Pub Date : 2024-09-18DOI: 10.1088/1741-4326/ad7967
Guanqiong Wang, Hang Li, Xin Li, Chenguang Li, Xindong Li, Ruihua Xu, Ruidong Zhu, Lulu Li, Huasen Zhang, Yingkui Zhao, Min Wang, Liang Guo, Jinhua Zheng, Longfei Jing, Wei Jiang, Bo Deng, Keli Deng, Yunsong Dong, Dong Yang, Jiamin Yang and Zongqing Zhao
Double shell capsule can provide a potential low-convergence to fusion ignition at relatively low temperature (∼3 keV). One of the main sources of degrading double shell implosion performance is the low-mode asymmetries. Recently, the experiments on the evolution of low-mode asymmetries introduced by x-ray P2 drive asymmetry during double shell implosions were carried out on the SG facility, where the outer shell and inner shell shapes were measured through the backlit radiography, and the fuel shape near stagnation was measured by core x-ray self-emission imaging. The time-dependent x-ray flux symmetry was controlled by varying the inner cone fraction, defined as the ratio of the inner cone power to the total laser power, while keeping the drive temperature histories same across experiments. Both the hohlraum radiation and the capsule implosions were analyzed using a two-dimensional radiation-hydrodynamics code. Comparing the experimental radiographs and self-emission images to the simulations, it is found that the simulated outer shell, inner shell and hot spot shapes are in qualitative agreement with experiments, especially, the symmetry swings of the hot spot shape near stagnation are observed from both experimental and simulation results. Further, the effect of x-ray drive asymmetries on double shell implosion performance is preliminarily investigated using numerical simulations. We find that the azimuthal variations in radial velocity caused by drive asymmetries can generate azimuthal mass flow of the inner shell, thus kinetic energy of the inner shell would be not converted into fuel internal energy with high efficiency, and the mass-averaged ion temperature of the fuel at stagnation would be reduced.
双壳囊可以在相对较低的温度（∼3 keV）下提供潜在的低聚变点火。双壳内爆性能下降的主要原因之一是低模不对称。最近，在 SG 设备上进行了双壳内爆过程中 X 射线 P2 驱动不对称引入的低模不对称演变实验，通过背光射线照相测量了外壳和内壳形状，并通过堆芯 X 射线自发射成像测量了停滞附近的燃料形状。随时间变化的 X 射线通量对称性是通过改变内锥体分数（定义为内锥体功率与激光总功率之比）来控制的，同时保持各次实验的驱动温度恒定不变。使用二维辐射流体力学代码分析了呼伦辐射和囊内爆。对比实验辐射图和自发射图像与模拟结果，发现模拟的外壳、内壳和热点形状与实验结果基本一致，特别是实验和模拟结果都观察到了停滞附近热点形状的对称摆动。此外，我们还利用数值模拟初步研究了 X 射线驱动不对称对双壳内爆性能的影响。我们发现，由驱动不对称引起的径向速度方位角变化会产生内壳的方位角质量流，因此内壳的动能不会高效地转化为燃料内能，燃料在停滞时的质量平均离子温度也会降低。
{"title":"Evolution of low-mode asymmetries introduced by x-ray P2 drive asymmetry during double shell implosions on the SG facility","authors":"Guanqiong Wang, Hang Li, Xin Li, Chenguang Li, Xindong Li, Ruihua Xu, Ruidong Zhu, Lulu Li, Huasen Zhang, Yingkui Zhao, Min Wang, Liang Guo, Jinhua Zheng, Longfei Jing, Wei Jiang, Bo Deng, Keli Deng, Yunsong Dong, Dong Yang, Jiamin Yang and Zongqing Zhao","doi":"10.1088/1741-4326/ad7967","DOIUrl":"https://doi.org/10.1088/1741-4326/ad7967","url":null,"abstract":"Double shell capsule can provide a potential low-convergence to fusion ignition at relatively low temperature (∼3 keV). One of the main sources of degrading double shell implosion performance is the low-mode asymmetries. Recently, the experiments on the evolution of low-mode asymmetries introduced by x-ray P2 drive asymmetry during double shell implosions were carried out on the SG facility, where the outer shell and inner shell shapes were measured through the backlit radiography, and the fuel shape near stagnation was measured by core x-ray self-emission imaging. The time-dependent x-ray flux symmetry was controlled by varying the inner cone fraction, defined as the ratio of the inner cone power to the total laser power, while keeping the drive temperature histories same across experiments. Both the hohlraum radiation and the capsule implosions were analyzed using a two-dimensional radiation-hydrodynamics code. Comparing the experimental radiographs and self-emission images to the simulations, it is found that the simulated outer shell, inner shell and hot spot shapes are in qualitative agreement with experiments, especially, the symmetry swings of the hot spot shape near stagnation are observed from both experimental and simulation results. Further, the effect of x-ray drive asymmetries on double shell implosion performance is preliminarily investigated using numerical simulations. We find that the azimuthal variations in radial velocity caused by drive asymmetries can generate azimuthal mass flow of the inner shell, thus kinetic energy of the inner shell would be not converted into fuel internal energy with high efficiency, and the mass-averaged ion temperature of the fuel at stagnation would be reduced.","PeriodicalId":19379,"journal":{"name":"Nuclear Fusion","volume":"25 1","pages":""},"PeriodicalIF":3.3,"publicationDate":"2024-09-18","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142259795","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 : 2024-09-18DOI: 10.1088/1741-4326/ad7969
