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3. Experimental investigation of kinetic instabilities driven by runaway electrons in the EXL-50 spherical torus

Author

Wang, Mingyuan, Tan, Mingsheng, Shi, Yuejiang, Wang, Ziqi, Dong, Jiaqi, Liu, Adi, Zhuang, Ge, Li, Songjian, Song, Shaodong, Yuan, Baoshan, and Peng, Y-K Martin

Subjects
Physics - Plasma Physics
Abstract

In this study, the first observation of high-frequency instabilities driven by runaway electrons has been reported in the EXL-50 spherical torus using a high-frequency magnetic pickup coil. The central frequency of these instabilities is found to be exponentially dependent on the plasma density, similar to the dispersion relation of the whistler wave. The instability frequency displays chirping characteristics consistent with the Berk-Breizman model of beam instability. Theoretically, the excitation threshold of the instability driven by runaway electrons is related to the ratio of the runaway electron density to the background plasma density, and such a relationship is first demonstrated experimentally in this study. The instability can be stabilized by increasing the plasma density, consistent with the wave-particle resonance mechanism. This investigation demonstrates the controlled excitation of chirping instabilities in a tokamak plasma and reveals new features of these instabilities, thereby advancing the understanding of the mechanisms for controlling and mitigating runaway electrons.

Published
2023

4. Observation of whistler wave instability driven by temperature anisotropy of energetic electrons on EXL-50 spherical torus

Author

Wang, Mingyuan, Shi, Yuejiang, Dong, Jiaqi, Gao, Xinliang, Lu, Quanming, Wang, Ziqi, Chen, Wei, Liu, Adi, Zhang, Ge, Wang, Yumin, Cheng, Shikui, Tan, Mingsheng, Li, Songjian, Song, Shaodong, Sun, Tiantian, Liu, Bing, Huang, Xianli, Li, Yingying, Song, Xianming, Yuan, Baoshan, Peng, Y-K Martin, and team, ENN

Subjects
Physics - Plasma Physics
Abstract

Electromagnetic modes in the frequency range of 30-120MHz were observed in electron cyclotron wave (ECW) steady state plasmas on the ENN XuanLong-50 (EXL-50) spherical torus. These modes were found to have multiple bands of frequencies proportional to the Alfv\'en velocity. This indicates that the observed mode frequencies satisfy the dispersion relation of whistler waves. In addition, suppression of the whistler waves by the synergistic effect of Lower Hybrid Wave (LHW) and ECW was also observed. This suggests that the whistler waves were driven by temperature anisotropy of energetic electrons. These are the first such observations (not runaway discharge) made in magnetically confined toroidal plasmas and may have important implications for studying wave-particle interactions, RF wave current driver, and runaway electron control in future fusion devices.

Published
2023

5. Parametric study of helicon wave current drive in CFETR

Author

Wu, Xianshu, Li, Jingchun, Chen, Jiale, Xu, Guosheng, Dong, Jiaqi, Wang, Zhanhui, Sun, Aiping, and zhong, Wulv

Subjects
Physics - Plasma Physics
Abstract

This paper evaluates the feasibility of helicon current drive (HCD) in a hybrid scenario for the China Fusion Engineering Test Reactor (CFETR). Utilizing the GENRAY/CQL3D package, a large number of simulations (over 5 000) were conducted, with parametric scans in the antenna's poloidal position, launched parallel refractive index, and wave frequency. The analysis reveals that helicon has excellent accessibility under reactor-level conditions, and smaller n|| and higher wave frequency result in enhanced wave absorption. The simulations demonstrate an optimal launched parallel refractive index of approximately 1.6 for the CFETR hybrid scenario. The best launch position is found to be within a poloidal angle range of 25 degrees to 65 degrees. Additionally, it is preferable to have a narrow parallel refractive index spectrum for wave absorption when operating below the threshold value of {\Delta}n|| (~0.6), beyond which the effect of {\Delta}n|| on wave absorption is negligible. This study provides valuable insights into the potential application of HCD in CFETR.

Published
2023

9. Research on Airworthiness Management of Changes to the Type Design with DAS

Author

Dong, Jiaqi, Lu, Jichun, Yuan, Ye, Appolloni, Andrea, Series Editor, Caracciolo, Francesco, Series Editor, Ding, Zhuoqi, Series Editor, Gogas, Periklis, Series Editor, Huang, Gordon, Series Editor, Nartea, Gilbert, Series Editor, Ngo, Thanh, Series Editor, Striełkowski, Wadim, Series Editor, Zailani, Suhaiza Hanim Binti Dato Mohamad, editor, Yagapparaj, Kosga, editor, and Zakuan, Norhayati, editor

Published
2024
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10. Impact of impurities on drift wave instabilities in reversed-field pinch plasmas

Author

Li, Jingchun, Liu, Songfen, Zhang, Yilong, Dong, Jiaqi, and Kong, Wei

Subjects
Physics - Plasma Physics
Abstract

The drift wave in the presence of impurity ions was investigated numerically in reversed field pinch (RFP) plasmas, using the gyrokinetic integral eigenmode equation. It was found that in RFP plasmas with hollow density profiles, an increase in $k_\theta \rho_s$ increases the growth rate of the ion temperature gradient (ITG). Comparing the results of regular and hollow plasma density profile shows that the ITG mode under the hollow density profile is much harder to be excited. For the impurities' effects, when the impurities' density gradient is opposite to the primary ions, namely when $L_{ez}$ is negative, impurities could enhance the instability. On the contrary, when $L_{ez}$ is positive, the instability is stabilized. Regarding the trapped electron mode (TEMs), the growth rate under the plasma with hollow density profile remained minor than that for the standard density gradient. There exists a threshold of $L_{ez}$. When $L_{ez}$ is less than this value, impurity destabilizes TEMs, while as $L_{ez}$ is greater than this, impurity stabilizes TEMs. The effects of $L_{ez}$ on TEM also depend on both the plasma density gradient and the impurity species. In addition, the influence of collisionality on TEMs was also studied.

