Pub Date : 2024-09-12DOI: 10.1088/1741-4326/ad6f29
L.W. Packer, P. Batistoni, C. Bearcroft, S.C. Bradnam, E. Eardley, M. Fabbri, N. Fonnesu, M.R. Gilbert, Z. Ghani, K. Gorzkiewicz, C.L. Grove, R. Kierepko, E. Łaszyńska, I. Lengar, X. Litaudon, S. Loreti, J.W. Mietelski, M. Pillon, M.I. Savva, C.R. Shand, I.E. Stamatelatos, A.N. Turner, T. Vasilopoulou, R. Villari, A. Wójcik-Gargula, A. Žohar and JET Contributors
This work presents the results following the first irradiation of ITER materials samples in a tokamak D–T plasma environment operating at significant fusion power. The materials exposed to this nuclear environment at the Joint European Torus during the DTE2 experimental campaign that took place in 2021 include representative ITER samples from various components such as poloidal field coil jacket samples, toroidal field coil radial closure plate steels, EUROFER 97 steel, W and CuCrZr materials from the divertor, Inconel-718 and 316L stainless steel for blanket modules, as well as vacuum vessel forging samples. The experimental results discussed include high-resolution gamma spectrometry measurements and analysis conducted with the post-irradiated samples, of which there were 68 in total. These samples were exposed through different experimental campaigns, including deuterium, deuterium–tritium and tritium phases. Diagnostics that supported the analysis included 25 dosimetry foil-based neutron diagnostics and two ‘VERDI’ neutron spectrometry diagnostics. A further 12 samples for positron annihilation spectroscopy were also irradiated. The irradiation of all these samples took place in a long-term irradiation assembly located near the JET vacuum vessel. The post-irradiation analysis of the ITER material samples has yielded valuable insights into their material activation levels and radiation fields. Comparative assessments between experimental measurements and comprehensive neutronics simulations have demonstrated a significant level of agreement in this work, while also revealing some discrepancies in specific material instances. The data and interpretation from this work not only serve as a robust experimental foundation for enhancing the precision and predictability of neutronics simulation approaches for ITER and next-step devices but also present some opportunities for the refinement of simulation methodologies. In light of these findings, a series of recommendations have been proposed, aimed at improving confidence in nuclear predictions associated with materials that have been exposed to fusion nuclear environments and advancing understanding in this important domain.
{"title":"ITER materials irradiation within the D–T neutron environment at JET: post-irradiation radioactivity analysis following the DTE2 experimental campaign","authors":"L.W. Packer, P. Batistoni, C. Bearcroft, S.C. Bradnam, E. Eardley, M. Fabbri, N. Fonnesu, M.R. Gilbert, Z. Ghani, K. Gorzkiewicz, C.L. Grove, R. Kierepko, E. Łaszyńska, I. Lengar, X. Litaudon, S. Loreti, J.W. Mietelski, M. Pillon, M.I. Savva, C.R. Shand, I.E. Stamatelatos, A.N. Turner, T. Vasilopoulou, R. Villari, A. Wójcik-Gargula, A. Žohar and JET Contributors","doi":"10.1088/1741-4326/ad6f29","DOIUrl":"https://doi.org/10.1088/1741-4326/ad6f29","url":null,"abstract":"This work presents the results following the first irradiation of ITER materials samples in a tokamak D–T plasma environment operating at significant fusion power. The materials exposed to this nuclear environment at the Joint European Torus during the DTE2 experimental campaign that took place in 2021 include representative ITER samples from various components such as poloidal field coil jacket samples, toroidal field coil radial closure plate steels, EUROFER 97 steel, W and CuCrZr materials from the divertor, Inconel-718 and 316L stainless steel for blanket modules, as well as vacuum vessel forging samples. The experimental results discussed include high-resolution gamma spectrometry measurements and analysis conducted with the post-irradiated samples, of which there were 68 in total. These samples were exposed through different experimental campaigns, including deuterium, deuterium–tritium and tritium phases. Diagnostics that supported the analysis included 25 dosimetry foil-based neutron diagnostics and two ‘VERDI’ neutron spectrometry diagnostics. A further 12 samples for positron annihilation spectroscopy were also irradiated. The irradiation of all these samples took place in a long-term irradiation assembly located near the JET vacuum vessel. The post-irradiation analysis of the ITER material samples has yielded valuable insights into their material activation levels and radiation fields. Comparative assessments between experimental measurements and comprehensive neutronics simulations have demonstrated a significant level of agreement in this work, while also revealing some discrepancies in specific material instances. The data and interpretation from this work not only serve as a robust experimental foundation for enhancing the precision and predictability of neutronics simulation approaches for ITER and next-step devices but also present some opportunities for the refinement of simulation methodologies. In light of these findings, a series of recommendations have been proposed, aimed at improving confidence in nuclear predictions associated with materials that have been exposed to fusion nuclear environments and advancing understanding in this important domain.","PeriodicalId":19379,"journal":{"name":"Nuclear Fusion","volume":"76 2 1","pages":""},"PeriodicalIF":3.3,"publicationDate":"2024-09-12","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142211941","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 : 2024-09-12DOI: 10.1088/1741-4326/ad73e8
Zichao Lin, Hongming Zhang, Fudi Wang, Cheonho Bae, Jia Fu, Yongcai Shen, Shuyu Dai, Yifei Jin, Dian Lu, Shengyu Fu, Huajian Ji and Bo Lyu
Artificial neural network models have been developed to predict rotation velocity and ion temperature profiles on the EAST tokamak based on spectral measurements from the x-ray crystal spectrometer. Both Deep Neural Network (DNN) and Convolutional Neural Network (CNN) models have been employed to infer line-integrated ion temperatures. The predicted results from these two models exhibit a strong correlation with the target values, providing an opportunity for cross-validation to enhance prediction accuracy. Notably, the computational speed of these models has been significantly increased, surpassing traditional methods by over tenfold. Furthermore, the investigation of input data range and error prediction serves as the foundation for future automated calculation process. Finally, CNNs have also been employed to predict line-integrated rotation velocity profiles and inverted ion temperature profiles for their robustness in the training process. It is noted that these algorithms are not restricted to any specific physics model and can be readily adapted to various fusion devices.
