Pub Date : 2024-09-09DOI: 10.1088/1741-4326/ad6a6e
K.A. Jadeja, J. Ghosh, K.M. Patel, A.B. Patel, R.L. Tanna, Kiran Patel, B.G. Arambhadiya, K.D. Galodiya, Rohit Kumar, S. Aich, Harshita Raj, L. Pradhan, M.B. Chowdhuri, R. Manchanda, N. Ramaiya, Nandini Yadava, Sharvil Patel, Kajal Shah, Dipexa Modi, A. Gauttam, K. Singh, S. Dolui, Ankit Kumar, B. Hegde, A. Kumawat, Minsha Shah, R. Rajpal, U. Nagora, P.K. Atrey, S.K. Pathak, Shishir Purohit, A. Adhiya, Manoj Kumar, Kumudni Assudani, D. Kumavat, S.K. Jha, K.S. Shah, M.N. Makwana, Shivam Gupta, Supriya Nair, Kishore Mishra, D. Raju, P.K. Chattopadhyay, B.R. Kataria
Effective control of impurities and precise regulation of the fueling gas are supreme prerequisites for optimal operation in any fusion device. Conventional wall-conditioning methods fall short of achieving optimal wall conditioning. Conventional wall-conditioning methods, such as vessel baking and H2/(D2)-fueled glow discharge cleaning (GDC), are generally required to remove wall-absorbed impurities in bulk after vessel venting. The excess amount of hydrogen, injected during H2 GDC, can be reduced by helium (He)-fueled GDC. However, He removal from the vessel is more challenging due to its low molecular mass, very low condensation temperature, and inert characteristics. In ADITYA-U, optimal wall conditioning cannot be achieved using H2 followed by He-fueled GDC when applied for extended periods spanning hours or days. A GDC with a mixture of argon and hydrogen (Ar–H2) is introduced in the ADITYA-U tokamak to obtain better wall conditioning than H2 followed by He GDC. In Ar–H2 GDC, long-lived ArH+ ions are formed in sufficient numbers and accelerated toward the vessel wall with high momentum. This results in the breaking of high energy bonds of impurities with the wall/plasma facing components, which is not possible by H+, H2+, H3+ ions in H2 GDC due to their lower momentum. An optimal blend ratio of Ar to H2 is established at 15%–20% for the mixture. This composition ensures that the introduction of high-Z Ar does not adversely affect tokamak plasma operations. The C- and O-containing impurities are reduced beyond the limit of the prolonged operation of H2 GDC. Relative low pressures of dominant impurities such as CO, CH4, and H2O are obtained due to the Ar–H2 GDC compared to routinely operated H2 GDC. A comparison study of H2 GDC and the developed Ar–H2 GDC is performed in terms of wall conditioning and tokamak plasma operation. The encouraging results of the Ar–H2 GDC are obtained in both wall cleaning and tokamak operation scenarios in the midsize tokamak ADITYA-U. This development and application of Ar–H2 GDC are beneficial for large-sized fusion devices, leading to improved impurity reduction, reduced operational fuel consumption (H2/D2/He), and enhanced control over fuel recycling/extraction.
有效控制杂质和精确调节燃料气体是任何聚变装置实现最佳运行的最高前提。传统的壁调节方法无法实现最佳的壁调节效果。传统的壁处理方法，如容器烘烤和以 H2/(D2)为燃料的辉光放电清洗 (GDC)，通常需要在容器排气后大量清除壁吸收的杂质。以氦（He）为燃料的 GDC 可以减少 H2 GDC 过程中注入的过量氢气。然而，由于氦气的分子质量低、冷凝温度极低，且具有惰性，因此从容器中去除氦气更具挑战性。在 ADITYA-U 中，使用 H2 后再使用以 He 为燃料的 GDC 时，如果使用时间长达数小时或数天，则无法达到最佳的壁调节效果。在 ADITYA-U 托卡马克中引入了氩氢混合物（Ar-H2）的 GDC，以获得比 H2 和 He GDC 更佳的壁调节效果。在 Ar-H2 GDC 中，会形成足够数量的长寿命 ArH+ 离子，并以高动量加速冲向容器壁。这将导致杂质与器壁/等离子面对的成分之间的高能键断裂，而 H2 GDC 中的 H+、H2+、H3+ 离子由于动量较小，无法实现这一点。混合物中 Ar 与 H2 的最佳混合比例为 15%-20%。这种成分可确保高 Z Ar 的引入不会对托卡马克等离子体的运行产生不利影响。含 C 和 O 的杂质减少到超过 H2 GDC 长期运行的极限。与常规运行的 H2 GDC 相比，Ar-H2 GDC 获得了 CO、CH4 和 H2O 等主要杂质的相对低压。在壁调节和托卡马克等离子体运行方面，对 H2 GDC 和开发的 Ar-H2 GDC 进行了比较研究。在中型托卡马克 ADITYA-U 中，Ar-H2 GDC 在壁清洁和托卡马克运行情况下都取得了令人鼓舞的结果。Ar-H2 GDC 的开发和应用有利于大型核聚变装置，从而减少杂质，降低运行燃料消耗（H2/D2/He），并加强对燃料回收/提取的控制。
{"title":"Plasma performance enhancement and impurity control using a novel technique of argon–hydrogen mixture fueled glow discharge wall conditioning in the ADITYA-U tokamak","authors":"K.A. Jadeja, J. Ghosh, K.M. Patel, A.B. Patel, R.L. Tanna, Kiran Patel, B.G. Arambhadiya, K.D. Galodiya, Rohit Kumar, S. Aich, Harshita Raj, L. Pradhan, M.B. Chowdhuri, R. Manchanda, N. Ramaiya, Nandini Yadava, Sharvil Patel, Kajal Shah, Dipexa Modi, A. Gauttam, K. Singh, S. Dolui, Ankit Kumar, B. Hegde, A. Kumawat, Minsha Shah, R. Rajpal, U. Nagora, P.K. Atrey, S.K. Pathak, Shishir Purohit, A. Adhiya, Manoj Kumar, Kumudni Assudani, D. Kumavat, S.K. Jha, K.S. Shah, M.N. Makwana, Shivam