L. Chen, E. Wolfrum, O. Pan, B. Kurzan, M. Bernert, D. Brida, M. Cavedon, R. Dux, R. Fischer, M. Griener, O. Grover, U. Plank, D. Stieglitz, A. Zito and the ASDEX Upgrade Team
The highly radiating nitrogen-seeded H-mode plasmas in unfavorable BT has been characterized in the ASDEX Upgrade tokamak (AUG). Three levels of nitrogen puffing rates have been injected into a fully detached H-mode plasma, which is run in lower single null configuration with the ion drift away from the X-point. A cold ( eV) highly radiating ( ) region forms close to the X-point immediately after nitrogen seeding, as evidenced by measurements of the divertor Thomson scattering (DTS) and the two-dimensional bolometry reconstructions. In addition, the radiator moves further upwards above the X-point along the separatrix at the high-field side (HFS) with increasing nitrogen puffing rates, as evidenced by the Absolute eXtended UltraViolet (AXUV) measurements. The formation of the highly radiating regime is closely correlated to the modifications of the divertor plasma conditions. Along the line of sight of the DTS measurement, the electron temperature reduces down to a few eV, which initials near the X-point and further extends to the HFS scrape-off layer (SOL) simultaneously with the upward movement of the radiator, however, the electron temperature sustains ( eV) at the low-field side (LFS) SOL with slightly decreased electron density. The highly radiating regime shows LFS/HFS divertor asymmetry, in contrast to that for H-mode plasmas in favorable BT, suggesting that the drifts play an important role for the formation of the highly radiating X-point regime at AUG. The neutral particle flux increases significantly (factor of ) in the private flux region, while it increases slightly ( ) in the main chamber, thus suggesting an enhanced sub-divertor neutral compression with the formation of the highly radiating regime. Furthermore, a degradation of the pedestal electron density was observed with an enhancement of the electron temperature further inside the pedestal, and complete divertor detachment was achieved by nitrogen seeding with sustained plasma confinement. Finally, particle sources and flow patterns of deuterium and nitrogen ions have been analyzed by SOLPS-ITER modelling, confirming that the drift plays an important role for the formation of the highly radiating regime in unfavorable BT at AUG.
在 ASDEX 升级托卡马克（AUG）中对不利 BT 条件下的高辐射氮封 H 模式等离子体进行了表征。向一个完全分离的 H 模式等离子体注入了三个级别的氮气膨化率，该等离子体以离子漂离 X 点的较低单空配置运行。氮气注入后，在 X 点附近立即形成了一个冷（eV）高辐射（）区，这一点可以从分流汤姆逊散射（DTS）测量和二维波长测量重建中得到证明。此外，随着氮气膨化率的增加，辐射器沿着高场侧（HFS）的分离矩阵在 X 点上方进一步向上移动，这一点可以通过绝对扩展紫外（AXUV）测量得到证明。高辐射机制的形成与改良分流器等离子体条件密切相关。沿着DTS测量的视线，电子温度降低到几个eV，最初在X点附近，随着辐射器的向上运动，电子温度进一步延伸到HFS刮除层（SOL），然而，在低场侧（LFS）SOL，电子温度维持在（eV），电子密度略有下降。高辐射体制显示出 LFS/HFS 分流器的不对称性，这与有利 BT 条件下的 H 模式等离子体相反，表明漂移在 AUG 高辐射 X 点体制的形成中起了重要作用。中性粒子通量在私人通量区显著增加（系数为 ），而在主室则略有增加（ ），这表明随着高辐射体制的形成，二分器下中性压缩增强。此外，随着基座内部电子温度的进一步提高，基座电子密度也出现了下降，而通过持续等离子体约束的氮气播种，实现了憩室的完全脱离。最后，通过 SOLPS-ITER 模型分析了氘和氮离子的粒子源和流动模式，证实了漂移在 AUG 的不利 BT 中形成高辐射状态的重要作用。
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Pub Date : 2024-09-17DOI: 10.1088/1741-4326/ad7611
Wladimir Zholobenko, Kaiyu Zhang, Andreas Stegmeir, Jan Pfennig, Konrad Eder, Christoph Pitzal, Philipp Ulbl, Michael Griener, Lidija Radovanovic, Ulrike Plank and the ASDEX Upgrade Team
The design of commercially feasible magnetic confinement fusion reactors strongly relies on the reduced turbulent transport in the plasma edge during operation in the high confinement mode (H-mode). We present first global turbulence simulations of the ASDEX Upgrade tokamak edge and scrape-off layer in ITER baseline H-mode conditions. Reasonable agreement with the experiment is obtained for outboard mid-plane measurements of plasma density, electron and ion temperature, as well as the radial electric field. The radial heat transport is underpredicted by roughly 1/3. These results were obtained with the GRILLIX code implementing a transcollisional, electromagnetic, global drift-fluid plasma model, coupled to diffusive neutrals. The transcollisional extensions include neoclassical corrections for the ion viscosity, as well as either a Landau-fluid or free-streaming limited model for the parallel heat conduction. Electromagnetic fluctuations are found to play a critical role in H-mode conditions. We investigate the structure of the significant E × B flow shear, finding both neoclassical components as well as zonal flows. But unlike in L-mode, geodesic acoustic modes are not observed. The turbulence mode structure is mostly that of drift-Alfvén waves. However, in the upper part of the pedestal, it is very weak and overshadowed by neoclassical transport. At the pedestal foot, on the other hand, we find instead the (electromagnetic) kinetic ballooning mode, most clearly just inside the separatrix. Our results pave the way towards predictive simulations of fusion reactors.
