Series-Connected Hybrid Research Articles

Design and Optimization of Series-connected Hybrid Excitation Permanent Magnet Synchronous Motor

Design and Optimization of Series-connected Hybrid Excitation Permanent Magnet Synchronous Motor

High-Voltage Si IGBT/SiC MOSFET Series-Connected Hybrid Switch

High-Voltage Si IGBT/SiC MOSFET Series-Connected Hybrid Switch

Exciting Opportunities for Solid-State 95Mo NMR Studies of MoS2 Nano-structures in Materials Research from Low to Ultra-high Magnetic Field (35.2 T).

Solid-state, natural-abundance 95Mo NMR experiments of four different MoS2 materials have been performed on a magnet B 0 = 19.6 T and on a new Series Connected Hybrid (SCH) magnet at 35.2 T. Employing two different 2H-MoS2 (2H phase) materials, a "pseudo-amorphous" MoS2 nano-material, and a MoS2 layer on the Al2O3 support of a hydrodesulphurization (HDS) catalyst have enabled introduction of solid-state 95Mo NMR as an important analytical tool in studies of MoS2 nano-materials. 95Mo spin-lattice relaxation time (T 1) studies of 160- and 4-layer 2H-MoS2 samples at 19.6 and 35.2 T show their relaxation rates (1/T 1) increase in proportion to B 0 2. This is in accord with chemical shift anisotropy (CSA) relaxation being the dominant T 1(95Mo) mechanism, with a large 95Mo CSA = 1025 ppm determined for all four MoS2 nano-materials. The dominant CSA mechanism suggests the MoS2 band-gap electrons are delocalized throughout the lattice-layer structures, thereby acting as a fast modulation source (ω oτc << 1) for 95Mo CSA in 2H-MoS2. A decrease in T 1(95Mo) is observed for an increase in B 0 field and for a decrease in the number of 2H-MoS2 layers. All four nano-materials exhibit identical 95Mo electric field gradient (EFG) parameters. The T 1 results account for the several failures to retrieve 95Mo spectral EFG and CSA parameters for multilayer 2H-MoS2 samples in the pioneering solid-state 95Mo NMR studies performed during the past two decades (1990-2010), because of the extremely long T 1(95Mo) = ~200-250 s observed at low B 0 (~9.4 T) used at that time. Much shorter T 1(95Mo) values are observed even at 19.6 T for the "pseudo-amorphous" and the HDS catalyst (MoS2-Al2O3 support) MoS2 nano-materials. These allowed useful solid-state 95Mo NMR spectra for these two samples to be obtained at 19.6 T in a few to < 24 h. Most importantly, this research led to observation of an impressive 95Mo MAS spectrum for an average of 1-4 thick MoS2-layers on a Al2O3 support, i.e., the first MAS NMR spectrum of a low natural-abundance, low-γ quadrupole-nucleus species layered on a catalyst support. While a huge gain in NMR sensitivity, factor ~ 60, is observed for the 95Mo MAS spectrum of the 160-layer sample at 35.2 T compared to 14.1 T, the MAS spectrum for the 4-layer sample is almost completely wiped out at 35.2 T. This unusual observation for the 4-layer sample (crumpled, rose-like and defective Mo-edge structures) is due to an increased distribution of the isotropic 95Mo shifts in the 95Mo MAS spectra at B 0 up to 35.2 T upon reduction of the number of sample layers.

Field-stepped ultra-wideline NMR at up to 36T: On the inequivalence between field and frequency stepping.

Field-stepped NMR spectroscopy at up to 36T using the series-connected hybrid (SCH) magnet at the U.S. National High Magnetic Field Laboratory is demonstrated for acquiring ultra-wideline powder spectra of nuclei with very large quadrupolar interactions. Historically, NMR evolved from the continuous-wave (cw) field-swept method in the early days to the pulsed Fourier-transform method in the modern era. Spectra acquired using field sweeping are generally considered to be equivalent to those acquired using the pulsed method. Here, it is shown that field-stepped wideline spectra of half-integer spin quadrupolar nuclei acquired using WURST/CPMG methods can be significantly different from those acquired with the frequency-stepped method commonly used with superconducting magnets. The inequivalence arises from magnetic field-dependent NMR interactions such as the anisotropic chemical shift and second-order quadrupolar interactions; the latter is often the main interaction leading to ultra-wideline powder patterns of half-integer spin quadrupolar nuclei. This inequivalence needs be taken into account to accurately and correctly determine the quadrupolar coupling and chemical shift parameters. A simulation protocol is developed for spectral fitting to facilitate analysis of field-stepped ultra-wideline NMR spectra acquired using powered magnets. A MATLAB program which implements this protocol is available on request.