根据 X 射线晶体光谱仪的光谱测量结果，开发了人工神经网络模型来预测 EAST 托卡马克的旋转速度和离子温度曲线。深度神经网络（DNN）和卷积神经网络（CNN）模型都被用来推断线积分离子温度。这两种模型的预测结果与目标值具有很强的相关性，为交叉验证提供了机会，从而提高了预测的准确性。值得注意的是，这些模型的计算速度有了显著提高，超过传统方法十倍以上。此外，对输入数据范围和误差预测的研究为未来的自动计算过程奠定了基础。最后，CNN 还被用于预测线积分旋转速度剖面和反转离子温度剖面，以确保其在训练过程中的鲁棒性。值得注意的是，这些算法并不局限于任何特定的物理模型，可随时适用于各种融合设备。
{"title":"Prediction of plasma rotation velocity and ion temperature profiles in EAST Tokamak using artificial neural network models","authors":"Zichao Lin, Hongming Zhang, Fudi Wang, Cheonho Bae, Jia Fu, Yongcai Shen, Shuyu Dai, Yifei Jin, Dian Lu, Shengyu Fu, Huajian Ji and Bo Lyu","doi":"10.1088/1741-4326/ad73e8","DOIUrl":"https://doi.org/10.1088/1741-4326/ad73e8","url":null,"abstract":"Artificial neural network models have been developed to predict rotation velocity and ion temperature profiles on the EAST tokamak based on spectral measurements from the x-ray crystal spectrometer. Both Deep Neural Network (DNN) and Convolutional Neural Network (CNN) models have been employed to infer line-integrated ion temperatures. The predicted results from these two models exhibit a strong correlation with the target values, providing an opportunity for cross-validation to enhance prediction accuracy. Notably, the computational speed of these models has been significantly increased, surpassing traditional methods by over tenfold. Furthermore, the investigation of input data range and error prediction serves as the foundation for future automated calculation process. Finally, CNNs have also been employed to predict line-integrated rotation velocity profiles and inverted ion temperature profiles for their robustness in the training process. It is noted that these algorithms are not restricted to any specific physics model and can be readily adapted to various fusion devices.","PeriodicalId":19379,"journal":{"name":"Nuclear Fusion","volume":"47 1","pages":""},"PeriodicalIF":3.3,"publicationDate":"2024-09-12","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142211947","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 : 2024-09-10DOI: 10.1088/1741-4326/ad6e9f
X. Garbet, P. Donnel, L. De Gianni, Z. Qu, Y. Melka, Y. Sarazin, V. Grandgirard, K. Obrejan, E. Bourne and G. Dif-Pradalier
A reduced model for trapped electron mode stability has been developed, which incorporates the basic effects of magnetic surface shaping, in particular, elongation and triangularity. This model shows that while elongation is stabilising, though weakly, negative triangularity usually leads to a more unstable plasma. This is in marked contrast with the experimental evidence of a better confinement at negative triangularity, and with recent gyrokinetic linear simulations. This paradox is solved when finite orbit and/or finite mode extent along field lines (mode ballooning) effects are included. These effects give more weight to particles trapped at low bounce angles, which are those that exhibit lower precession frequencies at negative—compared to positive—triangularity. As a result, the interchange growth rate becomes lower at negative triangularity and large temperature gradients, so that negative triangularity appears to have an overall stabilising effect. Mode ballooning appears to play the most important role in this reversal of stability.
