Pub Date : 2024-04-21DOI: 10.1088/1361-6587/ad3c1c
O Février, C K Tsui, G Durr-Legoupil-Nicoud, C Theiler, M Carpita, S Coda, C Colandrea, B P Duval, S Gorno, E Huett, B Linehan, A Perek, L Porte, H Reimerdes, O Sauter, E Tonello, M Zurita, T Bolzonella, F Sciortino, the TCV Team and the EUROfusion Tokamak Exploitation Team
In recent years, negative triangularity (NT) has emerged as a potential high-confinement L-mode reactor solution. In this work, detachment is investigated using core density ramps in lower single null Ohmic L-mode plasmas across a wide range of upper, lower, and average triangularity (the mean of upper and lower triangularity: δ) in the TCV tokamak. It is universally found that detachment is more difficult to access for NT shaping. The outer divertor leg of discharges with could not be cooled to below through core density ramps alone. The behavior of the upstream plasma and geometrical divertor effects (e.g. a reduced connection length with negative lower triangularity) do not fully explain the challenges in detaching NT plasmas. Langmuir probe measurements of the target heat flux widths (λq) were constant to within 30% across an upper triangularity scan, while the spreading factor S was lower by up to 50% for NT, indicating a generally lower integral scrape-off layer width, λint. The line-averaged core density was typically higher for NT discharges for a given fuelling rate, possibly linked to higher particle confinement in NT. Conversely, the divertor neutral pressure and integrated particle fluxes to the targets were typically lower for the same line-averaged density, indicating that NT configurations may be closer to the sheath-limited regime than their PT counterparts, which may explain why NT is more challenging to detach.
近年来,负三角形(NT)已成为一种潜在的高稠度 L 型反应堆解决方案。在这项工作中,我们在 TCV 托卡马克中使用下单空欧姆 L 模式等离子体中的堆芯密度斜坡来研究脱落问题,研究范围包括上三角度、下三角度和平均三角度(上三角度和下三角度的平均值:δ)。人们普遍发现,要对 NT 进行整形,分离是比较困难的。仅通过堆芯密度斜坡无法将放电的外侧分流段冷却到下方。上游等离子体的行为和分流器的几何效应(如负下三角的连接长度缩短)并不能完全解释分离 NT 等离子体所面临的挑战。对目标热通量宽度(λq)的朗缪尔探针测量结果在上三角扫描范围内保持稳定,误差在 30% 以内,而对于 NT 来说,扩展因子 S 降低了 50% 之多,这表明整体刮离层宽度 λint 普遍较低。在给定燃料率的情况下,NT 放电的线平均堆芯密度通常较高,这可能与 NT 中较高的粒子约束有关。与此相反,在相同的线均密度下,转发器中性压力和到达目标的综合粒子通量通常较低,这表明与 PT 相比,NT 配置可能更接近鞘限制机制,这也许可以解释为什么 NT 更难脱离。
{"title":"Comparison of detachment in Ohmic plasmas with positive and negative triangularity","authors":"O Février, C K Tsui, G Durr-Legoupil-Nicoud, C Theiler, M Carpita, S Coda, C Colandrea, B P Duval, S Gorno, E Huett, B Linehan, A Perek, L Porte, H Reimerdes, O Sauter, E Tonello, M Zurita, T Bolzonella, F Sciortino, the TCV Team and the EUROfusion Tokamak Exploitation Team","doi":"10.1088/1361-6587/ad3c1c","DOIUrl":"https://doi.org/10.1088/1361-6587/ad3c1c","url":null,"abstract":"In recent years, negative triangularity (NT) has emerged as a potential high-confinement L-mode reactor solution. In this work, detachment is investigated using core density ramps in lower single null Ohmic L-mode plasmas across a wide range of upper, lower, and average triangularity (the mean of upper and lower triangularity: δ) in the TCV tokamak. It is universally found that detachment is more difficult to access for NT shaping. The outer divertor leg of discharges with could not be cooled to below through core density ramps alone. The behavior of the upstream plasma and geometrical divertor effects (e.g. a reduced connection length with negative lower triangularity) do not fully explain the challenges in detaching NT plasmas. Langmuir probe measurements of the target heat flux widths (λq) were constant to within 30% across an upper triangularity scan, while the spreading factor S was lower by up to 50% for NT, indicating a generally lower integral scrape-off layer width, λint. The line-averaged core density was typically higher for NT discharges for a given fuelling rate, possibly linked to higher particle confinement in NT. Conversely, the divertor neutral pressure and integrated particle fluxes to the targets were typically lower for the same line-averaged density, indicating that NT configurations may be closer to the sheath-limited regime than their PT counterparts, which may explain why NT is more challenging to detach.","PeriodicalId":20239,"journal":{"name":"Plasma Physics and Controlled Fusion","volume":"47 1","pages":""},"PeriodicalIF":2.2,"publicationDate":"2024-04-21","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140804037","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-04-17DOI: 10.1088/1361-6587/ad3c19
E Tonello, F Mombelli, O Février, G Alberti, T Bolzonella, G Durr-Legoupil-Nicoud, S Gorno, H Reimerdes, C Theiler, N Vianello, M Passoni, the TCV Team and the WPTE Team
L-mode negative triangularity (NT) operation is a promising alternative to the positive triangularity (PT) H-mode as a high-confinement edge localised mode-free operational regime. In this work, two TCV Ohmic L-mode core density ramps with opposite triangularity are investigated using SOLPS-ITER modelling. This numerical study aims to investigate the power exhaust differences between NT and PT focusing, in particular, on the geometrical effect of triangularity. To disentangle the latter from differences related to cross-field transport, anomalous diffusivities for particle ( ) and energy ( ) transport are fixed to the same values in PT and NT. The simulation results clearly show dissimilar transport and accumulation of neutral particles in the scrape-off layer for the two configurations. This gives rise to different ionization sources in the edge and divertor regions and produces differences in the poloidal and cross-field fluxes, ultimately leading to different power and particle divertor fluxes in the two configurations. Simulations recover the experimental feature of a hotter and attached outer target ( ) in the NT scenario compared to the PT counterpart.