The Droserasin 1 PSI: A Membrane-Interacting Antimicrobial Peptide from the Carnivorous Plant Drosera capensis

The Droserasins, aspartic proteases from the carnivorous plant Drosera capensis, contain a 100-residue plant-specific insert (PSI) that is post-translationally cleaved and independently acts as an antimicrobial peptide. PSIs are of interest not only for their inhibition of microbial growth, but also because they modify the size of lipid vesicles and strongly interact with biological membranes. PSIs may therefore be useful for modulating lipid systems in NMR studies of membrane proteins. Here we present the expression and biophysical characterization of the Droserasin 1 PSI (D1 PSI.) This peptide is monomeric in solution and maintains its primarily -helical secondary structure over a wide range of temperatures and pH values, even under conditions where its three disulfide bonds are reduced. Vesicle fusion assays indicate that the D1 PSI strongly interacts with bacterial and fungal lipids at pH 5 and lower, consistent with the physiological pH of D. capensis mucilage. It binds lipids with a variety of head groups, highlighting its versatility as a potential stabilizer for lipid nanodiscs. Solid-state NMR spectra collected at a field strength of 36 T, using a unique series-connected hybrid magnet, indicate that the peptide is folded and strongly bound to the membrane. Molecular dynamics simulations indicate that the peptide is stable as either a monomer or a dimer in a lipid bilayer. Both the monomer and the dimer allow the passage of water through the membrane, albeit at different rates.

Structure and Catalytic Characterization of a Second Framework Al(IV) Site in Zeolite Catalysts Revealed by NMR at 35.2 T.

Ultrahigh field 27Al{1H} 2D correlation NMR experiments demonstrate that at least two framework Al(IV) sites with hydroxyl groups can exist in acidic zeolite catalysts in their dehydrated and catalytically active states. In addition to the known Al(IV) at the framework bridging acid site (BAS), a new site created by a second tetrahedral Al atom and its hydroxyl group protons in zeolite HZSM-5 is clearly resolved at 35.2 T field strengths, enabled by recently developed series-connected hybrid (SCH) magnet technology. Coupled with computational modeling, extensive 27Al MQMAS experiments at multiple field strengths, and 1H MAS NMR experiments, these data indicate that this second tetrahedrally coordinated Al site (denoted Al(IV)-2) experiences an increased chemical shift and unique quadrupolar parameters relative to the BAS in both dehydrated and hydrated states. These new experimental data, supported by computational and catalytic reaction work, indicate that the second site arises from partially bonded framework (SiO)4-n-Al(OH)n species that significantly increase catalyst reactivity in benzene hydride-transfer and n-hexane cracking reactions. Al(IV)-2 sites result either from framework crystallization defects or from incomplete postsynthetic hydrolysis of a framework Al, prior to the formation of extraframework Al. Populations of this second acidic proton site created by the Al(IV)-2 species are shown to be controlled via postsynthetic catalyst treatments, should be general to different catalyst structures, and significantly enhance catalyst reactivity in the cited probe reactions when they are present. The results herein communicate the highest magnetic field strength data on active zeolite catalyst structures to date and enable for the first time the detection of Al and H association on a dry HZSM-5 catalyst, i.e., under conditions representative of typical end-use processes.

Supercritical helium expansivity effects on magnet protection systems

The recent commissioning of the 36 T Series-Connected Hybrid Magnet at the National High Magnetic Field Laboratory has uncovered an undesirable consequence of using super critical helium for cooling of superconductors. This recent dry magnet cooling technology greatly reduces the LHe requirements of the magnet and may be utilized more frequently in the future. Because the supercritical helium does not complete a phase transition with the addition of heat, the fluid can quickly expand. The increased expansivity of supercritical helium over liquid helium for a given heat load is capable of creating larger pressure waves. The impact pressure for compressible helium gas flow is combined with the speed of sound for ideal gases to determine if a high-speed pressure wave is sufficient to explain the premature failure of the burst discs in the over-pressurization protection system. The addition of an impact pressure can explain, under the right conditions, a reduction of up to 40% in the burst disc pressure rating. The Grüneisen parameter is shown to relate to the expansivity and values for the parameter are given in the supercritical range. A proposal to reroute the pipe near the burst disc is made to mitigate the effects of the impact pressure.

