Pub Date : 2024-07-05DOI: 10.1088/1741-4326/ad5fa0
E. de la Luna, Jeronimo Garcia, M. Sertoli, Peter Lomas, Samuele Mazzi, Ž. Štancar, M. Dunne, Nobuyuki Aiba, S. Silburn, M. Faitsch, G. Szepesi, F. Auriemma, Itziar Balboa, L. Frassinetti, L. Garzotti, S. Menmuir, D. Réfy, F. Rimini, E. Solano, Carlo Sozzi, Milos Vecsei
A new H-mode regime at low density and low edge safety factor (q95=3.2, with Ip=3 MA) that combines high energy confinement, stationary conditions for density and radiation and small Edge Localized Modes (ELMs) have been found in JET with Be/W wall. Such a regime is achieved by operating without external gas puffing, leading to a decrease in the edge density and a substantial increase in rotation and ion temperature in both the pedestal and the core region. Transport modelling shows a reduction of the turbulence, which starts in the pedestal region and extends into the plasma core, and outward impurity convection, consistent with the improved energy confinement and the lack of W accumulation observed in those conditions. In addition, large type I ELMs, typically found in gas-fuelled plasmas, are replaced by smaller and more frequent ELMs, whose appearance is correlated with a substantial reduction of the pedestal density and its gradient. Pedestals in this operating regime are stable to peeling–ballooning modes, consistent with the lack of large ELMs. This is in contrast to results in unfuelled JET-C plasmas that typically operated at higher pedestal densities and developed low frequency, large type I ELMs, thus pointing to the low density as one of the critical parameters for accessing the small ELMs in JET. This small ELMs regime exhibits the same low pedestal collisionality (ν∗ e,ped ∼ 0.1) expected in ITER and operates at low q95, thus making it different from other small ELMs regimes typically obtained at higher q95 and higher pedestal collisionality. These features make this newly developed H-mode regime in JET with Be/W wall a valuable tool for exploring the underlying transport, the different mechanisms of turbulence stabilization, as well as the physics associated with the appearance of small ELMs in high-temperature plasmas at ITER relevant pedestal collisionality.
在带 Be/W 壁的 JET 中发现了低密度和低边缘安全系数（q95=3.2，Ip=3 MA）下的新 H 模式机制，它结合了高能量约束、密度和辐射的静态条件以及小边缘局部模式（ELM）。这种机制是在没有外部气体膨化的情况下实现的，从而导致边缘密度降低，基座和核心区域的旋转和离子温度大幅上升。传输模型显示，从基座区开始延伸到等离子体核心的湍流和向外的杂质对流减少了，这与在这些条件下观察到的能量限制改善和 W 积累的缺乏是一致的。此外，通常在气体燃料等离子体中出现的大型 I 型 ELM 被更小、更频繁的 ELM 所取代，而 ELM 的出现与基座密度及其梯度的大幅降低有关。在这种运行机制下，基座对剥离-气球模式是稳定的，这与缺乏大型 ELM 是一致的。这与未加燃料的 JET-C 等离子体的结果形成鲜明对比，后者通常在较高的基座密度下运行，并发展出低频、大型 I 型 ELM，从而表明低密度是在 JET 中获得小型 ELM 的关键参数之一。这种小型 ELMs 机制与预期在热核实验堆中出现的低基座碰撞性（ν∗ e,ped ∼ 0.1）相同，并在低 q95 下运行，因此有别于通常在较高 q95 和较高基座碰撞性下获得的其他小型 ELMs 机制。这些特点使得在带有 Be/W 壁的 JET 中新开发的 H 模式体系成为探索基本输运、湍流稳定的不同机制以及在热核实验堆相关基座碰撞性高温等离子体中出现小型 ELMs 的相关物理学的宝贵工具。
{"title":"Exploring the physics of a high-performance H-mode scenario with small ELMs at low collisionality in JET with Be/W wall","authors":"E. de la Luna, Jeronimo Garcia, M. Sertoli, Peter Lomas, Samuele Mazzi, Ž. Štancar, M. Dunne, Nobuyuki Aiba, S. Silburn, M. Faitsch, G. Szepesi, F. Auriemma, Itziar Balboa, L. Frassinetti, L. Garzotti, S. Menmuir, D. Réfy, F. Rimini, E. Solano, Carlo Sozzi, Milos Vecsei","doi":"10.1088/1741-4326/ad5fa0","DOIUrl":"https://doi.org/10.1088/1741-4326/ad5fa0","url":null,"abstract":"\u0000 A new H-mode regime at low density and low edge safety factor (q95=3.2, with Ip=3 MA) that combines high energy confinement, stationary conditions for density and radiation and small Edge Localized Modes (ELMs) have been found in JET with Be/W wall. Such a regime is achieved by operating without external gas puffing, leading to a decrease in the edge density and a substantial increase in rotation and ion temperature in both the pedestal and the core region. Transport modelling shows a reduction of the turbulence, which starts in the pedestal region and extends into the plasma core, and outward impurity convection, consistent with the improved energy confinement and the lack of W accumulation observed in those conditions. In addition, large type I ELMs, typically found in gas-fuelled plasmas, are replaced by smaller and more frequent ELMs, whose appearance is correlated with a substantial reduction of the pedestal density and its gradient. Pedestals in this operating regime are stable to peeling–ballooning modes, consistent with the lack of large ELMs. This is in contrast to results in unfuelled JET-C plasmas that typically operated at higher pedestal densities and developed low frequency, large type I ELMs, thus pointing to the low density as one of the critical parameters for accessing the small ELMs in JET. This small ELMs regime exhibits the same low pedestal collisionality (ν∗\u0000 e,ped ∼ 0.1) expected in ITER and operates at low q95, thus making it different from other small ELMs regimes typically obtained at higher q95 and higher pedestal collisionality. These features make this newly developed H-mode regime in JET with Be/W wall a valuable tool for exploring the underlying transport, the different mechanisms of turbulence stabilization, as well as the physics associated with the appearance of small ELMs in high-temperature plasmas at ITER relevant pedestal collisionality.","PeriodicalId":503481,"journal":{"name":"Nuclear Fusion","volume":" 47","pages":""},"PeriodicalIF":0.0,"publicationDate":"2024-07-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141673176","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-07-03DOI: 10.1088/1741-4326/ad5e99