商业上可行的磁约束聚变反应堆的设计在很大程度上依赖于高约束模式（H 模式）运行期间等离子体边缘湍流传输的减少。我们首次提出了在热核实验堆基线 H 模式条件下 ASDEX 升级版托卡马克边缘和刮离层的全局湍流模拟。等离子体密度、电子和离子温度以及径向电场的外侧中平面测量结果与实验结果基本一致。径向热传输的预测值低了大约 1/3。这些结果是通过 GRILLIX 代码获得的，该代码采用了跨碰撞、电磁、全局漂移-流体等离子体模型，并与扩散中性耦合。跨碰撞扩展包括离子粘度的新古典修正，以及平行热传导的朗道流体或自由流有限模型。我们发现电磁波动在 H 模式条件下起着关键作用。我们研究了重要的 E × B 流切变的结构，发现了新古典成分和带状流。但与 L 模式不同的是，没有观测到大地声模式。湍流模式结构主要是漂移-阿尔芬波。然而，在基座的上部，湍流非常微弱，被新古典传输所掩盖。另一方面，在基座底部，我们发现了（电磁）动气球模式，在分离矩阵内部最为明显。我们的研究结果为聚变反应堆的预测模拟铺平了道路。
{"title":"Tokamak edge-SOL turbulence in H-mode conditions simulated with a global, electromagnetic, transcollisional drift-fluid model","authors":"Wladimir Zholobenko, Kaiyu Zhang, Andreas Stegmeir, Jan Pfennig, Konrad Eder, Christoph Pitzal, Philipp Ulbl, Michael Griener, Lidija Radovanovic, Ulrike Plank and the ASDEX Upgrade Team","doi":"10.1088/1741-4326/ad7611","DOIUrl":"https://doi.org/10.1088/1741-4326/ad7611","url":null,"abstract":"The design of commercially feasible magnetic confinement fusion reactors strongly relies on the reduced turbulent transport in the plasma edge during operation in the high confinement mode (H-mode). We present first global turbulence simulations of the ASDEX Upgrade tokamak edge and scrape-off layer in ITER baseline H-mode conditions. Reasonable agreement with the experiment is obtained for outboard mid-plane measurements of plasma density, electron and ion temperature, as well as the radial electric field. The radial heat transport is underpredicted by roughly 1/3. These results were obtained with the GRILLIX code implementing a transcollisional, electromagnetic, global drift-fluid plasma model, coupled to diffusive neutrals. The transcollisional extensions include neoclassical corrections for the ion viscosity, as well as either a Landau-fluid or free-streaming limited model for the parallel heat conduction. Electromagnetic fluctuations are found to play a critical role in H-mode conditions. We investigate the structure of the significant E × B flow shear, finding both neoclassical components as well as zonal flows. But unlike in L-mode, geodesic acoustic modes are not observed. The turbulence mode structure is mostly that of drift-Alfvén waves. However, in the upper part of the pedestal, it is very weak and overshadowed by neoclassical transport. At the pedestal foot, on the other hand, we find instead the (electromagnetic) kinetic ballooning mode, most clearly just inside the separatrix. Our results pave the way towards predictive simulations of fusion reactors.","PeriodicalId":19379,"journal":{"name":"Nuclear Fusion","volume":"41 1","pages":""},"PeriodicalIF":3.3,"publicationDate":"2024-09-17","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142259775","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 : 2024-09-16DOI: 10.1088/1741-4326/ad69a2
C. Giroud, I.S. Carvalho, S. Brezinsek, A. Huber, D. Keeling, J. Mailloux, R.A. Pitts, E. Lerche, R. Henriques, J. Hillesheim, K. Lawson, M. Marin, E. Pawelec, M. Sos, H.J. Sun, M. Tomes, S. Aleiferis, A. Bleasdale, M. Brix, A. Boboc, J. Bernardo, P. Carvalho, I. Coffey, S. Henderson, D.B. King, F. Rimini, M. Maslov, E. Alessi, T. Craciunescu, M. Fontana, J.M. Fontdecaba, L. Garzotti, Z. Ghani, L. Horvath, I. Jepu, J. Karhunen, D. Kos, E. Litherland-Smith, A. Meigs, S. Menmuir, R.B. Morales, S. Nowak, E. Peluso, T. Pereira, V. Parail, G. Petravich, G. Pucella, P. Puglia, D. Refy, S. Scully, M. Sertoli, S. Silburn, D. Taylor, B. Thomas, A. Tookey, Ž. Štancar, G. Szepesi, B. Viola, A. Widdowson, E. de la Luna and JET Contributors
This paper reports the first experiment carried out in deuterium–tritium addressing the integration of a radiative divertor for heat-load control with good confinement. Neon seeding was carried out for the first time in a D–T plasma as part of the second D–T campaign of JET with its Be/W wall environment. The technical difficulties linked to the re-ionisation heat load are reported in T and D–T. This paper compares the impact of neon seeding on D–T plasmas and their D counterpart on the divertor detachment, localisation of the radiation, scrape-off profiles, pedestal structure, edge localised modes and global confinement.