14N overtone nuclear magnetic resonance of rotating solids.

By irradiating and observing at twice the 14N Larmor frequency, overtone (OT) nuclear magnetic resonance (NMR) is capable of obtaining 14NOT spectra without first-order quadrupolar broadening. Direct excitation and detection of the usually "forbidden" double-quantum transition is mediated by the perturbation from the large quadrupole interaction to the spin states quantized by the Zeeman interaction. A recent study [L. A. O'Dell and C. I. Ratcliffe, Chem. Phys. Lett. 514, 168 (2011)] has shown that 14NOT NMR under magic-angle spinning (MAS) can yield high-resolution spectra with typical second-order quadrupolar line shapes allowing the measurement of 14N chemical shift and quadrupolar coupling parameters. This article has also shown that under MAS the main 14NOT peak is shifted by twice the sample spinning frequency with respect to its static position. We present the theory of 14NOT NMR of static or rotating samples and the physical picture of the intriguing spinning-induced shift in the second case. We use perturbation theory for the case of static samples and Floquet theory for rotating samples. In both cases, the results can be described by a so-called OT parameter that scales down the 14NOT radio-frequency (rf) excitation and signal detection. This OT parameter shows that the components of the rf field, which are transverse and longitudinal with respect to the magnetic field, are both effective for 14NOTrf excitation and signal detection. In the case of MAS at angular frequency ωr , the superposition of the excitation and detection components in the OT parameter makes either the +2ωr or -2ωr term the dominant 14NOT signal, depending on the sense of sample spinning with respect to the magnetic field. This leads to an apparent 14NOT signal shifted at twice the spinning frequency. The features of 14NOT NMR spectra for both static and rotating samples are illustrated with simulations. The spinning induced shift and its dependence on the spinning direction are confirmed experimentally by reversing the spinning direction and the field of the 36 T series-connected hybrid magnet at the US National High Magnetic Field Laboratory.

Commissioning of the 36 T Series-Connected Hybrid Magnet at the NHMFL

The National High Magnetic Field Laboratory has commissioned a 36.1 T resistive/superconducting hybrid magnet with homogeneity and stability of 1 ppm over a 10 mm diameter spherical volume to be used for solid-state nuclear magnetic resonance (NMR). Most NMR magnets use single strands of superconducting wire carrying a few hundred amps and persistent joints and switches. This magnet uses a 20 kA superconducting cable in a steel conduit for the outer part of the magnet and copper-alloy sheet metal for the inner part of the magnet. While >15 hybrid magnets have been built worldwide, they typically have a field uniformity of ∼250 ppm/cm DSV and stability might be no better than 50 ppm. To attain 1 ppm uniformity, current density grading was employed in the resistive coils to cancel the z2 term. In addition, coils were shifted after the first map to reduce the z1 term. Ferroshims and resistive shims were installed in the bore to attain <1 ppm over 10 mm. The large inductance of the superconducting coil reduced the ripple sixfold compared with all-resistive magnets and essentially eliminated the 60 Hz ripple and its harmonics. An NMR lock reduced the low-frequency drift to attain ∼0.1 ppm stability.

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

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 36.1T. 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 48mm magnet bore and 42mm 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 1ppm homogeneity over a cylindrical volume of 1cm diameter and height. The magnetic field is regulated within 0.2ppm 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 1.5GHz. NMR at 1.5GHz reflects a 50% increase in field strength above the highest superconducting magnets currently available. 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.

The 36-T Series-Connected Hybrid Magnet System Design and Integration

The 36-T Series-Connected Hybrid Magnet System Design and Integration

Structural Integrity of the NHMFL Series-Connected Hybrid Magnet Cryostats

The National High Magnetic Field Laboratory has designed and built cryostats for two series-connected hybrid (SCH) magnets. The first one is for the Helmholtz Center Berlin. Its cryostat is designed to support up to 8 MW of resistive insert inside a water-cooled housing that has a conical warm bore with a 30-degree opening angle and a 5-ton superconducting outsert coil that is housed in a vacuum vessel. Normal operation includes 28 bar of water pressure and 52 kN of side load between the resistive insert coils and the superconducting outsert coils due to a potential 3-mm coil misalignment. Under a fault condition, the resistive coils can generate axial loads of up to 1.1 MN. The second cryostat for the Florida State University SCH houses the same superconducting outsert, but its resistive insert is a high-homogeneity solenoid. The system is designed to support a high-field 14-MW insert, operated at 30-bar water pressure, up to 42-kN side load, and 2.6-MN fault forces. Numerous complex two-dimensional and three-dimensional finite-element models have been developed and used for a systematic optimization of all critical load path items.

