Pub Date : 2024-09-16DOI: 10.1088/1361-6587/ad7889
F Lucchini, A Frescura, R Torchio, P Alotto and P Bettini
The real-time monitoring of the structural displacement of the vacuum vessel of thermonuclear fusion devices caused by electromagnetic loads is of great interest. In this paper, model order reduction is applied to the integral equation methods and the finite elements method to develop electromagnetic and structural reduced order models (ROMs) compatible with real-time execution which allows for the real-time monitoring of strain and displacement in critical positions of Tokamaks machines. Low-rank compression techniques based on hierarchical matrices are applied to reduce the computational cost during the offline stage when the ROMs are constructed. Numerical results show the accuracy of the approach and demonstrate the compatibility with real-time execution in standard hardware.
对热核聚变装置真空容器由电磁载荷引起的结构位移进行实时监测是一项非常有意义的工作。本文在积分方程法和有限元法中应用了模型阶次缩减法，以开发与实时执行兼容的电磁和结构缩减阶次模型（ROM），从而实现对托卡马克机器关键位置的应变和位移的实时监测。在构建 ROM 的离线阶段，应用了基于分层矩阵的低秩压缩技术来降低计算成本。数值结果表明了该方法的准确性，并证明了与标准硬件实时执行的兼容性。
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Pub Date : 2024-09-15DOI: 10.1088/1361-6587/ad75b9
K D Lawson, I H Coffey, M Groth, A G Meigs, S Menmuir, B Thomas and JET Contributors
An understanding of the behaviour of the D or He fuel used in tokamak discharges is essential in analyses such as modelling edge and divertor transport and the erosion of the vessel walls. However, poor agreement is found between measurements made on the JET tokamak and collisional-radiative models used to predict the hydrogen-like D and He line intensities. The range of temperatures of the plasmas emitting the radiation is also limited, in contrast to that for many impurities for which a wide range is possible. This is particularly so for He II whose line intensities tend to have the same near-constant ratios in most pulses, suggesting that the emission originates in plasma regions with very similar electron temperatures. To gain understanding and to allow quantitative comparisons with theoretical models, extensive observations of the VUV Lyman series have been made, for all discharge scenarios run during three He campaigns. Those for He discharges in both JET ITER-like wall (JET-ILW) and JET C (JET-C) campaigns are presented here. He discharges have the advantage of fewer impurities resulting in less complex spectra than when D is used as the fuel. However, the characteristics of the observed discrepancies are similar in both species, allowing He to be used as a proxy for D in order to gain understanding of the discrepancy. In addition, the study of He avoids the complication of molecular species contributing to the level populations. Opacity effects are also expected to be less severe in He discharges. Nevertheless, so as to ensure that the measurements are not unduly affected by opacity, comparisons have also been made with emission from Balmer and Paschen series members. Measurements of both line intensities and their ratios are presented for all-pulse surveys and for individual pulses. In exceptional cases in which the He emission is intense a dependence on the He II line intensity is demonstrated. The discrepancy between these measurements and the theoretical models is illustrated.
了解托卡马克放电中使用的 D 或 He 燃料的行为对于模拟边缘和分流器传输以及容器壁侵蚀等分析至关重要。然而，在 JET 托卡马克上进行的测量与用于预测类氢 D 和 He 线强度的碰撞辐射模型之间的一致性很差。发射辐射的等离子体的温度范围也很有限，而许多杂质的温度范围则很宽。对于 He II 来说尤其如此，在大多数脉冲中，其线强度往往具有相同的近乎恒定的比率，这表明辐射源自电子温度非常相似的等离子体区域。为了加深了解并与理论模型进行定量比较，我们在三次 He 活动期间对所有放电方案的紫外-紫外莱曼系列进行了广泛观测。本文介绍了在 JET ITER-like wall (JET-ILW) 和 JET C (JET-C) 活动中对氦放电进行的观测。与使用 D 作为燃料时相比，He 放电的优点是杂质较少，因此光谱不那么复杂。不过，这两种物质的观测差异特征相似，因此可以用 He 代替 D 来了解差异。此外，对 He 的研究避免了分子物种对水平种群的影响这一复杂问题。氦气排放的不透明效应预计也不会太严重。尽管如此，为了确保测量结果不会受到不透明度的过度影响，我们还与巴尔默和帕申系列成员的发射进行了比较。对所有脉冲勘测和单个脉冲的线强度及其比值都进行了测量。在 He 发射强度较高的特殊情况下，He II 线强度与之相关。说明了这些测量结果与理论模型之间的差异。
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Pub Date : 2024-09-12DOI: 10.1088/1361-6587/ad705a
A Geraldini, S Brunner and F I Parra
