Juan Bascunan | Massachusetts Institute of Technology (MIT) (original) (raw)
Papers by Juan Bascunan
IEEE Transactions on Applied Superconductivity
We present the operation result of a cryogen-free 23.5 T/ϕ12.5 mm-cold-bore magnet prototype comp... more We present the operation result of a cryogen-free 23.5 T/ϕ12.5 mm-cold-bore magnet prototype composed of a stack of 12 no-insulation (NI) REBCO single pancake coils—ten middle coils of 6-mm wide and two end coils of 8-mm wide tape—forming 6 double pancake (DP) coils with inner joints. Each coil was wound with the tape having only 1-μm-thick copper layer on each side to overcome the conductor thickness uniformity issue and enhance the mechanical strength within the winding, and then, additional electrical shunting by thin layers of solder was applied on the top and bottom surfaces of each DP coil for effective cooling and quench protection—called extreme-NI winding technique. With this small prototype magnet towards a benchtop 1-GHz NMR, we validate our coil design that include conductor performance, screening-current-induced field and stresses, and conduction-cooling cryogenics. Included in the paper are: 1) conductor issues and our counterproposal in winding; 2) screening-current reduction method; 3) design and manufacture summary of the magnet; and 4) operating test results of the magnet up to 25 Tesla.
IEEE Transactions on Applied Superconductivity, 2021
The No-Insulation (NI) winding provides intrinsic bypassing current paths that enable selfprotect... more The No-Insulation (NI) winding provides intrinsic bypassing current paths that enable selfprotection from overheating. The self-protection of the NI coil is one of the most promising protection techniques for the high field high-temperature superconductor (HTS) magnet applications. Since the additional paths are valid for an HTS magnet with a thinner matrix, the self-protection mechanism is applicable even for the higher current density magnet with reduced matrix thickness inside the HTS tape. However, reducing the matrix can cause damage to the magnet by producing excessive heat during the quench. This research introduces a new modeling method to investigate the hot-spot characteristics in the REBCO NI pancake coil. The model is also validated with a sample NI HTS coil experiment result. Radial direction Normal Zone Propagation (NZP) velocity of the sample coil is estimated based on the suggested model. The calculated radial direction NZP velocity is applied to calculate the center field drop of the NI HTS coil, and the result is well-matched with the experiment result. We also introduce one example of the model applications. The maximum current density that will not exceed a given reference temperature in the adiabatic cooling condition is estimated using the model.
IEEE Transactions on Applied Superconductivity, 2022
The No-insulation-like (NI) coil’s turn-to-turn current paths prevent local heating by forcing th... more The No-insulation-like (NI) coil’s turn-to-turn current paths prevent local heating by forcing the current to bypass into nearby turns when a hot spot appears in a coil. However, the changing direction of the current by bypassing will change the magnetic flux, which generates unwanted induced currents in the adjacent coils in a multiply-stacked HTS magnet. This induced current can temporarily exceed the designed maximum currents in the NI coils, damaging the magnet. A partial-insulation (PI) coil, in which a single or multiple insulated, with a polyimide-like material or a thin ceramic film, is inserted between windings to hinder the current paths, can reduce the peak induced currents in the NI HTS coil’s current paths. In this paper, we present the results of a simulation study on the peak-induced current upon a quench of the PI HTS magnet with a double pancake. The study shows that the peak-induced current varies with the number of insulated turns. We also discuss the induced current turn-by-turn simulation. According to the simulation result, the PI effectively reduces overall induced current, especially insulation applied every two turns.
Progress in Superconductivity and Cryogenics, 2009
The unique features of HTS offer Opportunities and challenges to a number of applications. In thi... more The unique features of HTS offer Opportunities and challenges to a number of applications. In this paper we focus on NMR and MRI magnets, illustrating them with the NMR/MRI magnets that we are currently and will shortly be engaged: a 1.3GHz NMR magnet, an "annulus" magnet, and an whole-body MRI magnet. The opportunities with HTS include: 1) high fields (e.g., 1.3GHz magnet); 2) compactness (annulus magnet); and 3) enhanced stability despite liquid-helium-free operation ( whole-body MRI magnet). The challenges include: 1) a large screening current Beld detrimental to spatial field homogeneity (e.g., 1.3 GHz magnet); 2) uniformity of critical current density (annulus magnet); and 3) superconducting joints ( magnet).
