High Magnetic Field Laboratory

The magnetic field is an outstanding experimental tool for physics. To go beyond the conventional commercially available superconducting (SC) magnets, very large infrastructures such as the ones gathered within the European Magnetic Field Laboratory (EMFL) are necessary. The SuperEMFL project is a design study aiming at providing the European high field user community with much higher superconducting fields. This is meant to be achieved by combining high temperature superconductor (HTS) insert magnets, an emerging technology that can work in fields above 25T, with low temperature superconductor (LTS) outsert magnets, a technology limited to fields below 25 T. The project has two design magnetic field targets, 32+T and 40+T. The first design target proposed to combined a single stack of HTS pancakes in combination with a 19 T / 150 mm LTS magnet; the second either a similar arrangement at the sake of a narrower central space or a design with two nested HTS coils combined with a 15 T/ 250 mm LTS magnet. The particular choice of the project is to use no insulation but a metallic tape co-wound with the bare HTS tape. This so-called Metal as Insulation (MI) technology enables a self-protection feature of the HTS coil by allowing the electrical bypass of defects as well as better mechanical performances in a very compact winding. The use of HTS inserts introduces a change of paradigm by providing an unprecedented combination of high magnetic field and long measurement times whilst saving vast amounts of energy in operation.

The normal zone propagation velocity (NZPV) in high-temperature superconductors (HTS) is two to three orders of magnitude lower than that in low-temperature superconductors (LTS). This slow quench propagation poses a critical challenge for quench detection in HTS applications. Fiber Bragg Grating (FBG) sensors have demonstrated potential as cryogenic sensors for quench detection in HTS applications. But determining an appropriate threshold value for the central wavelength shift (Δλ) in quench detection remains a question to be addressed. In this paper, both single superconducting tapes and stacked tapes, which serve as the fundamental building blocks of HTS cables, are investigated. The time delay of the FBG sensor is demonstrated to be shorter than that of voltage taps when a hotspot occurs at the grating location. The Δλ corresponding to quench temperature—the threshold examined in this study—decreases as the distance from the hotspot increases. The FBG can effectively respond to a quench event more quickly than voltage, when the distance from the hot spot is less than 10 mm.

Magnetic hopfions are 3D topological solitons - knotted, vortex-like spin configurations. In chiral magnets, hopfions can appear as isolated structures or they can be linked to skyrmion strings. Previous studies employed a sophisticated protocol and a special sample geometry to nucleate such hopfions linked to one or a few skyrmion strings. Here, we introduce an electric-current-assisted nucleation protocol that is simple and independent of the sample shape and size. The resulting hopfions exhibit extraordinary stability in the presence of both positive and negative magnetic fields, in perfect agreement with micromagnetic simulations. We also present a comprehensive framework for classifying hopfions, skyrmions, and merons by deriving the corresponding homotopygroup.

Abstract In this study, ZnFe 2 O 4 was synthesized at 200°C via a solvothermal pathway using acetilacetonate salts of zinc and iron as raw materials in self-developed magnetic fields of varying intensities. The following phenomena were observed. During the synthesis process, applying a magnetic field causes spherical assemblies with micrometer-scale diameters to transform into coarse chain-like aggregates exhibiting a length-to-diameter ratio of approximately 4.8. As the strength of the magnetic field increases, the ZnFe 2 O 4 particle size gradually decreases. The synthetic magnetic field causes the magnetization value of ZnFe 2 O 4 to increase or decrease. This is due to the interaction between surface spins and bulk spins, and this interaction is regulated by the particle size. The zero-field-cooling (ZFC) curves measured under a 100-Oe magnetic field obey the Curie-Weiss law in the high-temperature region. The effective magnetic moments of the superparamagnetic particles obtained through fitting are μ sp = 2.53×10 4 μ B (ZnFe 2 O 4 prepared under the condition without magnetic field), μ sp = 1.69×10 4 μ B (ZnFe 2 O 4 prepared under the condition of two magnets), and μ sp = 1.85×10 4 μ B (ZnFe 2 O 4 prepared under the condition of four magnets). The estimated magnetic particle sizes are 11.4, 10.6, and 9.9 nm, respectively, which are larger than the corresponding sizes (8.6, 7.2, and 6.2 nm) obtained from electron microscopy, indicating that the magnetic moments of adjacent particles tend to be parallel. This work reports a new approach that enables the preparation of magnetic particles with clean surfaces as well as tunable sizes, morphologies, and properties simply by adjusting the magnetic field strength without the need for any additives or templates, thus broadening their potential for various applications.

