Pub Date : 2024-08-14DOI: 10.1088/1361-6587/ad6a84
E d D Zapata-Cornejo, D Zarzoso, S D Pinches, S E Sharapov, M Fitzgerald
Magnetohydrodynamic (MHD) activity in fusion devices is typically analyzed by examining time-frequency spectrograms obtained from various diagnostics. MHD modes often co-exist with various types of noise and complex patterns generated by other events like pellet injection or active diagnostics. Traditionally, identifying MHD modes has been a manual task, making it labor-intensive. To overcome this issue, this study proposes the use of computer vision (CV) algorithms for noise removal and automatic feature extraction. First, the automatic detection of straight-line patterns is achieved by applying the Hough transform. Then, the discrete wavelet transform is proposed to break down spectrograms into sub-images of different scales, removing broadband noise and pellet injection signatures. The multiscale decomposition is subsequently extended to multiple directions using either 2D Fourier transforms or curvelets, achieving a high signal-to-noise ratio in spectrograms and eliminating undesired frequency sweeps of toroidal Alfvén eigenmodes antenna. Once MHD activity is successfully enhanced, a pipeline of algorithms for ridge detection, thresholding and labeling perform a segmentation of the image, automatically labeling individual modes. This study demonstrates the effectiveness of CV algorithms for the identification of MHD modes. The use of such algorithms may potentially help in the analysis process and the creation of large databases of modes.
{"title":"Segmentation of MHD modes using Fourier transform, wavelets and computer vision algorithms","authors":"E d D Zapata-Cornejo, D Zarzoso, S D Pinches, S E Sharapov, M Fitzgerald","doi":"10.1088/1361-6587/ad6a84","DOIUrl":"https://doi.org/10.1088/1361-6587/ad6a84","url":null,"abstract":"Magnetohydrodynamic (MHD) activity in fusion devices is typically analyzed by examining time-frequency spectrograms obtained from various diagnostics. MHD modes often co-exist with various types of noise and complex patterns generated by other events like pellet injection or active diagnostics. Traditionally, identifying MHD modes has been a manual task, making it labor-intensive. To overcome this issue, this study proposes the use of computer vision (CV) algorithms for noise removal and automatic feature extraction. First, the automatic detection of straight-line patterns is achieved by applying the Hough transform. Then, the discrete wavelet transform is proposed to break down spectrograms into sub-images of different scales, removing broadband noise and pellet injection signatures. The multiscale decomposition is subsequently extended to multiple directions using either 2D Fourier transforms or curvelets, achieving a high signal-to-noise ratio in spectrograms and eliminating undesired frequency sweeps of toroidal Alfvén eigenmodes antenna. Once MHD activity is successfully enhanced, a pipeline of algorithms for ridge detection, thresholding and labeling perform a segmentation of the image, automatically labeling individual modes. This study demonstrates the effectiveness of CV algorithms for the identification of MHD modes. The use of such algorithms may potentially help in the analysis process and the creation of large databases of modes.","PeriodicalId":20239,"journal":{"name":"Plasma Physics and Controlled Fusion","volume":"32 1","pages":""},"PeriodicalIF":2.2,"publicationDate":"2024-08-14","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142181245","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-08-14DOI: 10.1088/1361-6587/ad6c7d
A P L Robinson
It has been suggested that ‘transient surface currents’ caused by multi-MeV fast electrons can be responsible for the emission of low frequency radiation (e.g. in THz range) from ultra-intense laser–solid interactions. This mechanism has been analyzed, and analytic upper bounds on the intensity, electric field amplitude, and normalized vector potential have been developed and tested against 1D EM Particle-in-Cell simulations. The ‘transient surface current’ mechanism is effective and sufficiently efficient to fully account for all radiation that has been emitted in experiments so far.
