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141.
邓成成 刘子奚 夏天阳 刘彦君 厉鹏程 龙飞飞 高翔 王守信 李国强 刘海庆 臧庆 李玖瑛 杨康宁 吴茗甫 尹晓宇 李弘 谢锦林 兰涛 毛文哲 刘阿娣 周楚 丁卫星 庄革 刘万东 《等离子体科学和技术》2024,26(6):065103-1-065103-9
Many experiments have demonstrated that resonant magnetic perturbation (RMP) can affect the turbulent transport at the edge of the tokamak. Through the Experimental Advanced Superconducting Tokamak (EAST) density modulation experiment, the particle transport coefficients were calculated using the experimental data, and the result shows that the particle transport coefficients increase with RMP. In this study, the six-field two-fluid model in BOUT++ is used to simulate the transport before and after density pump-out induced by RMP, respectively referred as the case without RMP and the case with RMP. In the linear simulations, the instabilities generally decreases for cases with RMP. In the nonlinear simulation, ELM only appears in the case without RMP. Additionally, the particle transport coefficient was analyzed, and the result shows that the particle transport coefficient becomes larger for the case with RMP, which is consistent with the experimental conclusion. Moreover, its magnitude is comparable to the results calculated from experimental data. 相似文献
142.
Ping WANG Guanghai HU Liang WANG Ning YAN Xiaoming ZHONG Guosheng XU Xi FENG Yang YE Genfan DING Lin YU Adi LIU Yanmin DUAN Erzhong LI Liqing XU Haiqing LIU Rui DING Bin ZHANG Miaohui LI Bojiang DING Chengming QIN Xinjun ZHANG Xiaojie WANG Bo LYU Ling ZHANG Mingfu WU Qing ZANG Xin LIN Xiaolan ZOU Yuntao SONG 《等离子体科学和技术》2023,25(4)
143.
汪 平;胡 广海;王 亮;颜 宁;仲 小明;徐 国盛;冯 喜;叶 扬;丁 根凡;余 林;刘 阿娣;段 艳敏;李 二众;徐 立清;刘 海庆;丁 锐;张 斌;李 妙辉;丁 伯江;秦 成明;张 新军;王 晓洁;吕 波;张 凌;吴 茗甫;臧 庆;林 新;邹 晓岚;宋 云涛 《等离子体科学和技术》2023,25(4):045106-045106
The blob properties in I-mode and ELM-free H-mode plasmas compared to L-mode have been investigated on the EAST tokamak, including the blob detection rate
144.
冯喜;刘阿娣;周楚;邹晓岚;庄革;王守信;王明远;刘海庆;丁卫星;张寿彪;吴木泉;朱翔;郝保龙;张津;刘朝阳;季佳旭;仲小明;刘深;谢锦林;林晓东;黄建军;高翔;万元熙 《等离子体科学和技术》2023,25(11):115101-115101
To interpret the common symmetric peaks caused by the large-scale structure in the complex S (f ) spectrum from the heterodyne Doppler reflectometry (DR) measurement in EAST, a 2D circular-shaped O-mode full-wave model based on the finite-difference time-domain method is built. The scattering characteristics and the influences on the DR signal from various scales are investigated. When the structure is located around the cutoff layer, a moving radial or poloidal large-scale structure k θ ≲ k θ , match (k θ , match is the theoretic wavenumber of Bragg scattering) could both generate an oscillation phase term called ‘phase modulation’, and symmetrical peaks in the complex S (f ) spectrum. It was found that the image-rejection ratio A −1/A +1 (A ±1 represents the amplitudes of ±1 order modulation peaks) could be a feasible indicator for experiment comparison. In the case when the structure is near the cutoff layer with the same arrangement as the experiment for the edge DR channel, the curve of A −1/A +1 versus k θ can be divided into three regions, weak asymmetrical range with k θ /k 0 ≲ 0.15 (k 0 is the vacuum wavenumber), harmonics range with 0.15 ≲ k θ /k 0 ≲ 0.4, and Bragg scattering range of 0.4 ≲ k θ /k 0 ≲ 0.7. In the case when the structure is located away from the cutoff layer, the final complex S (f ) spectrum is the simple superimposing of modulation and Bragg scattering, and the modulation peaks have an amplitude response nearly proportional to the local density fluctuation, called the ‘propagation-route effect’. Under the H-mode experiment arrangement for the core DR, a critical fluctuation amplitude $ A m pleft(n_{mathrm{e}, text { Mod.@route }}right) / A m pleft(n_{mathrm{e}, text { Tur.@MSA }} sim 1.3-4.1left(operatorname{Amp}left(n_{mathrm{e}, text { Mod.@route }}right)right.right.$ refers to the pedestal large-scale structure amplitude and Amp (n e, Tur.@MSA) refers to turbulence amplitude at the main scattering area) is needed for the structure in the pedestal to be observed by the core DR measurement. The simulations are well consistent with the experimental results. These effects need to be carefully considered during the DR signal analyses as the injecting beam passes through the plasma region with large-scale structures. 相似文献
145.
A high-frequency magnetic probe is designed and developed on the XuanLong-50 (EXL-50) spherical torus to measure high-frequency magnetic field fluctuation. The magnetic loop, radio filters, radio-frequency limiter, and data acquisition system of the probe are comprehensively examined. The fluctuation data from the EXL-50 plasma are analyzed in the time–frequency domain using fast Fourier transforms. Moreover, distinct high-frequency instabilities are detected using this diagnostic system. In particular, significant frequency chirping is observed, which is consistent with the bump-on-tail drive instability predicted using the Berk–Breizman model. 相似文献
146.