Gupta, Supriya Nair, Kishore Mishra, D. Raju, P.K. Chattopadhyay, B.R. Kataria","doi":"10.1088/1741-4326/ad6a6e","DOIUrl":"https://doi.org/10.1088/1741-4326/ad6a6e","url":null,"abstract":"Effective control of impurities and precise regulation of the fueling gas are supreme prerequisites for optimal operation in any fusion device. Conventional wall-conditioning methods fall short of achieving optimal wall conditioning. Conventional wall-conditioning methods, such as vessel baking and H<sub>2</sub>/(D<sub>2</sub>)-fueled glow discharge cleaning (GDC), are generally required to remove wall-absorbed impurities in bulk after vessel venting. The excess amount of hydrogen, injected during H<sub>2</sub> GDC, can be reduced by helium (He)-fueled GDC. However, He removal from the vessel is more challenging due to its low molecular mass, very low condensation temperature, and inert characteristics. In ADITYA-U, optimal wall conditioning cannot be achieved using H<sub>2</sub> followed by He-fueled GDC when applied for extended periods spanning hours or days. A GDC with a mixture of argon and hydrogen (Ar–H<sub>2</sub>) is introduced in the ADITYA-U tokamak to obtain better wall conditioning than H<sub>2</sub> followed by He GDC. In Ar–H<sub>2</sub> GDC, long-lived ArH<sup>+</sup> ions are formed in sufficient numbers and accelerated toward the vessel wall with high momentum. This results in the breaking of high energy bonds of impurities with the wall/plasma facing components, which is not possible by H<sup>+</sup>, H<sub>2</sub><sup>+,</sup> H<sub>3</sub><sup>+</sup> ions in H<sub>2</sub> GDC due to their lower momentum. An optimal blend ratio of Ar to H<sub>2</sub> is established at 15%–20% for the mixture. This composition ensures that the introduction of high-<italic toggle=\"yes\">Z</italic> Ar does not adversely affect tokamak plasma operations. The C- and O-containing impurities are reduced beyond the limit of the prolonged operation of H<sub>2</sub> GDC. Relative low pressures of dominant impurities such as CO, CH<sub>4</sub>, and H<sub>2</sub>O are obtained due to the Ar–H<sub>2</sub> GDC compared to routinely operated H<sub>2</sub> GDC. A comparison study of H<sub>2</sub> GDC and the developed Ar–H<sub>2</sub> GDC is performed in terms of wall conditioning and tokamak plasma operation. The encouraging results of the Ar–H<sub>2</sub> GDC are obtained in both wall cleaning and tokamak operation scenarios in the midsize tokamak ADITYA-U. This development and application of Ar–H<sub>2</sub> GDC are beneficial for large-sized fusion devices, leading to improved impurity reduction, reduced operational fuel consumption (H<sub>2</sub>/D<sub>2</sub>/He), and enhanced control over fuel recycling/extraction.","PeriodicalId":19379,"journal":{"name":"Nuclear Fusion","volume":"12 1","pages":""},"PeriodicalIF":3.3,"publicationDate":"2024-09-09","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142211962","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"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}
We directly optimize stellarator neoclassical ion transport while holding neoclassical electron transport at a moderate level, creating a scenario favorable for impurity expulsion and retaining good ion confinement. Traditional neoclassical stellarator optimization has focused on minimizing , the geometric factor that characterizes the amount of radial transport due to particles in the regime. Under expected reactor-relevant conditions, core electrons will be in the regime and core fuel ions will be in the regime. Traditional optimizations thus minimize electron transport and rely on the radial electric field (Er) that develops to confine the ions. This often results in an inward-pointing Er that drives high-Z impurities into the core, which may be troublesome in future reactors. In this work, we increase the ratio of the thermal transport coefficients , which previous research has shown can create an outward-pointing Er. This effect is very beneficial for impurity expulsion. We obtain self-consistent density, temperature, and Er profiles at reactor-relevant conditions for an optimized equilibrium. This equilibrium is expected to enjoy significantly improved impurity transport properties.
