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In the design of ultrahigh field nuclear magnetic resonance (NMR) superconducting magnets, it typically requires a high homogeneous magnetic field in the diameter of spherical volume (DSV) to obtain high spectrum resolution. However, shimming technique presents challenges due to the magnet bore space limitations, as accurate measurement of magnetic field distribution is very difficult, especially for customized micro-bore magnets. In this study, we introduced an active shimming method that utilized iterative adjustment of shim coil currents to improve the magnetic field homogeneity based on the full width at half maximum (FWHM) of the spectrum. The proposed method can determine the optimal set of currents for shim coils, effectively enhancing spatial field homogeneity by converging the FWHM. Experimental validation on a 25 T NMR superconducting magnet demonstrated the efficacy of the proposed method. Specifically, the active shimming method improved the field homogeneity of a 10 mm DSV from 7.09 ppm to 2.27 ppm with only four shim coils, providing a superior magnetic field environment for solid NMR and further magnetic resonance imaging (MRI) experiment. Furthermore, the proposed method can be promoted to more customized micro-bore magnets that require high magnetic field homogeneity.

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High fracture toughness at cryogenic temperature and radiation hardness can be conflicting requirements for the resins for the impregnation of superconducting magnet coils. The fracture toughness of different epoxy-resin systems at room temperature (RT) and at 77 K was measured, and their toughness was compared with that determined for a polyurethane, polycarbonate (PC) and poly(methyl methacrylate) (PMMA). Among the epoxy resins tested in this study, the MY750 system has the highest 77 K fracture toughness of KIC = 4.6 MPa√m, which is comparable to the KIC of PMMA, which also exhibits linear elastic behaviour and unstable crack propagation. The polyurethane system tested has a much higher 77 K toughness than the epoxy resins, approaching the toughness of PC, which is known as one of the toughest polymer materials. CTD101K is the least performing in terms of fracture toughness. Despite this, it is used for the impregnation of large Nb3Sn coils for its good processing capabilities and relatively high radiation resistance. In this study, the fracture toughness of CTD101K was improved by adding the polyglycol flexibiliser Araldite DY040 as a fourth component. The different epoxy-resin systems were exposed to proton and gamma doses up to 38 MGy, and it was found that adding the DY040 flexibiliser to the CTD101K system did not significantly change the irradiation-induced ageing behaviour. The viscosity evolution of the uncured resin mix is not significantly changed when adding the DY040 flexibiliser, and at the processing temperature of 60 °C, the viscosity remains below 200 cP for more than 24 h. Therefore, the new resin referred to as POLAB Mix is now used for the impregnation of superconducting magnet coils.

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We present the design and performance of a novel scanning tunnelling microscope (STM) operating in a cryogen-free superconducting magnet. Our home-built STM head is compact (51.5 mm long and 20 mm in diameter) and has a single arm that provides complete openness in the scanning area between the tip and sample. The STM head consists of two piezoelectric tubes (PTs), a piezoelectric scanning tube (PST) mounted on a well-polished zirconia shaft, and a large PT housed in a sapphire tube called the motor tube. The main body of the STM head is made of tantalum. In this design, we fixed the sapphire tube to the frame with screws so that the tube's position can be changed quickly. To analyse the stiffness of the STM head unit, we identified the lowest eigenfrequencies with 3 and 4 kHz in the bending modes, 8 kHz in a torsional mode, and 9 kHz in a longitudinal mode by finite element analysis, and also measured the low drift rates in the X-Y plane and in the Z direction. The high performance of the home-built STM was demonstrated by images of the hexagonal graphite lattice at 300 K and in a sweeping magnetic field from 0 T to 9 T. Our results confirm the high stability, vibration resistance, insensitivity to high magnetic fields and the application potential of our newly developed STM for the investigation of low-frequency systems with high static support stiffness in physics, chemistry, material and biological sciences.