{"title":"The core–edge integrated neon-seeded scenario in deuterium–tritium at JET","authors":"C. Giroud, I.S. Carvalho, S. Brezinsek, A. Huber, D. Keeling, J. Mailloux, R.A. Pitts, E. Lerche, R. Henriques, J. Hillesheim, K. Lawson, M. Marin, E. Pawelec, M. Sos, H.J. Sun, M. Tomes, S. Aleiferis, A. Bleasdale, M. Brix, A. Boboc, J. Bernardo, P. Carvalho, I. Coffey, S. Henderson, D.B. King, F. Rimini, M. Maslov, E. Alessi, T. Craciunescu, M. Fontana, J.M. Fontdecaba, L. Garzotti, Z. Ghani, L. Horvath, I. Jepu, J. Karhunen, D. Kos, E. Litherland-Smith, A. Meigs, S. Menmuir, R.B. Morales, S. Nowak, E. Peluso, T. Pereira, V. Parail, G. Petravich, G. Pucella, P. Puglia, D. Refy, S. Scully, M. Sertoli, S. Silburn, D. Taylor, B. Thomas, A. Tookey, Ž. Štancar, G. Szepesi, B. Viola, A. Widdowson, E. de la Luna and JET Contributors","doi":"10.1088/1741-4326/ad69a2","DOIUrl":"https://doi.org/10.1088/1741-4326/ad69a2","url":null,"abstract":"This paper reports the first experiment carried out in deuterium–tritium addressing the integration of a radiative divertor for heat-load control with good confinement. Neon seeding was carried out for the first time in a D–T plasma as part of the second D–T campaign of JET with its Be/W wall environment. The technical difficulties linked to the re-ionisation heat load are reported in T and D–T. This paper compares the impact of neon seeding on D–T plasmas and their D counterpart on the divertor detachment, localisation of the radiation, scrape-off profiles, pedestal structure, edge localised modes and global confinement.","PeriodicalId":19379,"journal":{"name":"Nuclear Fusion","volume":"33 1","pages":""},"PeriodicalIF":3.3,"publicationDate":"2024-09-16","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142259796","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 : 2024-09-16DOI: 10.1088/1741-4326/ad75a4
P.J. Traverso, M. Knolker, M. Austin, C. Lasnier, A.W. Leonard, T. Osborne and H. Wang
Divertor heat flux and its correlation with pedestal parameters within various small edge localized mode (ELM) regimes, including high beta poloidal, type-II and ELMs with negative triangularity H-modes were investigated in DIII-D. The parallel energy fluences of type-II and high beta poloidal small ELM regimes fall below the linear scaling with pedestal electron pressure for type-I ELMs put forward in Eich et al 2017 (Nucl. Mater. Energy12 84–90). The negative triangularity of H-mode ELMs follow the Eich scaling for type-I ELMs. The parallel heat flux and total heat loads to the divertor were determined using high-time resolution infrared thermography, while pedestal parameters were obtained through self-consistent kinetic equilibrium reconstructions. Linear regressions for the type-II and high beta poloidal regimes demonstrate that an equivalent 7.5 MA small ELM scenario in ITER would fall below the ~5 leading edge melting limit for tungsten (Gunn et al 2017 Nucl. Fusion57 046025). Utilizing fast thermography, the scrape-off layer power fall-off length for both inter-ELM and intra-ELM was determined and compared to the Eich scaling with poloidal magnetic field in Eich et al (ASDEX Upgrade Team and JET EFDA Contributors 2013 Nucl. Fusion53 093031). Except for the high beta poloidal scenario, all the small ELM regimes during both inter- and intra-ELM periods had power fall-off lengths larger then would be expected from the scaling associated with type-I ELMs, signifying their potential in managing heat loads and offering a solution for core–edge integration.