L 模式负三角形(NT)运行是正三角形(PT)H 模式的一种很有前途的替代方案,是一种高引信边缘局部无模式运行机制。在这项工作中,使用 SOLPS-ITER 模型研究了两个具有相反三角形的 TCV 欧姆 L 模式磁芯密度斜坡。这项数值研究旨在调查 NT 和 PT 的功率耗尽差异,尤其侧重于三角形的几何效应。为了将后者与跨场传输的差异区分开来,粒子( )和能量( )传输的反常扩散率在 PT 和 NT 中被固定为相同的值。模拟结果清楚地表明,在两种配置下,中性粒子在刮除层中的传输和积累是不同的。这导致边缘和分流器区域产生不同的电离源,并产生不同的极射和跨场通量,最终导致两种配置中不同的功率和粒子分流器通量。模拟恢复了实验特征,即与 PT 相比,NT 方案中的外部目标( )温度更高,附着力更强。
{"title":"Modelling of power exhaust in TCV positive and negative triangularity L-mode plasmas","authors":"E Tonello, F Mombelli, O Février, G Alberti, T Bolzonella, G Durr-Legoupil-Nicoud, S Gorno, H Reimerdes, C Theiler, N Vianello, M Passoni, the TCV Team and the WPTE Team","doi":"10.1088/1361-6587/ad3c19","DOIUrl":"https://doi.org/10.1088/1361-6587/ad3c19","url":null,"abstract":"L-mode negative triangularity (NT) operation is a promising alternative to the positive triangularity (PT) H-mode as a high-confinement edge localised mode-free operational regime. In this work, two TCV Ohmic L-mode core density ramps with opposite triangularity are investigated using SOLPS-ITER modelling. This numerical study aims to investigate the power exhaust differences between NT and PT focusing, in particular, on the geometrical effect of triangularity. To disentangle the latter from differences related to cross-field transport, anomalous diffusivities for particle ( ) and energy ( ) transport are fixed to the same values in PT and NT. The simulation results clearly show dissimilar transport and accumulation of neutral particles in the scrape-off layer for the two configurations. This gives rise to different ionization sources in the edge and divertor regions and produces differences in the poloidal and cross-field fluxes, ultimately leading to different power and particle divertor fluxes in the two configurations. Simulations recover the experimental feature of a hotter and attached outer target ( ) in the NT scenario compared to the PT counterpart.","PeriodicalId":20239,"journal":{"name":"Plasma Physics and Controlled Fusion","volume":"1 1","pages":""},"PeriodicalIF":2.2,"publicationDate":"2024-04-17","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140804035","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-04-16DOI: 10.1088/1361-6587/ad3c1b
Nathan Mackey, Sergey Blinov, Adam Stanier, Ari Le
In curved magnetic geometries, field-aligned regions of enhanced plasma pressure and density, termed ‘blobs,’ move as coherent filaments across the magnetic field lines. Coherent blobs account for a significant fraction of transport at the edges of magnetic fusion experiments and arise in naturally-occurring space plasmas. This work examines the dynamics of blobs with a fully kinetic electromagnetic particle-in-cell code and with a drift-reduced fluid code. In low-beta regimes with moderate blob speeds, good agreement is found in the maximum blob velocity between the two simulation schemes and simple analytical estimates. The fully kinetic code demonstrates that blob speeds saturate near the initial sound speed, which is a regime outside the validity of the reduced fluid model.