{"title":"Scaling of the emission of low frequency radiation by transient surface currents in laser–solid interactions","authors":"A P L Robinson","doi":"10.1088/1361-6587/ad6c7d","DOIUrl":"https://doi.org/10.1088/1361-6587/ad6c7d","url":null,"abstract":"It has been suggested that ‘transient surface currents’ caused by multi-MeV fast electrons can be responsible for the emission of low frequency radiation (e.g. in THz range) from ultra-intense laser–solid interactions. This mechanism has been analyzed, and analytic upper bounds on the intensity, electric field amplitude, and normalized vector potential have been developed and tested against 1D EM Particle-in-Cell simulations. The ‘transient surface current’ mechanism is effective and sufficiently efficient to fully account for all radiation that has been emitted in experiments so far.","PeriodicalId":20239,"journal":{"name":"Plasma Physics and Controlled Fusion","volume":"9 1","pages":""},"PeriodicalIF":2.2,"publicationDate":"2024-08-14","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142181248","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-08-13DOI: 10.1088/1361-6587/ad6a87
Sangil Lee, Jeongwon Lee, Jaemin Kwon
Tungsten (W) is the most probable material for the plasma-facing components of fusion reactors due to its excellent thermal and physical properties. A W-wall sputtering model has been established to simulate the start-up of a tokamak plasma using the 0D simulation code DYON. This model incorporates the revised Bohdansky formula to calculate the sputtering yield and a modified formula for calculating the energy impacting the walls. This formula integrates the temporal behavior of electron and ion temperatures at the plasma edge, which has been partially verified by the Thomson scattering diagnostic data. With the new model in place, predictive simulations were conducted for KSTAR’s Ohmic plasma under two W-wall scenarios: one with the entire wall surface covered by W and the other with 95% coverage of W and 5% coverage of carbon (C). The results indicate that the full-W wall may perform better from the perspective of start-up performance. The disparity can primarily be attributed to impurities generated through sputtering and recycling on the C wall. The validity of this model will be finally confirmed when the Thomson diagnostic system is able to precisely measure the edge electron temperature during plasma start-up.
钨（W）因其优异的热性能和物理性能，最有可能成为聚变反应堆面向等离子体部件的材料。利用 0D 模拟代码 DYON 建立了一个 W 壁溅射模型，用于模拟托卡马克等离子体的启动。该模型采用了经修订的博丹斯基公式来计算溅射产率，并采用了经修订的公式来计算撞击壁面的能量。该公式综合了等离子体边缘电子和离子温度的时间行为，并通过汤姆逊散射诊断数据进行了部分验证。有了这个新模型，我们对 KSTAR 的欧姆等离子体进行了两种 W 壁情况下的预测模拟：一种是整个壁面都被 W 覆盖，另一种是 95% 的 W 和 5% 的碳（C）覆盖。结果表明，从启动性能的角度来看，全 W 壁的性能可能更好。这种差异主要是由于在 C 壁上通过溅射和回收产生的杂质造成的。当汤姆逊诊断系统能够精确测量等离子体启动过程中的边缘电子温度时，这一模型的有效性将得到最终证实。
{"title":"A tungsten-wall sputtering model for the plasma start-up simulation in tokamaks","authors":"Sangil Lee, Jeongwon Lee, Jaemin Kwon","doi":"10.1088/1361-6587/ad6a87","DOIUrl":"https://doi.org/10.1088/1361-6587/ad6a87","url":null,"abstract":"Tungsten (W) is the most probable material for the plasma-facing components of fusion reactors due to its excellent thermal and physical properties. A W-wall sputtering model has been established to simulate the start-up of a tokamak plasma using the 0D simulation code DYON. This model incorporates the revised Bohdansky formula to calculate the sputtering yield and a modified formula for calculating the energy impacting the walls. This formula integrates the temporal behavior of electron and ion temperatures at the plasma edge, which has been partially verified by the Thomson scattering diagnostic data. With the new model in place, predictive simulations were conducted for KSTAR’s Ohmic plasma under two W-wall scenarios: one with the entire wall surface covered by W and the other with 95% coverage of W and 5% coverage of carbon (C). The results indicate that the full-W wall may perform better from the perspective of start-up performance. The disparity can primarily be attributed to impurities generated through sputtering and recycling on the C wall. The validity of this model will be finally confirmed when the Thomson diagnostic system is able to precisely measure the edge electron temperature during plasma start-up.","PeriodicalId":20239,"journal":{"name":"Plasma Physics and Controlled Fusion","volume":"1 1","pages":""},"PeriodicalIF":2.2,"publicationDate":"2024-08-13","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142181249","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-08-11DOI: 10.1088/1361-6587/ad6707
A Panera Alvarez, A Ho, A Järvinen, S Saarelma, S Wiesen, JET Contributors and the ASDEX Upgrade Team
This work successfully generates an uncertainty-aware surrogate model of the EuroPED plasma pedestal model using the Bayesian neural network with noise contrastive prior (BNN-NCP) technique. This model is trained using data from the JET-ILW pedestal database and subsequent model evaluations, conforming to EuroPED-NN. The BNN-NCP technique has been proven to be a suitable method for generating uncertainty-aware surrogate models. It matches the output results of a regular neural network while providing confidence estimates for predictions as uncertainties. Additionally, it highlights out-of-distribution regions using surrogate model uncertainties. This provides critical insights into model robustness and reliability. EuroPED-NN has been physically validated, first, analyzing electron density with respect to increasing plasma current, , and second, validating the relation associated with the EuroPED model. This affirms the robustness of the underlying physics learned by the surrogate model. On top of that, the method was used to develop a EuroPED-like model fed with experimental data, i.e. an uncertainty aware experimental model, which is functional in JET database. Both models have been also tested in ∼50 AUG shots.
