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Bang, Jeseok,Kim, Seokho,Jang, Jae Young,Hwang, Young Jin,Cho, Mincheol,Kim, Jaemin,Lee, Jung Tae,Ahn, Min Cheol,Lee, SangGap,Hahn, Seungyong Institute of Electrical and Electronics Engineers 2019 IEEE transactions on applied superconductivity Vol.29 No.5
<P>This paper reports calculation and measurement of magnetic fields from a 3 T 66-mm room-temperature bore no-insulation high-temperature superconductor nuclear magnetic resonance (NMR) magnet with screening current and manufacturing uncertainty considered. The magnet reached its full field, 3 T under a conduction-cooling environment at 17 K. The measured magnetic fields along the magnet axis showed a substantial discrepancy to the originally designed ones. In simulation, measured dimensions of the 66 total single pancake coils of the magnet were used in consideration of the manufacturing errors of each pancake coil. And, the two-dimensional edge-element method with the domain homogenization technique was adopted to simulate screening currents within pancake coils and calculate the consequent screening current induced fields. The normalized magnetic fields between simulation and measurement showed good agreement that implies a potential to calculate “actual” magnetic fields of an REBCO NMR magnet with our approach.</P>
Bang, Jeseok,Kim, Seokho,Kim, Jaemin,An, Soobin,Im, Chaemin,Hahn, Seungyong The Korea Institute of Applied Superconductivity a 2019 한국초전도저온공학회논문지 Vol.21 No.2
This paper reports comparison between analytic and numerical simulation approaches for calculation of screening current and screening current induced field in a high temperature superconductor magnet. Bean slab model is adopted to calculate screening current and SCF analytically, while the finite element method numerically. A case study of screening current and SCF calculation are conducted with a magnet, a 7 T 68 mm cold-bore multi-width no-insulation GdBCO magnet built and tested by Massachusetts Institute of Technology Francis Bitter Magnet Laboratory. In this study, we assume the magnet is dunked in liquid nitrogen at 77 K. Furthermore, the simulation results are compared in terms of computation time and accuracy. Finally, discussion on the different methods together with the comparison between the calculations and experiment is provided.
Jeseok Bang,Seokho Kim,Jaemin Kim,Soobin An,Chaemin Im,Seungyong Hahn 한국초전도.저온공학회 2019 한국초전도저온공학회논문지 Vol.21 No.2
This paper reports comparison between analytic and numerical simulation approaches for calculation of screening current and screening current induced field in a high temperature superconductor magnet. Bean slab model is adopted to calculate screening current and SCF analytically, while the finite element method numerically. A case study of screening current and SCF calculation are conducted with a magnet, a 7 T 68 mm cold-bore multi-width no-insulation GdBCO magnet built and tested by Massachusetts Institute of Technology Francis Bitter Magnet Laboratory. In this study, we assume the magnet is dunked in liquid nitrogen at 77 K. Furthermore, the simulation results are compared in terms of computation time and accuracy. Finally, discussion on the different methods together with the comparison between the calculations and experiment is provided.
Current overshoot operation of a REBCO magnet to mitigate SCF
Lee, Changhyung,Hahn, Seungyong,Bang, Jeseok,Cho, Jeonwook,Kim, Seokho The Korean Society of Superconductivity and Cryoge 2018 한국초전도저온공학회논문지 Vol.20 No.4
Due to large in-field current carrying capacity and strong mechanical strength, a REBCO wire has been regarded as a viable high temperature superconductor (HTS) option for high field MRI and > 1 GHz (>23.5 T) NMR magnets. However, a REBCO magnet is well known to have an inherent problem of field inhomogeneity, so-called 'Screening Current induced magnetic Field (SCF)'. Recently, 'field shaking' and 'current overshoot operation' techniques have been successfully demonstrated to mitigate the SCF and enhance the field homogeneity by experiments. To investigate the effectiveness of current overshooting operation technique, a numerical simulation is conducted for a test REBCO magnet composed of a stack of double pancake coils using '2D edge-element magnetic field formulation' combined with 'domain homogenization' scheme. The simulation result demonstrates that an appropriate amount of current overshoot can negate the SCF. To verify the simulation results, current overshoot experiments are conducted for the REBCO magnet in liquid nitrogen. Experimental results also demonstrate the possible application of current overshoot technique to mitigate the SCF and enhance the field homogeneity.