在DIII-D中研究了各种小边缘局域模（ELM）状态下的掺杂热通量及其与基座参数的相关性，包括高β极性、II型和具有负三角形H模的ELM。II 型和高β极性小型 ELM 状态的平行能量通量低于 Eich 等人 2017 年提出的 I 型 ELM 与基座电子压力的线性比例（Nucl.）H 模式 ELM 的负三角形遵循 Eich 对 I 型 ELM 的缩放比例。分流器的平行热通量和总热负荷是通过高时间分辨率红外热成像确定的，而基座参数则是通过自洽动力学平衡重构获得的。II 型和高贝塔极坐标的线性回归表明，ITER 中等效的 7.5 MA 小型 ELM 方案将低于钨的 ~5 前缘熔化极限（Gunn 等 2017 Nucl.）利用快速热成像技术，确定了ELM间和ELM内的刮除层功率衰减长度，并与Eich等人的Eich缩放与极性磁场进行了比较（ASDEX升级团队和JET EFDA贡献者，2013 Nucl.Fusion53 093031）。除了高β极性情况外，所有小型ELM在ELM间期和ELM内期的功率衰减长度都比与I型ELM相关的缩放比例预期的要大，这表明它们在管理热负荷方面具有潜力，并为核边缘集成提供了一种解决方案。
{"title":"Investigation of pedestal parameters and divertor heat fluxes in small ELM regimes in DIII-D","authors":"P.J. Traverso, M. Knolker, M. Austin, C. Lasnier, A.W. Leonard, T. Osborne and H. Wang","doi":"10.1088/1741-4326/ad75a4","DOIUrl":"https://doi.org/10.1088/1741-4326/ad75a4","url":null,"abstract":"Divertor heat flux and its correlation with pedestal parameters within various small edge localized mode (ELM) regimes, including high beta poloidal, type-II and ELMs with negative triangularity H-modes were investigated in DIII-D. The parallel energy fluences of type-II and high beta poloidal small ELM regimes fall below the linear scaling with pedestal electron pressure for type-I ELMs put forward in Eich et al 2017 (Nucl. Mater. Energy12 84–90). The negative triangularity of H-mode ELMs follow the Eich scaling for type-I ELMs. The parallel heat flux and total heat loads to the divertor were determined using high-time resolution infrared thermography, while pedestal parameters were obtained through self-consistent kinetic equilibrium reconstructions. Linear regressions for the type-II and high beta poloidal regimes demonstrate that an equivalent 7.5 MA small ELM scenario in ITER would fall below the ~5 leading edge melting limit for tungsten (Gunn et al 2017 Nucl. Fusion57 046025). Utilizing fast thermography, the scrape-off layer power fall-off length for both inter-ELM and intra-ELM was determined and compared to the Eich scaling with poloidal magnetic field in Eich et al (ASDEX Upgrade Team and JET EFDA Contributors 2013 Nucl. Fusion53 093031). Except for the high beta poloidal scenario, all the small ELM regimes during both inter- and intra-ELM periods had power fall-off lengths larger then would be expected from the scaling associated with type-I ELMs, signifying their potential in managing heat loads and offering a solution for core–edge integration.","PeriodicalId":19379,"journal":{"name":"Nuclear Fusion","volume":"2 1","pages":""},"PeriodicalIF":3.3,"publicationDate":"2024-09-16","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142259798","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 : 2024-09-16DOI: 10.1088/1741-4326/ad7274
X. Chen, J. Cheng, Y. Xu, L.W. Yan, Q. Zou, Z.H. Huang, J. Chen, L. Liu, W.C. Wang, W. Zhang, N. Wu, C.F. Dong, Z.B. Shi, X.Q. Ji and W.L. Zhong
A low-frequency zonal flow-like (LFZF-like) structure peaking at f ≈ 2.0 kHz has been observed in HL-2A ohmically heated deuterium plasmas using a combined Langmuir probe array. This time-varying potential structure, which has axisymmetric characteristics (n = 0) and a finite radial correlation length (less than 1 cm), was identified to be generated by the three-wave interaction in small-scale turbulence. The results illustrate that the amplitude of the LFZF-like structure dramatically increases with the influence of impurity ions, which is mainly due to the increased strength in the nonlinear energy transfer by the turbulence vortex symmetry-breaking process. Consequently, the enhanced LFZF-like structure has the ability to stabilize the local turbulence via the shearing decorrelation mechanism as demonstrated in this experiment. The observed results given here reveal the essential role played by the LFZF-like structure in the reduction of turbulence levels, which could advance our understanding of the multi-scale physics governing turbulence and the resulting transport in magnetically confined plasmas.