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We demonstrate the construction of 7 Tesla and 12 Tesla all high-temperature-superconducting (HTS) magnets, small enough to fit on your wrist. The size of the magnet reduces the cost of fabrication, decreases the fringe field to permit facile siting of magnets, and decreases the stored energy of high field magnets. These small HTS-based magnets are being developed for gyrotron microwave sources for use in high-field nuclear magnetic resonance applications. The 7 Tesla and 12 Tesla magnets employ a no-insulation winding technique and are cooled to 4.2 Kelvin in a liquid helium cryostat. The 7 Tesla magnet is a single pancake coil, made of only 9.4 m of HTS tape, with an inner diameter of 8 mm and an outer diameter of 24 mm. This magnet was charged up to 1168 Amperes, generating a field of 7.3 Tesla. The 12 Tesla magnet is comprised of two pancake coils (inner diameter of 10 mm and outer diameter of 27 mm) connected in series. This magnet reached its maximum field at a current of 850 Amperes.

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We present the first nonmetallic scanning tunneling microscope (STM) featuring an ultra-stable tip-sample mechanical loop and capable of atomic-resolution imaging within a 12 T magnetic field that could be either perpendicular or parallel to the sample surface. This is also the first STM with an ultra-stable tip-sample mechanical loop but without a standalone scanner. The STM head is constructed only with two parts: an improved spider-drive motor and a zirconia tip holder. The motor performs both the coarse approach and atomic imaging. A supporting spring is set at the fixed end of the motor tube to decrease the tip-sample mechanical loop. The zirconia tip holder performs as the frame of the whole STM head. With the novel design, the STM head in three dimensions can be as small as 7.9 mm × 7.9 mm × 26.5 mm. The device's excellent performance is demonstrated by atomic-resolution images of graphite and NbSe2 obtained at 300 K and 2 K, as well as the high-resolution dI/dV spectrums of NbSe2 at variable temperatures. Low drift rates in the X-Y plane and Z direction further prove the imaging stability of our new STM. High-quality imaging of the Charge Density Wave (CDW) structure on a TaS2 surface shows the STM's good application capability. Continuous atomic images obtained in magnetic fields rangs from 0 T to 12 T with the direction of the magnetic field perpendicular or parallel to the sample surface show the STM's good immunity to high magnetic fields. Our results illustrate the new STM's broad application ability in extreme conditions of low temperature and high magnetic field.

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We present a novel homebuilt scanning tunneling microscope (STM) with atomic resolution integrated into a cryogen-free superconducting magnet system with a variable temperature insert. The STM head is designed as a nested structure of double piezoelectric tubes (PTs), which are connected coaxially through a sapphire frame whose top has a sample stage. A single shaft made of tantalum, with the STM tip on top, is held firmly by a spring strip inside the internal PT. The external PT drives the shaft to the tip-sample junction based on the SpiderDrive principle, and the internal PT completes the subsequent scanning and imaging work. The STM head is simple, compact, and easy to assemble. The excellent performance of the device was demonstrated by obtaining atomic-resolution images of graphite and low drift rates of 30.2 pm/min and 41.4 pm/min in the X-Y plane and Z direction, respectively, at 300K. In addition, we cooled the sample to 1.6 K and took atomic-resolution images of graphite and NbSe2. Finally, we performed a magnetic field sweep test from 0 T to 9 T at 70 K, obtaining distinct graphite images with atomic resolution under varying magnetic fields. These experiments show our newly developed STM's high stability, vibration resistance, and immunity to high magnetic fields.

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Presently, magnetic resonance imaging (MRI) magnets must deliver excellent magnetic field (B0 ) uniformity to achieve optimum image quality. Long magnets can satisfy the homogeneity requirements but require considerable superconducting material. These designs result in large, heavy, and costly systems that aggravate as field strength increases. Furthermore, the tight temperature tolerance of niobium titanium magnets adds instability to the system and requires operation at liquid helium temperature. These issues are crucial factors in the disparity of MR density and field strength use across the globe. Low-income settings show reduced access to MRI, especially to high field strengths. This article summarizes the proposed modifications to MRI superconducting magnet design and their impact on accessibility, including compact, reduced liquid helium, and specialty systems. Reducing the amount of superconductor inevitably entails shrinking the magnet size, resulting in higher field inhomogeneity. This work also reviews the state-of-the-art imaging and reconstruction methods to overcome this issue. Finally, we summarize the current and future challenges and opportunities in the design of accessible MRI.