{"title":"EuroPED-NN: uncertainty aware surrogate model","authors":"A Panera Alvarez, A Ho, A Järvinen, S Saarelma, S Wiesen, JET Contributors and the ASDEX Upgrade Team","doi":"10.1088/1361-6587/ad6707","DOIUrl":"https://doi.org/10.1088/1361-6587/ad6707","url":null,"abstract":"This work successfully generates an uncertainty-aware surrogate model of the EuroPED plasma pedestal model using the Bayesian neural network with noise contrastive prior (BNN-NCP) technique. This model is trained using data from the JET-ILW pedestal database and subsequent model evaluations, conforming to EuroPED-NN. The BNN-NCP technique has been proven to be a suitable method for generating uncertainty-aware surrogate models. It matches the output results of a regular neural network while providing confidence estimates for predictions as uncertainties. Additionally, it highlights out-of-distribution regions using surrogate model uncertainties. This provides critical insights into model robustness and reliability. EuroPED-NN has been physically validated, first, analyzing electron density with respect to increasing plasma current, , and second, validating the relation associated with the EuroPED model. This affirms the robustness of the underlying physics learned by the surrogate model. On top of that, the method was used to develop a EuroPED-like model fed with experimental data, i.e. an uncertainty aware experimental model, which is functional in JET database. Both models have been also tested in ∼50 AUG shots.","PeriodicalId":20239,"journal":{"name":"Plasma Physics and Controlled Fusion","volume":"83 1","pages":""},"PeriodicalIF":2.2,"publicationDate":"2024-08-11","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141933084","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-07-22DOI: 10.1088/1361-6587/ad5df9
Giovanni Di Giannatale, Alberto Bottino, Stephan Brunner, Moahan Murugappan and Laurent Villard
In this work, we explore the triangularity effects on turbulent transport employing global gyrokinetic simulations performed with the ORB5 code. Numerous experiments on the Tokamak á Configuration Variable (TCV) and, more recently, on the DIII-D machine, have demonstrated superior confinement properties in L-mode of negative triangularity (NT) over positive triangularity (PT) configuration. This presents a particularly attractive scenario, as L-mode operation eliminates or significantly mitigates the presence of hazardous edge-localized modes (ELMs). However, a full theoretical understanding of all these observations remains elusive. Specifically, questions remain about how NT improvements can extend to the core where triangularity is very small, and whether these improvements can scale to larger devices. This paper addresses these two questions. Our analysis is divided into two parts: we first demonstrate that the confinement enhancement in NT configurations arises from the interdependent edge-core dynamics, and then we present the results of a system size scan. Crucially, we find that the relative turbulent transport reduction of NT over PT appears not to be contingent on machine dimensions or fluctuation scales and is moreover robust with respect to variations in plasma profiles. This insight underscores the fundamental nature of the NT confinement advantage and paves the way for its potential application in future fusion devices, regardless of their size.
在这项工作中，我们利用 ORB5 代码进行了全局陀螺动力学模拟，探索了三角形对湍流传输的影响。托卡马克可变配置（TCV）以及最近在 DIII-D 机器上进行的大量实验证明，负三角形（NT）L 模式比正三角形（PT）配置具有更优越的约束特性。这提出了一个特别有吸引力的方案，因为 L 模式运行消除或显著减轻了危险的边缘定位模式（ELM）的存在。然而，对所有这些观测结果的全面理论理解仍然遥遥无期。具体来说，NT 改进如何扩展到三角形很小的内核，以及这些改进能否扩展到更大的器件，这些问题仍然存在。本文将探讨这两个问题。我们的分析分为两个部分：首先，我们证明了 NT 配置中的约束增强源于相互依赖的边核动力学；然后，我们展示了系统尺寸扫描的结果。重要的是，我们发现与 PT 相比，NT 的湍流传输相对减少似乎并不取决于机器尺寸或波动尺度，而且对于等离子体剖面的变化也是稳健的。这一洞察力强调了 NT 限制优势的基本性质，并为其在未来核聚变装置中的潜在应用铺平了道路，无论这些装置的大小如何。
{"title":"System size scaling of triangularity effects on global temperature gradient-driven gyrokinetic simulations","authors":"Giovanni Di Giannatale, Alberto Bottino, Stephan Brunner, Moahan Murugappan and Laurent Villard","doi":"10.1088/1361-6587/ad5df9","DOIUrl":"https://doi.org/10.1088/1361-6587/ad5df9","url":null,"abstract":"In this work, we explore the triangularity effects on turbulent transport employing global gyrokinetic simulations performed with the ORB5 code. Numerous experiments on the Tokamak á Configuration Variable (TCV) and, more recently, on the DIII-D machine, have demonstrated superior confinement properties in L-mode of negative triangularity (NT) over positive triangularity (PT) configuration. This presents a particularly attractive scenario, as L-mode operation eliminates or significantly mitigates the presence of hazardous edge-localized modes (ELMs). However, a full