O. Ford, M. Beurskens, S. Bozhenkov, S. Lazerson, Lilla Vano, Arturo Alonso, J. Baldzuhn, C. Beidler, Christoph Biedermann, R. Burhenn, Golo Fuchert, D. Hartmann, Matthias Hirsch, A. Langenberg, Heinrich Laqua, P. McNeely, N. Pablant, E. Pasch, Felix Reimold, T. Romba, N. Rust, Ralf Schroeder, Evan Scott, Torsten Stange, Hakan M Smith, D. Gradic, R. C. Wolf, Daihong Zhang
In the Wendelstein 7-X (W7-X) stellarator, turbulence is the dominant transport mechanism in most discharges. This leads to a 'clamping' of ion temperature over a wide range of heating power, predominantly flat density profiles where hollow profiles driven by neoclassical thermo-diffusion would be expected and by rapid impurity transport in injection experiments. Significantly reduced turbulent transport is observed in the presence of strong core density gradients found transiently after core pellet injection and irregularly after boronisation or boron pellet injection. Density peaking is also achieved in a controlled manner in purely neutral beam heated discharges where particle transport analysis reveals an abrupt reduction in the main-ion particle flux leading to significant density profile peaking not explained by the NBI particle source alone. The plasmas exhibit a heat diffusivity of around chi=0.25±0.1 m^2 s^-1 at mid radius, a factor of around 4 lower than ECRH dominated discharges. Despite the improved confinement, the achieved ion temperature is limited by broader heat deposition and the lower power-per-particle given the higher density. This is overcome with limited reintroduction of ECRH power, where the low heat diffusivity diffusivity is maintained, the density rise supressed and ion temperatures above the clamping limit are achieved. The applicability of these plasmas for a high performance scenario on transport relevant time scales is assessed, including initial predictions for planned heating upgrades of W7-X, based on a range of assumptions about particle transport.
{"title":"Turbulence-reduced high-performance scenarios in Wendelstein 7-X","authors":"O. Ford, M. Beurskens, S. Bozhenkov, S. Lazerson, Lilla Vano, Arturo Alonso, J. Baldzuhn, C. Beidler, Christoph Biedermann, R. Burhenn, Golo Fuchert, D. Hartmann, Matthias Hirsch, A. Langenberg, Heinrich Laqua, P. McNeely, N. Pablant, E. Pasch, Felix Reimold, T. Romba, N. Rust, Ralf Schroeder, Evan Scott, Torsten Stange, Hakan M Smith, D. Gradic, R. C. Wolf, Daihong Zhang","doi":"10.1088/1741-4326/ad5e99","DOIUrl":"https://doi.org/10.1088/1741-4326/ad5e99","url":null,"abstract":"\u0000 In the Wendelstein 7-X (W7-X) stellarator, turbulence is the dominant transport mechanism in most discharges. This leads to a 'clamping' of ion temperature over a wide range of heating power, predominantly flat density profiles where hollow profiles driven by neoclassical thermo-diffusion would be expected and by rapid impurity transport in injection experiments. Significantly reduced turbulent transport is observed in the presence of strong core density gradients found transiently after core pellet injection and irregularly after boronisation or boron pellet injection. Density peaking is also achieved in a controlled manner in purely neutral beam heated discharges where particle transport analysis reveals an abrupt reduction in the main-ion particle flux leading to significant density profile peaking not explained by the NBI particle source alone. The plasmas exhibit a heat diffusivity of around chi=0.25±0.1 m^2 s^-1 at mid radius, a factor of around 4 lower than ECRH dominated discharges. Despite the improved confinement, the achieved ion temperature is limited by broader heat deposition and the lower power-per-particle given the higher density. This is overcome with limited reintroduction of ECRH power, where the low heat diffusivity diffusivity is maintained, the density rise supressed and ion temperatures above the clamping limit are achieved. The applicability of these plasmas for a high performance scenario on transport relevant time scales is assessed, including initial predictions for planned heating upgrades of W7-X, based on a range of assumptions about particle transport.","PeriodicalId":503481,"journal":{"name":"Nuclear Fusion","volume":"94 8","pages":""},"PeriodicalIF":0.0,"publicationDate":"2024-07-03","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141683848","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-07-03DOI: 10.1088/1741-4326/ad5e95
Arzoo Malwal, B. P. Sahoo, Devendra Sharma, Yuhe Feng
Coupled plasma-neutral transport simulations are performed of ADITYA-Upgrade tokamak scrape-off layer (SOL) plasma where flows in the core and SOL were measured to reverse sign with density variation. The simulations per- formed using EMC3-Eirene plasma-neutral code combination incorporate the toroidally continuous high-field-side belt-limiter placed in a moderate-circular tokamak equilibrium. Development of mutually counter-propagating toroidal plasma flows in top and bottom regions of both SOL and core is recovered for relatively high upstream density cases with high input power (300 kW and 3 m 2 s −1 ). The origin of the flows is traced to the poloidal density variation introduced by high recycling on the inboard localized belt limiter. The results are compared with the similar observations, for example, in Doppler shifted passive charge exchange line emission on the ADITYA-Upgrade (ADITYA-U) tokamak , highlighting the role played by residual stress in the total Reynold stress. The external stimuli, like a localized gas puff, are discussed as potential drivers of flow, by means of residual stress, based on the existing resonant model of the tokamak plasma rotation.