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we present magnetic, mechanical and thermal modeling results for a 3 Tesla actively shielded whole body MRI (Magnetic Resonance Imaging) magnet consisting of coils with a square cross section of their windings. The magnet design was a segmented coil type optimized to minimize conductor length while hitting the standard field quality and DSV (Diameter of Spherical Volume) specifications as well as a standard, compact size 3 T system. It had an overall magnet length and conductor length which can lead to conduction cooled designs comparable to NbTi helium bath cooled 3 T MRI magnets. The design had a magnetic field homogeneity better than 10 ppm (part-per-million) within a DSV (Diameter of Spherical Volume) of 48 cm and the total magnet winding length of 1.37 m. A new class of MgB2 strand especially designed for MRI applications was considered as a possible candidate for winding such magnets. This work represents the first magnetic, mechanical and thermal design for a whole-body 3 T MgB2 short (1.37 m length) MRI magnet based on the performance parameters of existing MgB2 wire. 3 Tesla MRI magnet can operate at 20 K at 67 % of its critical current.

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The world of Fourier-transform ion cyclotron resonance (FT-ICR) mass spectrometry has witnessed, especially in the last 30 years significant advances in many fields of science, such as electronics, magnets, new ICR cell designs, developed ICR event sequences, modern external ionization sources, and linear ion beam guides, as well as modern vacuum technology. In this review, a brief account is given focusing especially on the studies performed in Wanczek's group and ICR research laboratory at the University of Bremen. An FT-ICR mass spectrometer has been developed with a high magnetic field superconducting magnet, operating at 4.7 T. At this magnetic field, a trapping time of 13.5 h was obtained with 30% efficiency. For the tetrachloromethane molecular ion, m/z 166, a mass-resolving power m/Δm = 1.5 × 106 was measured at a pressure of 2 × 10-8 Torr. The transition from magnet sweep to frequency sweep and the application of Fourier-transform has greatly enhanced the ICR technology. External ion sources were invented and differential pumping schemes were developed for enabling ultrahigh vacuum condition for ICR detection, while guiding ions at relatively higher pressures, during their flight to the ICR cell. With the external ion source, a time-of-flight ICR tandem instrument is built. A method to measure the ion flight time and to trap the ions in the ICR cell is described. Many ICR cell characteristics such as z-axis ion ejection and coupling of radial and axial ion motions in a superposed homogeneous magnetic and inhomogeneous trapping electric field were extensively studied. Gas-phase ion-molecule reactions of several reactive inorganic compounds with a focus on phosphorous and sulfur as well as silicon chemistry were also studied in great detail. The gas-phase ion chemistry of several trifluoromethyl-reagents such as trifluoromethyltrimethylsilane and tris(trifluoromethyl)phosphine were also investigated in ICR. Dual polarities multisegmented ICR cells were invented and deeply characterized. Sophisticated ICR pulse event programs were developed to enable long-range ion-ion interactions between simultaneously trapped positive and negative ions.

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Superconducting magnets used for Magnetic Resonance Imaging (MRI) scanners need to keep temperature gradients minimized in order to retain thermal and operating current margin. We have used 3D finite element analysis (FEA) simulation in COMSOL Multiphysics software that includes both conductive heat transfer and radiative heating to calculate the temperature distribution both along the winding direction and across the cross-section of an MRI segment coil at its equilibrium operating temperature. We have also modelled the evolution of the thermal properties during cool-down from ambient temperature. The heat capacity and thermal conductivity of the magnet winding were computed for use within this simulation. The heat capacity as a function of temperature was calculated using a rule of mixtures. This procedure was also used for the thermal conductivity along the direction of the wire. However, the thermal conductivity within the composite cross section (x- and y-directions) was computed using a 2D FEA model. Based on this, a time-dependent, 3D coil model was built to calculate the coil temperature throughout the winding during cool-down in our test cryostat system. The model included a heat leak component to the coil current contacts via conduction through the current leads as well as a radiative component from the surfaces of the cryostat. A key result was that a maximum coil ΔTmax = 5.1 K (=maximum temperature within the winding -minimum temperature in the winding) was seen and a coil Ic margin of 12.75 A was predicted at steady state, with our first current lead design. A second set of more optimized current leads significantly lowered the ΔTmax within the coil at the steady state. The coil Ic margin has been analyzed for different current lead designs.