theoretical understanding of all these observations remains elusive. Specifically, questions remain about how NT improvements can extend to the core where triangularity is very small, and whether these improvements can scale to larger devices. This paper addresses these two questions. Our analysis is divided into two parts: we first demonstrate that the confinement enhancement in NT configurations arises from the interdependent edge-core dynamics, and then we present the results of a system size scan. Crucially, we find that the relative turbulent transport reduction of NT over PT appears not to be contingent on machine dimensions or fluctuation scales and is moreover robust with respect to variations in plasma profiles. This insight underscores the fundamental nature of the NT confinement advantage and paves the way for its potential application in future fusion devices, regardless of their size.","PeriodicalId":20239,"journal":{"name":"Plasma Physics and Controlled Fusion","volume":"97 1","pages":""},"PeriodicalIF":2.2,"publicationDate":"2024-07-22","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141753891","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-07-11DOI: 10.1088/1361-6587/ad5c9a
Shi-Jie Liu, Feng Wang, Di Hu, Zheng-Xiong Wang and the JOREK team
In previous studies, it has been observed that the transport of energetic electrons decreases with increasing energy. This observation is a global and long-time-scale result, attributed to the space-averaged perturbations. In this work, we focus on the local and instantaneous transport characteristics of runaway electrons (REs) during the phase of tokamak disruption, with REs speeds close to the speed of light. To simulate the dynamics of REs, we utilize a particle tracing code called PTC. By coupling PTC with the MHD code JOREK, we are able to study the energy and spatial dependence of RE transport. Our investigations reveal that the finite orbit width (FOW) effect plays an important role in RE transport. This effect is influenced by the relative direction of the electron drift and the magnetic field line. Specifically, the FOW effect strengthens the transport when the drift direction aligns with the deflecting direction of the field line. And we compare the transport profiles among three time slices: at the beginning of the thermal quench, during the thermal quench, and at the beginning of the current quench. In this ITER disruption simulation, the perturbation scale is strong and is up to 0.05 at developed thermal quench stage. It is reasonable that the influence of FOW effect on transport is less than that of magnetic perturbation even if the energy of REs is about hundreds MeV and the orbit width is equal to or greater than the perturbation length. These analyses provide insights into the mechanisms of RE transport based on magnetic perturbations.
在以前的研究中，已经观察到高能电子的传输随着能量的增加而减少。这一观测结果是一个全局性的长时段结果，归因于空间平均扰动。在这项工作中，我们重点研究失控电子（REs）在托卡马克破坏阶段的局部和瞬时传输特性，REs的速度接近光速。为了模拟REs的动力学，我们使用了一种名为PTC的粒子追踪代码。通过将 PTC 与 MHD 代码 JOREK 相结合，我们能够研究 RE 传输的能量和空间依赖性。我们的研究发现，有限轨道宽度（FOW）效应在 RE 传输中起着重要作用。这种效应受电子漂移和磁场线相对方向的影响。具体来说，当漂移方向与磁场线的偏转方向一致时，有限轨道宽度效应会增强传输。我们还比较了三个时间片的传输剖面：热淬火开始时、热淬火期间和电流淬火开始时。在这次 ITER 破坏模拟中，扰动尺度很强，在发达热淬火阶段高达 0.05。即使 REs 的能量约为数百 MeV，轨道宽度等于或大于扰动长度，FOW 效应对传输的影响也小于磁扰动的影响，这是合理的。这些分析为基于磁扰动的RE输运机制提供了启示。
{"title":"Transport characteristic evaluation of runaway electrons in an ITER disruption simulation","authors":"Shi-Jie Liu, Feng Wang, Di Hu, Zheng-Xiong Wang and the JOREK team","doi":"10.1088/1361-6587/ad5c9a","DOIUrl":"https://doi.org/10.1088/1361-6587/ad5c9a","url":null,"abstract":"In previous studies, it has been observed that the transport of energetic electrons decreases with increasing energy. This observation is a global and long-time-scale result, attributed to the space-averaged perturbations. In this work, we focus on the local and instantaneous transport characteristics of runaway electrons (REs) during the phase of tokamak disruption, with REs speeds close to the speed of light. To simulate the dynamics of REs, we utilize a particle tracing code called PTC. By coupling PTC with the MHD code JOREK, we are able to study the energy and spatial dependence of RE transport. Our investigations reveal that the finite orbit width (FOW) effect plays an important role in RE transport. This effect is influenced by the relative direction of the electron drift and the magnetic field line. Specifically, the FOW effect strengthens the transport when the drift direction aligns with the deflecting direction of the field line. And we compare the transport profiles among three time slices: at the beginning of the thermal quench, during the thermal quench, and at the beginning of the current quench. In this ITER disruption