对ADITYA-Upgrade托卡马克刮除层（SOL）等离子体进行了等离子体-中性输运耦合模拟。模拟使用 EMC3-Eirene 等离子体中性代码组合，将环形连续高场边带限制器置于中圆托卡马克平衡中。在输入功率相对较高的情况下（300 kW 和 3 m 2 s -1 ），恢复了 SOL 和堆芯顶部和底部区域相互逆向推进的环形等离子体流的发展。等离子流的起源可追溯到内侧局部带限制器的高回收率所带来的极性密度变化。研究结果与类似的观测结果进行了比较，例如，ADITYA-U（ADITYA-U）托卡马克上多普勒频移的被动电荷交换线发射，突出了残余应力在总雷诺应力中所起的作用。在现有托卡马克等离子体旋转共振模型的基础上，通过残余应力，讨论了外部刺激（如局部气体脉冲）作为流动潜在驱动力的问题。
{"title":"Off-target gradient driven flows in 3D simulations of ADITYA-Upgrade tokamak scrape-off layer plasma transport","authors":"Arzoo Malwal, B. P. Sahoo, Devendra Sharma, Yuhe Feng","doi":"10.1088/1741-4326/ad5e95","DOIUrl":"https://doi.org/10.1088/1741-4326/ad5e95","url":null,"abstract":"\u0000 Coupled plasma-neutral transport simulations are performed of ADITYA-Upgrade tokamak scrape-off layer (SOL) plasma where flows in the core and SOL were measured to reverse sign with density variation. The simulations per- formed using EMC3-Eirene plasma-neutral code combination incorporate the toroidally continuous high-field-side belt-limiter placed in a moderate-circular tokamak equilibrium. Development of mutually counter-propagating toroidal plasma flows in top and bottom regions of both SOL and core is recovered for relatively high upstream density cases with high input power (300 kW and 3 m 2 s −1 ). The origin of the flows is traced to the poloidal density variation introduced by high recycling on the inboard localized belt limiter. The results are compared with the similar observations, for example, in Doppler shifted passive charge exchange line emission on the ADITYA-Upgrade (ADITYA-U) tokamak , highlighting the role played by residual stress in the total Reynold stress. The external stimuli, like a localized gas puff, are discussed as potential drivers of flow, by means of residual stress, based on the existing resonant model of the tokamak plasma rotation.","PeriodicalId":503481,"journal":{"name":"Nuclear Fusion","volume":"78 2","pages":""},"PeriodicalIF":0.0,"publicationDate":"2024-07-03","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141682769","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-07-03DOI: 10.1088/1741-4326/ad5e98
Xu Zhao, X. Yuan, Yufeng Dong, K. Glize, Yihang Zhang, Jun Zheng, C. Xing, Haochen Gu, Chenglong Zhang, Yu Dai, Ke Fang, Zhe Zhang, Yan Rui, Fuyuan Wu, Jie Zhang
Experiments have been performed to investigate laser-plasma instabilities (LPIs) relevant to the direct-drive inertial confinement fusion (ICF) conditions at the Shenguang-II Upgrade (SG-II UP) laser facility during the double-cone ignition (DCI) experimental campaigns, with the overlapped laser intensity ranging from 6×1014 W/cm2 to 1.8×1015 W/cm2. An overall LPI scenario has been built from the collection and investigation of angularly distributed scattered light. Across broad ranges of laser and plasma parameters, relevant to the direct-drive ICF conditions, the dominance of the stimulated Raman side scattering (SRSS) was confirmed, and its coexistence with the two-plasmon decay (TPD) was also observed. Significant SRSS scattered light was observed across an extremely wide range of emission angles, concentrated at large angles, and demonstrated to be robust throughout the parameter space. Time-resolved spectral measurements show distinctly different SRSS behaviors along different angles and a slightly higher threshold compared to the TPD. The overall SRSS energy loss was measured, indicating a scattered light energy fraction of up to 6%. These results are of crucial importance for the precise assessment of the LPIs in the DCI as well as other laser directly driven ICF schemes.