A solid target in contact with a plasma charges (negatively) to reflect the more mobile species (electrons) and thus keep the bulk plasma quasineutral. To shield the bulk plasma from the charged target, there is an oppositely (positively) charged sheath with a sharp electrostatic potential variation on the Debye length scale . In magnetised plasmas where the magnetic field is inclined at an oblique angle α with the target, some of the sheath potential variation occurs also on the ion sound gyroradius length scale , caused by finite ion gyro-orbit distortion and losses. We consider a collisionless and steady-state magnetised plasma sheath whose thickness is smaller than the characteristic length scale L of spatial fluctuations in the bulk plasma, such that the limit is appropriate. Spatial structures are assumed to be magnetic field-aligned. In the case of small magnetic field angle , electric fields tangential to the target transport ions towards the target via E × B drifts at a rate comparable to the one from parallel streaming. A generalised form of the kinetic Bohm–Chodura criterion at the sheath entrance is derived by requiring that the sheath electric field have a monotonic spatial decay far from the target. The criterion depends on tangential gradients of potential and ion distribution function, with additional nontrivial conditions.
与等离子体接触的固体目标会带电（负电），以反射移动性较强的物质（电子），从而保持等离子体的准中性。为了屏蔽带电目标对等离子体的影响，等离子体中存在一个带相反（正）电荷的鞘，其静电势在德拜长度尺度上有急剧的变化。在磁场与目标呈斜角 α 倾斜的磁化等离子体中，由于有限离子回旋轨道的扭曲和损耗，鞘势的部分变化也发生在离子声回旋长度尺度上。我们考虑的是一个无碰撞和稳态磁化等离子体鞘，其厚度小于体等离子体空间波动的特征长度尺度 L，因此极限是合适的。空间结构假定为磁场对齐。在磁场角较小的情况下，与目标相切的电场通过 E × B 漂移将离子输送到目标，其速率与平行流的速率相当。通过要求鞘电场在远离靶的地方有单调的空间衰减，得出了鞘入口处动力学博姆-乔杜拉准则的广义形式。该准则取决于电势和离子分布函数的切向梯度，以及附加的非难条件。
{"title":"Sheath constraints on turbulent magnetised plasmas","authors":"A Geraldini, S Brunner and F I Parra","doi":"10.1088/1361-6587/ad705a","DOIUrl":"https://doi.org/10.1088/1361-6587/ad705a","url":null,"abstract":"A solid target in contact with a plasma charges (negatively) to reflect the more mobile species (electrons) and thus keep the bulk plasma quasineutral. To shield the bulk plasma from the charged target, there is an oppositely (positively) charged sheath with a sharp electrostatic potential variation on the Debye length scale . In magnetised plasmas where the magnetic field is inclined at an oblique angle α with the target, some of the sheath potential variation occurs also on the ion sound gyroradius length scale , caused by finite ion gyro-orbit distortion and losses. We consider a collisionless and steady-state magnetised plasma sheath whose thickness is smaller than the characteristic length scale L of spatial fluctuations in the bulk plasma, such that the limit is appropriate. Spatial structures are assumed to be magnetic field-aligned. In the case of small magnetic field angle , electric fields tangential to the target transport ions towards the target via E × B drifts at a rate comparable to the one from parallel streaming. A generalised form of the kinetic Bohm–Chodura criterion at the sheath entrance is derived by requiring that the sheath electric field have a monotonic spatial decay far from the target. The criterion depends on tangential gradients of potential and ion distribution function, with additional nontrivial conditions.","PeriodicalId":20239,"journal":{"name":"Plasma Physics and Controlled Fusion","volume":"19 1","pages":""},"PeriodicalIF":2.2,"publicationDate":"2024-09-12","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142181224","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 : 2024-09-10DOI: 10.1088/1361-6587/ad75b7
Meihuizi He, Zongyu Yang, Songfen Liu, Fan Xia and Wulyu Zhong
During the operation of tokamak devices, addressing the thermal load issues caused by edge localized modes (ELMs) eruption is crucial. Ideally, mitigation and suppression measures for ELMs should be promptly initiated as soon as the first low-to-high confinement (L-H) transition occurs, which necessitates the real-time monitoring and accurate identification of the L-H transition process. Motivated by this, and by recent deep learning boom, we propose a deep learning-based L-H transition identification algorithm on HL-2A tokamak. In this work, we have constructed a neural network comprising layers of Residual long short-term memory and temporal convolutional network. Unlike previous work based on recognition for ELMs by slice, this method implements recognition on L-H transition process before the first ELMs crash. Therefore the mitigation techniques can be triggered in time to suppress the initial ELMs bursts. In order to further explain the effectiveness of the algorithm, we developed a series of evaluation indicators by shots, and the results show that this algorithm can provide necessary reference for the mitigation and suppression system.