simulation, the perturbation scale is strong and is up to 0.05 at developed thermal quench stage. It is reasonable that the influence of FOW effect on transport is less than that of magnetic perturbation even if the energy of REs is about hundreds MeV and the orbit width is equal to or greater than the perturbation length. These analyses provide insights into the mechanisms of RE transport based on magnetic perturbations.","PeriodicalId":20239,"journal":{"name":"Plasma Physics and Controlled Fusion","volume":"46 1","pages":""},"PeriodicalIF":2.2,"publicationDate":"2024-07-11","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141611215","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-07-08DOI: 10.1088/1361-6587/ad5c9c
Yue Zhang, Feng Wang, Jizhong Sun, Mao Li, Guangzhou Hao
The transport of beam ions in the presence of single/multiple tearing modes (TMs) under HL-2A geometry has been investigated by test particle method. Simulation results show that there exists a threshold behavior in the number of lost beam ions in the plasma under perturbation of a (2,1) TM with amplitude <inline-formula> <tex-math><?CDATA ${alpha _0}$?></tex-math> <mml:math overflow="scroll"><mml:mrow><mml:mrow><mml:msub><mml:mi>α</mml:mi><mml:mn>0</mml:mn></mml:msub></mml:mrow></mml:mrow></mml:math> <inline-graphic xlink:href="ppcfad5c9cieqn1.gif" xlink:type="simple"></inline-graphic> </inline-formula>: when the amplitude <inline-formula> <tex-math><?CDATA ${alpha _0}$?></tex-math> <mml:math overflow="scroll"><mml:mrow><mml:mrow><mml:msub><mml:mi>α</mml:mi><mml:mn>0</mml:mn></mml:msub></mml:mrow></mml:mrow></mml:math> <inline-graphic xlink:href="ppcfad5c9cieqn2.gif" xlink:type="simple"></inline-graphic> </inline-formula> is over a critical value, the number of lost beam ions increases linearly with <inline-formula> <tex-math><?CDATA ${alpha _0}$?></tex-math> <mml:math overflow="scroll"><mml:mrow><mml:mrow><mml:msub><mml:mi>α</mml:mi><mml:mn>0</mml:mn></mml:msub></mml:mrow></mml:mrow></mml:math> <inline-graphic xlink:href="ppcfad5c9cieqn3.gif" xlink:type="simple"></inline-graphic> </inline-formula> at a much faster pace. Further analysis finds that the lost beam ions have relatively higher percentage of high energy at <inline-formula> <tex-math><?CDATA ${alpha _0}$?></tex-math> <mml:math overflow="scroll"><mml:mrow><mml:mrow><mml:msub><mml:mi>α</mml:mi><mml:mn>0</mml:mn></mml:msub></mml:mrow></mml:mrow></mml:math> <inline-graphic xlink:href="ppcfad5c9cieqn4.gif" xlink:type="simple"></inline-graphic> </inline-formula> around the critical value. It also finds that the distribution of lost beam ions which is initially concentrated on the high field side expands gradually toward the low field side as the perturbation amplitude <inline-formula> <tex-math><?CDATA ${alpha _0}$?></tex-math> <mml:math overflow="scroll"><mml:mrow><mml:mrow><mml:msub><mml:mi>α</mml:mi><mml:mn>0</mml:mn></mml:msub></mml:mrow></mml:mrow></mml:math> <inline-graphic xlink:href="ppcfad5c9cieqn5.gif" xlink:type="simple"></inline-graphic> </inline-formula> increases. From the phase space analysis, it shows that the enhanced outward transport of fast ions in the presence of magnetic islands results from orbit stochasticity, which is due to the overlap of the drift islands in the interaction of fast ions with TMs. When two TMs are simultaneously present, the stochastic threshold of fast ion orbit is found to be lower than that in their individual TM case. The phase space analysis shows that in the presence of two modes with the same toroidal mode number, the modes increase the loss of fast ions when they are out of phase; however, such the effect of strengthening transport of fast ions turns to weaken when they are in phase. In contrast, when two modes each with a different toroida
{"title":"Numerical analysis of fast ions transport induced by magnetic islands in HL-2A","authors":"Yue Zhang, Feng Wang, Jizhong Sun, Mao Li, Guangzhou Hao","doi":"10.1088/1361-6587/ad5c9c","DOIUrl":"https://doi.org/10.1088/1361-6587/ad5c9c","url":null,"abstract":"The transport of beam ions in the presence of single/multiple tearing modes (TMs) under HL-2A geometry has been investigated by test particle method. Simulation results show that there exists a threshold behavior in the number of lost beam ions in the plasma under perturbation of a (2,1) TM with amplitude <inline-formula>\u0000<tex-math><?CDATA ${alpha _0}$?></tex-math>\u0000<mml:math overflow=\"scroll\"><mml:mrow><mml:mrow><mml:msub><mml:mi>α</mml:mi><mml:mn>0</mml:mn></mml:msub></mml:mrow></mml:mrow></mml:math>\u0000<inline-graphic xlink:href=\"ppcfad5c9cieqn1.gif\" xlink:type=\"simple\"></inline-graphic>\u0000</inline-formula>: when the amplitude <inline-formula>\u0000<tex-math><?CDATA ${alpha _0}$?