Fabrication and Testing of the 20 kA Binary Current Leads for the NHMFL Series-Connected Hybrid Magnet

A pair of binary vapor-cooled/high-temperature-superconducting current leads were fabricated at the National High Magnetic Field Laboratory (NHMFL) and tested at the High Field Magnet Laboratory (HFML) at the Radboud University Nijmegen. The leads supply current to the NHMFL series-connected hybrid magnet. Details of the fabrication are discussed, including that of the resistive and high-temperature-superconducting parts and the integration of the two sections. A test assembly was made, including the pair of current leads, a jumper made from NbTi cable-in-conduit, instrumentation, and mounting hardware. The test facility includes a liquid nitrogen supply vessel and a closed-loop supercritical helium supply system, to replicate the cooling used in the magnet assembly. Results from the testing of the leads to the full operating current, and under simulated loss-of-cooling conditions are presented.

First Hybrid Magnet for Neutron Scattering at Helmholtz-Zentrum Berlin

Helmholtz-Zentrum Berlin (HZB) operates two large-scale facilities: the research reactor BER 2 and the synchrotron source for soft X-rays BESSY 2. This year HZB's neutron instrument suite around BER 2 has been strengthened by a unique high-magnetic-field facility for neutron scattering. Its main components are the High Field Magnet (HFM), which is the most powerful dc magnet for neutron scattering worldwide, and the Extreme Environment Diffractometer (EXED), which is a dedicated neutron instrument for time-of-flight technique. The hybrid magnet system is projected according to the special geometric constraints of analyzing samples by neutron scattering in a high field magnet. Following our past experience, only steady-state fields are adequate to achieve the goals of the project. In particular, inelastic scattering studies would virtually be excluded when using pulsed magnets. The new series-connected hybrid magnet with a horizontal field orientation was designed and constructed in collaboration with the National High Magnetic Field Laboratory (NHMFL), Tallahassee, FL, USA. With a set consisting of a superconducting cable-in-conduit coil and different resistive coils of conical shape, maximum fields between 26-31 T are possible with cooling power between 4 and 8 MW for the resistive part. A series of commissioning activities of the magnet components and the technical infrastructure systems (20-kA power supply, water cooling, and 4-K Helium refrigerator) was completed at HZB. The maximum field achieved with a 4-MW resistive coil was 26 T.

Final Assembly of the Helmholtz-Zentrum Berlin Series-Connected Hybrid Magnet System

The final assembly of the Series-Connected Hybrid magnet system for the Helmholtz-Zentrum Berlin for Materials and Energy (HZB) has occurred with the integration of the superconducting cold mass, cryostat, resistive Florida-Bitter coils, and the cryogenic, chilled water, power, and control subsystems. The hybrid magnet consists of a 13-T superconducting $\hbox{Nb}_{3}\hbox{Sn/CICC}$ coil and a set of 12-T resistive, water cooled coils at 4.4 MW. Much of the cryostat and cold mass functional requirements were dictated by the electromagnetic interactions between the superconducting and resistive coils. This includes the radial decentering and axial aligning forces from normal operations and a 1.1 MN fault load. The system assembly was an international achievement with the cold mass being completed at the NHMFL in the USA, cryostat to cold mass interfaces made at Criotec Impianti in Italy, and final assembly at the HZB in Germany.

Fabrication of HTS Conductor Stacks for 20-kA Binary Current Leads for MagLab Series-Connected Hybrid and HFML Nijmegen Hybrid Magnets

The MagLab series-connected hybrid and the HFML Nijmegen hybrid outer superconducting coils each require a pair of binary current leads, comprised of a nitrogen vapor-cooled resistive section and a high-temperature superconducting (HTS) section, configured to minimize the heat load to the coils. The HTS sections of both pairs of leads are made with stacked and soldered Bi-2223 tapes supplied by Sumitomo. The MagLab fabricated and tested the tape stacks for both programs. The procedures and apparatus for fabricating the stacks and making the critical current measurements are described. Critical current and n-value measurement results are reported.