Superconductor Science and Technology, 2020
We present results—cool-down, energization, and persistent-mode operation—of a solid-nitrogen (SN... more We present results—cool-down, energization, and persistent-mode operation—of a solid-nitrogen (SN2)-cooled, magnesium diboride (MgB2) small-scale test coil. The test coil, immersed in a volume of solid nitrogen at 6 K, successfully operated in persistent-mode at 108 A for a period of 5 d. Although designated a ‘persistent-mode’ coil, its center field was measured to decay at a rate of <0.6 ppm h−1, which is still considered low enough to meet the temporal stability requirement of <0.1 ppm h−1, for most magnetic resonance imaging magnets. This decay rate translates to a calculated circuit resistance of <1.79 × 10–12 Ω, which is mainly from one MgB2-MgB2 joint in the circuit. However, when the coil temperature increased from 6 to 16 K, the field had dropped by 0.33%: we believe this was caused by the change of magnetization in the MgB2 superconductor, which in turn decreased a screening-current field (SCF) at the magnet center. We performed a finite element analysis with a si...
IEEE Transactions on Applied Superconductivity, 2018
In this paper, we present experimental results, of a small-model study, from which we plan to dev... more In this paper, we present experimental results, of a small-model study, from which we plan to develop and apply a full-scale field-shaking system to reduce the screening current-induced field (SCF) in the 800-MHz HTS Insert (H800) of the MIT 1.3-GHz LTS/HTS NMR magnet (1.3G) currently under construction-the H800 is composed of 3 nested coils, each a stack of noinsulation (NI) REBCO double-pancakes. In 1.3G, H800 is the chief source of a large error field generated by its own SCF. To study the effectiveness of the field-shaking technique, we used two NI REBCO double-pancakes, one from Coil 2 (HCoil2) and one from Coil 3 (HCoil3) of the 3 H800 coils, and placed them in the bore of a 5-T/300-mm room-temperature bore low-temperature superconducting (LTS) background magnet. The background magnet is used not only to induce the SCF in the double-pancakes but also to reduce it by the field-shaking technique. For each run, we
IEEE Transactions on Applied Superconductivity, 2019
The MIT 1.3-GHz LTS/HTS NMR magnet is currently under development. The unique features of this ma... more The MIT 1.3-GHz LTS/HTS NMR magnet is currently under development. The unique features of this magnet include a 3nested formation for an 800-MHz REBCO insert (H800) and the noinsulation (NI) winding technique for H800 coils. Because when it is driven to the normal state, an NI REBCO magnet will respond electromagnetically, thermally, and mechanically that may result in permanent magnet damage, analysis of a quenching magnet is a key aspect of HTS magnet protection. We have developed a partial element equivalent circuit method coupled to a thermal and stress finite element method to analyze electromagnetic and mechanical responses of a nested-coil REBCO magnet each a stack of NI pancake coils. Using this method, quench simulations of the MIT 1.3-GHz LTS (L500)/HTS (H800) NMR magnet (1.3G), we have evaluated currents, strains, and torques of H800 Coil 1 to Coil 3 and L500, and center fields of 1.3G, L500, and H800. Our analyses show H800 is vulnerable to mechanical damage.
IEEE Transactions on Applied Superconductivity, 2018
We present design and test results for a thermallyactivated persistent-current switch (PCS) appli... more We present design and test results for a thermallyactivated persistent-current switch (PCS) applied to a double pancake (DP) coil (151 mm ID, 172 mm OD), wound, using the no-insulation (NI) technique, from a 120-m long, 76-µm thick, 6mm wide REBCO tape. For the experiments reported in this paper, the NI DP assembly was immersed in a volume of solid nitrogen (SN2), cooled to a base temperature of 10 K by conduction to a two-stage cryocooler, and energized at up to 630 A. The DP assembly operated in quasi-persistent mode, with the conductor tails soldered together to form a close-out joint with resistance below 6 nΩ. The measurements confirm PCS activation at heating powers below our 1-W design target, and a field decay time constant in excess of 900 h (i.e 0.1% h-1 field decay rate), limited by the finite resistance of the close-out joint.
Superconductor Science and Technology, 2016
This paper presents construction details and test results of a persistent-mode 0.5-T MgB2 magnet ... more This paper presents construction details and test results of a persistent-mode 0.5-T MgB2 magnet developed at the Francis Bitter Magnet Lab, MIT. The magnet, of 276-mm inner diameter and 290-mm outer diameter, consisted of a stack of 8 solenoidal coils with a total height of 460 mm. Each coil was wound with monofilament MgB2 wire, equipped with a persistent-current switch and terminated with a superconducting joint, forming an individual superconducting loop. Resistive solder joints connected the 8 coils in series. The magnet, after being integrated into a testing system, immersed in solid nitrogen, was operated in a temperature range of 10-13 K. A two-stage cryocooler was deployed to cool a radiation shield and the cold mass that included mainly ~60 kg of solid nitrogen and the magnet. The solid nitrogen was capable of providing a uniform and stable cryogenic environment to the magnet. The magnet sustained a 0.47-T magnetic field at its center persistently in a range of 10-13 K. The current in each coil was inversely calculated from the measured field profile to determine the performance of each coil in persistent-mode operation. Persistent-current switches were successfully operated in solid nitrogen for ramping the magnet. They were also designed to absorb magnetic energy in a protection mechanism; its effectiveness was evaluated in an induced quench.