></tex-math>\u0000<mml:math overflow=\"scroll\"><mml:mrow><mml:mrow><mml:msub><mml:mi>α</mml:mi><mml:mn>0</mml:mn></mml:msub></mml:mrow></mml:mrow></mml:math>\u0000<inline-graphic xlink:href=\"ppcfad5c9cieqn2.gif\" xlink:type=\"simple\"></inline-graphic>\u0000</inline-formula> is over a critical value, the number of lost beam ions increases linearly with <inline-formula>\u0000<tex-math><?CDATA ${alpha _0}$?></tex-math>\u0000<mml:math overflow=\"scroll\"><mml:mrow><mml:mrow><mml:msub><mml:mi>α</mml:mi><mml:mn>0</mml:mn></mml:msub></mml:mrow></mml:mrow></mml:math>\u0000<inline-graphic xlink:href=\"ppcfad5c9cieqn3.gif\" xlink:type=\"simple\"></inline-graphic>\u0000</inline-formula> at a much faster pace. Further analysis finds that the lost beam ions have relatively higher percentage of high energy at <inline-formula>\u0000<tex-math><?CDATA ${alpha _0}$?></tex-math>\u0000<mml:math overflow=\"scroll\"><mml:mrow><mml:mrow><mml:msub><mml:mi>α</mml:mi><mml:mn>0</mml:mn></mml:msub></mml:mrow></mml:mrow></mml:math>\u0000<inline-graphic xlink:href=\"ppcfad5c9cieqn4.gif\" xlink:type=\"simple\"></inline-graphic>\u0000</inline-formula> around the critical value. It also finds that the distribution of lost beam ions which is initially concentrated on the high field side expands gradually toward the low field side as the perturbation amplitude <inline-formula>\u0000<tex-math><?CDATA ${alpha _0}$?></tex-math>\u0000<mml:math overflow=\"scroll\"><mml:mrow><mml:mrow><mml:msub><mml:mi>α</mml:mi><mml:mn>0</mml:mn></mml:msub></mml:mrow></mml:mrow></mml:math>\u0000<inline-graphic xlink:href=\"ppcfad5c9cieqn5.gif\" xlink:type=\"simple\"></inline-graphic>\u0000</inline-formula> increases. From the phase space analysis, it shows that the enhanced outward transport of fast ions in the presence of magnetic islands results from orbit stochasticity, which is due to the overlap of the drift islands in the interaction of fast ions with TMs. When two TMs are simultaneously present, the stochastic threshold of fast ion orbit is found to be lower than that in their individual TM case. The phase space analysis shows that in the presence of two modes with the same toroidal mode number, the modes increase the loss of fast ions when they are out of phase; however, such the effect of strengthening transport of fast ions turns to weaken when they are in phase. In contrast, when two modes each with a different toroida","PeriodicalId":20239,"journal":{"name":"Plasma Physics and Controlled Fusion","volume":"17 1","pages":""},"PeriodicalIF":2.2,"publicationDate":"2024-07-08","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141575817","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-07-08DOI: 10.1088/1361-6587/ad5934
X K Ai, W Zheng, M Zhang, Y H Ding, D L Chen, Z Y Chen, C S Shen, B H Guo, N C Wang, Z J Yang, Z P Chen, Y Pan, B Shen, B J Xiao, J-TEXT Team1
In the initial stages of operation for future tokamak, facing limited data availability, deploying data-driven disruption predictors requires optimal performance with minimal use of new device data. This paper studies the issue of data utilization in data-driven disruption predictor during cross tokamak deployment. Current predictors primarily employ supervised learning methods and require a large number of disruption and non-disruption shots for training. However, the scarcity and high cost of obtaining disruption shots for future tokamaks result in imbalanced training datasets, reducing the performance of supervised learning predictors. To solve this problem, we propose the Enhanced Convolutional Autoencoder Anomaly Detection (E-CAAD) predictor. E-CAAD can be trained only by non-disruption samples and can also be trained by disruption precursor samples when disruption shots occur. This model not only overcomes the sample imbalance in supervised learning predictors, but also overcomes the inefficient dataset utilization faced by traditional anomaly detection predictors that cannot use disruption precursor samples for training, making it more suitable for the unpredictable datasets of future tokamaks. Compared to traditional anomaly detection predictors, the E-CAAD predictor performs better in disruption prediction and is deployed faster on new devices. Additionally, we explore strategies to accelerate the deployment of the E-CAAD predictor on the new device by using data from existing devices. Two deployment strategies are presented: mixing data from existing devices and fine-tuning the predictor trained on existing devices. Our comparisons indicate that the data from existing device can accelerate the deployment of predictor on new device. Notably, the fine-tuning strategy yields the fastest deployment on new device among the designed strategies.