Published
2022

32. Selective modulation of electronic transport in VO2 induced by 10 keV helium ion irradiation.

Author

Gurrola, Rebeca M., Cain, John M., Oh, Sangheon, Brown, Timothy D., Jardali, Fatme, Schoell, Ryan M., Yadav, Digvijay R., Dong, Jiaqi, Smyth, Christopher M., Pharr, Matt, Kumar, Suhas, Xie, Kelvin, Hattar, Khalid, Talin, A. Alec, Lu, Tzu-Ming, and Shamberger, Patrick J.

Subjects
ELECTRONIC modulation, HELIUM ions, METAL-insulator transitions, POINT defects, VANADIUM dioxide, IRRADIATION
Abstract

Vanadium dioxide (VO2) manifests an abrupt metal–insulator transition (MIT) from monoclinic to rutile phases, with potential use for tunable electronic and optical properties and spiking neuromorphic devices. Understanding pathways to modulate electronic transport in VO2, as well as its response to irradiation (e.g., for space applications), is critical to better enable these applications. In this work, we investigate the selective modulation of electronic transport in VO2 films subject to different 10 keV helium ion (He+) fluences. Under these conditions, the resistivity in the individual monoclinic and rutile phases varied by 50%–200%, while the MIT transformation temperature remains constant within 4 °C independent of irradiation fluence. Importantly, different trends in the resistivity of the monoclinic and rutile phases were observed both as a function of total He fluence as well as in films grown on different substrates (amorphous SiO2/Si vs single crystal Al2O3). Through a combination of measurements including majority carrier sign via Seebeck, low frequency noise, and TEM, our investigation supports the presence of different kinds of point defects (V in; O in), which may arise due to grain boundary defect interactions. Our work suggests the utility of He irradiation for the selective modulation of VO2 transport properties for neuromorphic, in contrast to other established but non-selective methods, like doping. [ABSTRACT FROM AUTHOR]

Published
2024
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33. An Efficient and Wear-Leveling-Aware Frequent-Pattern Mining on Non-Volatile Memory

Author

Dong, Jiaqi, Zhang, Runyu, Yang, Chaoshu, Tan, Yujuan, and Liu, Duo

Subjects
Computer Science - Databases, Computer Science - Data Structures and Algorithms
Abstract

Frequent-pattern mining is a common approach to reveal the valuable hidden trends behind data. However, existing frequent-pattern mining algorithms are designed for DRAM, instead of persistent memories (PMs), which can lead to severe performance and energy overhead due to the utterly different characteristics between DRAM and PMs when they are running on PMs. In this paper, we propose an efficient and Wear-leveling-aware Frequent-Pattern Mining scheme, WFPM, to solve this problem. The proposed WFPM is evaluated by a series of experiments based on realistic datasets from diversified application scenarios, where WFPM achieves 32.0% performance improvement and prolongs the NVM lifetime of header table by 7.4x over the EvFP-Tree.

Published
2020
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45. Effect of Drip Irrigation Under Mulch on Nitrogen Transport in Deep Soil Layers in an Agricultural Region of the Xiliao River Plain, China

Author

Jing Zhang, Haihua Jing, Kebao Dong, Jiaqi Ma and Zexu Jin

Subjects
transport of water and nitrogen drip irrigation, mulch, no3-n, nh4-n, groundwater pollution, xiliao river plain, Environmental effects of industries and plants, TD194-195, Science (General), Q1-390
Abstract

In the agricultural region of the Xiliao River Plain, drip irrigation under mulch has been widely implemented. It not only saves irrigation water, but also changes the structure of the underlying surface of agricultural land, which affects the local hydrological cycle to a certain extent, and makes the process of nitrogen transportation in soil with new characteristics. This study analyzed the distribution of NH4-N, NO3-N, and NO2-N in different soil depths during the whole growth period under three underlying surface conditions, including drip irrigation under mulch, border irrigation, and bare area through field in-situ observation experiment, and analyzed the influence of drip irrigation under mulch on nitrogen transport in deep soil layers. The results showed that under the soil properties of the experimental area, drip irrigation under mulch creates more water to enter the deep soil layers, which was beneficial to alleviate the downward trend of local groundwater level to a certain extent. The average content of NH4-N and NO3-N under drip irrigation under mulch was higher than that under border irrigation. The average content of NH4-N under drip irrigation under mulch was 1.24 mg.kg-1 in soil depths of 80-300 cm, and 0.97 mg.kg-1 under border irrigation. The average content of NO3-N under drip irrigation under mulch was 2.73 mg.kg-1 in soil depths of 80-300 cm, and 1.99 mg.kg-1 under border irrigation. The increment of NH4-N and NO3-N distribution in deep soil layers under drip irrigation under mulch was greater than that under border irrigation, and the increment of NO3-N content is significantly greater than that under border irrigation. Soil water content has a significant impact on the contents of NH4-N and NO3-N. It indicated that compared with traditional border irrigation, drip irrigation under mulch was beneficial to alleviate the downward trend of local groundwater, but it would increase the risk of nitrogen pollution in local groundwater.

Published
2022
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