L. Bonalumi, E. Alessi, E. Lazzaro, S. Nowak, C. Sozzi, D. Frigione, L. Garzotti, E. Lerche, F. Rimini, D. van Eester
The problem of the trigger of the neoclassical tearing mode is addressed in this work by evaluating the non-linear terms of the generalized Rutherford equation (GRE) for a set of JET disruptions. The linear stability index Δ′0, even for positive values, is not enough to describe the trigger of the mode as the stabilizing non-linear effects tend to prevent the growth of a mode below a certain width. First, an analysis on the contribution of the stabilizing effect of the curvature and the destabilizing effect of the bootstrap is done. Second, the work focuses on the role of the ion polarization current, a return current that flows parallel to the magnetic field due to the difference in the drift motion of the electrons and ions. This contribution is thought to play an important role in the onset of an island of width W, because it scales as 1/W3, making it a dominant term in the GRE when W is small. The assessment is carried out over a subset of pulses, producing interesting observations that were then generalized across the entire database, obtaining consistent results.
本研究通过评估一组 JET 干扰的广义卢瑟福方程 (GRE) 的非线性项，解决了新古典撕裂模式的触发问题。线性稳定指数Δ′0，即使是正值，也不足以描述模式的触发，因为稳定非线性效应往往会阻止低于一定宽度的模式增长。首先，分析了曲率的稳定效应和自举的失稳效应的贡献。其次，工作重点是离子极化电流的作用，即由于电子和离子漂移运动的差异而产生的平行于磁场的返回电流。这一贡献被认为在宽度为 W 的磁岛出现时起着重要作用，因为它的比例为 1/W3，当 W 较小时，它是 GRE 中的主要项。评估是在一个脉冲子集上进行的，产生了一些有趣的观察结果，然后将这些观察结果推广到整个数据库中，得到了一致的结果。
{"title":"Analysis of the role of the ion polarization current on the onset of pre-disruptive magnetic islands in JET","authors":"L. Bonalumi, E. Alessi, E. Lazzaro, S. Nowak, C. Sozzi, D. Frigione, L. Garzotti, E. Lerche, F. Rimini, D. van Eester","doi":"10.1063/5.0189722","DOIUrl":"https://doi.org/10.1063/5.0189722","url":null,"abstract":"The problem of the trigger of the neoclassical tearing mode is addressed in this work by evaluating the non-linear terms of the generalized Rutherford equation (GRE) for a set of JET disruptions. The linear stability index Δ′0, even for positive values, is not enough to describe the trigger of the mode as the stabilizing non-linear effects tend to prevent the growth of a mode below a certain width. First, an analysis on the contribution of the stabilizing effect of the curvature and the destabilizing effect of the bootstrap is done. Second, the work focuses on the role of the ion polarization current, a return current that flows parallel to the magnetic field due to the difference in the drift motion of the electrons and ions. This contribution is thought to play an important role in the onset of an island of width W, because it scales as 1/W3, making it a dominant term in the GRE when W is small. The assessment is carried out over a subset of pulses, producing interesting observations that were then generalized across the entire database, obtaining consistent results.","PeriodicalId":510396,"journal":{"name":"Physics of Plasmas","volume":"142 ","pages":""},"PeriodicalIF":0.0,"publicationDate":"2024-04-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140760737","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}
C. F. B. Zimmermann, C. Angioni, R. McDermott, B. P. Duval, R. Dux, E. Fable, A. Salmi, U. Stroth, T. Tala, G. Tardini, T. Pütterich
This study employs the established momentum transport analysis at ASDEX Upgrade [Zimmermann et al., Nucl. Fusion 63, 124003 (2023)] to investigate the parametric variations of the momentum transport coefficients in the core of H-mode plasmas. These experimental results are compared to a comprehensive database of gyrokinetic calculations. Generally, good agreement between predicted and measured diffusive and convective transport coefficients is found. The predicted and measured Prandtl numbers correlate most dominantly with the magnetically trapped particle fraction. The experimentally inferred pinch numbers strongly depend on the logarithmic density gradient and magnetic shear, consistent with the theoretical predictions of the Coriolis pinch. The intrinsic torque from residual stress in the inner core is small, scales with the local logarithmic density gradient, and the data indicate a possible sign reversal. In the outer periphery of the core, the intrinsic torque is always co-current-directed and scales with the pressure gradient. This is consistent with prior experimental findings and global, non-linear gyrokinetic predictions. It suggests that profile shearing effects generate the intrinsic torque in the inner core. Toward the outer core, most likely, effects from E×B-shearing become more influential. These results offer the first comprehensive picture of this transport channel in the core plasma and contribute to validating the corresponding theoretical understanding. The derived scaling laws are used to construct a reduced momentum transport model, which has been validated against an additional dataset. This demonstrates that the model captures the essential contributions to momentum transport in the core of H-mode plasmas.