IEEE Transactions on Applied Superconductivity, 2016
This paper presents a high-resolution magnetic field mapping system in development that is capabl... more This paper presents a high-resolution magnetic field mapping system in development that is capable of collecting spatial magnetic field data for NMR magnets. An NMR probe was designed and built with a resonant frequency of 5.73 MHz. The measured Q-factor of the NMR probe is ~191 with a half-power bandwidth in the range of 5.72-5.75 MHz. An RF continuous-wave technique with magnetic field modulation was utilized to detect the power dispersion of water molecules. The zero-crossing frequency of the NMR dispersion signal corresponds to the magnetic
IEEE Transactions on Applied Superconductivity, 2016
A high-resolution 1.3-GHz/54-mm low-temperature superconducting/high-temperature superconducting ... more A high-resolution 1.3-GHz/54-mm low-temperature superconducting/high-temperature superconducting (HTS) nuclear magnetic resonance magnet (1.3 G) is currently being built at Francis Bitter Magnet Laboratory, Massachusetts Institute of Technology. One of its key components is an 800-MHz HTS insert (H800) comprising three nested coils. Each coil is a stack
AIP Conference Proceedings, 2010
A solid cryogen cooled 500 MHz/200 mm RT bore MRI magnet has been built and tested. The magnet is... more A solid cryogen cooled 500 MHz/200 mm RT bore MRI magnet has been built and tested. The magnet is a low temperature superconductor (LTS) Nb3Sn system of compensated coils that can operate in persistent mode at 250 A and in the range from 4.2 K to 6 K. Here we present details of the magnet integration to the cryostat and
Superconductor Science and Technology, 2015
This paper presents a warm bore ferromagnetic shimming design for a high resolution NMR magnet ba... more This paper presents a warm bore ferromagnetic shimming design for a high resolution NMR magnet based on spherical harmonic coefficient reduction techniques. The passive ferromagnetic shimming along with the active shimming is a critically important step to improve magnetic field homogeneity for an NMR Magnet. Here, the technique is applied to an NMR magnet already designed and built at the MIT's Francis Bitter Magnet Lab. Based on the actual magnetic field measurement data, a total of twenty-two low order spherical harmonic coefficients is derived. Another set of spherical harmonic coefficients was calculated for iron pieces attached to a 54 mm diameter and 72 mm high tube. To improve the homogeneity of the magnet, a multiple objective linear programming method was applied to minimize unwanted spherical harmonic coefficients. A ferromagnetic shimming set with seventy-four iron pieces was presented. Analytical comparisons are made for the expected magnetic field after Ferromagnetic shimming. The theoretically reconstructed magnetic field plot after ferromagnetic shimming has shown that the magnetic field homogeneity was significantly improved.
IEEE Transactions on Applied Superconductivity, 2015
Two types of shaking coils are focused on reducing screening currents induced in solenoid coils w... more Two types of shaking coils are focused on reducing screening currents induced in solenoid coils wound with hightemperature superconducting (HTS) tapes. One is a pair of copper shaking coils coaxially located inside and outside the HTS coil to apply an ac magnetic field in the axial direction. The other is an HTS shaking coil with notch located only outside the HTS coil to minimize the radial components of local ac fields applied to windings of the HTS coil as small as possible. It is found that the copper shaking coils yield the allowable amount of power dissipation in liquid helium. The effectiveness of the HTS shaking coil to reduce screening-current-induced fields generated by another magnetized HTS coil is also experimentally validated in liquid nitrogen using a commercially available coated conductor with narrow width.