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We present a mechanical rotatable magnetic force microscope (MFM) with precise angle control that can be operated in a 7 T superconducting magnet. An inertial piezoelectric motor called a SpiderDrive was used for the coarse approach because of its high compactness, high rigidity, and small size. Due to the mechanical rotation design, the MFM head can be rotated in a 7 T superconducting magnet with a bore size of 89 mm so that the direction of the magnetic field can be changed from 0° to 90° continuously. The highest in-plane magnetic field strength tested was 7 T. This is the first rotatable MFM ever reported. Using the homemade rotatable MFM, we investigated a 40 nm thick La0.67Ca0.33MnO3 (LCMO) thin film on NdGaO3 (100) substrate with anisotropy, determining that the charge-ordering insulating (COI) phase of the LCMO disappears as the direction of the magnetic field changed from 0° to 90°. Furthermore, the ferromagnetic pattern, appearing as bright and dark contrasts and similar to that formed by the S and N of a magnet, was seen parallel to the direction of the magnetic field. The rotatable MFM in this paper is expected to be widely used in studying the anisotropy of magnetic materials.

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Superconducting magnet technology changed dramatically with the discovery of high temperature superconductors (HTS) in 1986, an event which drove the development of much higher field magnets. However, this technology paradigm shift has been delayed by as much as a decade in the case of NMR magnets. In this paper, we will provide a historical perspective to the reasons for this delay and assess the future prospects for high- and ultrahigh-field NMR magnets resulting from current trends in the development of HTS magnet technology.

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We present a probe-type scanning tunnelling microscope (STM) with atomic resolution that is designed to be directly inserted and work in a harsh vibrational cryogen-free superconducting magnet system. When a commercial variable temperature insert (VTI) is installed in the magnet and the STM is housed in the VTI, a lowest temperature of 1.6 K can be achieved, at which the STM still operates well. We tested the STM in an 8 T superconducting magnet cooled with a pulse-tube cryocooler and obtained atomically resolved graphite and NbSe2 images as well as the scanning tunnelling spectrum (i.e., dI/dV spectrum) data of the latter near its critical temperature, which show the formation process of the superconducting gap as a function of temperature. The drifting rates of the STM at 1.6 K in the X-Y plane and Z direction are 1.15 and 1.71 pm/min, respectively. Noise analysis for the tunnelling current shows that the amplitudes of the dominant peaks (6.84 and 10.25 Hz) are as low as 1.5 pA.Hz-1/2 when we set the current to 0.5 nA and open the feedback loop. This is important as a cryogen-free magnet system has long been considered too harsh for any atomic resolution measurement.

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We present post-quench analyses of the MIT 800-MHz REBCO insert magnet (H800), unexpectedly quenched during operation in March 2018, and design study of a new 800-MHz HTS insert (H800N). The as-wound H800 was supposed to contribute 18.7 T and, with an LTS background magnet (L500), produce 30.5 T corresponding to a proton resonance frequency of 1.3 GHz. The H800 was operated at 4.2 K in liquid helium and, about 5 minutes after the power supply reached a target operating current of 251.3 A, it experienced a quench. Because the damage in the H800 was more widespread than it first appeared, we decided to design and build a new insert magnet, H800N. In designing H800N, we try to eliminate unanticipated flaws in our H800 design. H800N is to be more stable not to quench and more reliably survive against quench without permanent damage by: 1) adopting a single solenoid structure composed of 40 stacked double pancake coils with improved cross-over sections; 2) enhancing thermal stability; and 3) reducing excessive current margin for quench protection.

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Multifilamentary Bi2Sr2CaCu2Ox (Bi-2212) wire made by the powder-in-tube technique is the only high temperature superconductor made in the round shape preferred by magnet builders. The critical current density (J C ) of Bi-2212 round wire was improved significantly by the development of overpressure heat treatment in the past few years. Bi-2212 wire is commercially available in multiple architectures and kilometer-long pieces and a very promising conductor for very high field NMR and accelerator magnets. We studied the effects of precursor powder and heat treatment conditions on the superconducting properties and microstructure of recent Bi-2212 wires. Short samples of recent wire with optimized overpressure processing showed J C (4.2 K, 15 T) = 6640 A/mm2 and J C (4.2 K, 30 T) = 4670 A/mm2, which correspond to engineering critical current densities J E (4.2 K, 15 T) = 1320 A/mm2 and J E (4.2 K, 30 T) = 930 A/mm2.