我们直接优化了恒星器的新古典离子传输，同时将新古典电子传输保持在中等水平，从而创造了一种有利于杂质驱逐并保持良好离子约束的环境。传统的新古典恒星器优化主要集中在最大限度地减小 ，该几何因子表征了粒子在该系统中的径向传输量。在预期的反应堆相关条件下，堆芯电子将处于态，堆芯燃料离子将处于态。因此，传统的优化方法最大限度地减少了电子传输，而依赖于为限制离子而形成的径向电场（Er）。这通常会导致向内的 Er，从而将高 Z 杂质带入堆芯，这可能会给未来的反应堆带来麻烦。在这项工作中，我们提高了热传输系数的比值，之前的研究表明这可以产生向外的 Er。这种效应对杂质排出非常有利。我们在反应堆相关条件下获得了自洽的密度、温度和 Er 曲线，并优化了平衡。这种平衡有望显著改善杂质迁移特性。
{"title":"Direct optimization of neoclassical ion transport in stellarator reactors","authors":"B.F. Lee, S.A. Lazerson, H.M. Smith, C.D. Beidler and N.A. Pablant","doi":"10.1088/1741-4326/ad75a6","DOIUrl":"https://doi.org/10.1088/1741-4326/ad75a6","url":null,"abstract":"We directly optimize stellarator neoclassical ion transport while holding neoclassical electron transport at a moderate level, creating a scenario favorable for impurity expulsion and retaining good ion confinement. Traditional neoclassical stellarator optimization has focused on minimizing , the geometric factor that characterizes the amount of radial transport due to particles in the regime. Under expected reactor-relevant conditions, core electrons will be in the regime and core fuel ions will be in the regime. Traditional optimizations thus minimize electron transport and rely on the radial electric field (Er) that develops to confine the ions. This often results in an inward-pointing Er that drives high-Z impurities into the core, which may be troublesome in future reactors. In this work, we increase the ratio of the thermal transport coefficients , which previous research has shown can create an outward-pointing Er. This effect is very beneficial for impurity expulsion. We obtain self-consistent density, temperature, and Er profiles at reactor-relevant conditions for an optimized equilibrium. This equilibrium is expected to enjoy significantly improved impurity transport properties.","PeriodicalId":19379,"journal":{"name":"Nuclear Fusion","volume":"61 1","pages":""},"PeriodicalIF":3.3,"publicationDate":"2024-09-09","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142211952","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"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: 10.1088/1741-4326/ad7304
Minseok Kim, W.H. Ko, Sehyun Kwak, Semin Joung, Wonjun Lee, B. Kim, D. Kim, J.H. Lee, Choongki Sung, Yong-Su Na and Y.-C. Ghim
We propose an outlier-resilient Gaussian process regression (GPR) model supported by support vector machine regression (SVMR) for kinetic profile inference. GPR, being a non-parametric regression using Bayesian statistics, has advantages in that it imposes no constraints on profile shapes and can be readily used to integrate different kinds of diagnostics, while it is vulnerable to the presence of even a single outlier among a measured dataset. As an outlier classifier, an optimized SVMR is developed based only on the measurements. Hyper-parameters of the developed GPR model with informative prior distributions are treated in two different ways, i.e. maximum a posteriori (MAP) estimator and marginalization using a Markov Chain Monte Carlo sampler. Our SVMR-supported GPR model is applied to infer ion temperature Ti profiles using measured data from the KSTAR charge exchange spectroscopy system. The GPR-inferred Ti profiles with and without an outlier are compared and show prominent improvement when the outlier is removed by the SVMR. Ti profiles inferred with the MAP estimator and the marginalization scheme are compared. They are noticeably different when observation uncertainties are not small enough, and the marginalization scheme generally provides a smoother profile.