在托卡马克装置的运行过程中，解决边缘局部模式（ELMs）爆发引起的热负荷问题至关重要。理想情况下，一旦发生第一次低约束到高约束（L-H）转变，就应立即启动缓解和抑制 ELM 的措施，这就需要实时监测和准确识别 L-H 转变过程。受此启发，并结合最近的深度学习热潮，我们在 HL-2A 托卡马克上提出了一种基于深度学习的 L-H 转换识别算法。在这项工作中，我们构建了一个由残余长短期记忆层和时序卷积网络层组成的神经网络。与以往基于分片识别 ELM 的工作不同，该方法在第一个 ELM 崩溃之前对 L-H 过渡过程进行识别。因此，缓解技术可以及时触发，以抑制最初的 ELMs 爆发。为了进一步说明该算法的有效性，我们通过拍摄制定了一系列评价指标，结果表明该算法可以为缓解和抑制系统提供必要的参考。
{"title":"Identifying L-H transition in HL-2A through deep learning","authors":"Meihuizi He, Zongyu Yang, Songfen Liu, Fan Xia and Wulyu Zhong","doi":"10.1088/1361-6587/ad75b7","DOIUrl":"https://doi.org/10.1088/1361-6587/ad75b7","url":null,"abstract":"During the operation of tokamak devices, addressing the thermal load issues caused by edge localized modes (ELMs) eruption is crucial. Ideally, mitigation and suppression measures for ELMs should be promptly initiated as soon as the first low-to-high confinement (L-H) transition occurs, which necessitates the real-time monitoring and accurate identification of the L-H transition process. Motivated by this, and by recent deep learning boom, we propose a deep learning-based L-H transition identification algorithm on HL-2A tokamak. In this work, we have constructed a neural network comprising layers of Residual long short-term memory and temporal convolutional network. Unlike previous work based on recognition for ELMs by slice, this method implements recognition on L-H transition process before the first ELMs crash. Therefore the mitigation techniques can be triggered in time to suppress the initial ELMs bursts. In order to further explain the effectiveness of the algorithm, we developed a series of evaluation indicators by shots, and the results show that this algorithm can provide necessary reference for the mitigation and suppression system.","PeriodicalId":20239,"journal":{"name":"Plasma Physics and Controlled Fusion","volume":"21 1","pages":""},"PeriodicalIF":2.2,"publicationDate":"2024-09-10","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142181219","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 : 2024-09-10DOI: 10.1088/1361-6587/ad7531
M Tobin, S A Sabbagh, V Zamkovska, J D Riquezes, J Butt, G Cunningham, L Kogan, J Measures, S Blackmore, C Ham, J Harrison, J W Berkery, S Gerhardt, J G Bak, J Lee, S W Yoon and the MAST Upgrade Team
Reliable vertical position control will be an essential element of any future tokamak-based fusion power plant in order to reduce disruptions and maximize performance. We investigate methods to improve vertical controllability boundary determination in plasma operational space and demonstrate a data-driven approach based on direct pseudoinversion of operational space data that is rigorously quantitative, applicable in real-time plasma control systems, and physically intuitive to interpret. Applied to historical shot data from entire run campaigns on the MAST-U, KSTAR, and NSTX tokamaks, this approach, implemented in DECAF, improves vertical displacement event identification accuracy to 98.9%–100%. Further, we explore the application of a physics-based vertical stability metric as an early warning forecaster for vertical displacement events. The development of a linear surrogate model for the plasma current density profile, with a coefficient of determination of 0.992 on the training dataset, enables potential employment of this forecaster in real-time. The application of this approach on historical data from the MAST-U MU02 campaign yields a forecaster with 62.6% accuracy, indicating promise for this method when further refined and potentially coupled with other stability metrics.
