Resolution improvement of low frequency AC magnetic field detection for modulated MR sensors

Hu, Jinghua; Pan, Mengchun; Hu, Jiafei; Li, Sizhong; Chen, Dixiang; Sun, Kun; Du, Qingfa; Wang, Yuan; Pan, Long; Zhou, Wei; Zhang, Qi; Li, Peisen; Peng, Junping; Qiu, Weicheng; Zhou, Jianjiang

doi:10.1063/1.5003618

Cited by 5 publications

(4 citation statements)

References 32 publications

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“…Figure 1(d) gives a time trace of the D α signal, which can characterize the edge radiation emission and the activity of the instabilities in the pedestal. Figure 1(e) shows the spectrum of the density fluctuations in the pedestal measured by the Doppler backscattering (DBS) [35,36]. There is a CM with frequency about 15-20 kHz.…”

Section: The Experiments and Analysismentioning

confidence: 99%

The simulation of ELMs mitigation by pedestal coherent mode in EAST using BOUT++

Li¹,

Xia²,

Zou³

et al. 2022

Nucl. Fusion

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A general phenomenon that the edge localized modes (ELMs) can be effectively mitigated with the enhanced coherent modes (CMs) has been observed on EAST. For this phenomenon, the experimental statistical analysis and electromagnetic (EM) simulations have been performed. There is a threshold value of the CM intensity in the experiments, which plays a key role in ELMs mitigation. Through the ELITE and conventional BOUT++ analysis, we found that when the insignificant ELM and enhanced CM co-exist, the pedestal is located in unstable P-B region and the ELM is relatively large. The simulation results only using the experimental profiles without considering other factors cannot reproduce the no significant ELM experiment. The CM enhances the edge turbulence, which can control ELMs. Therefore, the effects of CM are considered to explain the ELM mitigation. Modifying the three-field reduced model in BOUT++, an imposed perturbation is added as the CM. The simulation results indicate that: without the CM, the ELM size belongs to the relative large ELM region; after considering the CM, the ELM is mitigated and the energy loss is reduced by about 44.5%. Analysis shows that the CM enhances the three-wave nonlinear interactions in the pedestal and reduces the phase coherence time (PCT) between the pressure and potential, which lead the perturbation to tend to be ‘multiple-mode’ coupling. The competition of free energy between the multiple modes leads to the lack of obvious filament structures and the decreased energy loss. The above reveals that there is a competitive relationship between turbulence and ELMs, and the CM-enhanced turbulence can effectively reduce ELM energy loss. In addition, through the parameter scanning, there is a threshold of the amplitude A, which is consistent with the statistical results in the experiments.

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Section: The Experiments and Analysismentioning

confidence: 99%

The simulation of ELMs mitigation by pedestal coherent mode in EAST using BOUT++

Li¹,

Xia²,

Zou³

et al. 2022

Nucl. Fusion

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show abstract

“…The turbulence measurements are achieved by the DBS8 system, [1] and it can simultaneously launch eight different frequencies (55, 57.5, 60, 62.5, 67.5, 70, 72.5 and 75 GHz) into the plasma. Because the probing beam is obliquely launched to the cutoff layer, the Doppler shift caused by the movement of the turbulence at the cutoff layer f d can be written as f d = u ⊥ k ⊥ /2π, where u ⊥ is the perpendicular velocity, and k ⊥ is the perpendicular wavenumber at the cutoff layer.…”

Section: Experimental Conditions and Diagnosticsmentioning

confidence: 99%

I-mode investigation on the Experimental Advanced Superconducting Tokamak

et al. 2019

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By analyzing large quantities of discharges in the unfavorable ion B ×∇B drift direction, the I-mode operation has been confirmed in EAST tokamak. During the L-mode to I-mode transition, the energy confinement has a prominent improvement by the formation of a high-temperature edge pedestal, while the particle confinement remains almost identical to that in the L-mode. Similar with the I-mode observation on other devices, the E r profiles obtained by the eight-channel Doppler backscattering system (DBS8)[1] show a deeper edge E r well in the I-mode than that in the L-mode. And a weak coherent mode (WCM) with the frequency range of 40-150 kHz is observed at the edge plasma with the radial extend of about 2-3 cm. WCM could be observed in both density fluctuation and radial electric field fluctuation, and the bicoherence analyses showed significant couplings between WCM and high frequency turbulence, implying that the E r fluctuation and the caused flow shear from WCM should play an important role during I-mode. In addition, a low-frequency oscillation with a frequency range of 5-10 kHz is always accompanied with WCM, where GAM intensity is decreased or disappeared. Many evidences show that the a low-frequency oscillation may be a arXiv:1902.04750v3 [physics.plasm-ph]

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“…Fortunately, the low detectivity of our MTJ sensor was mainly caused by the high intrinsic noise of our MTJ device, which has demonstrated suppression to pT/√Hz by the design of a multilayer film, optimizing the micro-fabrication process and the annealing process [7]. What is more, the sensor can operate at a high frequency by the vertical motion modulation method, which would result in a drastic reduction of the 1/ f noise [29,30].…”

Section: Resultsmentioning

confidence: 99%

Double-Gap Magnetic Flux Concentrator Design for High-Sensitivity Magnetic Tunnel Junction Sensors

Qiu

et al. 2019

Sensors

Self Cite

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To improve the sensitivity of the magnetic tunnel junction(MTJ)sensor, a novel architecture for a double-gap magnetic flux concentrator (MFC) was studied theoretically and experimentally in this paper. The three-dimensional finite element model of magnetic flux was established to optimize the magnetic field amplification factor, with different gaps. The simulation results indicate that the sensitivity of an MTJ sensor with a double-gap MFC can be significantly better than that of a sensor with a traditional single-gap MFC, due to the fact that the magnetic magnification sharply increases with the decrease in effective gap width. Besides this, the half-bridge MTJ sensors with the double-gap MFC were fabricated using photolithography, ion milling, evaporation, and electroplating processes. Experimental results show that the sensitivity of the MTJ sensor increased by ten times compared to the sensor without the double-gap MFC, which underlines the theoretical predictions. Furthermore, there is no significant increase in the sensor noise. The work in this paper contributes to the development of high-performance MTJ sensors.

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Resolution improvement of low frequency AC magnetic field detection for modulated MR sensors

Cited by 5 publications

References 32 publications

The simulation of ELMs mitigation by pedestal coherent mode in EAST using BOUT++

The simulation of ELMs mitigation by pedestal coherent mode in EAST using BOUT++

I-mode investigation on the Experimental Advanced Superconducting Tokamak

Double-Gap Magnetic Flux Concentrator Design for High-Sensitivity Magnetic Tunnel Junction Sensors

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