{"title":"The effect of shaping on trapped electron mode stability: an analytical model","authors":"X. Garbet, P. Donnel, L. De Gianni, Z. Qu, Y. Melka, Y. Sarazin, V. Grandgirard, K. Obrejan, E. Bourne and G. Dif-Pradalier","doi":"10.1088/1741-4326/ad6e9f","DOIUrl":"https://doi.org/10.1088/1741-4326/ad6e9f","url":null,"abstract":"A reduced model for trapped electron mode stability has been developed, which incorporates the basic effects of magnetic surface shaping, in particular, elongation and triangularity. This model shows that while elongation is stabilising, though weakly, negative triangularity usually leads to a more unstable plasma. This is in marked contrast with the experimental evidence of a better confinement at negative triangularity, and with recent gyrokinetic linear simulations. This paradox is solved when finite orbit and/or finite mode extent along field lines (mode ballooning) effects are included. These effects give more weight to particles trapped at low bounce angles, which are those that exhibit lower precession frequencies at negative—compared to positive—triangularity. As a result, the interchange growth rate becomes lower at negative triangularity and large temperature gradients, so that negative triangularity appears to have an overall stabilising effect. Mode ballooning appears to play the most important role in this reversal of stability.","PeriodicalId":19379,"journal":{"name":"Nuclear Fusion","volume":"21 1","pages":""},"PeriodicalIF":3.3,"publicationDate":"2024-09-10","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142211951","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 : 2024-09-10DOI: 10.1088/1741-4326/ad5a21
M. Hoelzl, G.T.A. Huijsmans, F.J. Artola, E. Nardon, M. Becoulet, N. Schwarz, A. Cathey, S.J.P. Pamela, K. Aleynikova, F. Antlitz, V. Bandaru, H. Bergström, A. Bhole, T. Bogaarts, D. Bonfiglio, F. Cipolletta, T. Driessen, L. Edes, S. Futatani, G. Hao, F. Hindenlang, I. Holod, D. Hu, S. Hu, N. Isernia, H. Isliker, S.K. Kim, M. Kong, S. Korving, L. Kos, I. Krebs, S.J. Lee, Y.C. Liang, Z. Liang, S.J. Liu, Z.X. Lu, L. Meier, L. Messfeldt, V. Mitterauer, N. Nikulsin, B. Nkonga, R. Ramasamy, J. Reinking, C. Rogge, G. Rubinacci, K. Särkimäki, T. Smits, C. Sommariva, R. Sparago, K. Strien, M. Szucs, W. Tang, J. van Tongeren, F. Vannini, S. Ventre, F. Villone, C. Wang, L. Wang, F. Wieschollek, F. Wouters, J. Zielinski and H. Zhang
Transient magneto-hydrodynamic (MHD) events like edge localized modes (ELMs) or disruptions are a concern for magnetic confinement fusion power plants. Research with the MHD code JOREK towards understanding control of such instabilities is reviewed here in a concise way to provide a complete overview, while we refer to the original publications for details. Experimental validation for unmitigated vertical displacement events progressed. The mechanism of vertical force mitigation by impurity injection was identified. Two-way eddy current coupling to CARIDDI was completed. Shattered pellet injection was simulated in JET, KSTAR, ASDEX Upgrade (AUG) and ITER. Benign runaway electron beam termination in JET and ITER was studied. Coupling of kinetic REs to the MHD is ongoing and a virtual RE synchrotron radiation diagnostic was developed. Regarding pedestal physics, regimes devoid of large ELMs in AUG were simulated and predictive JT60-SA simulations are ongoing. For ELM suppression by resonant magnetic perturbations (RMPs), AUG, ITER and EAST simulations were performed. A free boundary RMP model was validated against experiments. Evidence for penetrated magnetic islands at the pedestal top based on AUG experiments and simulations was found. Simulations of the naturally ELM-free quiescent H-mode in AUG and HL-3 show external kink mode formation prevents pedestal build-up towards an ELM within windows of the edge safety factor. With kinetic neutral particles, high field side high density formation in ITER was simulated and with kinetic impurities, tungsten transport in AUG RMP plasmas was studied. To capture turbulent transport, electro-static full-f particle in cell models for ion temperature gradient and trapped electron modes were established and benchmarked. Application to RMP plasmas shows enhanced turbulence in comparison to unperturbed states. Energetic particle interactions with MHD were studied. Flux pumping that prevents the safety factor on axis from dropping below unity was simulated. First non-linear stellarator applications include current relaxation in l = 2 stellarators, while verification for advanced stellarators progresses.