{"title":"Reduction of turbulence by enhanced low-frequency zonal flow-like structures in HL-2A edge plasmas","authors":"X. Chen, J. Cheng, Y. Xu, L.W. Yan, Q. Zou, Z.H. Huang, J. Chen, L. Liu, W.C. Wang, W. Zhang, N. Wu, C.F. Dong, Z.B. Shi, X.Q. Ji and W.L. Zhong","doi":"10.1088/1741-4326/ad7274","DOIUrl":"https://doi.org/10.1088/1741-4326/ad7274","url":null,"abstract":"A low-frequency zonal flow-like (LFZF-like) structure peaking at f ≈ 2.0 kHz has been observed in HL-2A ohmically heated deuterium plasmas using a combined Langmuir probe array. This time-varying potential structure, which has axisymmetric characteristics (n = 0) and a finite radial correlation length (less than 1 cm), was identified to be generated by the three-wave interaction in small-scale turbulence. The results illustrate that the amplitude of the LFZF-like structure dramatically increases with the influence of impurity ions, which is mainly due to the increased strength in the nonlinear energy transfer by the turbulence vortex symmetry-breaking process. Consequently, the enhanced LFZF-like structure has the ability to stabilize the local turbulence via the shearing decorrelation mechanism as demonstrated in this experiment. The observed results given here reveal the essential role played by the LFZF-like structure in the reduction of turbulence levels, which could advance our understanding of the multi-scale physics governing turbulence and the resulting transport in magnetically confined plasmas.","PeriodicalId":19379,"journal":{"name":"Nuclear Fusion","volume":"1 1","pages":""},"PeriodicalIF":3.3,"publicationDate":"2024-09-16","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142260323","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 : 2024-09-16DOI: 10.1088/1741-4326/ad7474
Enrico Aymerich, Alessandra Fanni, Fabio Pisano, Giuliana Sias, Barbara Cannas, JET Contributors and WPTE Team
This paper introduces a disruption predictor constructed through a fully unsupervised two-dimensional mapping of the high-dimensional JET operational space. The primary strength of this disruption predictor lies in its inherent self-organization capability. Diverging from both supervised disruption predictors and earlier approaches suggested by the same authors, which were based on unsupervised models such as Self-Organizing or Generative Topographic Maps, this predictor eliminates the need for labeling data of disruption terminated pulses during training. In prior methods, labels were indeed required post-mapping to inform the model about the presence or absence of disruption precursors at each time instant during the disrupted discharges. In contrast, our approach in this study involves no labeling of data from disruption-terminated experiments. The Self-Organizing Map, operating without any a priori information, adeptly identifies the regions characterizing the pre-disruptive phase. Moreover, SOM discovers non-trivial relationships and captures the complicated interplay of device diagnostics on the internal plasma states from the experimental data. The provided model is highly interpretable; it allows the visualization of high-dimensional data and facilitates easy interrogation of the model to understand the reasons behind its correlations. Hence, utilizing SOMs across various devices can prove invaluable in extracting rules and identifying common patterns, thereby facilitating extrapolation to ITER of the knowledge acquired from existing tokamaks.
本文介绍了通过对高维 JET 运行空间进行完全无监督的二维映射而构建的中断预测器。这种中断预测器的主要优势在于其固有的自组织能力。与监督中断预测器和同一作者早期提出的基于自组织或生成地形图等无监督模型的方法不同，该预测器在训练过程中无需对中断终止脉冲数据进行标记。在之前的方法中，确实需要在映射后使用标签来告知模型在中断放电期间的每个时间瞬间是否存在中断前兆。相比之下，我们在本研究中采用的方法无需对中断终止实验的数据进行标记。自组织图在没有任何先验信息的情况下，就能很好地识别出中断前阶段的特征区域。此外，自组织图还能发现非对称关系，并从实验数据中捕捉设备诊断对内部等离子状态的复杂相互作用。所提供的模型具有很强的可解释性；它允许高维数据的可视化，并便于对模型进行询问，以了解其相关性背后的原因。因此，在各种装置中使用 SOM 可以证明在提取规则和识别共同模式方面非常有价值，从而有助于将从现有托卡马克获得的知识推广到热核实验堆。
{"title":"A self-organised partition of the high dimensional plasma parameter space for plasma disruption prediction","authors":"Enrico Aymerich, Alessandra Fanni, Fabio Pisano, Giuliana Sias, Barbara Cannas, JET Contributors and WPTE Team","doi":"10.1088/1741-4326/ad7474","DOIUrl":"https://doi.org/10.1088/1741-4326/ad7474","url":null,"abstract":"This paper introduces a disruption predictor constructed through a fully unsupervised two-dimensional mapping of the high-dimensional JET operational space. The primary strength of this disruption predictor lies in its inherent self-organization capability. Diverging from both supervised disruption predictors and earlier approaches suggested by the same authors, which were based on unsupervised models such as Self-Organizing or Generative Topographic Maps, this predictor eliminates the need for labeling data of disruption terminated pulses during training. In prior methods, labels were indeed required post-mapping to inform the model about the presence or absence of disruption precursors at each time instant during the disrupted discharges. In contrast, our approach in this study involves no labeling of data from disruption-terminated experiments. The Self-Organizing Map, operating without any a priori information, adeptly identifies the regions characterizing the pre-disruptive phase. Moreover, SOM discovers non-trivial relationships and captures the complicated interplay of device diagnostics on the internal plasma states from the experimental data. The provided model is highly interpretable; it allows the visualization of high-dimensional data and facilitates easy interrogation of the model to understand the reasons behind its correlations. Hence, utilizing SOMs across various devices can prove invaluable in extracting rules and identifying common patterns, thereby facilitating extrapolation to ITER of the knowledge acquired from existing tokamaks.","PeriodicalId":19379,"journal":{"name":"Nuclear Fusion","volume":"6 1","pages":""},"PeriodicalIF":3.3,"publicationDate":"2024-09-16","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142259797","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/ad7743
K. Lim, P. Ricci, L. Stenger, B. De Lucca, G. Durr-Legoupil-Nicoud, O. Février, C. Theiler and K. Verhaegh
The physical mechanisms regulating the power sharing at the outer targets of L-mode double-null (DN) configurations are investigated using nonlinear, flux-driven, three-dimensional two-fluid simulations. Scans of parameters that regulate the turbulent level, such as the plasma resistivity and the magnetic imbalance, reveal that the power asymmetry in DN configurations is determined by the combined effects of diamagnetic drift, turbulence, and geometrical factor. Leveraging these observations, an analytical theory-based scaling law for the power-sharing asymmetry is derived and compared with nonlinear simulations. These comparisons indicate that the scaling law effectively captures the trends observed in simulations. Validation with experimental data from TCV DN discharges demonstrates agreement of the scaling law with the experimental results.
