Reduction of magnetic field fluctuations in powered magnets for NMR using inductive measurements and sampled-data feedback control

Li, Mingzhou; Schiano, J.L.; Samra, Jenna; Shetty, Kiran Kumar; Brey, Wallace S.

doi:10.1016/j.jmr.2011.05.010

Cited by 15 publications

(8 citation statements)

References 33 publications

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“…The utility of a resistive magnet such as the Keck for wide line NMR was demonstrated [15] and pulse techniques to take advantage of the high field of this resistive magnet for high resolution NMR have been explored [12, 16]. The limitations of both stability and homogeneity, however, led to the Keck magnet serving as a test facility for further improvements in field homogeneity and suppression of field fluctuations [21] rather than as a tool for routine high-field NMR investigations.…”

Section: Sch Magnetmentioning

confidence: 99%

“…For narrow lines sidebands at ±60 Hz are induced; for 120 Hz line widths, peak distortions may be observed, and for broader lines the effect becomes negligible. An integrated NMR lock with magnetic field flux stabilization is under development which will suppress these residual field oscillations [21]. …”

Section: Magnetic Field Regulationmentioning

confidence: 99%

“…For each probe, in addition to the external 7 Li lock coil that tracks slow B 0 drift, an inductive B 0 sensor to detect high frequency fluctuations has been added in preparation for the integrated NMR lock with magnetic field flux stabilization instrumentation that is currently in development [21]. …”

Section: Nmr Probesmentioning

confidence: 99%

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NMR spectroscopy up to 35.2 T using a series-connected hybrid magnet

Gan

Hung

Wang

et al. 2017

Journal of Magnetic Resonance

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The National High Magnetic Field Laboratory has brought to field a Series-Connected Hybrid magnet for NMR spectroscopy. As a DC powered magnet it can be operated at fields up to 36.1 T. The series connection between a superconducting outsert and a resistive insert dramatically minimizes the high frequency fluctuations of the magnetic field typically observed in purely resistive magnets. Current-density-grading among various resistive coils was used for improved field homogeneity. The 48 mm magnet bore and 42 mm outer diameter of the probes leaves limited space for conventional shims and consequently a combination of resistive and ferromagnetic shims are used. Field maps corrected for field instabilities were obtained and shimming achieved better than 1 ppm homogeneity over a cylindrical volume of 1 cm diameter and height. The magnetic field is regulated within 0.2 ppm using an external 7Li lock sample doped with paramagnetic MnCl2. The improved field homogeneity and field regulation using a modified AVANCE NEO console enables NMR spectroscopy at 1H frequencies of 1.0, 1.2 and 1.5 GHz. NMR at 1.5 GHz reflects a 50% increase in field strength above the highest superconducting magnets available presently. Three NMR probes have been constructed each equipped with an external lock rf coil for field regulation. Initial NMR results obtained from the SCH magnet using these probes illustrate the very exciting potential of ultra-high magnetic fields.

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Section: Sch Magnetmentioning

confidence: 99%

Section: Magnetic Field Regulationmentioning

confidence: 99%

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NMR spectroscopy up to 35.2 T using a series-connected hybrid magnet

Gan

Hung

Wang

et al. 2017

Journal of Magnetic Resonance

Self Cite

148

200

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show abstract

“…The idea is to exploit the dependence of the NMR signal on the field, and obtain an indirect but very fine grained measure of the magnetic field fluctuations from a parallel NMR experiment, called the "lock experiment", which is carried out over Towards a Model-Based Field-Frequency Lock for Fast-Field… a known nuclear specie (i.e. a known ) [2][3][4][5][6][7][8]. Note that the two nuclear species must be different to avoid interference of the two experiments.…”

Section: Introductionmentioning

confidence: 99%

Towards a Model-Based Field-Frequency Lock for Fast-Field Cycling NMR

et al. 2019

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Fast-field cycling nuclear magnetic resonance (FFC NMR) relaxometry allows to investigate molecular dynamics of complex materials. FFC relaxometry experiments require the magnetic field to reach different values in few milliseconds and field oscillations to stay within few ppms during signal acquisition. Such specifications require the introduction of a novel field-frequency lock (FFL) system. In fact, control schemes based only on current feedback may not guarantee field stability, while standard FFLs are designed to handle very slow field fluctuations, such as thermal derives, and may be ineffective in rejecting faster ones. The aim of this work is then to propose a methodology for the synthesis of a regulator that guarantees rejection of field fluctuations and short settling time. Experimental trials are performed for both model validation and evaluation of the closed-loop performances. Relaxometry experiments are performed to verify the improvement obtained with the new FFL. The results highlight the reliability of the model and the effectiveness of the overall approach.

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“…Sigmund proposed using a conductive cylindrical shield to reduce the decoherence effect of fluctuating fields [16,17]. Li proposed using feedback control based on an inductive sensor to reduce high frequency fluctuations [18]. Additionally, several investigators introduced experimental techniques to minimize the effect of field fluctuations and inhomogeneity [19,20].…”

Section: Introductionmentioning

confidence: 99%

Achieving 1 ppm field homogeneity above 24 T: Application of differential mapping for shimming Keck and the Series Connected Hybrid magnets at the NHMFL

Litvak

Griffin

Paulino

et al. 2019

Journal of Magnetic Resonance

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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-channel (measurement + reference) mapper probe. We used this system to map and then to shim two magnets of Florida Bitter type at the National High Magnetic Field Laboratory in Tallahassee, FL. With a combination of passive (ferromagnetic) and active shims we achieved 2.3 ppm homogeneity in 1 cm diameter spherical volume (dsv) at 25.0 T in the Keck resistive magnet, and 0.9 ppm homogeneity in 1 cm dsv at 23.5, 28.2, and 35.2 T in the series-connected resistive-superconductive hybrid (SCH) magnet.

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Reduction of magnetic field fluctuations in powered magnets for NMR using inductive measurements and sampled-data feedback control

Cited by 15 publications

References 33 publications

NMR spectroscopy up to 35.2 T using a series-connected hybrid magnet

NMR spectroscopy up to 35.2 T using a series-connected hybrid magnet

Towards a Model-Based Field-Frequency Lock for Fast-Field Cycling NMR

Achieving 1 ppm field homogeneity above 24 T: Application of differential mapping for shimming Keck and the Series Connected Hybrid magnets at the NHMFL

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Reduction of magnetic field fluctuations in powered magnets for NMR using inductive measurements and sampled-data feedback control

Cited by 15 publications

References 33 publications

NMR spectroscopy up to 35.2 T using a series-connected hybrid magnet

NMR spectroscopy up to 35.2 T using a series-connected hybrid magnet

Towards a Model-Based Field-Frequency Lock for Fast-Field Cycling NMR

Achieving 1 ppm field homogeneity above 24 T: Application of differential mapping for shimming Keck and the Series Connected Hybrid magnets at the NHMFL

Contact Info

Product

Resources

About

Achieving 1 ppm field homogeneity above 24 T: Application of differential mapping for shimming Keck and the Series Connected Hybrid magnets at the NHMFL