Achieving 1 ppm field homogeneity above 24 T: Application of differential mapping for shimming Keck and the Series Connected Hybrid magnets at the NHMFL
Abstract:Powered resistive and resistive-superconductive hybrid magnets can reach fields higher than superconducting NMR magnets but lack the field homogeneity and temporal stability needed for high resolution NMR. Due to field fluctuations in powered magnets, commercially available mapping systems fail to produce maps of these magnets with sufficient reproducibility, thus hampering attempts to improve homogeneity of the field they generate. Starting with a commercial mapper, we built a mapping system which uses a two-… Show more
“…The first-step design requirements for HTS Z1 and Z2 shim coils, for 1.3G and Micro-1G, are: (1) maximum strength of ~ 200 kHz/cm n , where n = 1 for Z1 and n = 2 for Z2; (2) uniformity of < 1% high-order harmonic errors in 1-cm DSV, i.e., for Z1 of 100 ppm shim strength, < 1 ppm errors in higher odd harmonics: Z3, Z5, … and for Z2, those in higher even harmonics: Z4, Z6, …; (3) minimum B0 field that adds to the main field; (4) minimum inductive coupling with the main magnets; and (5) no overlapping coils to minimize a radial build, i.e., both Z1 and Z2 shim coils to be wound on the same layer. To achieve the ultimate field homogeneity goal for our UHF NMR magnets, 1.3G and Mircro-1G, we will first minimize SCF-induced error fields by our proposed Z1 and Z2 HTS inner shim coils, then apply ferromagnetic shims, which are widely used in conventional LTS NMR 13 , 14 , HTS NMR 4 , 5 , 15 , 16 and other UHF NMR magnets 17 , 18 , and finally rely on room-temperature (RT) copper shim coils 19 , 20 for fine tuning. Figure 1 MIT 1.3-GHz HTS/LTS NMR magnet (left) and 1-GHz REBCO microcoil NMR magnet (right) with REBCO Z1, Z2 shim coils.…”
Section: Introductionmentioning
confidence: 99%
“…goal for our UHF NMR magnets, 1.3G and Mircro-1G, we will first minimize SCF-induced error fields by our proposed Z1 and Z2 HTS inner shim coils, then apply ferromagnetic shims, which are widely used in conventional LTS NMR 13,14 , HTS NMR 4,5,15,16 and other UHF NMR magnets 17,18 , and finally rely on room-temperature (RT) copper shim coils 19,20 for fine tuning.…”
We present promising results of novel high-temperature superconducting (HTS) shim coil prototypes that circumvent the size and strength limitation of our earlier innovative HTS shim concept based on 46-mm wide REBCO tape. The HTS shim coil is placed inside the HTS magnet, mainly for ultra-high-field (> 1 GHz or 23.5 T) NMR magnets, and thus unaffected from the windings’ diamagnetic wall effects. One full-scale version will be applied to clean up Z1 and Z2 harmonic errors in the MIT 1.3-GHz high-resolution NMR magnet composed of an 835-MHz HTS insert, while another version for an MIT 1-GHz microcoil NMR magnet whose small-scale model we are currently building. The prototype sets were wound with a 2-pile, 1.03-mm wide, 0.30-mm thick REBCO conductor. Operated at 77 K, the Z1 shim set generated a 1st harmonic field strength of 179 kHz/cm at 70 A, while the Z2 shim set, composed of two pairs, Z21 and Z22, generated the 2nd harmonic field of 141 kHz/cm2 at 50 A. Together with discussion on technical challenges for this REBCO shim coil concept, we demonstrate its feasibility for the next generation of ultra-high-field (UHF) HTS NMR magnets.
“…The first-step design requirements for HTS Z1 and Z2 shim coils, for 1.3G and Micro-1G, are: (1) maximum strength of ~ 200 kHz/cm n , where n = 1 for Z1 and n = 2 for Z2; (2) uniformity of < 1% high-order harmonic errors in 1-cm DSV, i.e., for Z1 of 100 ppm shim strength, < 1 ppm errors in higher odd harmonics: Z3, Z5, … and for Z2, those in higher even harmonics: Z4, Z6, …; (3) minimum B0 field that adds to the main field; (4) minimum inductive coupling with the main magnets; and (5) no overlapping coils to minimize a radial build, i.e., both Z1 and Z2 shim coils to be wound on the same layer. To achieve the ultimate field homogeneity goal for our UHF NMR magnets, 1.3G and Mircro-1G, we will first minimize SCF-induced error fields by our proposed Z1 and Z2 HTS inner shim coils, then apply ferromagnetic shims, which are widely used in conventional LTS NMR 13 , 14 , HTS NMR 4 , 5 , 15 , 16 and other UHF NMR magnets 17 , 18 , and finally rely on room-temperature (RT) copper shim coils 19 , 20 for fine tuning. Figure 1 MIT 1.3-GHz HTS/LTS NMR magnet (left) and 1-GHz REBCO microcoil NMR magnet (right) with REBCO Z1, Z2 shim coils.…”
Section: Introductionmentioning
confidence: 99%
“…goal for our UHF NMR magnets, 1.3G and Mircro-1G, we will first minimize SCF-induced error fields by our proposed Z1 and Z2 HTS inner shim coils, then apply ferromagnetic shims, which are widely used in conventional LTS NMR 13,14 , HTS NMR 4,5,15,16 and other UHF NMR magnets 17,18 , and finally rely on room-temperature (RT) copper shim coils 19,20 for fine tuning.…”
We present promising results of novel high-temperature superconducting (HTS) shim coil prototypes that circumvent the size and strength limitation of our earlier innovative HTS shim concept based on 46-mm wide REBCO tape. The HTS shim coil is placed inside the HTS magnet, mainly for ultra-high-field (> 1 GHz or 23.5 T) NMR magnets, and thus unaffected from the windings’ diamagnetic wall effects. One full-scale version will be applied to clean up Z1 and Z2 harmonic errors in the MIT 1.3-GHz high-resolution NMR magnet composed of an 835-MHz HTS insert, while another version for an MIT 1-GHz microcoil NMR magnet whose small-scale model we are currently building. The prototype sets were wound with a 2-pile, 1.03-mm wide, 0.30-mm thick REBCO conductor. Operated at 77 K, the Z1 shim set generated a 1st harmonic field strength of 179 kHz/cm at 70 A, while the Z2 shim set, composed of two pairs, Z21 and Z22, generated the 2nd harmonic field of 141 kHz/cm2 at 50 A. Together with discussion on technical challenges for this REBCO shim coil concept, we demonstrate its feasibility for the next generation of ultra-high-field (UHF) HTS NMR magnets.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