我们提出了一种由支持向量机回归（SVMR）支持的抗离群高斯过程回归（GPR）模型，用于动力学剖面推断。高斯过程回归是一种使用贝叶斯统计的非参数回归，它的优点是对剖面形状不加限制，可随时用于整合不同类型的诊断，但它也容易受到测量数据集中即使是一个离群点的影响。作为离群点分类器，我们只根据测量数据开发了一种优化的 SVMR。所开发的具有信息先验分布的 GPR 模型的超参数以两种不同的方式处理，即最大后验（MAP）估计器和使用马尔可夫链蒙特卡罗采样器的边际化。利用 KSTAR 电荷交换光谱系统的测量数据，我们将 SVMR 支持的 GPR 模型应用于推断离子温度 Ti 曲线。比较了有离群点和无离群点的 GPR 推断 Ti 曲线，结果表明 SVMR 去除离群点后，推断结果有明显改善。比较了使用 MAP 估计器和边际化方案推断出的 Ti 剖面。在观测不确定性不够小的情况下，它们之间存在明显差异，边际化方案通常能提供更平滑的曲线。
{"title":"Kinetic profile inference with outlier detection using support vector machine regression and Gaussian process regression","authors":"Minseok Kim, W.H. Ko, Sehyun Kwak, Semin Joung, Wonjun Lee, B. Kim, D. Kim, J.H. Lee, Choongki Sung, Yong-Su Na and Y.-C. Ghim","doi":"10.1088/1741-4326/ad7304","DOIUrl":"https://doi.org/10.1088/1741-4326/ad7304","url":null,"abstract":"We propose an outlier-resilient Gaussian process regression (GPR) model supported by support vector machine regression (SVMR) for kinetic profile inference. GPR, being a non-parametric regression using Bayesian statistics, has advantages in that it imposes no constraints on profile shapes and can be readily used to integrate different kinds of diagnostics, while it is vulnerable to the presence of even a single outlier among a measured dataset. As an outlier classifier, an optimized SVMR is developed based only on the measurements. Hyper-parameters of the developed GPR model with informative prior distributions are treated in two different ways, i.e. maximum a posteriori (MAP) estimator and marginalization using a Markov Chain Monte Carlo sampler. Our SVMR-supported GPR model is applied to infer ion temperature Ti profiles using measured data from the KSTAR charge exchange spectroscopy system. The GPR-inferred Ti profiles with and without an outlier are compared and show prominent improvement when the outlier is removed by the SVMR. Ti profiles inferred with the MAP estimator and the marginalization scheme are compared. They are noticeably different when observation uncertainties are not small enough, and the marginalization scheme generally provides a smoother profile.","PeriodicalId":19379,"journal":{"name":"Nuclear Fusion","volume":"9 1","pages":""},"PeriodicalIF":3.3,"publicationDate":"2024-09-09","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142211950","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"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: 10.1088/1741-4326/ad70cc
Yu.V. Kovtun, S. Kamio, V.E. Moiseenko, H. Kasahara, T. Seki, K. Saito, R. Seki, S. Masuzaki, S. Brezinsek, A. Dinklage
The results of the first experimental series to produce a plasma using the radio frequency discharge (RF) above the ion cyclotron frequency at relatively low magnetic fields (0.5–0.6 T) in the Large Helical Device (LHD) are presented 1.43 MW of RF power produced target plasma with density up to 6 × 1018 m−3 to deuterium. Tangential NBI application into such a plasma increases plasma parameters. Electron temperatures up to ≈0.9 keV and densities up to ≈2.4 × 1019 m−3 had been achieved, and the maximum value of <βdia> was 2.6%. These experiments open possibilities for new regimes of LHD operation which are also interested to W7-X.
{"title":"First experiments on RF plasma production at relatively low magnetic fields in the LHD","authors":"Yu.V. Kovtun, S. Kamio, V.E. Moiseenko, H. Kasahara, T. Seki, K. Saito, R. Seki, S. Masuzaki, S. Brezinsek, A. Dinklage","doi":"10.1088/1741-4326/ad70cc","DOIUrl":"https://doi.org/10.1088/1741-4326/ad70cc","url":null,"abstract":"The results of the first experimental series to produce a plasma using the radio frequency discharge (RF) above the ion cyclotron frequency at relatively low magnetic fields (0.5–0.6 T) in the Large Helical Device (LHD) are presented 1.43 MW of RF power produced target plasma with density up to 6 × 10<sup>18</sup> m<sup>−3</sup> to deuterium. Tangential NBI application into such a plasma increases plasma parameters. Electron temperatures up to ≈0.9 keV and densities up to ≈2.4 × 10<sup>19</sup> m<sup>−3</sup> had been achieved, and the maximum value of <<italic toggle=\"yes\">β</italic><sub>dia</sub>> was 2.6%. These experiments open possibilities for new regimes of LHD operation which are also interested to W7-X.","PeriodicalId":19379,"journal":{"name":"Nuclear Fusion","volume":"18 1","pages":""},"PeriodicalIF":3.3,"publicationDate":"2024-09-06","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142211969","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"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: 10.1088/1741-4326/ad751b
G. Grenfell, L. Gil, P. Manz, C. Silva, J. Adamek, D. Brida, G.D. Conway, T. Eich, M. Faitsch, T. Happel, M. Spolaore, U. Stroth, B. Tal, B. Vanovac, E. Wolfrum, the ASDEX Upgrade Teama, the EUROfusion Tokamak Exploitation Teamb
In order to extend the enhanced D-Alpha H-mode to future devices, it is crucial to understand the properties of the main signature of this regime, the quasicoherent mode (QCM), that likely clamps the pressure gradient below the ideal magnetohydrodynamic limit. The turbulent character of the QCM is investigated with scanning probes in ASDEX Upgrade. Analysis reveals the multi-faced character of the mode that spans both the confined region (where the radial electric field is negative) and the near scrape-off layer (SOL) (where it is positive). Fluctuations of density and potential at the QCM frequency are more anti-correlated towards the confined region, which is a fingerprint of electromagnetic instabilities, while they become more correlated in the SOL, as expected for a drift-wave, inducing cross-field transport across the separatrix.