{"title":"Measurements of laser-plasma instabilities in double-cone ignition experiments relevant to the direct-drive conditions at Shenguang-II Upgrade laser facility","authors":"Xu Zhao, X. Yuan, Yufeng Dong, K. Glize, Yihang Zhang, Jun Zheng, C. Xing, Haochen Gu, Chenglong Zhang, Yu Dai, Ke Fang, Zhe Zhang, Yan Rui, Fuyuan Wu, Jie Zhang","doi":"10.1088/1741-4326/ad5e98","DOIUrl":"https://doi.org/10.1088/1741-4326/ad5e98","url":null,"abstract":"\u0000 Experiments have been performed to investigate laser-plasma instabilities (LPIs) relevant to the direct-drive inertial confinement fusion (ICF) conditions at the Shenguang-II Upgrade (SG-II UP) laser facility during the double-cone ignition (DCI) experimental campaigns, with the overlapped laser intensity ranging from 6×1014 W/cm2 to 1.8×1015 W/cm2. An overall LPI scenario has been built from the collection and investigation of angularly distributed scattered light. Across broad ranges of laser and plasma parameters, relevant to the direct-drive ICF conditions, the dominance of the stimulated Raman side scattering (SRSS) was confirmed, and its coexistence with the two-plasmon decay (TPD) was also observed. Significant SRSS scattered light was observed across an extremely wide range of emission angles, concentrated at large angles, and demonstrated to be robust throughout the parameter space. Time-resolved spectral measurements show distinctly different SRSS behaviors along different angles and a slightly higher threshold compared to the TPD. The overall SRSS energy loss was measured, indicating a scattered light energy fraction of up to 6%. These results are of crucial importance for the precise assessment of the LPIs in the DCI as well as other laser directly driven ICF schemes.","PeriodicalId":503481,"journal":{"name":"Nuclear Fusion","volume":"112 4","pages":""},"PeriodicalIF":0.0,"publicationDate":"2024-07-03","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141681716","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-07-03DOI: 10.1088/1741-4326/ad5e97
A. Cathey, M. Hölzl, Lorenz Meier, M. Dunne, G. Huijsmans, Luís Gil, G. Harrer, Nobuyuki Aiba, D. Cruz-Zabala, Karl Lackner, Stanislas Pamela, E. Viezzer, Elisabeth Wolfrum, Sibylle Günter
Large edge localised modes (ELMs) would cause an unacceptable reduction of material lifetime in future large tokamaks due to the significant amount of energy expelled from the magnetically confined region towards the plasma facing components. Thoroughly validated modelling of regimes devoid of large ELMs is crucial as it may then provide predictive insights prior to tokamak operation and design. This paper describes recent efforts pursued with the non-linear extended MHD code JOREK in the modelling of three scenarios without large ELMs: quiescent H-mode (QH-mode), quasi-continuous exhaust regime (QCE regime), and the enhanced D-alpha H-mode (EDA H-mode). For each of these regimes, the non-linear dynamics observed in the simulations are detailed and compared to experimental observations of the underlying instabilities of each regime (edge harmonic oscillation for QH-mode, small ELMs for QCE regime, and quasi-coherent mode for EDA H-mode). For QH-mode, the kink-peeling mode is found to govern the dynamics and a transition to a large ELM is obtained above the same density threshold as in the modelled experiment. For the QCE regime and EDA H-mode, resistive peeling-ballooning modes dominate and pedestal fluctuation amplitudes correspond well to experimental observations. The dominant mechanisms for the excitation and suppression of these instabilities is presented and their influence on simulation dynamics is shown. Finally, predictive simulations of edge instabilities at different values of plasma resistivity in a 4.60 MA scenario with low edge safety factor in JT-60SA are presented.
在未来的大型托卡马克中，由于从磁约束区域向等离子体面对的部件释放大量能量，大的边缘局部模态（ELMs）会导致材料寿命不可接受地缩短。对没有大型 ELM 的情况进行彻底验证建模至关重要，因为它可以在托卡马克运行和设计之前提供预测性见解。本文介绍了最近利用非线性扩展 MHD 代码 JOREK 对三种没有大型 ELM 的情况进行建模的工作：静态 H 模式（QH 模式）、准连续排气系统（QCE 系统）和增强 D-α H 模式（EDA H 模式）。针对每种模式，我们都详细介绍了模拟中观察到的非线性动力学，并将其与实验中观察到的每种模式的基本不稳定性（QH 模式的边缘谐波振荡、QCE 模式的小 ELM 和 EDA H 模式的准相干模式）进行了比较。对于 QH-模式，发现 Kink-peeling 模式控制着动力学，并且在与模拟实验中相同的密度阈值之上会过渡到大 ELM。对于 QCE 体系和 EDA H-模式，电阻剥离-气泡模式占主导地位，基座波动振幅与实验观测结果十分吻合。介绍了激发和抑制这些不稳定性的主要机制，并说明了它们对模拟动力学的影响。最后，介绍了在 JT-60SA 中边缘安全系数较低的 4.60 MA 情况下不同等离子体电阻率值的边缘不稳定性预测模拟。
{"title":"Non-linear MHD investigations of high-confinement regimes without type-I ELMs in ASDEX Upgrade and JT-60SA","authors":"A. Cathey, M. Hölzl, Lorenz Meier, M. Dunne, G. Huijsmans, Luís Gil, G. Harrer, Nobuyuki Aiba, D. Cruz-Zabala, Karl Lackner, Stanislas Pamela, E. Viezzer, Elisabeth Wolfrum, Sibylle Günter","doi":"10.1088/1741-4326/ad5e97","DOIUrl":"https://doi.org/10.1088/1741-4326/ad5e97","url":null,"abstract":"\u0000 Large edge localised modes (ELMs) would cause an unacceptable reduction of material lifetime in future large tokamaks due to the significant amount of energy expelled from the magnetically confined region towards the plasma facing components. Thoroughly validated modelling of regimes devoid of large ELMs is crucial as it may then provide predictive insights prior to tokamak operation and design. This paper describes recent efforts pursued with the non-linear extended MHD code JOREK in the modelling of three scenarios without large ELMs: quiescent H-mode (QH-mode), quasi-continuous exhaust regime (QCE regime), and the enhanced D-alpha H-mode (EDA H-mode). For each of these regimes, the non-linear dynamics observed in the simulations are detailed and compared to experimental observations of the underlying instabilities of each regime (edge harmonic oscillation for QH-mode, small ELMs for QCE regime, and quasi-coherent mode for EDA H-mode). For QH-mode, the kink-peeling mode is found to govern the dynamics and a transition to a large ELM is obtained above the same density threshold as in the modelled experiment. For the QCE regime and EDA H-mode, resistive peeling-ballooning modes dominate and pedestal fluctuation amplitudes correspond well to experimental observations. The dominant mechanisms for the excitation and suppression of these instabilities is presented and their influence on simulation dynamics is shown. Finally, predictive simulations of edge instabilities at different values of plasma resistivity in a 4.60 MA scenario with low edge safety factor in JT-60SA are presented.","PeriodicalId":503481,"journal":{"name":"Nuclear Fusion","volume":"82 3","pages":""},"PeriodicalIF":0.0,"publicationDate":"2024-07-03","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141683883","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-07-03DOI: 10.1088/1741-4326/ad5e96