IEEE Transactions on Applied Superconductivity, 2015
This paper presents construction and persistentmode operation results of MgB 2 coils for a 0.5-T/... more This paper presents construction and persistentmode operation results of MgB 2 coils for a 0.5-T/240-mm cold bore MRI magnet, wound-and-react with monofilament MgB 2 wire, at the MIT Francis Bitter Magnet Laboratory. The magnet, of respective inner and outer diameters of 276 and 290 mm and a total height of 460 mm, has center field of 0.5 T and current density of 11 kA/cm 2. To limit the continuous length of Hyper Tech supplied MgB 2 monofilament wire to ≤300 m, the magnet was divided into 8 series-connected coils, each equipped with a persistent current switch (PCS) and a superconducting joint. We have manufactured 3 coil modules. Before tested as an assembly, each coil was tested individually to ensure its capacity to carry 100-A superconducting current in the range 10-15 K. The 3 coils were then assembled, connected in series, and operated as a 3-coil assembly in persistent mode at nearly 100 A in the range 10-15 K. We present results that include: 1) construction details; 2) component performances; and 3) a 3-coil assembly performance.
IEEE Transactions on Applied Superconductivity, 2014
This paper presents experimental and analytical results of electromagnetic forces between no-insu... more This paper presents experimental and analytical results of electromagnetic forces between no-insulation (NI) and insulation (INS) coils under time-varying conditions for NI coils that may be used in wind power generator. Three test pancake coils, one NI and the others INS, of the identical winding i.d., bore size, and number of turns, are wound with GdBCO coated tape. To determine an electric circuit model of the NI coil, the coil was charged-and-discharged at different ramping rates. The data were used to compute a characteristic resistance of a parallel inductor/resistor circuit model. In force measurement, two sets of pancake pairs were tested, NI-INS and INS-INS, the later for comparison. The coils were tested in a bath of liquid nitrogen at 77 K. The dynamic force response of the NI-INS pair was compared with that of INS-INS. The analysis based on the circuit model was tested with the experimental results. Analysis agrees well with experiment, validating our technique to analyze the time-varying forces between the NI-INS pair.
IEEE Transactions on Applied Superconductivity, 2015
In this paper, we present results, experimental and numerical, of the electromagnetic interaction... more In this paper, we present results, experimental and numerical, of the electromagnetic interaction forces between pairs of racetrack coils under time-varying conditions. Three turn-toturn insulation designs were applied to wind three racetrack coils with GdBCO coated conductor: 1) no insulation (NI); 2) partial insulation (PI) of a polyimide layer every eight turns; and 3) insulation (INS) of a polyimide layer between each, i.e., NI, PI, and INS racetracks. Two racetrack pairs, namely, NI-INS and PI-INS, were tested for their interaction forces, measured with load cell under current-ramping conditions in a bath of liquid nitrogen at 77 K. Good experimental and simulation results validate our equivalent circuit model to compute interaction forces of PI-INS racetrack pair. Overcurrent test of NI and PI coils, where each racetrack coil was charged above critical current (I c), was also performed to compare coil stability. This result implies that, although the PI winding technique improves the dynamic response, stability will be somewhat compromised.
Advances in Cryogenic Engineering, 1992
A self-contained heat switch with no moving parts has been designed, assembled, and tested. The d... more A self-contained heat switch with no moving parts has been designed, assembled, and tested. The device utilizes concentric cylinders separated by a small gap, filled or emptied of gas to achieve its switching action. The presence or absence of gas is controlled by an adsorption pump containing activated charcoal. During the development of the switch, different geometries were studied -
IEEE Transactions on Applied Superconductivity, 2015
We present the results of tape-to-tape joint resistances in a 1.3-GHz/54-mm nuclear-magneticreson... more We present the results of tape-to-tape joint resistances in a 1.3-GHz/54-mm nuclear-magneticresonance magnet comprising a 500-MHz low-temperature-superconducting magnet and an 800-MHz high-temperature-superconducting insert (H800), which is currently in the fabrication stage at the Massachusetts Institute of Technology Francis Bitter Magnet Laboratory. The H800, which is a three-coil assembly of double-pancake coils and wound with a 6-mm-wide (RE)BCO tape (rare earth element), requires a total of 94 tape-to-tape joints. Specific results obtained are: 1) an extrapolation technique to predict the resistances of the tape-to-tape curved bridge joints from those of the curved lap joint samples with the same 6-mm-wide tape batch and joint area; 2) increased resistance owing to a small gap (< 0.4 mm) in the outer radii of the two adjacent pancakes, which is mainly caused by the variation in the (RE)BCO tape thickness (on the order of several micrometers); 3) a method to minimize solder-heating influences on the pancake currentcarrying capacity; 4) the dependence of resistance on solder materials; and 5) the experience with the 25 joints on Coil 1, which is the first of three coils for our H800 insert (H800 Coil 1). Keywords (RE)BCO coil; (RE)BCO joints; second generation (2G) high-temperature superconducting (HTS) joints
IEEE Transactions on Applied Superconductivity
We present the operation result of a cryogen-free 23.5 T/ϕ12.5 mm-cold-bore magnet prototype comp... more We present the operation result of a cryogen-free 23.5 T/ϕ12.5 mm-cold-bore magnet prototype composed of a stack of 12 no-insulation (NI) REBCO single pancake coils—ten middle coils of 6-mm wide and two end coils of 8-mm wide tape—forming 6 double pancake (DP) coils with inner joints. Each coil was wound with the tape having only 1-μm-thick copper layer on each side to overcome the conductor thickness uniformity issue and enhance the mechanical strength within the winding, and then, additional electrical shunting by thin layers of solder was applied on the top and bottom surfaces of each DP coil for effective cooling and quench protection—called extreme-NI winding technique. With this small prototype magnet towards a benchtop 1-GHz NMR, we validate our coil design that include conductor performance, screening-current-induced field and stresses, and conduction-cooling cryogenics. Included in the paper are: 1) conductor issues and our counterproposal in winding; 2) screening-current reduction method; 3) design and manufacture summary of the magnet; and 4) operating test results of the magnet up to 25 Tesla.