通过非线性、通量驱动、三维二流体模拟，研究了调节 L 模式双空（DN）配置外部目标功率共享的物理机制。对调节湍流水平的参数（如等离子体电阻率和磁不平衡）的扫描显示，DN 配置中的功率不对称是由二磁漂移、湍流和几何因素的综合影响决定的。利用这些观察结果，我们推导出了基于分析理论的功率分享不对称比例定律，并将其与非线性模拟进行了比较。这些比较表明，缩放定律有效地捕捉到了模拟中观察到的趋势。用 TCV DN 放电的实验数据进行验证表明，缩放定律与实验结果一致。
{"title":"Predictive power-sharing scaling law in double-null L-mode plasmas","authors":"K. Lim, P. Ricci, L. Stenger, B. De Lucca, G. Durr-Legoupil-Nicoud, O. Février, C. Theiler and K. Verhaegh","doi":"10.1088/1741-4326/ad7743","DOIUrl":"https://doi.org/10.1088/1741-4326/ad7743","url":null,"abstract":"The physical mechanisms regulating the power sharing at the outer targets of L-mode double-null (DN) configurations are investigated using nonlinear, flux-driven, three-dimensional two-fluid simulations. Scans of parameters that regulate the turbulent level, such as the plasma resistivity and the magnetic imbalance, reveal that the power asymmetry in DN configurations is determined by the combined effects of diamagnetic drift, turbulence, and geometrical factor. Leveraging these observations, an analytical theory-based scaling law for the power-sharing asymmetry is derived and compared with nonlinear simulations. These comparisons indicate that the scaling law effectively captures the trends observed in simulations. Validation with experimental data from TCV DN discharges demonstrates agreement of the scaling law with the experimental results.","PeriodicalId":19379,"journal":{"name":"Nuclear Fusion","volume":"63 1","pages":""},"PeriodicalIF":3.3,"publicationDate":"2024-09-12","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142211946","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/ad751c
K.J. Callahan, L. Schmitz, Q. Pratt, T.A. Carter, G. Wang, H. Zhang, C. Holland, S.R. Haskey, A. Angulo, A. Bortolon, F. Effenberg, E.A. Belli, C. Chrystal, K.E. Thome, A. Ashourvan, T. Neiser, M. Knolker, F. Khabanov, Z. Yan, G.R. McKee, R. Chaban, R.S. Wilcox, A. Holm, F. Scotti, D. Truong and R. Gerrú
It is determined that while heat flux differences between hydrogen and deuterium isotope experiments result from natural differences in carbon impurity content at DIII-D, it is not the origin of the low to high confinement mode (L-H) transition isotope effect. More specifically, a two times larger edge radial electric field in hydrogen compared to deuterium is uncovered and believed to play an important role. The origin of this radial electric field difference is determined to have two possible origins: differences in poloidal rotation and turbulent Reynolds stress in the closed field line region, and increased outer strike point temperatures and space potentials on open field lines. Experimental observations from both profile and turbulence diagnostics are supported by nonlinear gyrokinetic simulations using the code CGYRO. Simulations illustrated heat transport isotope effects in the plasma edge and shear layer resulting from differences in impurity content, electron non-adiabaticity, and main ion mass dependent E × B shear stabilization. Turbulence prediction comparisons from flux-matched CGYRO simulations to experimental measurements including electron temperature, density and velocity fluctuations are found to be in good agreement with available data. A dedicated DIII-D experiment in hydrogen was performed to seed more carbon than naturally occurring, to match deuterium experiments, and possibly reduce the L-H power threshold based on gyro-kinetic predictions. To our surprise, while ion temperature gradient (ITG) turbulence was stabilized, nodiscernible change in L-H power threshold were observed in these special hydrogen experiments. In particular, it is noticed that the edge radial electric field and Reynolds stress were observed as nearly unchanging in the presence of ITG stabilization. These experimental data have enabled a more comprehensive picture of the multitude of isotope effects at play in fusion experiments, and the important potential connection between the confined and unconfined plasma regions in regulating L-H transition dynamics.