Reaction Heat Treatment and Epoxy Impregnation of a Large &lt;formula formulatype="inline"&gt; &lt;tex Notation="TeX"&gt;$\hbox{Nb}_{3}\hbox{Sn}$&lt;/tex&gt;&lt;/formula&gt; CICC Coil for a Series-Connected Hybrid Magnet

Recent activities that were conducted on the Helmholtz Zentrum Berlin Series-Connected Hybrid outsert coil included the reaction heat treatment and vacuum-pressure impregnation. A thermocouple was wound into the windings for diagnostic purposes during processing of the coil. To maintain a reasonable temperature differential across the coil, the ramp rate was limited to approximately 2.7°C/hr. Epoxy impregnation was conducted with an epoxy developed in-house. The epoxy is transferred in vacuum but cured with one atmosphere gage pressure applied. Subsequently, the winding hardware was removed including the stainless steel mandrel through a machining operation. After assembly of voltage breaks and voltage taps, Paschen tests to 4 kV were conducted successfully that qualified the ground insulation. In addition, surge tests to qualified the internal insulation with 3 kV applied across the leads were conducted. Impedance measurements were conducted to confirm the internal insulation integrity.

Homogeneity Study for the NHMFL Series Connected Hybrid Magnet System

The first Series Connected Hybrid (SCH) Magnet presently being designed and built at the NHMFL has targeted 36 T with 1 ppm maximum inhomogeneity over a 10-mm-diameter spherical volume at the midplane of a 40-mm clear bore for scientific users interested in medium resolution NMR studies. The SCH comprises a 13T superconducting outsert built with Nb3Sn cable-in-conduit conductors, a 23 T resistive insert using Florida-Bitter technology, and water-cooled resistive shims providing up to 90 ppm correction. The insert and outsert are connected electrically in series. Inhomogeneity predictions for the unshimmed SCH were made using various finite element analyses on a preliminary SCH design. Manufacturing tolerances were benchmarked by performing a sensitivity analysis and comparing the finite element analyses results to inhomogeneity measurements on the Keck and Cell 2 magnets, two NHMFL magnets, which represent the state-of-the-art for producing high homogeneity fields with resistive Florida-Bitter technology. Next, the shim terms from the measured and predicted 3-D field maps were analyzed with an NHMFL in-house code, which provided the inhomogeneity specification of the unshimmed SCH. Finally, a design of the SCH water-cooled resistive shims was developed based on all the measured and calculated data including additional engineering safety factors. This analysis is an essential step for achieving the targeted overall performance of a record 1 ppm inhomogeneity at 36 T.

Fabrication Progress of the Outsert Coils of the Series-Connected Hybrid Magnets

The series-connected hybrid magnets for the National High Magnetic Field Laboratory and the Helmholtz Zentrum Berlin (HZB) that are under construction utilize three grades of cable-in-conduit conductor (CICC). Each coil contains over 5000 kg of Nb <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> Sn/Cu CICC in five piece-lengths. Fabrication of the coils has commenced with the winding of the outsert coil for HZB first. Work on both coils will proceed in parallel as the winding for the HZB coil is completed and is prepared for reaction heat treatment. Aspects of the coil fabrication process and quality controls will be discussed with attention given to the coil winding and joint assembly.

HTS Current Leads for the NHMFL Series-Connected Hybrid Magnet

A design for the current leads for the National High Magnetic Field Laboratory series-connected hybrid magnet is described. The leads are comprised of a nitrogen vapor cooled resistive heat exchanger section, operating between 296 and 79 K. The heat exchanger uses the “pierced jelly roll” lead technology proven at the National High Magnetic Field Laboratory. A conduction-cooled high-temperature superconducting (HTS) section, operating between 79 and 6 K, uses Sumitomo Type G Bi-2223/Ag5%Au conductors, stacked and soldered into a stainless steel and copper shunt brazement. The leads are located in close proximity to the magnet, and the magnitude of the fringe field on the HTS tapes is 0.37 tesla. The configuration of the HTS section is determined by careful analysis of the self-field and fringe field at the warm end of the HTS section, and by findings from a program of conductor testing.