IEEE Transactions on Applied Superconductivity, 2021
The No-Insulation (NI) winding provides intrinsic bypassing current paths that enable selfprotect... more The No-Insulation (NI) winding provides intrinsic bypassing current paths that enable selfprotection from overheating. The self-protection of the NI coil is one of the most promising protection techniques for the high field high-temperature superconductor (HTS) magnet applications. Since the additional paths are valid for an HTS magnet with a thinner matrix, the self-protection mechanism is applicable even for the higher current density magnet with reduced matrix thickness inside the HTS tape. However, reducing the matrix can cause damage to the magnet by producing excessive heat during the quench. This research introduces a new modeling method to investigate the hot-spot characteristics in the REBCO NI pancake coil. The model is also validated with a sample NI HTS coil experiment result. Radial direction Normal Zone Propagation (NZP) velocity of the sample coil is estimated based on the suggested model. The calculated radial direction NZP velocity is applied to calculate the center field drop of the NI HTS coil, and the result is well-matched with the experiment result. We also introduce one example of the model applications. The maximum current density that will not exceed a given reference temperature in the adiabatic cooling condition is estimated using the model.
IEEE Transactions on Applied Superconductivity, 2022
The No-insulation-like (NI) coil’s turn-to-turn current paths prevent local heating by forcing th... more The No-insulation-like (NI) coil’s turn-to-turn current paths prevent local heating by forcing the current to bypass into nearby turns when a hot spot appears in a coil. However, the changing direction of the current by bypassing will change the magnetic flux, which generates unwanted induced currents in the adjacent coils in a multiply-stacked HTS magnet. This induced current can temporarily exceed the designed maximum currents in the NI coils, damaging the magnet. A partial-insulation (PI) coil, in which a single or multiple insulated, with a polyimide-like material or a thin ceramic film, is inserted between windings to hinder the current paths, can reduce the peak induced currents in the NI HTS coil’s current paths. In this paper, we present the results of a simulation study on the peak-induced current upon a quench of the PI HTS magnet with a double pancake. The study shows that the peak-induced current varies with the number of insulated turns. We also discuss the induced current turn-by-turn simulation. According to the simulation result, the PI effectively reduces overall induced current, especially insulation applied every two turns.
Progress in Superconductivity and Cryogenics, 2009
The unique features of HTS offer Opportunities and challenges to a number of applications. In thi... more The unique features of HTS offer Opportunities and challenges to a number of applications. In this paper we focus on NMR and MRI magnets, illustrating them with the NMR/MRI magnets that we are currently and will shortly be engaged: a 1.3GHz NMR magnet, an "annulus" magnet, and an whole-body MRI magnet. The opportunities with HTS include: 1) high fields (e.g., 1.3GHz magnet); 2) compactness (annulus magnet); and 3) enhanced stability despite liquid-helium-free operation ( whole-body MRI magnet). The challenges include: 1) a large screening current Beld detrimental to spatial field homogeneity (e.g., 1.3 GHz magnet); 2) uniformity of critical current density (annulus magnet); and 3) superconducting joints ( magnet).