本研究利用在 ASDEX 升级项目[Zimmermann 等人，Nucl. Fusion 63, 124003 (2023)]中建立的动量传输分析来研究 H 模式等离子体核心中动量传输系数的参数变化。这些实验结果与陀螺动力学计算的综合数据库进行了比较。一般来说，预测和测量的扩散和对流传输系数之间具有良好的一致性。预测和测量的普朗特尔数主要与磁捕获粒子分数相关。实验推断出的挤压数很大程度上取决于对数密度梯度和磁剪切力，这与科里奥利挤压的理论预测一致。内核残余应力产生的固有扭矩很小，与当地的对数密度梯度成比例，数据表明可能存在符号反转。在内核外围，固有扭矩始终是同向流动的，并与压力梯度成比例关系。这与之前的实验结果和全局非线性陀螺动力学预测相一致。这表明，剖面剪切效应产生了内核的固有扭矩。在外核，很可能是 E×B 剪切效应的影响更大。这些结果首次全面描述了内核等离子体中的这一传输通道，并有助于验证相应的理论认识。推导出的缩放定律被用于构建一个简化的动量传输模型，该模型已通过一个额外的数据集进行了验证。这表明该模型捕捉到了 H 模式等离子体内核动量传输的基本贡献。
{"title":"Experimental validation of momentum transport theory in the core of H-mode plasmas in the ASDEX Upgrade tokamak","authors":"C. F. B. Zimmermann, C. Angioni, R. McDermott, B. P. Duval, R. Dux, E. Fable, A. Salmi, U. Stroth, T. Tala, G. Tardini, T. Pütterich","doi":"10.1063/5.0203092","DOIUrl":"https://doi.org/10.1063/5.0203092","url":null,"abstract":"This study employs the established momentum transport analysis at ASDEX Upgrade [Zimmermann et al., Nucl. Fusion 63, 124003 (2023)] to investigate the parametric variations of the momentum transport coefficients in the core of H-mode plasmas. These experimental results are compared to a comprehensive database of gyrokinetic calculations. Generally, good agreement between predicted and measured diffusive and convective transport coefficients is found. The predicted and measured Prandtl numbers correlate most dominantly with the magnetically trapped particle fraction. The experimentally inferred pinch numbers strongly depend on the logarithmic density gradient and magnetic shear, consistent with the theoretical predictions of the Coriolis pinch. The intrinsic torque from residual stress in the inner core is small, scales with the local logarithmic density gradient, and the data indicate a possible sign reversal. In the outer periphery of the core, the intrinsic torque is always co-current-directed and scales with the pressure gradient. This is consistent with prior experimental findings and global, non-linear gyrokinetic predictions. It suggests that profile shearing effects generate the intrinsic torque in the inner core. Toward the outer core, most likely, effects from E×B-shearing become more influential. These results offer the first comprehensive picture of this transport channel in the core plasma and contribute to validating the corresponding theoretical understanding. The derived scaling laws are used to construct a reduced momentum transport model, which has been validated against an additional dataset. This demonstrates that the model captures the essential contributions to momentum transport in the core of H-mode plasmas.","PeriodicalId":510396,"journal":{"name":"Physics of Plasmas","volume":"355 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2024-04-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140781813","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}
{"title":"Reviewer acknowledgment for 2023","authors":"M. Mauel","doi":"10.1063/5.0208999","DOIUrl":"https://doi.org/10.1063/5.0208999","url":null,"abstract":"","PeriodicalId":510396,"journal":{"name":"Physics of Plasmas","volume":"109 ","pages":""},"PeriodicalIF":0.0,"publicationDate":"2024-04-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140788713","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}
The conditions in laser-produced plasmas are frequently determined with x-ray spectroscopy by comparing calculated to measured spectra. Line spectra from K-shell transitions of low- to mid-atomic number elements are most often used since the important physical processes are well understood and reliable spectra can be readily measured and calculated. Radiation transfer effects due to large optical depths of strong lines can influence the spectra. In this work, the effects of radiation transfer on the emission spectra of short-laser pulse-heated targets are studied. The possible errors made in inferring electron temperature by not including radiation transfer are quantified. The inclusion of radiative transfer in spectral calculations improves the accuracy of typical temperature diagnostics and allows the use of strong lines for diagnostics.