Na Wu, Jun Cheng, K. Yi, Rui Wang, Mingkun Han, Zhihui Huang, Weice Wang, Yu He, Longwen Yan, Hailong Du, Jinming Gao, Huicong Ma, Xiaoxue He, Zengchen Yang, J. Wen, Kai Zhang, Ting Wu, Wenping Guo, Xin Yu, Liang Liu, Yonggao Li, Lin Nie, Zhongbing Shi, Dezhen Wang, Wulyu Zhong
Divertor detachment with the sustainable high-performance plasmas has been achieved through divertor nitrogen seeding in the HL-2A tokamak. The closed divertor structure facilitates achieving high divertor neutral pressure due to its efficient particle containment effect as demonstrated by both experimental and SOLPS simulation results, which aids in achieving the divertor detachment. The radiative divertor is conducive to high-frequency small ELMs operation, characterized by the reduced pedestal ion temperature gradient ∇T_i and the enhanced electron density gradient ∇n_e. The presence of minority nitrogen at the edge plasma, which results from the divertor nitrogen seeding, contributes to the rise of ion temperature T_i in the confinement region by suppressing the turbulence through the impurity dilution effect and E×B shear. The increased ion temperature T_i and electron density n_e compensate the energy loss resulted from the increased edge radiation during detachment, which contributes to the confinement sustainment combined with reduced pedestal energy loss caused by small ELMs. This work advances our understanding on the fundamental physics governing the closed divertor detachment with sustainable high-performance plasmas through divertor nitrogen seeding.
通过在 HL-2A 托卡马克中的憩室氮气播种，实现了可持续高性能等离子体的憩室脱离。实验和 SOLPS 模拟结果都证明，封闭式憩室结构由于其高效的粒子遏制效应，有助于实现高憩室中性压力，从而帮助实现憩室脱离。辐射分流器有利于小型 ELM 的高频运行，其特点是基座离子温度梯度∇T_i 减小，电子密度梯度∇n_e 增大。边缘等离子体中少数氮的存在是由分流器氮气播种造成的，通过杂质稀释效应和 E×B 剪切力抑制湍流，从而促进了约束区离子温度 T_i 的升高。离子温度 T_i 和电子密度 n_e 的增加补偿了脱离过程中边缘辐射增加所造成的能量损失，这有助于禁锢的维持，同时减少了小 ELM 造成的基座能量损失。这项工作加深了我们对通过导流器氮气播种实现可持续高性能等离子体的闭合导流器分离的基本物理原理的理解。
{"title":"Facilitated core-edge integration through divertor nitrogen seeding in the HL-2A tokamak","authors":"Na Wu, Jun Cheng, K. Yi, Rui Wang, Mingkun Han, Zhihui Huang, Weice Wang, Yu He, Longwen Yan, Hailong Du, Jinming Gao, Huicong Ma, Xiaoxue He, Zengchen Yang, J. Wen, Kai Zhang, Ting Wu, Wenping Guo, Xin Yu, Liang Liu, Yonggao Li, Lin Nie, Zhongbing Shi, Dezhen Wang, Wulyu Zhong","doi":"10.1088/1741-4326/ad5e96","DOIUrl":"https://doi.org/10.1088/1741-4326/ad5e96","url":null,"abstract":"\u0000 Divertor detachment with the sustainable high-performance plasmas has been achieved through divertor nitrogen seeding in the HL-2A tokamak. The closed divertor structure facilitates achieving high divertor neutral pressure due to its efficient particle containment effect as demonstrated by both experimental and SOLPS simulation results, which aids in achieving the divertor detachment. The radiative divertor is conducive to high-frequency small ELMs operation, characterized by the reduced pedestal ion temperature gradient ∇T_i and the enhanced electron density gradient ∇n_e. The presence of minority nitrogen at the edge plasma, which results from the divertor nitrogen seeding, contributes to the rise of ion temperature T_i in the confinement region by suppressing the turbulence through the impurity dilution effect and E×B shear. The increased ion temperature T_i and electron density n_e compensate the energy loss resulted from the increased edge radiation during detachment, which contributes to the confinement sustainment combined with reduced pedestal energy loss caused by small ELMs. This work advances our understanding on the fundamental physics governing the closed divertor detachment with sustainable high-performance plasmas through divertor nitrogen seeding.","PeriodicalId":503481,"journal":{"name":"Nuclear Fusion","volume":"87 11","pages":""},"PeriodicalIF":0.0,"publicationDate":"2024-07-03","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141683545","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-07-03DOI: 10.1088/1741-4326/ad5e93
Inhwan Choi, Yueqiang Liu, Yongkyoon In
Recent edge-localized modes (ELM) control experiments via Resonant Magnetic Perturbation (RMP) in KSTAR have shown a strong up/down poloidal asymmetric coupling dependence. Specifically, in lower single null (LSN) plasmas at q95≳5, the lower two-row (middle/bottom) RMPs among ITER-like three-row (top/middle/bottom) in-vessel control coils (IVCC) in KSTAR were more effective in suppressing ELM-crashes than the upper two-row (top/middle) RMPs. In contrast, at q95~4, the upper two-row RMPs turned out to be more effective than the lower counterpart. Since the ITER baseline scenario is planned to operate at q95~3, the understanding of the origin of such up/down poloidal asymmetric coupling dependence, as well as the prediction about ITER-relevant conditions at a lower q95, would be quite important and potentially impactful to the RMP ELM control in ITER. A linear, resistive, single-fluid MHD code MARS-F has been utilized to address and model the up/down poloidal asymmetric RMP coupling dependence. Specifically, based on two contrasting exemplary discharges with up/down poloidal (i) asymmetric at q95~4 and (ii) symmetric behavior at q95~5, among tens of otherwise similar discharges, a systematic MARS-F modeling has been thoroughly conducted. As a result, the plasma response investigation suggests that the X-point displacement (ξX), rather than any other figures of merit, would be a directly relevant metric for the up/down poloidal asymmetric coupling in RMP-driven, ELM-crash suppression in KSTAR. Based on a sensitivity study of the edge safety factor in MARS-F modeling, the ξX variation follows the same quantitative trend as observed in experiments. However, no or little plasma pressure dependence has been found, though ξX increases with plasma pressure. At the ITER-relevant low q95~3 in a scaled KSTAR equilibrium, such modeling predicts the upper two-row RMPs would be more favorable in suppressing the ELM-crashes than the lower counterpart.