{"title":"Radial drift of plasma blobs in a toroidal magnetic field with fully kinetic and reduced fluid models","authors":"Nathan Mackey, Sergey Blinov, Adam Stanier, Ari Le","doi":"10.1088/1361-6587/ad3c1b","DOIUrl":"https://doi.org/10.1088/1361-6587/ad3c1b","url":null,"abstract":"In curved magnetic geometries, field-aligned regions of enhanced plasma pressure and density, termed ‘blobs,’ move as coherent filaments across the magnetic field lines. Coherent blobs account for a significant fraction of transport at the edges of magnetic fusion experiments and arise in naturally-occurring space plasmas. This work examines the dynamics of blobs with a fully kinetic electromagnetic particle-in-cell code and with a drift-reduced fluid code. In low-beta regimes with moderate blob speeds, good agreement is found in the maximum blob velocity between the two simulation schemes and simple analytical estimates. The fully kinetic code demonstrates that blob speeds saturate near the initial sound speed, which is a regime outside the validity of the reduced fluid model.","PeriodicalId":20239,"journal":{"name":"Plasma Physics and Controlled Fusion","volume":"66 1","pages":""},"PeriodicalIF":2.2,"publicationDate":"2024-04-16","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140611271","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-04-16DOI: 10.1088/1361-6587/ad3c1e
Yuwen Yang, Jianglong Wei, Yuming Gu, Yahong Xie, Chundong Hu
The negative ion based neutral beam injection is a desirable plasma heating and current drive method for the large-scale magnetic fusion devices. Due to the strict requirements and difficult development of the negative ion source for fusion, a long-pulse negative ion source has been developed under the framework of the Comprehensive Research Facility for Fusion Technology in China. This negative ion source consists of a single radio frequency (RF) driver plasma source and a three-electrode accelerator. The typical extraction and acceleration voltage are 4–8 kV and 40–50 kV, respectively. During one shot of the long-pulse (∼100 s) beam extraction, the gas pressure in the vacuum vessel increased sharply and the temperature of the cryopump rise from 8 K to 20 K. Moreover, the vessel wall appeared a high temperature after several long-pulse shots. A self-consistent simulation of beam-gas interaction revealed that the heat loads on the vessel wall should be caused by the stray electrons ejecting from the accelerator. Those stray electrons are mainly generated via the stripping or ionization collisions and strongly deflected by the downstream side of the deflection magnetic field for the co-extracted electron. The location of hot spots measured by infrared thermography is consistent with the simulation results. To solve this problem, a series of electron dumps are designed to avoid the direct impinging of the ejecting electrons on the cryopump and the vessel wall. And the results suggest that the hot spots are almost eliminated.
{"title":"Study on stray electrons ejecting from a long-pulse negative ion source for fusion","authors":"Yuwen Yang, Jianglong Wei, Yuming Gu, Yahong Xie, Chundong Hu","doi":"10.1088/1361-6587/ad3c1e","DOIUrl":"https://doi.org/10.1088/1361-6587/ad3c1e","url":null,"abstract":"The negative ion based neutral beam injection is a desirable plasma heating and current drive method for the large-scale magnetic fusion devices. Due to the strict requirements and difficult development of the negative ion source for fusion, a long-pulse negative ion source has been developed under the framework of the Comprehensive Research Facility for Fusion Technology in China. This negative ion source consists of a single radio frequency (RF) driver plasma source and a three-electrode accelerator. The typical extraction and acceleration voltage are 4–8 kV and 40–50 kV, respectively. During one shot of the long-pulse (∼100 s) beam extraction, the gas pressure in the vacuum vessel increased sharply and the temperature of the cryopump rise from 8 K to 20 K. Moreover, the vessel wall appeared a high temperature after several long-pulse shots. A self-consistent simulation of beam-gas interaction revealed that the heat loads on the vessel wall should be caused by the stray electrons ejecting from the accelerator. Those stray electrons are mainly generated via the stripping or ionization collisions and strongly deflected by the downstream side of the deflection magnetic field for the co-extracted electron. The location of hot spots measured by infrared thermography is consistent with the simulation results. To solve this problem, a series of electron dumps are designed to avoid the direct impinging of the ejecting electrons on the cryopump and the vessel wall. And the results suggest that the hot spots are almost eliminated.","PeriodicalId":20239,"journal":{"name":"Plasma Physics and Controlled Fusion","volume":"78 1","pages":""},"PeriodicalIF":2.2,"publicationDate":"2024-04-16","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140611267","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-04-15DOI: 10.1088/1361-6587/ad3aa0
X Bai, A Loarte, Y Q Liu, S D Pinches, F Koechl, L Li, M Dubrov, Y Gribov
The impact of increasing plasma-wall gap on controlling edge-localized modes (ELMs) is numerically evaluated for the ITER 5 MA/2.65 T H-mode scenarios with full tungsten wall, based on the MARS-F computed plasma response to the applied n= 3–5 (n is the toroidal mode number) resonant magnetic perturbation (RMP) fields. Three new scenarios, referred to as standard, clearance and outergap, are considered assuming different plasma-wall gap sizes over a range on which vertically stability can be maintained by in-vessel coils in ITER. The latter are shown to have both direct and indirect effects on the plasma response and hence ELM control in ITER. The indirect and also primary influence occurs via change of the equilibrium edge safety factor q95