{"title":"Vertical instability forecasting and controllability assessment of multi-device tokamak plasmas in DECAF with data-driven optimization","authors":"M Tobin, S A Sabbagh, V Zamkovska, J D Riquezes, J Butt, G Cunningham, L Kogan, J Measures, S Blackmore, C Ham, J Harrison, J W Berkery, S Gerhardt, J G Bak, J Lee, S W Yoon and the MAST Upgrade Team","doi":"10.1088/1361-6587/ad7531","DOIUrl":"https://doi.org/10.1088/1361-6587/ad7531","url":null,"abstract":"Reliable vertical position control will be an essential element of any future tokamak-based fusion power plant in order to reduce disruptions and maximize performance. We investigate methods to improve vertical controllability boundary determination in plasma operational space and demonstrate a data-driven approach based on direct pseudoinversion of operational space data that is rigorously quantitative, applicable in real-time plasma control systems, and physically intuitive to interpret. Applied to historical shot data from entire run campaigns on the MAST-U, KSTAR, and NSTX tokamaks, this approach, implemented in DECAF, improves vertical displacement event identification accuracy to 98.9%–100%. Further, we explore the application of a physics-based vertical stability metric as an early warning forecaster for vertical displacement events. The development of a linear surrogate model for the plasma current density profile, with a coefficient of determination of 0.992 on the training dataset, enables potential employment of this forecaster in real-time. The application of this approach on historical data from the MAST-U MU02 campaign yields a forecaster with 62.6% accuracy, indicating promise for this method when further refined and potentially coupled with other stability metrics.","PeriodicalId":20239,"journal":{"name":"Plasma Physics and Controlled Fusion","volume":"145 1","pages":""},"PeriodicalIF":2.2,"publicationDate":"2024-09-10","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142181200","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 : 2024-09-09DOI: 10.1088/1361-6587/ad6f40
K E Thome, M E Austin, A Hyatt, A Marinoni, A O Nelson, C Paz-Soldan, F Scotti, W Boyes, L Casali, C Chrystal, S Ding, X D Du, D Eldon, D Ernst, R Hong, G R McKee, S Mordijck, O Sauter, L Schmitz, J L Barr, M G Burke, S Coda, T B Cote, M E Fenstermacher, A Garofalo, F O Khabanov, G J Kramer, C J Lasnier, N C Logan, P Lunia, A G McLean, M Okabayashi, D Shiraki, S Stewart, Y Takemura, D D Truong, T Osborne, M A Van Zeeland, B S Victor, H Q Wang, J G Watkins, W P Wehner, A S Welander, T M Wilks, J Yang, G Yu, L Zeng and the DIII-D Team
Negative triangularity (NT) is a potentially transformative configuration for tokamak-based fusion energy with its high-performance core, edge localized mode (ELM)-free edge, and low-field-side divertors that could readily scale to an integrated reactor solution. Previous NT work on the TCV and DIII-D tokamaks motivated the installation of graphite-tile armor on the low-field-side lower outer wall of DIII-D. A dedicated multiple-week experimental campaign was conducted to qualify the NT scenario for future reactors. During the DIII-D NT campaign, high confinement ( 1), high current ( 3), and high normalized pressure plasmas ( 2.5) were simultaneously attained in strongly NT-shaped discharges with average triangularity = −0.5 that were stably controlled. Experiments covered a wide range of DIII-D operational space (plasma current, toroidal field, electron density and pressure) and did not trigger an ELM in a single discharge as long as sufficiently strong NT was maintained; in contrast, to other high-performance ELM-suppression scenarios that have narrower operating windows. These strong NT plasmas had a lower outer divertor X-point shape and maintained a non-ELMing edge with an electron temperature pedestal, exceeding that of typical L-mode plasmas. Also, the following was achieved during the campaign: high normalized density ( / of at least 1.7), particle confinement comparable to energy confinement with , a detached divertor without impurity seeding, and a mantle radiation scenario using extrinsic impurities. These results are promising for a NT fusion pilot plant but further questions on confinement extrapolation and core-edge integration remain, which motivate future NT studies on DIII-D and beyond.