{"title":"Understanding the L-H isotope effect at the DIII-D tokamak and advancements in synthetic turbulence diagnostics","authors":"K.J. Callahan, L. Schmitz, Q. Pratt, T.A. Carter, G. Wang, H. Zhang, C. Holland, S.R. Haskey, A. Angulo, A. Bortolon, F. Effenberg, E.A. Belli, C. Chrystal, K.E. Thome, A. Ashourvan, T. Neiser, M. Knolker, F. Khabanov, Z. Yan, G.R. McKee, R. Chaban, R.S. Wilcox, A. Holm, F. Scotti, D. Truong and R. Gerrú","doi":"10.1088/1741-4326/ad751c","DOIUrl":"https://doi.org/10.1088/1741-4326/ad751c","url":null,"abstract":"It is determined that while heat flux differences between hydrogen and deuterium isotope experiments result from natural differences in carbon impurity content at DIII-D, it is not the origin of the low to high confinement mode (L-H) transition isotope effect. More specifically, a two times larger edge radial electric field in hydrogen compared to deuterium is uncovered and believed to play an important role. The origin of this radial electric field difference is determined to have two possible origins: differences in poloidal rotation and turbulent Reynolds stress in the closed field line region, and increased outer strike point temperatures and space potentials on open field lines. Experimental observations from both profile and turbulence diagnostics are supported by nonlinear gyrokinetic simulations using the code CGYRO. Simulations illustrated heat transport isotope effects in the plasma edge and shear layer resulting from differences in impurity content, electron non-adiabaticity, and main ion mass dependent E × B shear stabilization. Turbulence prediction comparisons from flux-matched CGYRO simulations to experimental measurements including electron temperature, density and velocity fluctuations are found to be in good agreement with available data. A dedicated DIII-D experiment in hydrogen was performed to seed more carbon than naturally occurring, to match deuterium experiments, and possibly reduce the L-H power threshold based on gyro-kinetic predictions. To our surprise, while ion temperature gradient (ITG) turbulence was stabilized, nodiscernible change in L-H power threshold were observed in these special hydrogen experiments. In particular, it is noticed that the edge radial electric field and Reynolds stress were observed as nearly unchanging in the presence of ITG stabilization. These experimental data have enabled a more comprehensive picture of the multitude of isotope effects at play in fusion experiments, and the important potential connection between the confined and unconfined plasma regions in regulating L-H transition dynamics.","PeriodicalId":19379,"journal":{"name":"Nuclear Fusion","volume":"410 1","pages":""},"PeriodicalIF":3.3,"publicationDate":"2024-09-12","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142211943","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/ad703c
Yeongsun Lee, Jong-Kyu Park and Yong-Su Na
Resonant layers in a tokamak respond to non-axisymmetric magnetic perturbations by amplifying the mode amplitude and balancing the plasma rotation through magnetic reconnection and force balance, respectively. This resonant response can be characterized by local layer parameters and especially by a single quantity in the linear regime, the so-called inner-layer Δ. The computation of Δ under two-fluid drift-MHD formalism has been progressed by reducing the order of the system in the phase space, where the shielding current is approximated as being only carried by electrons, a posteriori. In this study, we relax the approximation and compute Δ accounted for by the parallel flow associated with the ion shielding current. The posteriori is numerically verified in great agreement with the original SLAYER developed in a previous paper (J.-K. Park 2022 Phys. Plasmas29 072506). Extending the resonant layer response theory to high β plasmas, our research findings answer two important questions: how the parallel flow influences the resonant layer response and why the parallel flow effect appears in high β plasmas. The complicated plasma compression in high β regime allows the parallel flow response to give rise to the ion shielding current, which not only shifts the zero-crossing condition of the ExB flow but also enhances the field penetration threshold. Technically, the Riccati matrix transformation method is adapted to handle the numerical stiffness due to the increased order of the system. The high fidelity of this numerical method makes use of further extension of the model to higher-order systems to take other physical phenomena into account. This work is envisaged to predict the resonant layer response under high β fusion reactor conditions.
{"title":"Effect of parallel flow on resonant layer responses in high beta plasmas","authors":"Yeongsun Lee, Jong-Kyu Park and Yong-Su Na","doi":"10.1088/1741-4326/ad703c","DOIUrl":"https://doi.org/10.1088/1741-4326/ad703c","url":null,"abstract":"Resonant layers in a tokamak respond to non-axisymmetric magnetic perturbations by amplifying the mode amplitude and balancing the plasma rotation through magnetic reconnection and force balance, respectively. This resonant response can be characterized by local layer parameters and especially by a single quantity in the linear regime, the so-called inner-layer Δ. The computation of Δ under two-fluid drift-MHD formalism has been progressed by reducing the order of the system in the phase space, where the shielding current is approximated as being only carried by electrons, a posteriori. In this study, we relax the approximation and compute Δ accounted for by the parallel flow associated with the ion shielding current. The posteriori is numerically verified in great agreement with the original SLAYER developed in a previous paper (J.-K. Park 2022 Phys. Plasmas29 072506). Extending the resonant layer response theory to high β plasmas, our research findings answer two important questions: how the parallel flow influences the resonant layer response and why the parallel flow effect appears in high β plasmas. The complicated plasma compression in high β regime allows the parallel flow response to give rise to the ion shielding current, which not only shifts the zero-crossing condition of the ExB flow but also enhances the field penetration threshold. Technically, the Riccati matrix transformation method is adapted to handle the numerical stiffness due to the increased order of the system. The high fidelity of this numerical method makes use of further extension of the model to higher-order systems to take other physical phenomena into account. This work is envisaged to predict the resonant layer response under high β fusion reactor conditions.","PeriodicalId":19379,"journal":{"name":"Nuclear Fusion","volume":"28 1","pages":""},"PeriodicalIF":3.3,"publicationDate":"2024-09-12","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142211961","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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