边缘局部模态（ELM）或中断等瞬态磁流体动力（MHD）事件是磁约束核聚变电站所关注的问题。本文简要回顾了利用 MHD 代码 JOREK 开展的研究，旨在了解此类不稳定性的控制情况，以提供完整的概述，详细内容请参阅原始出版物。针对未缓解垂直位移事件的实验验证取得了进展。确定了通过注入杂质减轻垂直力的机制。完成了与 CARIDDI 的双向涡流耦合。在 JET、KSTAR、ASDEX 升级版（AUG）和 ITER 中模拟了碎丸注入。研究了 JET 和 ITER 中的良性失控电子束终止。正在进行动能 RE 与 MHD 的耦合，并开发了虚拟 RE 同步辐射诊断。关于基座物理学，模拟了AUG中没有大ELM的情况，并正在进行JT60-SA的预测模拟。关于共振磁扰动（RMP）对 ELM 的抑制，进行了 AUG、ITER 和 EAST 模拟。根据实验验证了自由边界 RMP 模型。根据 AUG 实验和模拟发现了基座顶部穿透磁岛的证据。对 AUG 和 HL-3 中自然无 ELM 的静态 H 模式的模拟显示，外部扭结模式的形成阻止了基座在边缘安全系数窗口内向 ELM 方向聚集。利用动力学中性粒子，模拟了国际热核聚变实验堆中的高场边高密度形成；利用动力学杂质，研究了 AUG RMP 等离子体中的钨传输。为了捕捉湍流输运，建立了离子温度梯度和困电子模式的静电全f粒子池模型，并对其进行了基准测试。对 RMP 等离子体的应用表明，与未扰动状态相比，湍流增强了。研究了能量粒子与 MHD 的相互作用。模拟了防止轴上的安全系数降到一以下的通量泵。非线性恒星仪的首次应用包括 l = 2 恒星仪中的电流松弛，而高级恒星仪的验证正在进行中。
{"title":"Non-linear MHD modelling of transients in tokamaks: a review of recent advances with the JOREK code","authors":"M. Hoelzl, G.T.A. Huijsmans, F.J. Artola, E. Nardon, M. Becoulet, N. Schwarz, A. Cathey, S.J.P. Pamela, K. Aleynikova, F. Antlitz, V. Bandaru, H. Bergström, A. Bhole, T. Bogaarts, D. Bonfiglio, F. Cipolletta, T. Driessen, L. Edes, S. Futatani, G. Hao, F. Hindenlang, I. Holod, D. Hu, S. Hu, N. Isernia, H. Isliker, S.K. Kim, M. Kong, S. Korving, L. Kos, I. Krebs, S.J. Lee, Y.C. Liang, Z. Liang, S.J. Liu, Z.X. Lu, L. Meier, L. Messfeldt, V. Mitterauer, N. Nikulsin, B. Nkonga, R. Ramasamy, J. Reinking, C. Rogge, G. Rubinacci, K. Särkimäki, T. Smits, C. Sommariva, R. Sparago, K. Strien, M. Szucs, W. Tang, J. van Tongeren, F. Vannini, S. Ventre, F. Villone, C. Wang, L. Wang, F. Wieschollek, F. Wouters, J. Zielinski and H. Zhang","doi":"10.1088/1741-4326/ad5a21","DOIUrl":"https://doi.org/10.1088/1741-4326/ad5a21","url":null,"abstract":"Transient magneto-hydrodynamic (MHD) events like edge localized modes (ELMs) or disruptions are a concern for magnetic confinement fusion power plants. Research with the MHD code JOREK towards understanding control of such instabilities is reviewed here in a concise way to provide a complete overview, while we refer to the original publications for details. Experimental validation for unmitigated vertical displacement events progressed. The mechanism of vertical force mitigation by impurity injection was identified. Two-way eddy current coupling to CARIDDI was completed. Shattered pellet injection was simulated in JET, KSTAR, ASDEX Upgrade (AUG) and ITER. Benign runaway electron beam termination in JET and ITER was studied. Coupling of kinetic REs to the MHD is ongoing and a virtual RE synchrotron radiation diagnostic was developed. Regarding pedestal physics, regimes devoid of large ELMs in AUG were simulated and predictive JT60-SA simulations are ongoing. For ELM suppression by resonant magnetic perturbations (RMPs), AUG, ITER and EAST simulations were performed. A free boundary RMP model was validated against experiments. Evidence for penetrated magnetic islands at the pedestal top based on AUG experiments and simulations was found. Simulations of the naturally ELM-free quiescent H-mode in AUG and HL-3 show external kink mode formation prevents pedestal build-up towards an ELM within windows of the edge safety factor. With kinetic neutral particles, high field side high density formation in ITER was simulated and with kinetic impurities, tungsten transport in AUG RMP plasmas was studied. To capture turbulent transport, electro-static full-f particle in cell models for ion temperature gradient and trapped electron modes were established and benchmarked. Application to RMP plasmas shows enhanced turbulence in comparison to unperturbed states. Energetic particle interactions with MHD were studied. Flux pumping that prevents the safety factor on axis from dropping below unity was simulated. First non-linear stellarator applications include current relaxation in l = 2 stellarators, while verification for advanced stellarators progresses.","PeriodicalId":19379,"journal":{"name":"Nuclear Fusion","volume":"7 1","pages":""},"PeriodicalIF":3.3,"publicationDate":"2024-09-10","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142211948","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 : 2024-09-10DOI: 10.1088/1741-4326/ad724d
M.D. Boyer, F. Scotti and V. Gajaraj
Deep learning approaches have been applied to images of C III emission in the lower divertor of DIII-D to develop models for estimating the level of detachment and magnetic configuration (X-point location and strike point radial location). The poloidal distance from the target to the C III emission front is used to represent the level of detachment. The models perform well on a test dataset not used in training, achieving F1 scores as high as 0.99 for detachment state classification and root mean squared error (RMSE) as low as 2 cm for front location regression. Predictions for shots with intermittent reattachment are studied, with class activation mapping used to aid in interpretation of the model predictions. Based on the success of these models, a third model was trained to predict the X-point location and strike point radial position from C III images. Though the dataset covers only a small range of possible magnetic configurations, the model shows promising results, achieving RMSE around 1 cm for the test data.