负三角形（NT）是托卡马克核聚变能源的一种潜在变革性配置，它具有高性能堆芯、无边缘局部模式（ELM）边缘和低场边分流器，可以很容易地扩展到集成反应堆解决方案。先前在 TCV 和 DIII-D 托卡马克上进行的 NT 工作促使在 DIII-D 的低场侧下部外壁上安装石墨瓦铠装。为了验证未来反应堆的NT方案，专门进行了为期多周的实验活动。在 DIII-D NT 活动期间，在稳定控制的平均三角形 = -0.5 的强 NT 形放电中，同时实现了高约束（1）、高电流（3）和高归一化压力等离子体（2.5）。实验覆盖了 DIII-D 的广泛操作空间（等离子体电流、环形场、电子密度和压力），只要保持足够强的 NT，就不会在单次放电中触发 ELM；这与其他操作窗口较窄的高性能 ELM 抑制方案形成了鲜明对比。这些强NT等离子体具有较低的外部分流器X点形状，并保持着非ELM边缘和电子温度基座，超过了典型的L模式等离子体。此外，在这项活动中还取得了以下成果：高归一化密度（/至少为1.7），粒子约束与能量约束、无杂质播种的分离式分流器和使用外在杂质的地幔辐射方案相当。这些结果对于建立一个近地核聚变试验装置是很有希望的，但在约束外推法和核边缘整合方面仍存在进一步的问题，这促使未来在DIII-D及更远的地方开展近地核聚变研究。
{"title":"Overview of results from the 2023 DIII-D negative triangularity campaign","authors":"K E Thome, M E Austin, A Hyatt, A Marinoni, A O Nelson, C Paz-Soldan, F Scotti, W Boyes, L Casali, C Chrystal, S Ding, X D Du, D Eldon, D Ernst, R Hong, G R McKee, S Mordijck, O Sauter, L Schmitz, J L Barr, M G Burke, S Coda, T B Cote, M E Fenstermacher, A Garofalo, F O Khabanov, G J Kramer, C J Lasnier, N C Logan, P Lunia, A G McLean, M Okabayashi, D Shiraki, S Stewart, Y Takemura, D D Truong, T Osborne, M A Van Zeeland, B S Victor, H Q Wang, J G Watkins, W P Wehner, A S Welander, T M Wilks, J Yang, G Yu, L Zeng and the DIII-D Team","doi":"10.1088/1361-6587/ad6f40","DOIUrl":"https://doi.org/10.1088/1361-6587/ad6f40","url":null,"abstract":"Negative triangularity (NT) is a potentially transformative configuration for tokamak-based fusion energy with its high-performance core, edge localized mode (ELM)-free edge, and low-field-side divertors that could readily scale to an integrated reactor solution. Previous NT work on the TCV and DIII-D tokamaks motivated the installation of graphite-tile armor on the low-field-side lower outer wall of DIII-D. A dedicated multiple-week experimental campaign was conducted to qualify the NT scenario for future reactors. During the DIII-D NT campaign, high confinement ( 1), high current ( 3), and high normalized pressure plasmas ( 2.5) were simultaneously attained in strongly NT-shaped discharges with average triangularity = −0.5 that were stably controlled. Experiments covered a wide range of DIII-D operational space (plasma current, toroidal field, electron density and pressure) and did not trigger an ELM in a single discharge as long as sufficiently strong NT was maintained; in contrast, to other high-performance ELM-suppression scenarios that have narrower operating windows. These strong NT plasmas had a lower outer divertor X-point shape and maintained a non-ELMing edge with an electron temperature pedestal, exceeding that of typical L-mode plasmas. Also, the following was achieved during the campaign: high normalized density ( / of at least 1.7), particle confinement comparable to energy confinement with , a detached divertor without impurity seeding, and a mantle radiation scenario using extrinsic impurities. These results are promising for a NT fusion pilot plant but further questions on confinement extrapolation and core-edge integration remain, which motivate future NT studies on DIII-D and beyond.","PeriodicalId":20239,"journal":{"name":"Plasma Physics and Controlled Fusion","volume":"17 1","pages":""},"PeriodicalIF":2.2,"publicationDate":"2024-09-09","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142181220","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 : 2024-09-09DOI: 10.1088/1361-6587/ad6c7c
A von Boetticher, F I Parra, M Barnes
We introduce a gyrokinetic, linearised Fokker–Planck collision model that satisfies conservation laws and is accurate at arbitrary collisionalities. The differential test-particle component of the operator is exact; the integral field-particle component is approximated using a spherical harmonic and a modified Laguerre polynomial expansion developed by Hirshman and Sigmar (1976 Phys. Fluids19 1532). The numerical methods of the implementation in the δf-gyrokinetic code stella (Barnes et al 2019 J. Comput. Phys.391 365–80) are discussed, and conservation properties of the operator are demonstrated. The collision model is then benchmarked against the collision model of the gyrokinetic solver GS2 in the limiting cases of a reduced test-particle collision operator and energy- and momentum-conserving operator. The accuracy of the full collision model is investigated by solving the parallel Spitzer-Härm problem for the transport coefficients. It is shown that retaining collisional energy flux and higher-order terms in the field-particle operator reduces errors in the transport coefficients from 10%–25% for a simple momentum- and energy-conserving model to under 1%.
