Scientists proposed a flat top pulsed strong magnetic field nuclear magnetic resonance spectrometer scheme

Strong magnetic field is an important experimental condition to support cutting-edge basic research in physics, chemistry, materials and other fields, which can affect the electronic state and quantization of matter, and then detect the singular properties of special systems, and the higher the magnetic field strength, the greater the chance of scientific discovery. The reporter of “China Science News” learned from Huazhong University of Science and Technology that the team of Professor Han Xiaotao of the National Pulsed Strong Magnetic Field Science Center of the University has made important progress in the technology of flat-top pulsed strong magnetic field NMR spectrometer, and the relevant results have recently been published online in the form of two papers in the international journal IEEE Instruments and Measurement Transactions.

“Field path coupling-linear feedback” flat-top pulsed strong magnetic field. Photo courtesy of interviewee

At present, the highest magnetic field that can be achieved by non-destructive pulse magnets in the world has reached 100 Tesla (T), but due to its inherent time-varying and transient nature, it is difficult to carry out high-precision measurement experiments in which magnetic fields such as nuclear magnetic resonance (NMR), specific heat, and I-V curves need to be stable for a certain period of time, and it is urgent to develop new strong magnetic field technology. Flat-top pulsed magnetic field is a special time-varying magnetic field, which has the dual advantages of high magnetic field strength and high stability, which makes scientific testing that can only be carried out under steady-state strong magnetic field before, and also provides a new magnetic field environment for strong magnetic field scientific research.

Taking NMR as an example, it has a wide range of applications in condensed matter physics, life sciences and medical imaging, and is one of the main means to analyze microstructure. Pulsed strong magnetic field nuclear magnetic resonance measurement (PMF-NMR) technology has the ability to regulate the physical properties of pulsed strong magnetic field and the atomic-level microscopic detection ability of nuclear magnetic resonance, which is expected to bring new opportunities for discovering new phenomena, proposing new principles and synthesizing new materials, but the existing PMF-NMR is measured under changing magnetic fields, and there are problems such as field frequency accurate synchronous resonance difficulties, serious signal line distortion, and commercial NMR spectrometers are difficult to meet the needs of high-frequency broadband applications, and it is difficult to effectively carry out corresponding scientific research.

In this context, Han Xiaotao’s team further developed the flat-top pulsed strong magnetic field technology by relying on the pulsed strong magnetic field experimental device, took the lead in the world to propose the flat-top pulsed strong magnetic field nuclear magnetic resonance spectrometer scheme (FTPMF-NMR), invented the “field-path coupling-linear feedback” magnetic field waveform regulation method, solved the problem of nonlinear time-varying high stability waveform regulation of pulsed strong magnetic field, and successfully realized the peak value of 45.199T, the flat top duration of 8ms, and the ± of magnetic field fluctuations in the flat top interval 5mT (stability about 110ppm) high stability flat top pulsed magnetic field; The team independently developed the interaction program between key components of the RF link of the NMR spectrometer and hierarchical control, and realized a high-frequency wideband modular NMR spectrometer with a transmit/receive frequency of 1GHz, a real-time bandwidth of 20MHz, and a double-ended isolation of 100dB.

On this basis, the team built a corresponding scientific experiment platform, and realized NMR signal measurement of 93Nb core under a 40T flat-top magnetic field, laying a solid foundation for NMR scientific measurement under ultra-strong pulsed magnetic field. FTPMF-NMR technology will provide new testing methods for cutting-edge scientific research under strong magnetic fields, support cutting-edge basic research such as high-temperature superconductivity mechanism, quantum critical point of heavy fermion materials, ground state and phase transition of quantum spin system, etc., which is of great significance for solving major scientific problems in related fields.

In recent years, relying on the pulsed strong magnetic field experimental device, Han Xiaotao’s team has actively committed to the research of flat-top pulsed strong magnetic field regulation technology and its related experimental test system, realized 23.370T/100ms/64ppm, 45.199T/8ms/110ppm and other flat-top pulsed strong magnetic fields, and built a physical property measurement system such as NMR and I-V curves under flat-top pulsed strong magnetic fields, providing a unique experimental platform for related cutting-edge basic scientific research. (Source: China Science News, Li Sihui, Liao Xin)

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