深度学习方法已被应用于 DIII-D 下岔道的 C III 辐射图像，以开发用于估算脱离程度和磁配置（X 点位置和撞击点径向位置）的模型。从目标到 C III 辐射前沿的极坐标距离被用来表示脱离程度。模型在未用于训练的测试数据集上表现良好，脱离状态分类的 F1 分数高达 0.99，前沿位置回归的均方根误差 (RMSE) 低至 2 厘米。对间歇性再附着的射击预测进行了研究，并使用类激活映射来帮助解释模型预测。在这些模型取得成功的基础上，对第三个模型进行了训练，以预测 C III 图像中的 X 点位置和打击点径向位置。虽然数据集仅涵盖了一小部分可能的磁性配置，但该模型显示出良好的效果，测试数据的均方根误差（RMSE）约为 1 厘米。
{"title":"Neural networks for estimation of divertor conditions in DIII-D using C III imaging","authors":"M.D. Boyer, F. Scotti and V. Gajaraj","doi":"10.1088/1741-4326/ad724d","DOIUrl":"https://doi.org/10.1088/1741-4326/ad724d","url":null,"abstract":"Deep learning approaches have been applied to images of C III emission in the lower divertor of DIII-D to develop models for estimating the level of detachment and magnetic configuration (X-point location and strike point radial location). The poloidal distance from the target to the C III emission front is used to represent the level of detachment. The models perform well on a test dataset not used in training, achieving F1 scores as high as 0.99 for detachment state classification and root mean squared error (RMSE) as low as 2 cm for front location regression. Predictions for shots with intermittent reattachment are studied, with class activation mapping used to aid in interpretation of the model predictions. Based on the success of these models, a third model was trained to predict the X-point location and strike point radial position from C III images. Though the dataset covers only a small range of possible magnetic configurations, the model shows promising results, achieving RMSE around 1 cm for the test data.","PeriodicalId":19379,"journal":{"name":"Nuclear Fusion","volume":"28 1","pages":""},"PeriodicalIF":3.3,"publicationDate":"2024-09-10","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142211949","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/ad75a5
Bo Simmendefeldt Schmidt, Jakob Sauer Jørgensen, José Rueda-Rueda, Joaquín Galdon-Quíroga, Manuel García-Muñoz, Mirko Salewski and the ASDEX Upgrade Team
We introduce an anisotropic regularization framework for the reconstruction of distribution functions from measurements, utilizing an approach that applies distinct regularization techniques such as non-negative constrained Tikhonov, total variation, and Besov-space priors, either penalizing the one-norm or the two-norm, in each dimension to reflect the anisotropic characteristics of the multidimensional data. This method, applied to fast-ion loss detector (FILD) measurements, demonstrates a significant improvement over conventional nonnegative-constrained zeroth-order Tikhonov regularization because the prior information of the form of the distribution allows better reconstructions. The validity of the approach is corroborated through FILD measurements of prompt fast-ion losses in an ASDEX Upgrade discharge, where the reconstructed distribution function agrees well with the prompt-loss distribution predicted by ASCOT simulations. Moreover, we develop a composite quality metric, Q, that combines the mean squared error and the Jaccard index for a comprehensive evaluation of reconstruction accuracy and spatial fidelity. Finally, anisotropic regularization is applied to FILD measurements at ASDEX Upgrade to study fast-ion acceleration by edge-localized modes. The refined analysis resolves fine structure in the pitch of the accelerated ions and clearly shows that some ions are accelerated to over twice the injection energy.
{"title":"Anisotropic regularization for inversion of fast-ion loss detector measurements","authors":"Bo Simmendefeldt Schmidt, Jakob Sauer Jørgensen, José Rueda-Rueda, Joaquín Galdon-Quíroga, Manuel García-Muñoz, Mirko Salewski and the ASDEX Upgrade Team","doi":"10.1088/1741-4326/ad75a5","DOIUrl":"https://doi.org/10.1088/1741-4326/ad75a5","url":null,"abstract":"We introduce an anisotropic regularization framework for the reconstruction of distribution functions from measurements, utilizing an approach that applies distinct regularization techniques such as non-negative constrained Tikhonov, total variation, and Besov-space priors, either penalizing the one-norm or the two-norm, in each dimension to reflect the anisotropic characteristics of the multidimensional data. This method, applied to fast-ion loss detector (FILD) measurements, demonstrates a significant improvement over conventional nonnegative-constrained zeroth-order Tikhonov regularization because the prior information of the form of the distribution allows better reconstructions. The validity of the approach is corroborated through FILD measurements of prompt fast-ion losses in an ASDEX Upgrade discharge, where the reconstructed distribution function agrees well with the prompt-loss distribution predicted by ASCOT simulations. Moreover, we develop a composite quality metric, Q, that combines the mean squared error and the Jaccard index for a comprehensive evaluation of reconstruction accuracy and spatial fidelity. Finally, anisotropic regularization is applied to FILD measurements at ASDEX Upgrade to study fast-ion acceleration by edge-localized modes. The refined analysis resolves fine structure in the pitch of the accelerated ions and clearly shows that some ions are accelerated to over twice the injection energy.","PeriodicalId":19379,"journal":{"name":"Nuclear Fusion","volume":"19 1","pages":""},"PeriodicalIF":3.3,"publicationDate":"2024-09-09","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142211954","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/ad73e9