为了将增强型 D-Alpha H 模式扩展到未来的设备，了解这一机制的主要特征--准相干模式（QCM）--的特性至关重要，它可能会将压力梯度限制在理想磁流体力学极限以下。通过 ASDEX 升级版中的扫描探针对 QCM 的湍流特性进行了研究。分析表明，该模式具有多面性，既横跨约束区（径向电场为负值），也横跨近刮除层（SOL）（径向电场为正值）。QCM 频率下的密度和电势波动与约束区的反相关性更强，这是电磁不稳定性的特征；而在 SOL 中，它们的相关性则更强，这也是漂移波的预期特征，从而诱发了跨越分离矩阵的跨场传输。
{"title":"The multi-faced nature of the quasicoherent mode in EDA H-mode","authors":"G. Grenfell, L. Gil, P. Manz, C. Silva, J. Adamek, D. Brida, G.D. Conway, T. Eich, M. Faitsch, T. Happel, M. Spolaore, U. Stroth, B. Tal, B. Vanovac, E. Wolfrum, the ASDEX Upgrade Teama, the EUROfusion Tokamak Exploitation Teamb","doi":"10.1088/1741-4326/ad751b","DOIUrl":"https://doi.org/10.1088/1741-4326/ad751b","url":null,"abstract":"In order to extend the enhanced D-Alpha H-mode to future devices, it is crucial to understand the properties of the main signature of this regime, the quasicoherent mode (QCM), that likely clamps the pressure gradient below the ideal magnetohydrodynamic limit. The turbulent character of the QCM is investigated with scanning probes in ASDEX Upgrade. Analysis reveals the multi-faced character of the mode that spans both the confined region (where the radial electric field is negative) and the near scrape-off layer (SOL) (where it is positive). Fluctuations of density and potential at the QCM frequency are more anti-correlated towards the confined region, which is a fingerprint of electromagnetic instabilities, while they become more correlated in the SOL, as expected for a drift-wave, inducing cross-field transport across the separatrix.","PeriodicalId":19379,"journal":{"name":"Nuclear Fusion","volume":"13 1","pages":""},"PeriodicalIF":3.3,"publicationDate":"2024-09-06","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142211971","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"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: 10.1088/1741-4326/ad703d
Dingkun Yang, Shengming Li, Yong Xiao, Zhihong Lin
This study employs gyrokinetic simulations to investigate ion temperature gradient (ITG) turbulence in realistic fusion reactor plasmas featuring reversed magnetic shear. The weakly negative magnetic shear is observed to be more stable for the ITG instability than strongly positive shear in this equilibrium configuration, primarily stemming from the scarcity of mode rational surfaces induced by the weak negative shear. This superiority in suppression for the negative shear persists in nonlinear turbulence with zonal flow artificially eliminated, where the emergence of turbulence solitons is observed and found associated with locally dense mode rational surfaces. However, the difference in transport levels among different magnetic shears diminishes in the presence of self-consistently generated zonal flow, accompanied by the disappearance of turbulence solitons. The nonlinear generation of zonal flow is found to be significantly affected by the magnetic shear. The study reveals a remarkable phenomenon that the Dimits shift no longer exists for negative magnetic shear, which is attributed to the weakness of the zonal flow generation near the ITG marginal stability.
{"title":"Disappearance of dimits shift in realistic fusion reactor plasmas with negative magnetic shear","authors":"Dingkun Yang, Shengming Li, Yong Xiao, Zhihong Lin","doi":"10.1088/1741-4326/ad703d","DOIUrl":"https://doi.org/10.1088/1741-4326/ad703d","url":null,"abstract":"This study employs gyrokinetic simulations to investigate ion temperature gradient (ITG) turbulence in realistic fusion reactor plasmas featuring reversed magnetic shear. The weakly negative magnetic shear is observed to be more stable for the ITG instability than strongly positive shear in this equilibrium configuration, primarily stemming from the scarcity of mode rational surfaces induced by the weak negative shear. This superiority in suppression for the negative shear persists in nonlinear turbulence with zonal flow artificially eliminated, where the emergence of turbulence solitons is observed and found associated with locally dense mode rational surfaces. However, the difference in transport levels among different magnetic shears diminishes in the presence of self-consistently generated zonal flow, accompanied by the disappearance of turbulence solitons. The nonlinear generation of zonal flow is found to be significantly affected by the magnetic shear. The study reveals a remarkable phenomenon that the Dimits shift no longer exists for negative magnetic shear, which is attributed to the weakness of the zonal flow generation near the ITG marginal stability.","PeriodicalId":19379,"journal":{"name":"Nuclear Fusion","volume":"5 1","pages":""},"PeriodicalIF":3.3,"publicationDate":"2024-09-06","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142211968","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"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: 10.1088/1741-4326/ad73e7
D. Matveev, C. Baumann, J. Romazanov, S. Brezinsek, S. Ratynskaia, L. Vignitchouk, P. Tolias, K. Paschalidis, D. Tskhakaya, M. Komm, A. Podolník, J. Mougenot, Y. Charles, R. Delaporte-Mathurin, E. Hodille, C. Grisolia, F. Montupet-Leblond, K. Schmid, U. Von Toussaint, F. Granberg, F. Kporha, J. Kovačič, S. Costea