{"title":"Origin of the up/down poloidal asymmetric dependence of ELM control in ITER-like RMP configuration in KSTAR","authors":"Inhwan Choi, Yueqiang Liu, Yongkyoon In","doi":"10.1088/1741-4326/ad5e93","DOIUrl":"https://doi.org/10.1088/1741-4326/ad5e93","url":null,"abstract":"\u0000 Recent edge-localized modes (ELM) control experiments via Resonant Magnetic Perturbation (RMP) in KSTAR have shown a strong up/down poloidal asymmetric coupling dependence. Specifically, in lower single null (LSN) plasmas at q95≳5, the lower two-row (middle/bottom) RMPs among ITER-like three-row (top/middle/bottom) in-vessel control coils (IVCC) in KSTAR were more effective in suppressing ELM-crashes than the upper two-row (top/middle) RMPs. In contrast, at q95~4, the upper two-row RMPs turned out to be more effective than the lower counterpart. Since the ITER baseline scenario is planned to operate at q95~3, the understanding of the origin of such up/down poloidal asymmetric coupling dependence, as well as the prediction about ITER-relevant conditions at a lower q95, would be quite important and potentially impactful to the RMP ELM control in ITER. A linear, resistive, single-fluid MHD code MARS-F has been utilized to address and model the up/down poloidal asymmetric RMP coupling dependence. Specifically, based on two contrasting exemplary discharges with up/down poloidal (i) asymmetric at q95~4 and (ii) symmetric behavior at q95~5, among tens of otherwise similar discharges, a systematic MARS-F modeling has been thoroughly conducted. As a result, the plasma response investigation suggests that the X-point displacement (ξX), rather than any other figures of merit, would be a directly relevant metric for the up/down poloidal asymmetric coupling in RMP-driven, ELM-crash suppression in KSTAR. Based on a sensitivity study of the edge safety factor in MARS-F modeling, the ξX variation follows the same quantitative trend as observed in experiments. However, no or little plasma pressure dependence has been found, though ξX increases with plasma pressure. At the ITER-relevant low q95~3 in a scaled KSTAR equilibrium, such modeling predicts the upper two-row RMPs would be more favorable in suppressing the ELM-crashes than the lower counterpart.","PeriodicalId":503481,"journal":{"name":"Nuclear Fusion","volume":"72 4","pages":""},"PeriodicalIF":0.0,"publicationDate":"2024-07-03","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141684182","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-07-03DOI: 10.1088/1741-4326/ad5e94
Yiren Zhu, Wulyu Zhong, Xiao Lan Zou, Jiaxian Li, M. Xue, Zhengji Li, Lei Xue, Guoliang Xiao, Ruihai Tong, Y. Zou, Jiao Yin, Anshu Liang, Linzi Liu, B. Yuan, Min Xu
As the newly built tokamak in China, HL-3 is going to explore high performance operation scenario such as super H-mode. The energy confinement and core parameters in super H-mode can be much larger than that in normal H-mode. Based on the pedestal simulation code EPED, the operation space of super H-mode is obtained in HL-3. Magnetic shear decreases with increasing triangularity, and then the super H-mode can be achieved. The threshold of triangularity for accessing super H-mode in HL-3 is around 0.4. By using BOUT++, nonlinear simulation study of the pedestal instabilities in super H-mode equilibrium is executed for the first time. As expected, low n peeling mode which can cause much energy loss (17%) from the pedestal region is dominant in super H-mode. Such a big collapse at pedestal region will lead the transition of super H-mode to H-mode. It is crucial to expand the parameter space of the super H-mode or mitigate the ELM size for sustaining the super H-mode operation. E×B velocity shear is found to play an important role for controlling the ELMs in HL-3. On the one hand, small E×B velocity shear leads to large growth rate but small ELM size around peeling boundary. ELM size is closely related with both of growth rate of peeling-ballooning mode and duration time of linear phase. On the other hand, large E×B velocity shear can stabilize the instabilities near ballooning boundary, and then the parameter space of super H-mode will be enlarged.