{"title":"Linearised Fokker–Planck collision model for gyrokinetic simulations","authors":"A von Boetticher, F I Parra, M Barnes","doi":"10.1088/1361-6587/ad6c7c","DOIUrl":"https://doi.org/10.1088/1361-6587/ad6c7c","url":null,"abstract":"We introduce a gyrokinetic, linearised Fokker–Planck collision model that satisfies conservation laws and is accurate at arbitrary collisionalities. The differential test-particle component of the operator is exact; the integral field-particle component is approximated using a spherical harmonic and a modified Laguerre polynomial expansion developed by Hirshman and Sigmar (1976 <italic toggle=\"yes\">Phys. Fluids</italic> <bold>19</bold> 1532). The numerical methods of the implementation in the δ<italic toggle=\"yes\">f</italic>-gyrokinetic code <inline-formula>\u0000<tex-math><?CDATA $texttt{stella}$?></tex-math><mml:math overflow=\"scroll\"><mml:mrow><mml:mtext mathvariant=\"monospace\">stella</mml:mtext></mml:mrow></mml:math><inline-graphic xlink:href=\"ppcfad6c7cieqn1.gif\"></inline-graphic></inline-formula> (Barnes <italic toggle=\"yes\">et al</italic> 2019 <italic toggle=\"yes\">J. Comput. Phys.</italic> <bold>391</bold> 365–80) are discussed, and conservation properties of the operator are demonstrated. The collision model is then benchmarked against the collision model of the gyrokinetic solver <monospace>GS2</monospace> in the limiting cases of a reduced test-particle collision operator and energy- and momentum-conserving operator. The accuracy of the full collision model is investigated by solving the parallel Spitzer-Härm problem for the transport coefficients. It is shown that retaining collisional energy flux and higher-order terms in the field-particle operator reduces errors in the transport coefficients from 10%–25% for a simple momentum- and energy-conserving model to under 1%.","PeriodicalId":20239,"journal":{"name":"Plasma Physics and Controlled Fusion","volume":"2 1","pages":""},"PeriodicalIF":2.2,"publicationDate":"2024-09-09","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142181221","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 : 2024-09-09DOI: 10.1088/1361-6587/ad75b8
J Yang, E D Fredrickson, Q Hu, M Podestà, J W Berkery, L Bardóczi, R J La Haye, O Sauter, M Austin, E Strait and C Chrystal
The measurements using the high resolution electron cyclotron emission radiometry and the charge exchange and recombination spectroscopy are processed using analytic formulas to allow for the detection of islands as small as 1.9 cm. In contrast to large, saturated magnetic islands which are relatively well understood to be governed by the loss of bootstrap current inside the island, small islands are less well understood due to the difficulty of their accurate measurement in tokamaks. Here, ‘small’ islands are islands comparable in size to the ion banana width, which can be as small as 0.8 cm at DIII-D. The new measurement methods allow for the detection of small island widths when the predicted increase of mode frequency to match the Doppler shifted ion diamagnetic frequency is observed. Therefore, for the first time, the mode frequency increase can be unambiguously associated to the acceleration of the magnetic island propagation. Such association allows for a further development and validation of the much-debated theory of ion polarization currents, which is thought to govern the small island growth.