An integral approach to plasma-wall interaction (PWI) modelling for DEMO is presented, which is part of the EUROfusion Theory and Advanced Simulation Coordination activities that were established to advance the understanding and predictive capabilities for the modelling of existing and future fusion devices using a modern advanced computing approach. In view of the DEMO design, the aim of PWI modelling activities is to assess safety-relevant information regarding the erosion of plasma-facing components (PFCs), including its impact on plasma contamination, dust production, fuel inventory, and material response to transient events. This is achieved using a set of powerful and validated computer codes that deal with particular PWI aspects and interact with each other by means of relevant data exchange. Steady state erosion of tungsten PFC and subsequent transport and re-deposition of eroded material are simulated with the ERO2.0 code using a DEMO plasma background produced by dedicated SOLPS-ITER simulations. Dust transport simulations in steady state plasma also rely on the respective SOLPS-ITER solutions and are performed with the MIGRAINe code. In order to improve simulations of tungsten erosion in the divertor of DEMO, relevant high density sheath models are being developed based on particle-in-cell (PIC) simulations with the state-of-the-art BIT code family. PIC codes of the SPICE code family, in turn, provide relevant information on multi-emissive sheath physics, such as semi-empirical scaling laws for field-assisted thermionic emission. These scaling laws are essential for simulations of material melting under transient heat loads that are performed with the recently developed MEMENTO code, the successor of MEMOS-U. Fuel retention simulations assess tritium retention in tungsten and structural materials, as well as fuel permeation to the coolant, accounting for neutron damage. Simulations for divertor monoblocks of different sizes are performed using the FESTIM code, while for the first wall the TESSIM code is applied. Respective code-code dependencies and interactions, as well as modelling results achieved to date are discussed in this contribution.
{"title":"An integral approach to plasma-wall interaction modelling for EU-DEMO","authors":"D. Matveev, C. Baumann, J. Romazanov, S. Brezinsek, S. Ratynskaia, L. Vignitchouk, P. Tolias, K. Paschalidis, D. Tskhakaya, M. Komm, A. Podolník, J. Mougenot, Y. Charles, R. Delaporte-Mathurin, E. Hodille, C. Grisolia, F. Montupet-Leblond, K. Schmid, U. Von Toussaint, F. Granberg, F. Kporha, J. Kovačič, S. Costea","doi":"10.1088/1741-4326/ad73e7","DOIUrl":"https://doi.org/10.1088/1741-4326/ad73e7","url":null,"abstract":"An integral approach to plasma-wall interaction (PWI) modelling for DEMO is presented, which is part of the EUROfusion Theory and Advanced Simulation Coordination activities that were established to advance the understanding and predictive capabilities for the modelling of existing and future fusion devices using a modern advanced computing approach. In view of the DEMO design, the aim of PWI modelling activities is to assess safety-relevant information regarding the erosion of plasma-facing components (PFCs), including its impact on plasma contamination, dust production, fuel inventory, and material response to transient events. This is achieved using a set of powerful and validated computer codes that deal with particular PWI aspects and interact with each other by means of relevant data exchange. Steady state erosion of tungsten PFC and subsequent transport and re-deposition of eroded material are simulated with the ERO2.0 code using a DEMO plasma background produced by dedicated SOLPS-ITER simulations. Dust transport simulations in steady state plasma also rely on the respective SOLPS-ITER solutions and are performed with the MIGRAINe code. In order to improve simulations of tungsten erosion in the divertor of DEMO, relevant high density sheath models are being developed based on particle-in-cell (PIC) simulations with the state-of-the-art BIT code family. PIC codes of the SPICE code family, in turn, provide relevant information on multi-emissive sheath physics, such as semi-empirical scaling laws for field-assisted thermionic emission. These scaling laws are essential for simulations of material melting under transient heat loads that are performed with the recently developed MEMENTO code, the successor of MEMOS-U. Fuel retention simulations assess tritium retention in tungsten and structural materials, as well as fuel permeation to the coolant, accounting for neutron damage. Simulations for divertor monoblocks of different sizes are performed using the FESTIM code, while for the first wall the TESSIM code is applied. Respective code-code dependencies and interactions, as well as modelling results achieved to date are discussed in this contribution.","PeriodicalId":19379,"journal":{"name":"Nuclear Fusion","volume":"71 1","pages":""},"PeriodicalIF":3.3,"publicationDate":"2024-09-06","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142211970","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"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: 10.1088/1741-4326/ad75a7
T. Wakatsuki, H. Urano, M. Yoshida, N. Tsujii, S. Inoue, S. Kojima, T. Nakano, M. Fukumoto, Y. Ohtani, R. Sano, S. Ide
The world’s largest superconducting tokamak, JT-60SA, has successfully achieved its first plasma operation under the constraint of a low toroidal inductive electric field of 0.15 V m−1. A plasma start-up scenario, leveraging the effective confinement of electrons accelerated by the electron cyclotron wave, proved to be instrumental in reaching this milestone under the challenging conditions. The demonstration of plasma start-up using second harmonic electron cyclotron heating, with an applied toroidal electric field of 0.15 V m−1, strongly validates the feasibility of achieving first plasma operation in ITER.