作为中国新建的托卡马克，HL-3 将探索超 H 模式等高性能运行方案。超 H 模式的能量约束和堆芯参数可能远大于普通 H 模式。基于基座模拟代码 EPED，HL-3 获得了超 H 模式的运行空间。磁剪切随三角形度的增大而减小，进而实现超 H 模式。HL-3 中进入超 H 模式的三角度临界值约为 0.4。通过使用 BOUT++，首次对超 H 模式平衡中的基座不稳定性进行了非线性模拟研究。不出所料，在超 H 模式中，低 n 剥离模式占主导地位，这种模式会导致基座区能量损失很大（17%）。基座区如此大的塌陷将导致超 H 模式向 H 模式过渡。因此，扩大超 H 模式的参数空间或减小 ELM 的尺寸对于维持超 H 模式的运行至关重要。研究发现，E×B 速度剪切对控制 HL-3 中的 ELM 起着重要作用。一方面，小的 E×B 速度剪切力会导致剥离边界附近的 ELM 增长率大而 ELM 尺寸小。ELM 尺寸与剥离-气泡模式的增长率和线性阶段的持续时间密切相关。另一方面，大的 E×B 速度剪切力可以稳定气球边界附近的不稳定性，从而扩大超 H 模式的参数空间。
{"title":"Nonlinear simulation of peeling-ballooning instability of super H-mode in the HL-3 tokamak","authors":"Yiren Zhu, Wulyu Zhong, Xiao Lan Zou, Jiaxian Li, M. Xue, Zhengji Li, Lei Xue, Guoliang Xiao, Ruihai Tong, Y. Zou, Jiao Yin, Anshu Liang, Linzi Liu, B. Yuan, Min Xu","doi":"10.1088/1741-4326/ad5e94","DOIUrl":"https://doi.org/10.1088/1741-4326/ad5e94","url":null,"abstract":"\u0000 As the newly built tokamak in China, HL-3 is going to explore high performance operation scenario such as super H-mode. The energy confinement and core parameters in super H-mode can be much larger than that in normal H-mode. Based on the pedestal simulation code EPED, the operation space of super H-mode is obtained in HL-3. Magnetic shear decreases with increasing triangularity, and then the super H-mode can be achieved. The threshold of triangularity for accessing super H-mode in HL-3 is around 0.4. By using BOUT++, nonlinear simulation study of the pedestal instabilities in super H-mode equilibrium is executed for the first time. As expected, low n peeling mode which can cause much energy loss (17%) from the pedestal region is dominant in super H-mode. Such a big collapse at pedestal region will lead the transition of super H-mode to H-mode. It is crucial to expand the parameter space of the super H-mode or mitigate the ELM size for sustaining the super H-mode operation. E×B velocity shear is found to play an important role for controlling the ELMs in HL-3. On the one hand, small E×B velocity shear leads to large growth rate but small ELM size around peeling boundary. ELM size is closely related with both of growth rate of peeling-ballooning mode and duration time of linear phase. On the other hand, large E×B velocity shear can stabilize the instabilities near ballooning boundary, and then the parameter space of super H-mode will be enlarged.","PeriodicalId":503481,"journal":{"name":"Nuclear Fusion","volume":"155 2","pages":""},"PeriodicalIF":0.0,"publicationDate":"2024-07-03","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141681796","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-07-02DOI: 10.1088/1741-4326/ad5dcd
U. Fantz, Dirk Wünderlich, Christian Wimmer, M. Barnes, N. den Harder, B. Heinemann, Adrian Heiler, M. Lindqvist, F. Merk, Araceli Navarro, R. Nocentini, G. Orozco, R. Riedl, D. Yordanov, D. Zielke
ITER’s NBI systems are a first of its kind system with very challenging targets for the RF-driven ion source and the acceleration stage. In a step ladder approach, the ion source test facilities BATMAN Upgrade (BUG) and ELISE support the activities carried out at the Neutral Beam Test Facility (NBTF), Padua, which is equipped with the ion source facility SPIDER and with MITICA being equivalent to the ITER Heating Neutral Beam injector (HNB), capable of operating at the full power and pulse length of the ITER HNBs. The contributions of the prototype ion source at BUG (1/8 scale) and the size scaling experiment ELISE (1/2 size ITER source) to the roadmap are manifold: for hydrogen operation the ion source performance is demonstrated in several sequential 1000 s pulses, whereas long pulse deuterium operation is limited by the heat load of the co-extracted electrons on the extraction grid. Measures like special magnetic filter field configurations or biasing of surfaces and improved Cs management are identified. Both facilities have recently been extended to full steady state compatibility and very first insights of the ion source performance are already gained. A pulse length of 400 s, as required for the first deuterium campaigns at ITER, seems to be feasible soon, whereas the one hour pulse imposes the highest challenge to overcome. Investigations on beam divergence revealed a divergence at the upper limit of the acceptable value for the HNB. Measurements on the beam uniformity on the scale of beamlet groups and grid segments at ELISE demonstrated a uniformity of better than the required 90%. BUG and ELISE gave input to recent implementations at SPIDER; MITICA and ITER’s NBI. Still open points and challenges are addressed, for which a continuation of the step ladder approach is essential.