Superconductor Science and Technology, 2020
We present results—cool-down, energization, and persistent-mode operation—of a solid-nitrogen (SN... more We present results—cool-down, energization, and persistent-mode operation—of a solid-nitrogen (SN2)-cooled, magnesium diboride (MgB2) small-scale test coil. The test coil, immersed in a volume of solid nitrogen at 6 K, successfully operated in persistent-mode at 108 A for a period of 5 d. Although designated a ‘persistent-mode’ coil, its center field was measured to decay at a rate of <0.6 ppm h−1, which is still considered low enough to meet the temporal stability requirement of <0.1 ppm h−1, for most magnetic resonance imaging magnets. This decay rate translates to a calculated circuit resistance of <1.79 × 10–12 Ω, which is mainly from one MgB2-MgB2 joint in the circuit. However, when the coil temperature increased from 6 to 16 K, the field had dropped by 0.33%: we believe this was caused by the change of magnetization in the MgB2 superconductor, which in turn decreased a screening-current field (SCF) at the magnet center. We performed a finite element analysis with a si...
IEEE Transactions on Applied Superconductivity, 2018
In this paper, we present experimental results, of a small-model study, from which we plan to dev... more In this paper, we present experimental results, of a small-model study, from which we plan to develop and apply a full-scale field-shaking system to reduce the screening current-induced field (SCF) in the 800-MHz HTS Insert (H800) of the MIT 1.3-GHz LTS/HTS NMR magnet (1.3G) currently under construction-the H800 is composed of 3 nested coils, each a stack of noinsulation (NI) REBCO double-pancakes. In 1.3G, H800 is the chief source of a large error field generated by its own SCF. To study the effectiveness of the field-shaking technique, we used two NI REBCO double-pancakes, one from Coil 2 (HCoil2) and one from Coil 3 (HCoil3) of the 3 H800 coils, and placed them in the bore of a 5-T/300-mm room-temperature bore low-temperature superconducting (LTS) background magnet. The background magnet is used not only to induce the SCF in the double-pancakes but also to reduce it by the field-shaking technique. For each run, we
IEEE Transactions on Applied Superconductivity, 2019
The MIT 1.3-GHz LTS/HTS NMR magnet is currently under development. The unique features of this ma... more The MIT 1.3-GHz LTS/HTS NMR magnet is currently under development. The unique features of this magnet include a 3nested formation for an 800-MHz REBCO insert (H800) and the noinsulation (NI) winding technique for H800 coils. Because when it is driven to the normal state, an NI REBCO magnet will respond electromagnetically, thermally, and mechanically that may result in permanent magnet damage, analysis of a quenching magnet is a key aspect of HTS magnet protection. We have developed a partial element equivalent circuit method coupled to a thermal and stress finite element method to analyze electromagnetic and mechanical responses of a nested-coil REBCO magnet each a stack of NI pancake coils. Using this method, quench simulations of the MIT 1.3-GHz LTS (L500)/HTS (H800) NMR magnet (1.3G), we have evaluated currents, strains, and torques of H800 Coil 1 to Coil 3 and L500, and center fields of 1.3G, L500, and H800. Our analyses show H800 is vulnerable to mechanical damage.
IEEE Transactions on Applied Superconductivity, 2018
We present design and test results for a thermallyactivated persistent-current switch (PCS) appli... more We present design and test results for a thermallyactivated persistent-current switch (PCS) applied to a double pancake (DP) coil (151 mm ID, 172 mm OD), wound, using the no-insulation (NI) technique, from a 120-m long, 76-µm thick, 6mm wide REBCO tape. For the experiments reported in this paper, the NI DP assembly was immersed in a volume of solid nitrogen (SN2), cooled to a base temperature of 10 K by conduction to a two-stage cryocooler, and energized at up to 630 A. The DP assembly operated in quasi-persistent mode, with the conductor tails soldered together to form a close-out joint with resistance below 6 nΩ. The measurements confirm PCS activation at heating powers below our 1-W design target, and a field decay time constant in excess of 900 h (i.e 0.1% h-1 field decay rate), limited by the finite resistance of the close-out joint.
Superconductor Science and Technology, 2016
This paper presents construction details and test results of a persistent-mode 0.5-T MgB2 magnet ... more This paper presents construction details and test results of a persistent-mode 0.5-T MgB2 magnet developed at the Francis Bitter Magnet Lab, MIT. The magnet, of 276-mm inner diameter and 290-mm outer diameter, consisted of a stack of 8 solenoidal coils with a total height of 460 mm. Each coil was wound with monofilament MgB2 wire, equipped with a persistent-current switch and terminated with a superconducting joint, forming an individual superconducting loop. Resistive solder joints connected the 8 coils in series. The magnet, after being integrated into a testing system, immersed in solid nitrogen, was operated in a temperature range of 10-13 K. A two-stage cryocooler was deployed to cool a radiation shield and the cold mass that included mainly ~60 kg of solid nitrogen and the magnet. The solid nitrogen was capable of providing a uniform and stable cryogenic environment to the magnet. The magnet sustained a 0.47-T magnetic field at its center persistently in a range of 10-13 K. The current in each coil was inversely calculated from the measured field profile to determine the performance of each coil in persistent-mode operation. Persistent-current switches were successfully operated in solid nitrogen for ramping the magnet. They were also designed to absorb magnetic energy in a protection mechanism; its effectiveness was evaluated in an induced quench.