世界上最大的超导托卡马克 JT-60SA 在 0.15 V m-1 的低环形感应电场约束下成功实现了首次等离子体运行。事实证明，利用电子回旋加速器波加速电子的有效约束，等离子体启动方案有助于在极具挑战性的条件下实现这一里程碑。在 0.15 V m-1 的环形电场作用下，利用二次谐波电子回旋加热进行等离子体启动演示，有力地验证了在热核实验堆中实现首次等离子体运行的可行性。
{"title":"Achievement of the first tokamak plasma with low inductive electric field in JT-60SA","authors":"T. Wakatsuki, H. Urano, M. Yoshida, N. Tsujii, S. Inoue, S. Kojima, T. Nakano, M. Fukumoto, Y. Ohtani, R. Sano, S. Ide","doi":"10.1088/1741-4326/ad75a7","DOIUrl":"https://doi.org/10.1088/1741-4326/ad75a7","url":null,"abstract":"The world’s largest superconducting tokamak, JT-60SA, has successfully achieved its first plasma operation under the constraint of a low toroidal inductive electric field of 0.15 V m<sup>−1</sup>. A plasma start-up scenario, leveraging the effective confinement of electrons accelerated by the electron cyclotron wave, proved to be instrumental in reaching this milestone under the challenging conditions. The demonstration of plasma start-up using second harmonic electron cyclotron heating, with an applied toroidal electric field of 0.15 V m<sup>−1</sup>, strongly validates the feasibility of achieving first plasma operation in ITER.","PeriodicalId":19379,"journal":{"name":"Nuclear Fusion","volume":"12 1","pages":""},"PeriodicalIF":3.3,"publicationDate":"2024-09-06","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142211972","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"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: 10.1088/1741-4326/ad6f28
G.F. Ding, G.S. Xu, Y.Q. Tao, K. Wu, L. Yu, X. Lin, L.Y. Meng, L. Wang, Q.Q Yang, R. Chen, R.R. Liang, K.D. Li, Q. Zang, Z.Q. Zhou, Q.P. Yuan, J.C. Xu
One of the key challenges facing magnetic fusion research is to demonstrate the compatibility between high confinement and radiative divertors in long-pulse discharges with a metal wall environment. A small edge-localized-mode (ELM) high-confinement plasma with an energy confinement factor H98 ∼ 1.1 and Greenwald density fraction fGW ∼ 0.65 maintained for 26 s is obtained in the upgraded lower divertor of the Experimental Advanced Superconducting Tokamak (EAST), and periodical detachment is achieved through active control of neon impurity seeding in this long-pulse discharge. For the divertor region, partial detachment is achieved periodically on the outer divertor target plates with the plasma temperature near the outer strike point decreasing to below 5 eV and the peak surface temperature on the outer divertor target plates maintained below 350 °C. The peak heat flux of the lower outer divertor decreases significantly and its profile along the target becomes very flat in the detached state. Two low-frequency (<10 kHz) fluctuations that are related to the rippling mode caused by a resistive instability appear in the detached state. For the pedestal region, the electron pressure profile is flatter and the ELM amplitude is smaller in the detached state than that in the attached state. Edge-coherent mode appears in the attached state and disappears in the detached state. To achieve this experimentally, a new impurity seeding feedback control scheme is applied, where the floating potential measured by divertor Langmuir probes is used as a feedback sensor, which is more reliable in long-pulse discharges with high heat fluxes and thus more suitable for application in future devices. This study provides a new approach for the actively controlled radiative divertor as a solution to the divertor heat loads of future fusion reactors.
磁核聚变研究面临的关键挑战之一是证明在金属壁环境下的长脉冲放电中高约束和辐射分流器之间的兼容性。在先进超导实验托卡马克（EAST）的升级版下分流器中获得了一个小型边缘局域模式（ELM）高约束等离子体，其能量约束因子H98∼ 1.1，格林瓦尔德密度分数fGW∼ 0.65，可维持26秒，并通过主动控制长脉冲放电中的氖杂质播种实现了周期性脱离。对于分流器区域，外侧分流器靶板实现了周期性部分脱离，外侧撞击点附近的等离子体温度降至 5 eV 以下，外侧分流器靶板的峰值表面温度保持在 350 °C 以下。在脱离状态下，下部外岔道的峰值热通量显著下降，其沿靶的剖面变得非常平坦。分离状态下出现了两个低频（10 kHz）波动，这与电阻不稳定性引起的波纹模式有关。对于基座区域，分离状态下的电子压力曲线更平坦，ELM 振幅也比附着状态下的更小。边缘相干模式在附着态出现，在分离态消失。为了在实验中实现这一目标，我们采用了一种新的杂质播种反馈控制方案，即使用分流朗缪尔探针测量的浮动电势作为反馈传感器，这种方案在高热流量的长脉冲放电中更加可靠，因此更适合在未来的器件中应用。这项研究为主动控制辐射分流器提供了一种新方法，可作为未来聚变反应堆分流器热负荷的解决方案。
{"title":"A long-pulse small edge-localized-mode high-confinement plasma with detachment feedback control by floating potential in an experimental advanced superconducting tokamak in a metal wall environment","authors":"G.F. Ding, G.S. Xu, Y.Q. Tao, K. Wu, L. Yu, X. Lin, L.Y. Meng, L. Wang, Q.Q Yang, R. Chen, R.R. Liang, K.D. Li, Q. Zang, Z.Q. Zhou, Q.P. Yuan, J.C. Xu","doi":"10.1088/1741-4326/ad6f28","DOIUrl":"https://doi.org/10.1088/1741-4326/ad6f28","url":null,"abstract":"One of the key challenges facing magnetic fusion research is to demonstrate the compatibility between high confinement and radiative divertors in long-pulse discharges with a metal wall environment. A small edge-localized-mode (ELM) high-confinement plasma with an energy confinement factor <italic toggle=\"yes\">H</italic><sub>98</sub> ∼ 1.1 and Greenwald