The wave union (WU) method can improve the performance of time-to-digital converters (TDCs) without consuming additional logic resources, and has therefore been widely adopted in field-programmable gate array (FPGA)-TDC designs. However, the propagation requirement of the WU pulse train forces the tapped delay line (TDL) to span longer than one clock period, such that conventional encoders must introduce extra dead time to ensure correct decoding. This article presents a low-deadtime, high-precision FPGA-based TDC that combines a 4edge WU-A scheme, dual sampling, and a resource-efficient event-aggregation encoder. With the proposed eventaggregation encoding, the WU edge positions associated with different events on the TDL are aggregated and encoded with negligible additional FPGA logic-resource usage, reducing the dead time of WU-based FPGA-TDCs to one clock cycle. In addition, to address the more severe bubble errors in advanced FPGA technology nodes, we apply clock-skew-aware placement constraints to optimize the TDL clock distribution. For the first time, a 4-edge WU-A TDC is implemented within a single clock region on a 16nm UltraScale+ FPGA. The optimized design achieves an equivalent bin width of 0.9 ps and an equivalent quantization error of 0.26 ps, improving the measured timing precision to 1.45-2.19 ps.

Exploring accurate and noninvasive methods for detecting pulmonary hypertension (PH) has always been a focal point of research. Owing to its exceptional spatiotemporal resolution, magnetocardiography (MCG) has demonstrated potential value in cardiovascular diseases. This exploratory study aims to investigate the characteristics of MCG variations in PH patients and evaluate their potential utility in distinguishing healthy subjects from those with PH. This study analyzed 175 PH patients and 333 healthy subjects who underwent MCG examination. The training cohort consisted of patients with PH previously diagnosed by right heart catheterization (RHC) and age-frequency-matched healthy controls (HC). The testing cohort comprised age- and frequency-matched HC and PH patients who underwent both MCG and RHC on the same day. Nine MCG parameters were included. Logistic regression was used to screen for significant parameters and develop a model. By comparing the pseudo-current density maps, it was found that the current vector at the R-wave peak of HC points toward the lower-left quadrant, whereas in PH patients, it points toward the lower-right quadrant. The MCG detection model demonstrated robust performance, achieving a sensitivity of 86.1% and a specificity of 94.1% in the testing cohort. Compared to the ECG of PH patients, MCG demonstrated greater sensitivity; however, it exhibited slightly lower specificity. Furthermore, MCG can detect PH in patients with normal ECG findings. MCG demonstrates highly promising potential for the noninvasive detection of PH.

We present a brief review focusing on recent research progress in high-field electron spin resonance (ESR) spectrometer with a focus on the construction and application of a 25-Tesla high-field ESR system. The spectrometer is based on a water-cooled resistive magnet at the Steady High Magnetic Field Facility in Hefei, China. Sample temperatures can be regulated between 2 to 300 K using a 4 He variable-temperature insert cryostat. A broadband microwave source, covering a frequency range of 50 to 690 GHz is achieved through a series of multiplier chain amplifiers, and signal detection is performed using an InSb bolometer. Key components of the spectrometer, including the probe, waveguide, and LabVIEW-based data acquisition software, are also described. The system’s performance was evaluated using the standard sample 2,2-diphenyl-1-picrlyhydrazyl. The spectrometer was primarily designed to support external users in investigating spin systems under extreme conditions—such as observing antiferromagnetic resonance in spin-ordered phases or detecting resonance signals in systems with large zero-field splitting, which are typically inaccessible to conventional X-band spectrometers. To illustrate its applicability, representative examples from materials science and condensed matter physics are provided.