IEEE Transactions on Applied Superconductivity, 2016
This paper presents a high-resolution magnetic field mapping system in development that is capabl... more This paper presents a high-resolution magnetic field mapping system in development that is capable of collecting spatial magnetic field data for NMR magnets. An NMR probe was designed and built with a resonant frequency of 5.73 MHz. The measured Q-factor of the NMR probe is ~191 with a half-power bandwidth in the range of 5.72-5.75 MHz. An RF continuous-wave technique with magnetic field modulation was utilized to detect the power dispersion of water molecules. The zero-crossing frequency of the NMR dispersion signal corresponds to the magnetic
IEEE Transactions on Applied Superconductivity, 2016
A high-resolution 1.3-GHz/54-mm low-temperature superconducting/high-temperature superconducting ... more A high-resolution 1.3-GHz/54-mm low-temperature superconducting/high-temperature superconducting (HTS) nuclear magnetic resonance magnet (1.3 G) is currently being built at Francis Bitter Magnet Laboratory, Massachusetts Institute of Technology. One of its key components is an 800-MHz HTS insert (H800) comprising three nested coils. Each coil is a stack
AIP Conference Proceedings, 2010
A solid cryogen cooled 500 MHz/200 mm RT bore MRI magnet has been built and tested. The magnet is... more A solid cryogen cooled 500 MHz/200 mm RT bore MRI magnet has been built and tested. The magnet is a low temperature superconductor (LTS) Nb3Sn system of compensated coils that can operate in persistent mode at 250 A and in the range from 4.2 K to 6 K. Here we present details of the magnet integration to the cryostat and
Superconductor Science and Technology, 2015
This paper presents a warm bore ferromagnetic shimming design for a high resolution NMR magnet ba... more This paper presents a warm bore ferromagnetic shimming design for a high resolution NMR magnet based on spherical harmonic coefficient reduction techniques. The passive ferromagnetic shimming along with the active shimming is a critically important step to improve magnetic field homogeneity for an NMR Magnet. Here, the technique is applied to an NMR magnet already designed and built at the MIT's Francis Bitter Magnet Lab. Based on the actual magnetic field measurement data, a total of twenty-two low order spherical harmonic coefficients is derived. Another set of spherical harmonic coefficients was calculated for iron pieces attached to a 54 mm diameter and 72 mm high tube. To improve the homogeneity of the magnet, a multiple objective linear programming method was applied to minimize unwanted spherical harmonic coefficients. A ferromagnetic shimming set with seventy-four iron pieces was presented. Analytical comparisons are made for the expected magnetic field after Ferromagnetic shimming. The theoretically reconstructed magnetic field plot after ferromagnetic shimming has shown that the magnetic field homogeneity was significantly improved.
IEEE Transactions on Applied Superconductivity, 2015
Two types of shaking coils are focused on reducing screening currents induced in solenoid coils w... more Two types of shaking coils are focused on reducing screening currents induced in solenoid coils wound with hightemperature superconducting (HTS) tapes. One is a pair of copper shaking coils coaxially located inside and outside the HTS coil to apply an ac magnetic field in the axial direction. The other is an HTS shaking coil with notch located only outside the HTS coil to minimize the radial components of local ac fields applied to windings of the HTS coil as small as possible. It is found that the copper shaking coils yield the allowable amount of power dissipation in liquid helium. The effectiveness of the HTS shaking coil to reduce screening-current-induced fields generated by another magnetized HTS coil is also experimentally validated in liquid nitrogen using a commercially available coated conductor with narrow width.