{"title":"Cross-tokamak deployment study of plasma disruption predictors based on convolutional autoencoder","authors":"X K Ai, W Zheng, M Zhang, Y H Ding, D L Chen, Z Y Chen, C S Shen, B H Guo, N C Wang, Z J Yang, Z P Chen, Y Pan, B Shen, B J Xiao, J-TEXT Team1","doi":"10.1088/1361-6587/ad5934","DOIUrl":"https://doi.org/10.1088/1361-6587/ad5934","url":null,"abstract":"In the initial stages of operation for future tokamak, facing limited data availability, deploying data-driven disruption predictors requires optimal performance with minimal use of new device data. This paper studies the issue of data utilization in data-driven disruption predictor during cross tokamak deployment. Current predictors primarily employ supervised learning methods and require a large number of disruption and non-disruption shots for training. However, the scarcity and high cost of obtaining disruption shots for future tokamaks result in imbalanced training datasets, reducing the performance of supervised learning predictors. To solve this problem, we propose the Enhanced Convolutional Autoencoder Anomaly Detection (E-CAAD) predictor. E-CAAD can be trained only by non-disruption samples and can also be trained by disruption precursor samples when disruption shots occur. This model not only overcomes the sample imbalance in supervised learning predictors, but also overcomes the inefficient dataset utilization faced by traditional anomaly detection predictors that cannot use disruption precursor samples for training, making it more suitable for the unpredictable datasets of future tokamaks. Compared to traditional anomaly detection predictors, the E-CAAD predictor performs better in disruption prediction and is deployed faster on new devices. Additionally, we explore strategies to accelerate the deployment of the E-CAAD predictor on the new device by using data from existing devices. Two deployment strategies are presented: mixing data from existing devices and fine-tuning the predictor trained on existing devices. Our comparisons indicate that the data from existing device can accelerate the deployment of predictor on new device. Notably, the fine-tuning strategy yields the fastest deployment on new device among the designed strategies.","PeriodicalId":20239,"journal":{"name":"Plasma Physics and Controlled Fusion","volume":"42 1","pages":""},"PeriodicalIF":2.2,"publicationDate":"2024-07-08","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141575816","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-07-03DOI: 10.1088/1361-6587/ad5bfe
Sagar Choudhary, Jugal Chowdhury, Gopal Krishna M, Jagannath Mahapatra, Amit K Singh, Rajaraman Ganesh and Laurent Villard
The ubiquitous mode is investigated in the linear regime for the first time using a global gyrokinetic model. These modes are driven by the density gradient in trapped electron population but with mode frequency in the ion diamagnetic drift direction, in contrast to the conventional trapped electron mode. The dispersion relation is calculated along with the global mode structure. The ubiquitous mode is quite global although appears at a shorter wavelength ( ). We show that the main driving mechanism is the density gradient and the temperature gradient has only a modest effect; the mode can persist at higher temperature gradient scenarios making it another possible channel of anomalous transport. The magnetic shear reduces the growth of the mode; while the electron to ion temperature ratio has a nonmonotonic effect on the mode growth rate—growth rate increases initially for the ubiquitous branch of the mode and decreases afterwards as the conventional trapped electron mode starts dominating. The role of safety factor and toroidicity is also analyzed. Finally, a mixing length-based estimation of transport is presented.