仲 小明;邹 晓岚;周 楚;刘 阿娣;庄 革;冯 喜;张 津;季 佳旭;范 泓锐;刘 深;王 士凡;高 刘天;史 文祥;兰 涛;李 弘;谢 锦林;毛 文哲;刘 子奚;刘 万东 《等离子体科学和技术》2023,25(9):095104-095104
The Doppler reflectometer (DR), a powerful diagnostic for the plasma perpendicular velocity (u ⊥) and turbulence measurement, has been widely used in various fusion devices. Many efforts have been put into extracting the Doppler shift from the DR signal. There are several commonly used methods for Doppler shift extraction, such as the phase derivative, the center of gravity, and symmetric fitting (SFIT). However, the strong zero-order reflection component around 0 kHz may interfere with the calculation of the Doppler shift. To avoid the influence of the zero-frequency peak, the asymmetric fitting (AFIT) method was designed to calculate the Doppler shift. Nevertheless, the AFIT method may lead to an unacceptable error when the Doppler shift is relatively small compared to the half width at half maximum (HWHM). Therefore, an improved method, which can remove the zero-frequency peak and fit the remaining Doppler peak with a Gaussian function, is devised to extract the Doppler shift. This method can still work reliably whether the HWHM is larger than the Doppler shift or not. 相似文献
147.
Zhaoyang LIU Yangzhong ZHANG Swadesh Mitter MAH AJAN Adi LIU Tao XIE Chu ZHOU Tao LAN Jinlin XIE Hong LI Ge ZHUANG Wandong LIU 《等离子体科学和技术》2021,23(3):35101-50
Through a systematically developed theory, we demonstrate that the motion of Instanton identified in Zhang et al(2017 Phys. Plasmas 24 122304) is highly correlated to the intermittent excitation and propagation of geodesic acoustic mode(GAM) that is observed in tokamaks.While many numerical simulations have observed the phenomena, it is the first theory that reveals the physical mechanism behind GAM intermittent excitation and propagation. The preceding work is based on the micro-turbulence associated with toroidal ion temperature gradient mode, and slab-based phenomenological model of zonal flow. When full toroidal effect is introduced into the system, two branches of zonal flow emerge: the torus-modified low frequency zonal flow(TLFZF), and GAM, necessitating a unified exploration of GAM and TLFZF. Indeed, we observe that the transition from the Caviton to Instanton is triggered by a rapid zero-crossing of radial group velocity of drift wave and is found to be strongly correlated with the GAM onset. Many features peculiar to intermittent GAMs, observed in real machines,are thus identified in the numerical experiment. The results will be displayed in figures and in a movie; first for single central rational surface, and then with coupled multiple central rational surfaces. The periodic bursting first shown disappears as being replaced by irregular one, more similar to the intermittent characteristics observed in GAM experiments. 相似文献
148.
An upgraded electron cyclotron emission imaging (ECEI) system consisting of new optics lenses with necessary electronics for receiving and processing signals for two dimension (2D) ECEI diagnostics was installed on EAST. Hyperboloid lens were adopted in the new system to optimize the spatial resolutions. The mixers array of sixteen elements measured the plasma electron cyclotron emission at eight frequencies simultaneously, and the profiles of the electron temperature and its fluctuation in an area of 20 cm (vertical) × 6 cm (horizontal) could then be analyzed. Eevolution of sawtooth precursor and crash in EAST was observed. 相似文献
149.
Elena Andreeva Charles Bouillaguet Orr Dunkelman Pierre-Alain Fouque Jonathan Hoch John Kelsey Adi Shamir Sébastien Zimmer 《Journal of Cryptology》2016,29(4):657-696
In this work, we present several new generic second-preimage attacks on hash functions. Our first attack is based on the herding attack and applies to various Merkle–Damgård-based iterative hash functions. Compared to the previously known long-message second-preimage attacks, our attack offers more flexibility in choosing the second-preimage message at the cost of a small computational overhead. More concretely, our attack allows the adversary to replace only a few blocks in the original target message to obtain the second preimage. As a result, our new attack is applicable to constructions previously believed to be immune to such second-preimage attacks. Among others, these include the dithered hash proposal of Rivest, Shoup’s UOWHF, and the ROX constructions. In addition, we also suggest several time-memory-data tradeoff attack variants, allowing for a faster online phase, and even finding second preimages for shorter messages. We further extend our attack to sequences stronger than the ones suggested in Rivest’s proposal. To this end we introduce the kite generator as a new tool to attack any dithering sequence over a small alphabet. Additionally, we analyse the second-preimage security of the basic tree hash construction. Here we also propose several second-preimage attacks and their time-memory-data tradeoff variants. Finally, we show how both our new and the previous second-preimage attacks can be applied even more efficiently when multiple short messages, rather than a single long target message, are available. 相似文献
150.
In this paper, we propose a novel intrusion detection technique with a fully automatic attack signatures generation capability. The proposed approach exploits a honeypot traffic data analysis to build an attack scenarios database, used to detect potential intrusions. Furthermore, for an effective and efficient intrusion detection mechanism, we introduce several new or adapted algorithms for signature generation, signature comparison, etc. Finally, we use DARPA’99 and UNSW-NB15 traffic to evaluate the proposed approach. The results indicate that the generated attack signatures are of high quality with low rates of false negatives and false positives. 相似文献