A. Fil, L. Henden, S. Newton, M. Hoppe, O. Vallhagen
Generation of Runaway Electrons (REs) during plasma disruptions is of great concern for ITER and future reactors based on the tokamak concept. Unmitigated RE generation in the current STEP (Spherical Tokamak for Energy Production) concept design is modelled using the code DREAM, with hot-tail generation found to be the dominant primary generation mechanism and avalanche multiplication of REs found to be extremely high. Varying assumptions for the prescribed thermal quench (TQ) phase (duration, final electron temperature) as well as the wall time, the plasma-wall distance, and shaping effects, all STEP full-power and full-current unmitigated disruptions generate large RE beams (from 10 MA up to full conversion). RE mitigation is first studied by modelling idealised mixed impurity injections, with ad-hoc particle transport arising from the stochasticity of the magnetic field during the TQ, but no combination of argon and deuterium quantities allows runaways to be avoided while respecting the other constraints of disruption mitigation. Initial concept of STEP disruption mitigation system is then tested with DREAM, assuming two-stage shattered pellet injections (SPI) of pure D2 followed by Ar+D2. Such a scheme is found to reduce the generation of REs by the hot-tail mechanism, but still generates a RE beam of about 13 MA. Options for further optimising the SPI scheme, for mitigating a large RE beam in STEP (benign termination scheme), as well as estimations of required RE losses during the current quench (from a potential passive RE mitigation coil) will also be discussed.
等离子体中断期间产生的失控电子（REs）是热核实验堆和未来基于托卡马克概念的反应堆非常关注的问题。在当前的 STEP（用于能源生产的球形托卡马克）概念设计中，使用 DREAM 代码对失控电子的产生进行了模拟，发现热尾产生是主要的主要产生机制，并且发现失控电子的雪崩倍增非常高。由于对规定的热淬火（TQ）阶段（持续时间、最终电子温度）以及壁时间、等离子体-壁距离和塑形效应的假设不同，所有 STEP 全功率和全电流未缓解中断都会产生大量 RE 光束（从 10 MA 到全转换）。首先通过模拟理想化的混合杂质注入来研究 RE 减缓问题，TQ 期间磁场的随机性引起了临时粒子传输，但氩和氘的数量组合无法在遵守中断缓解的其他限制条件的同时避免失控。随后，利用 DREAM 对 STEP 干扰缓解系统的初步概念进行了测试，假定先进行纯 D2 后进行 Ar+D2 的两阶段碎裂颗粒注入 (SPI)。结果发现，这种方案可以减少热尾机制产生的 RE，但仍会产生约 13 MA 的 RE 光束。此外，还将讨论进一步优化 SPI 方案、在 STEP（良性终止方案）中减缓大 RE 射束的方案，以及在电流淬火期间所需 RE 损失的估算（来自潜在的被动 RE 减缓线圈）。
{"title":"Disruption runaway electron generation and mitigation in the Spherical Tokamak for Energy Production (STEP)","authors":"A. Fil, L. Henden, S. Newton, M. Hoppe, O. Vallhagen","doi":"10.1088/1741-4326/ad73e9","DOIUrl":"https://doi.org/10.1088/1741-4326/ad73e9","url":null,"abstract":"Generation of Runaway Electrons (REs) during plasma disruptions is of great concern for ITER and future reactors based on the tokamak concept. Unmitigated RE generation in the current STEP (Spherical Tokamak for Energy Production) concept design is modelled using the code DREAM, with hot-tail generation found to be the dominant primary generation mechanism and avalanche multiplication of REs found to be extremely high. Varying assumptions for the prescribed thermal quench (TQ) phase (duration, final electron temperature) as well as the wall time, the plasma-wall distance, and shaping effects, all STEP full-power and full-current unmitigated disruptions generate large RE beams (from 10 MA up to full conversion). RE mitigation is first studied by modelling idealised mixed impurity injections, with ad-hoc particle transport arising from the stochasticity of the magnetic field during the TQ, but no combination of argon and deuterium quantities allows runaways to be avoided while respecting the other constraints of disruption mitigation. Initial concept of STEP disruption mitigation system is then tested with DREAM, assuming two-stage shattered pellet injections (SPI) of pure <inline-formula>\u0000<tex-math><?CDATA $mathrm D_2$?></tex-math><mml:math overflow=\"scroll\"><mml:mrow><mml:msub><mml:mrow><mml:mi mathvariant=\"normal\">D</mml:mi></mml:mrow><mml:mn>2</mml:mn></mml:msub></mml:mrow></mml:math><inline-graphic xlink:href=\"nfad73e9ieqn1.gif\"></inline-graphic></inline-formula> followed by Ar+<inline-formula>\u0000<tex-math><?CDATA $mathrm D_2$?></tex-math><mml:math overflow=\"scroll\"><mml:mrow><mml:msub><mml:mrow><mml:mi mathvariant=\"normal\">D</mml:mi></mml:mrow><mml:mn>2</mml:mn></mml:msub></mml:mrow></mml:math><inline-graphic xlink:href=\"nfad73e9ieqn2.gif\"></inline-graphic></inline-formula>. Such a scheme is found to reduce the generation of REs by the hot-tail mechanism, but still generates a RE beam of about 13 MA. Options for further optimising the SPI scheme, for mitigating a large RE beam in STEP (benign termination scheme), as well as estimations of required RE losses during the current quench (from a potential passive RE mitigation coil) will also be discussed.","PeriodicalId":19379,"journal":{"name":"Nuclear Fusion","volume":"34 1","pages":""},"PeriodicalIF":3.3,"publicationDate":"2024-09-09","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142211966","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/ad6ba6
