5 MJ SMES
Sangyeop Kwak,Seyeon Lee,Sangyeop Lee,Woo-Seok Kim,Ji-Kwang Lee,Chan Park,Joonhan Bae,Jung-Bin Song,Haigun Lee,Kyeongdal Choi,Kichul Seong,Hyunkyo Jung,Song-yop Hahn IEEE 2009 IEEE transactions on applied superconductivity Vol.19 No.3
<P>A 600 kJ HTS SMES system has been developed for power system stabilization as a national project in Korea. Successful operating tests of the 600 kJ were recently completed. In this paper, a 2.5 MJ class SMES with HTS magnets of single solenoid, multiple solenoid and modular toroid type were optimized using a recently developed multi-modal optimization technique named multi-grouped particle swarm optimization (MGPSO). The objective of the optimization was to minimize the total length of HTS superconductor wires satisfying some equality and inequality constraints. The stored energy and constraints were calculated using 3-D magnetic field analysis techniques and an automatic tetrahedral mesh generator. Optimized results were verified by 3D finite element method (FEM).</P>
Magnetic Field Stability of a Small YBCO Magnet in Persistent Current Mode
Woo-Seok Kim,Chan Park,Sang Ho Park,Jikwang Lee,Jung-Bin Song,Haigun Lee,Hee-Gyoun Lee,Gye-Won Hong,Kyeongdal Choi IEEE 2009 IEEE transactions on applied superconductivity Vol.19 No.3
<P>It is well known that HTS (high temperature superconductor) is promising for magnet applications, but it has been almost impossible so far to apply them to magnets in persistent current mode because of poor qualities of their superconducting joints at higher current as well as their lower index values. To get rid of the non-superconducting joints from an HTS superconducting magnet, a wind-and-flip technique for demonstrating a persistent current mode operation of HTS magnet using YBCO coated conductors had been suggested. This paper presents experimental results of measured drift of a persistent current in the YBCO pancake coil which was made by using the wind-and-flip technique. The pancake coil was wound by YBCO coated conductor with a width of 12 mm, which was slit longitudinally at the center of the conductor along the conductor by a specially designed slitter. A stainless steel heater was attached on the one end of the YBCO conductor as a persistent current switch to energize the pancake coil. A temporal stability of the magnetic field was analyzed by monitoring the long-term drift of the magnetic field at 77.3 K by Hall sensors.</P>