{"title":"Measurement of small island characteristics using high resolution ECE and CER at DIII-D","authors":"J Yang, E D Fredrickson, Q Hu, M Podestà, J W Berkery, L Bardóczi, R J La Haye, O Sauter, M Austin, E Strait and C Chrystal","doi":"10.1088/1361-6587/ad75b8","DOIUrl":"https://doi.org/10.1088/1361-6587/ad75b8","url":null,"abstract":"The measurements using the high resolution electron cyclotron emission radiometry and the charge exchange and recombination spectroscopy are processed using analytic formulas to allow for the detection of islands as small as 1.9 cm. In contrast to large, saturated magnetic islands which are relatively well understood to be governed by the loss of bootstrap current inside the island, small islands are less well understood due to the difficulty of their accurate measurement in tokamaks. Here, ‘small’ islands are islands comparable in size to the ion banana width, which can be as small as 0.8 cm at DIII-D. The new measurement methods allow for the detection of small island widths when the predicted increase of mode frequency to match the Doppler shifted ion diamagnetic frequency is observed. Therefore, for the first time, the mode frequency increase can be unambiguously associated to the acceleration of the magnetic island propagation. Such association allows for a further development and validation of the much-debated theory of ion polarization currents, which is thought to govern the small island growth.","PeriodicalId":20239,"journal":{"name":"Plasma Physics and Controlled Fusion","volume":"115 1","pages":""},"PeriodicalIF":2.2,"publicationDate":"2024-09-09","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142181222","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 : 2024-09-06DOI: 10.1088/1361-6587/ad7289
Jasmin Joshi-Thompson, Mirko Ramisch
Langmuir probes have been widely used in the field of plasma diagnostics for the characterisation of plasma properties. These probes play a crucial role in understanding the behaviour of a diverse range of plasmas, e.g. edge plasmas in fusion experiments. The measurement of electron density (ne) and electron temperature (Te) provides valuable insights into the plasma’s state, stability, and confinement properties. Conventionally, this analysis involves post-experiment fitting methods to calculate plasma properties from the measured current–voltage curves obtained from Langmuir probes. This work introduces a neural-network approach for analysing probe data from the TJ-K stellarator, allowing for fast associative plasma characterisation. The results show a reliable performance on test data within the domain of the training set, predicting both ne and Te within the 10 % intrinsic error. Performance on unseen data outside the domain of the training set was on average within a 26 % and 21 % error on ne and Te, respectively. The network’s further abilities, including the identification of low-quality and falsely-labelled data, were also explored. The use of neural networks (NNs) offers fast predictions, enabling further research into real-time applications and live feedback control. This paper highlights the promising role of NNs in enhancing the analysis of Langmuir-probe characteristics.
朗缪尔探针已广泛应用于等离子体诊断领域，用于描述等离子体的特性。这些探针在了解各种等离子体（如核聚变实验中的边缘等离子体）的行为方面发挥着至关重要的作用。通过测量电子密度（ne）和电子温度（Te），可以深入了解等离子体的状态、稳定性和约束特性。传统的分析方法是在实验后采用拟合方法，根据朗缪尔探针测得的电流-电压曲线计算等离子体特性。这项工作引入了一种神经网络方法，用于分析来自 TJ-K 恒星仪的探针数据，从而实现快速关联等离子体特性分析。结果表明，在训练集域内的测试数据上，神经网络具有可靠的性能，对 ne 和 Te 的预测误差在 10% 的固有误差范围内。在训练集范围之外的未见数据上，氖和碲的平均误差分别为 26% 和 21%。此外，还探讨了该网络的其他能力，包括识别低质量数据和虚假标签数据的能力。神经网络（NN）的使用提供了快速预测，使实时应用和实时反馈控制方面的研究得以深入。本文强调了神经网络在增强朗缪尔探针特性分析中的重要作用。
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Pub Date : 2024-09-05DOI: 10.1088/1361-6587/ad6a83
A O Nelson, L Schmitz, T Cote, J F Parisi, S Stewart, C Paz-Soldan, K E Thome, M E Austin, F Scotti, J L Barr, A Hyatt, N Leuthold, A Marinoni, T Neiser, T Osborne, N Richner, A S Welander, W P Wehner, R Wilcox, T M Wilks, J Yang, the DIII-D Team3
Tokamak plasmas with strong negative triangularity (NT) shaping typically exhibit fundamentally different edge behavior than conventional L-mode or H-mode plasmas. On DIII-D, every plasma with sufficiently negative triangularity (δ<δcrit≃−0.12) is found to be inherently free of edge localized modes (ELMs), even at injected powers well above the predicted L-H power threshold. It is also possible to access an ELM-free state at weaker average triangularities, provided that at least one of the two x-points is still sufficiently negative. Access to the ELM-free NT scenario is found to coincide with the closure of the second stability region for infinite-n ballooning modes, suggesting that ballooning stability may play a role in limiting the accessible pressure gradient in NT plasmas. Despite this, NT plasmas are able to support small pedestals and are typically characterized by an enhancement of edge pressure gradients beyond those found in traditional L-mode plasmas. Furthermore, the pressure gradient inside of this small pedestal is unusually steep, allowing access to high core performance that is competitive with other ELM-free regimes previously achieved on DIII-D. Since ELM-free operation in NT is linked directly to the magnetic geometry, NT fusion pilot plants are predicted to maintain advantageous edge conditions even in burning plasma regimes, potentially eliminating reactor core-integration issues caused by ELMs.