G. Lo Presti, A. La Magna
Describing the time evolution of Plasma Facing Materials (PFMs), through quantitative evaluations of erosion, roughness, and physical properties degradation, is one of the difficult challenges to reach the goal of efficient energy production by nuclear fusion. To follow all the aging-connected physical and chemical phenomena through their characteristic dimensional scale, and to estimate the PFM microstructural transformation over time, we propose a predictive sequential multiscale methodology, consisting of two database-provided coupled codes. The first is a time-dependent, volume-averaged, plasma simulator which describes completely this system in terms of thermodynamics, composition and evaluation of the sheath potential. Plasma solutions are geometrically rearranged by adding surface reactions and 3D geometric features. To increase sensitivity, plasma information is provided to the second code as an initial condition. Such a code is a 3D kinetic Monte Carlo in-cell algorithm for the nano-scale erosion simulation describing the PFM interactions through an extendable set of physical phenomena, such as sticking, sputtering, ion enhanced removals and ion penetration. In this paper, we perform simulations for the case of study of Hydrogen (H) plasmas produced in linear devices, reaching the quasi-atomic detail of the plasma induced material modification of tungsten (W) as PFM.
{"title":"Damage evolution in Plasma Facing Materials by a sequential multiscale approach","authors":"G. Lo Presti, A. La Magna","doi":"10.1088/1741-4326/ad6ba6","DOIUrl":"https://doi.org/10.1088/1741-4326/ad6ba6","url":null,"abstract":"Describing the time evolution of Plasma Facing Materials (PFMs), through quantitative evaluations of erosion, roughness, and physical properties degradation, is one of the difficult challenges to reach the goal of efficient energy production by nuclear fusion. To follow all the aging-connected physical and chemical phenomena through their characteristic dimensional scale, and to estimate the PFM microstructural transformation over time, we propose a predictive sequential multiscale methodology, consisting of two database-provided coupled codes. The first is a time-dependent, volume-averaged, plasma simulator which describes completely this system in terms of thermodynamics, composition and evaluation of the sheath potential. Plasma solutions are geometrically rearranged by adding surface reactions and 3D geometric features. To increase sensitivity, plasma information is provided to the second code as an initial condition. Such a code is a 3D kinetic Monte Carlo in-cell algorithm for the nano-scale erosion simulation describing the PFM interactions through an extendable set of physical phenomena, such as sticking, sputtering, ion enhanced removals and ion penetration. In this paper, we perform simulations for the case of study of Hydrogen (H) plasmas produced in linear devices, reaching the quasi-atomic detail of the plasma induced material modification of tungsten (W) as PFM.","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":"142211963","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/ad6e03
C. Sommariva, A. Pau, S. Silburn, C. Reux, M. Hoppe, P. Buratti, O. Ficker, Rennan B. Morales, M. Fontana, H. Sun, P. Carvalho, M. Sheena, S. Gerasimov, G. Szepesi, A. Boboc, I. Coffey, V. Kiptily, O. Sauter, G. Pautasso, C. Paz-Soldan, J. Decker, JET Contributors2a
The publication provide further insights into the dynamics of JET runaway electron (RE) beams mitigated by D2-rich shattered pellet injection (SPI) (Reux et al 2022 Plasma Phys. Control. Fusion64 034002). Multi-diagnostic analyses show that mechanisms causing continuous RE losses and energy transfer from hot electrons to cold background plasma can act before the SPI. After the SPI, measurements are compatible with a reduction of the maximum energy and pitch angle of the RE distribution while the population of supra-thermal electrons increases. The RE population growth is likely due to electron avalanche. Dark island-like pattern chains, characterised by an integer poloidal mode number and a certain minor radius, are identified in the JET RE beam synchrotron radiation videos. The synchrotron island dynamics is studied via a newly developed computer vision code (Sommariva and Silburn https://c4science.ch/source/pSpiPTV/). The radial motion of synchrotron island chains is found to be consistent with the most plausible time evolution of the radial current density profile compatible with both the RE synchrotron videos and the total RE current time trace. Similarly, correlations are identified between the temporal progression of the synchrotron islands poloidal rotation frequency and sudden MHD relaxation events. Loss-of-RE events probably caused by non-linear interactions between synchrotron islands are observed for the first time. Experimental evidences suggest that synchrotron islands are possibly related to the existence of magnetic islands which may lead to the development of new RE beam mitigation strategies.