{"title":"Contributions of the extended ELISE and BATMAN Upgrade test facilities to the roadmap towards ITER NBI","authors":"U. Fantz, Dirk Wünderlich, Christian Wimmer, M. Barnes, N. den Harder, B. Heinemann, Adrian Heiler, M. Lindqvist, F. Merk, Araceli Navarro, R. Nocentini, G. Orozco, R. Riedl, D. Yordanov, D. Zielke","doi":"10.1088/1741-4326/ad5dcd","DOIUrl":"https://doi.org/10.1088/1741-4326/ad5dcd","url":null,"abstract":"\u0000 ITER’s NBI systems are a first of its kind system with very challenging targets for the RF-driven ion source and the acceleration stage. In a step ladder approach, the ion source test facilities BATMAN Upgrade (BUG) and ELISE support the activities carried out at the Neutral Beam Test Facility (NBTF), Padua, which is equipped with the ion source facility SPIDER and with MITICA being equivalent to the ITER Heating Neutral Beam injector (HNB), capable of operating at the full power and pulse length of the ITER HNBs. The contributions of the prototype ion source at BUG (1/8 scale) and the size scaling experiment ELISE (1/2 size ITER source) to the roadmap are manifold: for hydrogen operation the ion source performance is demonstrated in several sequential 1000 s pulses, whereas long pulse deuterium operation is limited by the heat load of the co-extracted electrons on the extraction grid. Measures like special magnetic filter field configurations or biasing of surfaces and improved Cs management are identified. Both facilities have recently been extended to full steady state compatibility and very first insights of the ion source performance are already gained. A pulse length of 400 s, as required for the first deuterium campaigns at ITER, seems to be feasible soon, whereas the one hour pulse imposes the highest challenge to overcome. Investigations on beam divergence revealed a divergence at the upper limit of the acceptable value for the HNB. Measurements on the beam uniformity on the scale of beamlet groups and grid segments at ELISE demonstrated a uniformity of better than the required 90%. BUG and ELISE gave input to recent implementations at SPIDER; MITICA and ITER’s NBI. Still open points and challenges are addressed, for which a continuation of the step ladder approach is essential.","PeriodicalId":503481,"journal":{"name":"Nuclear Fusion","volume":"23 8","pages":""},"PeriodicalIF":0.0,"publicationDate":"2024-07-02","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141685594","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-07-01DOI: 10.1088/1741-4326/ad5d7b
Xuan Sun, Cihan Akcay, Torrin Bechtel, Scott Kruger, L. Lao, Yueqiang Liu, Sandeep Madireddy, Joseph McClenaghan
Kinetic equilibrium reconstructions make use of profile information such as particle density and temperature measurements in addition to magnetics data to compute a self-consistent equilibrium. They are used in a multitude of physics-based modeling. This work develops a multi-layer perceptron (MLP) neural network (NN) model as a surrogate for kinetic Equilibrium Fitting (EFITs) and trains on the 2019 DIIID discharge campaign database of kinetic equilibrium reconstructions. We investigate the impact of including various diagnostic data and machine actuator controls as input into the NN. When giving various categories of data as input into NN models that have been trained using those same categories of data, the predictions on multiple equilibrium reconstruction solutions (poloidal magnetic flux, global scalars, pressure profile, current profile) are highly accurate. When comparing different models with different diagnostics as input, the magnetics-only model outputs accurate kinetic profiles and the inclusion of additional data does not significantly impact the accuracy. When the NN is tasked with inferring only a single target such as the EFIT pressure profile or EFIT current profile, we see a large increase in the accuracy of the prediction of the kinetic profiles as more data is included. These results indicate that certain MLP NN configurations can be reasonably robust to different burning-plasma-relevant diagnostics depending on the accuracy requirements for equilibrium reconstruction tasks.
动力学平衡重构除了利用磁学数据外，还利用颗粒密度和温度测量等剖面信息来计算自洽平衡。它们被用于多种基于物理的建模。这项工作开发了一种多层感知器（MLP）神经网络（NN）模型，作为动力学平衡拟合（EFITs）的替代物，并在2019年DIIID放电活动动力学平衡重建数据库上进行训练。我们研究了将各种诊断数据和机器致动器控制作为 NN 输入的影响。当将各类数据输入到使用同类数据训练的 NN 模型中时，对多种平衡重构方案（极磁通量、全局标量、压力剖面、电流剖面）的预测非常准确。在比较以不同诊断结果为输入的不同模型时，仅有磁性的模型能输出准确的动力学剖面图，加入其他数据对准确性没有显著影响。当 NN 只负责推断单个目标（如 EFIT 压力剖面或 EFIT 电流剖面）时，我们发现随着数据的增加，动能剖面预测的准确性也大幅提高。这些结果表明，根据平衡重建任务的精度要求，某些 MLP NN 配置对不同的燃烧等离子体相关诊断具有合理的鲁棒性。
{"title":"Impact of various DIII-D diagnostics on the accuracy of neural network surrogates for kinetic EFIT reconstructions","authors":"Xuan Sun, Cihan Akcay, Torrin Bechtel, Scott Kruger, L. Lao, Yueqiang Liu, Sandeep Madireddy, Joseph McClenaghan","doi":"10.1088/1741-4326/ad5d7b","DOIUrl":"https://doi.org/10.1088/1741-4326/ad5d7b","url":null,"abstract":"\u0000 Kinetic equilibrium reconstructions make use of profile information such as particle density and temperature measurements in addition to magnetics data to compute a self-consistent equilibrium. They are used in a multitude of physics-based modeling. This work develops a multi-layer perceptron (MLP) neural network (NN) model as a surrogate for kinetic Equilibrium Fitting (EFITs) and trains on the 2019 DIIID discharge campaign database of kinetic equilibrium reconstructions. We investigate the impact of including various diagnostic data and machine actuator controls as input into the NN. When giving various categories of data as input into NN models that have been trained using those same categories of data, the predictions on multiple equilibrium reconstruction solutions (poloidal magnetic flux, global scalars, pressure profile, current profile) are highly accurate. When comparing different models with different diagnostics as input, the magnetics-only model outputs accurate kinetic profiles and the inclusion of additional data does not significantly impact the accuracy. When the NN is tasked with inferring only a single target such as the EFIT pressure profile or EFIT current profile, we see a large increase in the accuracy of the prediction of the kinetic profiles as more data is included. These results indicate that certain MLP NN configurations can be reasonably robust to different burning-plasma-relevant diagnostics depending on the accuracy requirements for equilibrium reconstruction tasks.","PeriodicalId":503481,"journal":{"name":"Nuclear Fusion","volume":"28 3","pages":""},"PeriodicalIF":0.0,"publicationDate":"2024-07-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141691093","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
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