An, Soobin,Choi, Kibum,Bang, Jeseok,Bong, Uijong,Hahn, Seungyong The Korea Institute of Applied Superconductivity a 2019 한국초전도저온공학회논문지 Vol.21 No.1
This paper presents an analytic method to calculate energy conversion between electromagnetically coupled high-temperature superconducting and copper coils. The energy transfer from one coil to the other is commonly observed during quench of a no-insulation (NI) high temperature superconductor (HTS) magnet. Proper understanding of this phenomenon is particularly important to protect an NI HTS magnet, especially to avoid any potential mechanical damages. In this paper, analytic equations are obtained to estimate the energy transfer between the NI and copper coils. The well-known lumped-parameter circuit model is adopted provided that key parameters of the coils are given.
Contact resistance increment of no-insulation REBCO magnet during a quench
Chaemin Im,Mincheol Cho,Jeseok Bang,Jaemin Kim,Seungyong Hahn 한국초전도.저온공학회 2019 한국초전도저온공학회논문지 Vol.21 No.1
The lumped-parameter circuit model for a no- insulation (NI) high temperature superconductor (HTS) magnet has been well understood after many experimental and analytic studies over a decade. It successfully explains the non-linear charging behaviors of NI magnets. Yet, recently, multiple groups reported that the post-quench electromechanical behaviors of an NI HTS magnet may not be well explained by the lumped circuit model. The characteristic resistance of an NI magnet is one of the key parameters to characterize the so-called “NI behaviors” of an NI magnet and recently a few groups reported a potential that the characteristic resistance of an NI magnet may substantially vary during a quench. This paper deals with this issue, the increment of contact resistance of the no-insulation (NI) REBCO magnet during a quench and its impact on the post-quench behaviors. A 7 T 78 mm NI REBCO magnet that was previously built by the MIT Francis Bitter Magnet Laboratory was chosen for our simulation to investigate the increment of contact resistance to better duplicate the post-quench coil voltages in the simulation. The simulation results showed that using the contact resistance value measured in the liquid nitrogen test, the magnitude of the current through the coil must be much greater than the critical current. This indicates that the value of the contact resistance should increase sharply after the quench occurs, depending on the lumped circuit model.
Soobin An,Kibum Choi,Jeseok Bang,Uijong Bong,Seungyong Hahn 한국초전도.저온공학회 2019 한국초전도저온공학회논문지 Vol.21 No.1
This paper presents an analytic method to calculate energy conversion between electromagnetically coupled high-temperature superconducting and copper coils. The energy transfer from one coil to the other is commonly observed during quench of a noinsulation (NI) high temperature superconductor (HTS) magnet. Proper understanding of this phenomenon is particularly important to protect an NI HTS magnet, especially to avoid any potential mechanical damages. In this paper, analytic equations are obtained to estimate the energy transfer between the NI and copper coils. The well-known lumped-parameter circuit model is adopted provided that key parameters of the coils are given.
Contact resistance increment of no-insulation REBCO magnet during a quench
Im, Chaemin,Cho, Mincheol,Bang, Jeseok,Kim, Jaemin,Hahn, Seungyong The Korea Institute of Applied Superconductivity a 2019 한국초전도저온공학회논문지 Vol.21 No.1
The lumped-parameter circuit model for a no- insulation (NI) high temperature superconductor (HTS) magnet has been well understood after many experimental and analytic studies over a decade. It successfully explains the non-linear charging behaviors of NI magnets. Yet, recently, multiple groups reported that the post-quench electromechanical behaviors of an NI HTS magnet may not be well explained by the lumped circuit model. The characteristic resistance of an NI magnet is one of the key parameters to characterize the so-called "NI behaviors" of an NI magnet and recently a few groups reported a potential that the characteristic resistance of an NI magnet may substantially vary during a quench. This paper deals with this issue, the increment of contact resistance of the no-insulation (NI) REBCO magnet during a quench and its impact on the post-quench behaviors. A 7 T 78 mm NI REBCO magnet that was previously built by the MIT Francis Bitter Magnet Laboratory was chosen for our simulation to investigate the increment of contact resistance to better duplicate the post-quench coil voltages in the simulation. The simulation results showed that using the contact resistance value measured in the liquid nitrogen test, the magnitude of the current through the coil must be much greater than the critical current. This indicates that the value of the contact resistance should increase sharply after the quench occurs, depending on the lumped circuit model.