这篇论文进一步揭示了通过富含D2-的碎丸注入（SPI）缓解的JET失控电子束（RE）的动力学（Reux等人，2022年，《等离子体物理控制》，聚变64，034002）。多重诊断分析表明，导致热电子向冷背景等离子体的持续 RE 损耗和能量转移的机制可能在 SPI 之前就已发生作用。在 SPI 之后，测量结果表明 RE 分布的最大能量和俯仰角减小，同时超热电子群增加。RE 数量的增加可能是由于电子雪崩。在 JET RE 光束同步辐射视频中发现了暗岛状模式链，其特征是具有整数极模数和一定的小半径。通过新开发的计算机视觉代码（Sommariva 和 Silburn https://c4science.ch/source/pSpiPTV/）对同步辐射岛的动态进行了研究。研究发现，同步辐射岛链的径向运动与径向电流密度剖面最合理的时间演化相一致，与 RE 同步辐射视频和总的 RE 电流时间轨迹相匹配。同样，在同步辐射岛极坐标旋转频率的时间进展与突发性 MHD 松弛事件之间也发现了相关性。首次观测到可能由同步辐射岛之间的非线性相互作用引起的 RE 丢失事件。实验证据表明，同步辐射岛可能与磁岛的存在有关，这可能导致新的可再生能源光束缓解策略的开发。
{"title":"Dynamics of JET runaway electron beams in D2-rich shattered pellet injection mitigation experiments","authors":"C. Sommariva, A. Pau, S. Silburn, C. Reux, M. Hoppe, P. Buratti, O. Ficker, Rennan B. Morales, M. Fontana, H. Sun, P. Carvalho, M. Sheena, S. Gerasimov, G. Szepesi, A. Boboc, I. Coffey, V. Kiptily, O. Sauter, G. Pautasso, C. Paz-Soldan, J. Decker, JET Contributors2a","doi":"10.1088/1741-4326/ad6e03","DOIUrl":"https://doi.org/10.1088/1741-4326/ad6e03","url":null,"abstract":"The publication provide further insights into the dynamics of JET runaway electron (RE) beams mitigated by D2-rich shattered pellet injection (SPI) (Reux <italic toggle=\"yes\">et al</italic> 2022 <italic toggle=\"yes\">Plasma Phys. Control. Fusion</italic> <bold>64</bold> 034002). Multi-diagnostic analyses show that mechanisms causing continuous RE losses and energy transfer from hot electrons to cold background plasma can act before the SPI. After the SPI, measurements are compatible with a reduction of the maximum energy and pitch angle of the RE distribution while the population of supra-thermal electrons increases. The RE population growth is likely due to electron avalanche. Dark island-like pattern chains, characterised by an integer poloidal mode number and a certain minor radius, are identified in the JET RE beam synchrotron radiation videos. The synchrotron island dynamics is studied via a newly developed computer vision code (Sommariva and Silburn <ext-link ext-link-type=\"uri\" xlink:href=\"https://c4science.ch/source/pSpiPTV/\">https://c4science.ch/source/pSpiPTV/</ext-link>). The radial motion of synchrotron island chains is found to be consistent with the most plausible time evolution of the radial current density profile compatible with both the RE synchrotron videos and the total RE current time trace. Similarly, correlations are identified between the temporal progression of the synchrotron islands poloidal rotation frequency and sudden MHD relaxation events. Loss-of-RE events probably caused by non-linear interactions between synchrotron islands are observed for the first time. Experimental evidences suggest that synchrotron islands are possibly related to the existence of magnetic islands which may lead to the development of new RE beam mitigation strategies.","PeriodicalId":19379,"journal":{"name":"Nuclear Fusion","volume":"106 1","pages":""},"PeriodicalIF":3.3,"publicationDate":"2024-09-09","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142211965","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/ad7741
Zihuan Jiang, Zhigang Wang, Tianxing Hu, Yunqing Fu, Ke Yao and Bin He
In their paper the abnormal variation of the projectile range with the plasma density was found for fusion products, and some explanations were presented for the results. However, we could not find such abnormal behavior by the calculation of stopping powers under different models. And their explanations are not appropriate. Finally the revised results corresponding to figure 3 in their paper are presented.
{"title":"Comment on ‘Stopping power in D6Li plasmas for target ignition studies’","authors":"Zihuan Jiang, Zhigang Wang, Tianxing Hu, Yunqing Fu, Ke Yao and Bin He","doi":"10.1088/1741-4326/ad7741","DOIUrl":"https://doi.org/10.1088/1741-4326/ad7741","url":null,"abstract":"In their paper the abnormal variation of the projectile range with the plasma density was found for fusion products, and some explanations were presented for the results. However, we could not find such abnormal behavior by the calculation of stopping powers under different models. And their explanations are not appropriate. Finally the revised results corresponding to figure 3 in their paper are presented.","PeriodicalId":19379,"journal":{"name":"Nuclear Fusion","volume":"178 1","pages":""},"PeriodicalIF":3.3,"publicationDate":"2024-09-09","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142211953","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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