与传统的 L 模式或 H 模式等离子体相比，具有强负三角形（NT）形状的托卡马克等离子体通常会表现出根本不同的边缘行为。在 DIII-D 上，我们发现每一个具有足够负三角形（δ<δcrit≃-0.12）的等离子体本质上都不存在边缘局部模式（ELM），即使注入功率远高于预测的 L-H 功率阈值。只要两个 x 点中至少有一个仍然足够负，也有可能在较弱的平均三角形下进入无 ELM 状态。进入无 ELM 的 NT 情景与无限 n 气球模式第二个稳定区域的关闭相吻合，这表明气球稳定性可能在限制 NT 等离子体中可获得的压力梯度方面发挥作用。尽管如此，NT 等离子体仍能支持小基座，其典型特征是边缘压力梯度的增强超过了传统 L 模式等离子体。此外，这种小基座内部的压力梯度异常陡峭，因此可以获得与之前在 DIII-D 上实现的其他无 ELM 状态相媲美的高核心性能。由于 NT 中的无 ELM 运行与磁几何学直接相关，因此预计 NT 核聚变试验装置即使在燃烧等离子体状态下也能保持有利的边缘条件，从而有可能消除 ELM 导致的反应堆堆芯集成问题。
{"title":"Characterization of the ELM-free negative triangularity edge on DIII-D","authors":"A O Nelson, L Schmitz, T Cote, J F Parisi, S Stewart, C Paz-Soldan, K E Thome, M E Austin, F Scotti, J L Barr, A Hyatt, N Leuthold, A Marinoni, T Neiser, T Osborne, N Richner, A S Welander, W P Wehner, R Wilcox, T M Wilks, J Yang, the DIII-D Team3","doi":"10.1088/1361-6587/ad6a83","DOIUrl":"https://doi.org/10.1088/1361-6587/ad6a83","url":null,"abstract":"Tokamak plasmas with strong negative triangularity (NT) shaping typically exhibit fundamentally different edge behavior than conventional L-mode or H-mode plasmas. On DIII-D, every plasma with sufficiently negative triangularity (<inline-formula>\u0000<tex-math><?CDATA $delta lt delta_mathrm{crit}simeq-0.12$?></tex-math><mml:math overflow=\"scroll\"><mml:mrow><mml:mi>δ</mml:mi><mml:mo><</mml:mo><mml:msub><mml:mi>δ</mml:mi><mml:mrow><mml:mi>crit</mml:mi></mml:mrow></mml:msub><mml:mo>≃</mml:mo><mml:mo>−</mml:mo><mml:mn>0.12</mml:mn></mml:mrow></mml:math><inline-graphic xlink:href=\"ppcfad6a83ieqn1.gif\"></inline-graphic></inline-formula>) is found to be inherently free of edge localized modes (ELMs), even at injected powers well above the predicted L-H power threshold. It is also possible to access an ELM-free state at weaker average triangularities, provided that at least one of the two <italic toggle=\"yes\">x</italic>-points is still sufficiently negative. Access to the ELM-free NT scenario is found to coincide with the closure of the second stability region for infinite-<italic toggle=\"yes\">n</italic> ballooning modes, suggesting that ballooning stability may play a role in limiting the accessible pressure gradient in NT plasmas. Despite this, NT plasmas are able to support small pedestals and are typically characterized by an enhancement of edge pressure gradients beyond those found in traditional L-mode plasmas. Furthermore, the pressure gradient inside of this small pedestal is unusually steep, allowing access to high core performance that is competitive with other ELM-free regimes previously achieved on DIII-D. Since ELM-free operation in NT is linked directly to the magnetic geometry, NT fusion pilot plants are predicted to maintain advantageous edge conditions even in burning plasma regimes, potentially eliminating reactor core-integration issues caused by ELMs.","PeriodicalId":20239,"journal":{"name":"Plasma Physics and Controlled Fusion","volume":"86 1","pages":""},"PeriodicalIF":2.2,"publicationDate":"2024-09-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142181225","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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