density fraction <italic toggle=\"yes\">f</italic><sub>GW</sub> ∼ 0.65 maintained for 26 s is obtained in the upgraded lower divertor of the Experimental Advanced Superconducting Tokamak (EAST), and periodical detachment is achieved through active control of neon impurity seeding in this long-pulse discharge. For the divertor region, partial detachment is achieved periodically on the outer divertor target plates with the plasma temperature near the outer strike point decreasing to below 5 eV and the peak surface temperature on the outer divertor target plates maintained below 350 °C. The peak heat flux of the lower outer divertor decreases significantly and its profile along the target becomes very flat in the detached state. Two low-frequency (<10 kHz) fluctuations that are related to the rippling mode caused by a resistive instability appear in the detached state. For the pedestal region, the electron pressure profile is flatter and the ELM amplitude is smaller in the detached state than that in the attached state. Edge-coherent mode appears in the attached state and disappears in the detached state. To achieve this experimentally, a new impurity seeding feedback control scheme is applied, where the floating potential measured by divertor Langmuir probes is used as a feedback sensor, which is more reliable in long-pulse discharges with high heat fluxes and thus more suitable for application in future devices. This study provides a new approach for the actively controlled radiative divertor as a solution to the divertor heat loads of future fusion reactors.","PeriodicalId":19379,"journal":{"name":"Nuclear Fusion","volume":"46 1","pages":""},"PeriodicalIF":3.3,"publicationDate":"2024-09-06","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142211967","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"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 : 2024-09-04DOI: 10.1088/1741-4326/ad6ea1
S.-J. Lee, D. Hu, M. Lehnen, E. Nardon, Jayhyun Kim, D. Bonfiglio, F.J. Artola, M. Hoelzl, Yong-Su Na, JOREK teama
3D nonlinear MHD simulations of neon-doped single shattered pellet injection (SPI) conducted with the JOREK code reveal rich physics during SPI-induced disruptions in KSTAR. In the early phase, pressure-driven modes dominate, and the perturbation of the plasma current is largely consistent with the perturbation of the Pfirsch–Schlüter current. As shards reach the q = 1 surface, resistive current perturbations by helical electron cooling start to dominate, and the electron temperature in the core begins to collapse with convective mixing of the density driven by the internal 1/1 kink mode. The confinement of the plasma is later completely destroyed as a cold bubble convects into the core via quasi-interchange mode. Comparisons with available experimental data demonstrate qualitative agreements between JOREK results and experiments, and possible reasons for deviations are discussed.
{"title":"Nonlinear MHD modeling of neon doped shattered pellet injection with JOREK and its comparison to experiments in KSTAR","authors":"S.-J. Lee, D. Hu, M. Lehnen, E. Nardon, Jayhyun Kim, D. Bonfiglio, F.J. Artola, M. Hoelzl, Yong-Su Na, JOREK teama","doi":"10.1088/1741-4326/ad6ea1","DOIUrl":"https://doi.org/10.1088/1741-4326/ad6ea1","url":null,"abstract":"3D nonlinear MHD simulations of neon-doped single shattered pellet injection (SPI) conducted with the JOREK code reveal rich physics during SPI-induced disruptions in KSTAR. In the early phase, pressure-driven modes dominate, and the perturbation of the plasma current is largely consistent with the perturbation of the Pfirsch–Schlüter current. As shards reach the <italic toggle=\"yes\">q</italic> = 1 surface, resistive current perturbations by helical electron cooling start to dominate, and the electron temperature in the core begins to collapse with convective mixing of the density driven by the internal <inline-formula>\u0000<tex-math><?CDATA $1/1$?></tex-math><mml:math overflow=\"scroll\"><mml:mrow><mml:mn>1</mml:mn><mml:mrow><mml:mo>/</mml:mo></mml:mrow><mml:mn>1</mml:mn></mml:mrow></mml:math><inline-graphic xlink:href=\"nfad6ea1ieqn1.gif\"></inline-graphic></inline-formula> kink mode. The confinement of the plasma is later completely destroyed as a cold bubble convects into the core via quasi-interchange mode. Comparisons with available experimental data demonstrate qualitative agreements between JOREK results and experiments, and possible reasons for deviations are discussed.","PeriodicalId":19379,"journal":{"name":"Nuclear Fusion","volume":"28 1","pages":""},"PeriodicalIF":3.3,"publicationDate":"2024-09-04","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142211973","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"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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