激光产生的等离子体中的条件经常是通过 X 射线光谱比较计算光谱和测量光谱来确定的。最常用的是低原子序数至中原子序数元素 K 壳跃迁的线光谱，因为重要的物理过程已被很好地理解，可靠的光谱可以很容易地测量和计算出来。由于强线的光学深度大，辐射传递效应会影响光谱。在这项工作中，研究了辐射传递对短激光脉冲加热目标发射光谱的影响。量化了在推断电子温度时如果不考虑辐射传递可能产生的误差。将辐射传递纳入光谱计算可提高典型温度诊断的准确性，并允许使用强谱线进行诊断。
{"title":"Radiation transfer in the spectra of short-pulse laser-heated targets","authors":"R. A. London, H. A. Scott, Madison E. Martin","doi":"10.1063/5.0191273","DOIUrl":"https://doi.org/10.1063/5.0191273","url":null,"abstract":"The conditions in laser-produced plasmas are frequently determined with x-ray spectroscopy by comparing calculated to measured spectra. Line spectra from K-shell transitions of low- to mid-atomic number elements are most often used since the important physical processes are well understood and reliable spectra can be readily measured and calculated. Radiation transfer effects due to large optical depths of strong lines can influence the spectra. In this work, the effects of radiation transfer on the emission spectra of short-laser pulse-heated targets are studied. The possible errors made in inferring electron temperature by not including radiation transfer are quantified. The inclusion of radiative transfer in spectral calculations improves the accuracy of typical temperature diagnostics and allows the use of strong lines for diagnostics.","PeriodicalId":510396,"journal":{"name":"Physics of Plasmas","volume":"185 ","pages":""},"PeriodicalIF":0.0,"publicationDate":"2024-04-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140766556","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}
We consider the propagation of magnetoacoustic (MA) and acoustic waves of various frequency ranges in a partially ionized plasma at an arbitrary angle to the magnetic field, taking into account the influence of heating, radiative, and thermo-conductive cooling, as well as ion-neutral collisions. A dispersion equation that describes the evolution of nine modes was obtained in a compact mathematical form using the two-fluid model. The number and type of propagating waves (modified fast and slow MA waves, MA waves in the ion component, acoustic waves in the neutral component, as well as isothermal MA and isothermal acoustic waves) vary in different frequency ranges depending on the parameters of the medium. Analytical expressions are found for the speed and damping rates of all these propagating waves, and it is shown how dispersion and damping are formed by three processes: thermal misbalance, ion-neutral collisions, and thermal conductivity. Comparison of analytical calculations of the velocity and damping rates of MA waves with the numerical solution of the dispersion relation under conditions characteristic of the low solar atmosphere and prominences showed high accuracy of the obtained analytical expressions. The strong influence of thermal misbalance caused by gasdynamic perturbations on the speed and damping rate of modified magnetoacoustic waves in a strongly coupled region is shown as well.