IEEE Transactions on Applied Superconductivity, 2015
This paper presents construction and persistentmode operation results of MgB 2 coils for a 0.5-T/... more This paper presents construction and persistentmode operation results of MgB 2 coils for a 0.5-T/240-mm cold bore MRI magnet, wound-and-react with monofilament MgB 2 wire, at the MIT Francis Bitter Magnet Laboratory. The magnet, of respective inner and outer diameters of 276 and 290 mm and a total height of 460 mm, has center field of 0.5 T and current density of 11 kA/cm 2. To limit the continuous length of Hyper Tech supplied MgB 2 monofilament wire to ≤300 m, the magnet was divided into 8 series-connected coils, each equipped with a persistent current switch (PCS) and a superconducting joint. We have manufactured 3 coil modules. Before tested as an assembly, each coil was tested individually to ensure its capacity to carry 100-A superconducting current in the range 10-15 K. The 3 coils were then assembled, connected in series, and operated as a 3-coil assembly in persistent mode at nearly 100 A in the range 10-15 K. We present results that include: 1) construction details; 2) component performances; and 3) a 3-coil assembly performance.
IEEE Transactions on Applied Superconductivity, 2014
This paper presents experimental and analytical results of electromagnetic forces between no-insu... more This paper presents experimental and analytical results of electromagnetic forces between no-insulation (NI) and insulation (INS) coils under time-varying conditions for NI coils that may be used in wind power generator. Three test pancake coils, one NI and the others INS, of the identical winding i.d., bore size, and number of turns, are wound with GdBCO coated tape. To determine an electric circuit model of the NI coil, the coil was charged-and-discharged at different ramping rates. The data were used to compute a characteristic resistance of a parallel inductor/resistor circuit model. In force measurement, two sets of pancake pairs were tested, NI-INS and INS-INS, the later for comparison. The coils were tested in a bath of liquid nitrogen at 77 K. The dynamic force response of the NI-INS pair was compared with that of INS-INS. The analysis based on the circuit model was tested with the experimental results. Analysis agrees well with experiment, validating our technique to analyze the time-varying forces between the NI-INS pair.
IEEE Transactions on Applied Superconductivity, 2015
In this paper, we present results, experimental and numerical, of the electromagnetic interaction... more In this paper, we present results, experimental and numerical, of the electromagnetic interaction forces between pairs of racetrack coils under time-varying conditions. Three turn-toturn insulation designs were applied to wind three racetrack coils with GdBCO coated conductor: 1) no insulation (NI); 2) partial insulation (PI) of a polyimide layer every eight turns; and 3) insulation (INS) of a polyimide layer between each, i.e., NI, PI, and INS racetracks. Two racetrack pairs, namely, NI-INS and PI-INS, were tested for their interaction forces, measured with load cell under current-ramping conditions in a bath of liquid nitrogen at 77 K. Good experimental and simulation results validate our equivalent circuit model to compute interaction forces of PI-INS racetrack pair. Overcurrent test of NI and PI coils, where each racetrack coil was charged above critical current (I c), was also performed to compare coil stability. This result implies that, although the PI winding technique improves the dynamic response, stability will be somewhat compromised.
Advances in Cryogenic Engineering, 1992
A self-contained heat switch with no moving parts has been designed, assembled, and tested. The d... more A self-contained heat switch with no moving parts has been designed, assembled, and tested. The device utilizes concentric cylinders separated by a small gap, filled or emptied of gas to achieve its switching action. The presence or absence of gas is controlled by an adsorption pump containing activated charcoal. During the development of the switch, different geometries were studied -
IEEE Transactions on Applied Superconductivity, 2015
We present the results of tape-to-tape joint resistances in a 1.3-GHz/54-mm nuclear-magneticreson... more We present the results of tape-to-tape joint resistances in a 1.3-GHz/54-mm nuclear-magneticresonance magnet comprising a 500-MHz low-temperature-superconducting magnet and an 800-MHz high-temperature-superconducting insert (H800), which is currently in the fabrication stage at the Massachusetts Institute of Technology Francis Bitter Magnet Laboratory. The H800, which is a three-coil assembly of double-pancake coils and wound with a 6-mm-wide (RE)BCO tape (rare earth element), requires a total of 94 tape-to-tape joints. Specific results obtained are: 1) an extrapolation technique to predict the resistances of the tape-to-tape curved bridge joints from those of the curved lap joint samples with the same 6-mm-wide tape batch and joint area; 2) increased resistance owing to a small gap (< 0.4 mm) in the outer radii of the two adjacent pancakes, which is mainly caused by the variation in the (RE)BCO tape thickness (on the order of several micrometers); 3) a method to minimize solder-heating influences on the pancake currentcarrying capacity; 4) the dependence of resistance on solder materials; and 5) the experience with the 25 joints on Coil 1, which is the first of three coils for our H800 insert (H800 Coil 1). Keywords (RE)BCO coil; (RE)BCO joints; second generation (2G) high-temperature superconducting (HTS) joints