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We have developed a high-pressure electron spin resonance probe and successfully installed into the world's highest-field cryogen-free superconducting magnet having a maximum central field of 24.6 T. The high pressure of 2.5 GPa is achieved by the specially designed piston-cylinder pressure cell using THz-wave-transparent components. In the first application of this high-pressure high-field ESR system, we observed that the orthogonal dimer spin system SrCu2(BO3)2 undergoes a quantum phase transition from the dimer singlet ground to the plaquette singlet ground states.

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Spiral MRI sequences were developed for a 9.4T vertical standard bore (54 mm) superconducting magnet using unshielded and self-shielded gradient coils. Clear spiral images with 64-shot scan were obtained with the self-shielded gradient coil, but severe shading artifacts were observed for the spiral-scan images acquired with the unshielded gradient coil. This shading artifact was successfully corrected with a phase-correction technique using reference scans that we developed based on eddy current field measurements. We therefore concluded that spiral imaging sequences can be installed even for unshielded gradient coils if phase corrections are performed using the reference scans.

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This paper focuses on the construction and test results of Coil 2 that is part of a trio of nested coils composing the REBCO 800 MHz insert. Upon its completion, the REBCO 800 MHz insert will be placed in the bore of a 500 MHz low temperature superconducting (LTS) NMR magnet (L500) to form the MIT 1.3 GHz high-resolution NMR magnet. Coil 2 is a stack of 32 double pancake (DP) coils wound with 6-mm wide REBCO tape using the no-insulation (NI) technique. Each pancake is wound on a stainless steel inner supporting ring to prevent the collapsing of its crossover due to the external pressure exerted by the winding pack. Coil 2 will be constructed in the following sequence: 1) after winding each DP will be individually tested in a bath of liquid nitrogen at atmospheric pressure to determine its current carrying capabilities; 2) DPs will be then assembled as a stack with interconnecting joints, and 3) as in Coil 1, each pancake will be overbanded with a stainless steel tape, this time to a thickness of 5 mm, thickness determined by a stress analysis previously performed. Finally the fully assembled Coil 2 will be tested in liquid nitrogen at 77 K and then in liquid helium at 4.2 K. We present here details of the stress analysis leading to the sizing of the DP inner supporting stainless steel ring and of the overbanding thickness required. Test results include coil index, critical current, charging time constant.

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Bi2Sr2CaCu2Ox (Bi-2212) conductor is the only high temperature superconductor manufactured as a round wire and is a very promising conductor for very high field applications. One of the key design parameters of Bi-2212 wire is its filament size, which has been previously reported to affect the critical current density (Jc ) and ac losses. Work with 1 bar heat treatment showed that the optimal filament diameter was about 15 µm but it was not well understood at that time that gas bubbles were the main current limiting mechanism. Here we investigated a recent Bi-2212 wire with a 121×18 filament architecture with varying wire diameter (1.0 to 1.5 mm) using 50 bar overpressure processing. This wire is part of a 1.2 km piece length of 1.0 mm diameter made by Oxford Superconducting Technology. We found that Jc is independent of the filament size in the range from 9 to 14 µm, although the n value increased with increasing filament size. A new record Jc (4.2 K, 15 T) of 4200 A/mm2 and JE (4.2 K, 15 T) of 830 A/mm2 were achieved.

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BACKGROUND: Performance test of the China Fusion Engineering Test Reactor (CFETR) central solenoid (CS) and toroidal field (TF) insert coils is of great importance to evaluate the CFETR magnet performance in relevant operation conditions. The superconducting magnet of the coil test facility for CFETR is being designed with the aim of providing a background magnetic field to test the CFETR CS insert and TF insert coils. RESULTS: The superconducting magnet consists of the inner module with Nb3Sn coil and the outer module with NbTi coil. The superconducting magnet is designed to have a maximum magnetic field of 12.59 T and a stored energy of 436.6 MJ. An active quench protection circuit and the positive temperature coefficient dump resistor were adopted to transfer the stored magnetic energy. CONCLUSIONS: The temperature margin behavior of the test facility for CFETR satisfies the design criteria. The quench analysis of the test facility shows that the cable temperature and the helium pressure inside the jacket are within the design criteria.