{"title":"Global gyrokinetic study of density gradient driven instability in tokamaks: the ubiquitous mode","authors":"Sagar Choudhary, Jugal Chowdhury, Gopal Krishna M, Jagannath Mahapatra, Amit K Singh, Rajaraman Ganesh and Laurent Villard","doi":"10.1088/1361-6587/ad5bfe","DOIUrl":"https://doi.org/10.1088/1361-6587/ad5bfe","url":null,"abstract":"The ubiquitous mode is investigated in the linear regime for the first time using a global gyrokinetic model. These modes are driven by the density gradient in trapped electron population but with mode frequency in the ion diamagnetic drift direction, in contrast to the conventional trapped electron mode. The dispersion relation is calculated along with the global mode structure. The ubiquitous mode is quite global although appears at a shorter wavelength ( ). We show that the main driving mechanism is the density gradient and the temperature gradient has only a modest effect; the mode can persist at higher temperature gradient scenarios making it another possible channel of anomalous transport. The magnetic shear reduces the growth of the mode; while the electron to ion temperature ratio has a nonmonotonic effect on the mode growth rate—growth rate increases initially for the ubiquitous branch of the mode and decreases afterwards as the conventional trapped electron mode starts dominating. The role of safety factor and toroidicity is also analyzed. Finally, a mixing length-based estimation of transport is presented.","PeriodicalId":20239,"journal":{"name":"Plasma Physics and Controlled Fusion","volume":"45 1","pages":""},"PeriodicalIF":2.2,"publicationDate":"2024-07-03","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141547051","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-07-03DOI: 10.1088/1361-6587/ad5c9b
Garima Patel, R Uma and R P Sharma
This study investigates the interaction between kinetic Alfvén waves (KAWs) and magnetic islands in solar corona region. KAWs and magnetic islands are believed to be one of the key players in the heating of the coronal plasma and particle acceleration. We have used the dynamical model for KAWs to simulate its propagation through magnetic islands. The equation is solved numerically by using the finite difference and pseudospectral technique for spatial and temporal variations. The simulation results have been studied and signatures of turbulent structures evolving with time have been observed. Turbulence plays a considerable role in tapping out magnetic energy to thermal energy. The plot of the energy spectrum as a function of wavenumber exhibits a power law behavior in the inertial range, characterized with an exponent around . Beyond this range, the spectrum becomes steeper. In order to gain a more thorough knowledge of the physical processes that underlie the development of localized structures and to estimate the current sheet scale sizes, a semi-analytically model is also performed. The results indicate that the size of localized structures are comparable to ion gyro-radius, and different intensities of KAW further modify this length scale formed at different times. The purpose of the study is to acquire an understanding of the KAW propagation in magnetic islands and the way it contributes to the formation of turbulence and energy release in the solar corona. A comparative aspect of the non-linear interaction of 3D KAW with magnetic island and null point is also presented which shows that non-linear interaction of 3D KAW with null point, leads to rapid disorganization of the magnetic field and the creation of localized structures.
{"title":"Turbulence generation in the solar corona through nonlinear interaction between 3D kinetic Alfvén wave and magnetic islands","authors":"Garima Patel, R Uma and R P Sharma","doi":"10.1088/1361-6587/ad5c9b","DOIUrl":"https://doi.org/10.1088/1361-6587/ad5c9b","url":null,"abstract":"This study investigates the interaction between kinetic Alfvén waves (KAWs) and magnetic islands in solar corona region. KAWs and magnetic islands are believed to be one of the key players in the heating of the coronal plasma and particle acceleration. We have used the dynamical model for KAWs to simulate its propagation through magnetic islands. The equation is solved numerically by using the finite difference and pseudospectral technique for spatial and temporal variations. The simulation results have been studied and signatures of turbulent structures evolving with time have been observed. Turbulence plays a considerable role in tapping out magnetic energy to thermal energy. The plot of the energy spectrum as a function of wavenumber exhibits a power law behavior in the inertial range, characterized with an exponent around . Beyond this range, the spectrum becomes steeper. In order to gain a more thorough knowledge of the physical processes that underlie the development of localized structures and to estimate the current sheet scale sizes, a semi-analytically model is also performed. The results indicate that the size of localized structures are comparable to ion gyro-radius, and different intensities of KAW further modify this length scale formed at different times. The purpose of the study is to acquire an understanding of the KAW propagation in magnetic islands and the way it contributes to the formation of turbulence and energy release in the solar corona. A comparative aspect of the non-linear interaction of 3D KAW with magnetic island and null point is also presented which shows that non-linear interaction of 3D KAW with null point, leads to rapid disorganization of the magnetic field and the creation of localized structures.","PeriodicalId":20239,"journal":{"name":"Plasma Physics and Controlled Fusion","volume":"29 1","pages":""},"PeriodicalIF":2.2,"publicationDate":"2024-07-03","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141547052","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
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