我们考虑了加热、辐射和热传导冷却以及离子-中性碰撞的影响，研究了与磁场成任意角度的部分电离等离子体中各种频率范围的磁声波和声波的传播。利用双流体模型，以紧凑的数学形式获得了描述九种模式演变的弥散方程。传播波的数量和类型（修正的快速和慢速 MA 波、离子分量中的 MA 波、中性分量中的声波以及等温 MA 波和等温声波）根据介质参数的不同而在不同频率范围内变化。我们找到了所有这些传播波的速度和阻尼率的分析表达式，并展示了热失衡、离子-中性碰撞和热导率这三个过程是如何形成色散和阻尼的。在低太阳大气层和突出物的特征条件下，对 MA 波的速度和阻尼率的分析计算与色散关系的数值解进行了比较，结果表明所获得的分析表达式具有很高的准确性。气体动力扰动引起的热失衡对强耦合区域中修正磁声波的速度和阻尼率也有很大影响。
{"title":"Magnetoacoustic waves in a partially ionized astrophysical plasma with the thermal misbalance: A two-fluid approach","authors":"N. Molevich, S. Pichugin, D. Riashchikov","doi":"10.1063/5.0201945","DOIUrl":"https://doi.org/10.1063/5.0201945","url":null,"abstract":"We consider the propagation of magnetoacoustic (MA) and acoustic waves of various frequency ranges in a partially ionized plasma at an arbitrary angle to the magnetic field, taking into account the influence of heating, radiative, and thermo-conductive cooling, as well as ion-neutral collisions. A dispersion equation that describes the evolution of nine modes was obtained in a compact mathematical form using the two-fluid model. The number and type of propagating waves (modified fast and slow MA waves, MA waves in the ion component, acoustic waves in the neutral component, as well as isothermal MA and isothermal acoustic waves) vary in different frequency ranges depending on the parameters of the medium. Analytical expressions are found for the speed and damping rates of all these propagating waves, and it is shown how dispersion and damping are formed by three processes: thermal misbalance, ion-neutral collisions, and thermal conductivity. Comparison of analytical calculations of the velocity and damping rates of MA waves with the numerical solution of the dispersion relation under conditions characteristic of the low solar atmosphere and prominences showed high accuracy of the obtained analytical expressions. The strong influence of thermal misbalance caused by gasdynamic perturbations on the speed and damping rate of modified magnetoacoustic waves in a strongly coupled region is shown as well.","PeriodicalId":510396,"journal":{"name":"Physics of Plasmas","volume":"143 ","pages":""},"PeriodicalIF":0.0,"publicationDate":"2024-04-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140758706","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}
A. A. Kartasheva, K. M. Gutorov, V. Podkovyrov, E. A. Muravyeva, K. S. Lukyanov, N. S. Klimov
The spatial and temporal dependencies of the characteristics of the hydrogen plasma flow generated in quasi-stationary plasma accelerator were investigated. The spatiotemporal structure of discharge radiation in the interelectrode gap was studied. The range of changes in the length of the plasma glowing region in the interelectrode gap during the discharge pulse was determined. The region with bright plasma radiation located in the output face of the accelerator electrode system was observed. The presence of impurities and increased electron concentration values were observed in this region. Fluctuations in the radiation intensity of the plasma flow were detected along the entire length of its propagation. The spatial and temporal characteristics of these fluctuations were determined. The electron concentration values near the output face of the electrode system were obtained by measuring the Stark broadening of the Hβ line. For the first time, the time dependence of the electron concentration of free plasma flow was obtained using two methods simultaneously. The measurements were conducted at a distance, which significantly exceeds the characteristic size of the electrode system and where the influence of interelectrode processes of plasma flow generation is reduced. The first is based on measuring the Stark broadening of Hβ. As a second method, heterodyne interferometry was used.
{"title":"Experimental investigation of the characteristics of the plasma flow generated in quasi-stationary plasma accelerator using optical methods","authors":"A. A. Kartasheva, K. M. Gutorov, V. Podkovyrov, E. A. Muravyeva, K. S. Lukyanov, N. S. Klimov","doi":"10.1063/5.0198341","DOIUrl":"https://doi.org/10.1063/5.0198341","url":null,"abstract":"The spatial and temporal dependencies of the characteristics of the hydrogen plasma flow generated in quasi-stationary plasma accelerator were investigated. The spatiotemporal structure of discharge radiation in the interelectrode gap was studied. The range of changes in the length of the plasma glowing region in the interelectrode gap during the discharge pulse was determined. The region with bright plasma radiation located in the output face of the accelerator electrode system was observed. The presence of impurities and increased electron concentration values were observed in this region. Fluctuations in the radiation intensity of the plasma flow were detected along the entire length of its propagation. The spatial and temporal characteristics of these fluctuations were determined. The electron concentration values near the output face of the electrode system were obtained by measuring the Stark broadening of the Hβ line. For the first time, the time dependence of the electron concentration of free plasma flow was obtained using two methods simultaneously. The measurements were conducted at a distance, which significantly exceeds the characteristic size of the electrode system and where the influence of interelectrode processes of plasma flow generation is reduced. The first is based on measuring the Stark broadening of Hβ. As a second method, heterodyne interferometry was used.","PeriodicalId":510396,"journal":{"name":"Physics of Plasmas","volume":"517 3","pages":""},"PeriodicalIF":0.0,"publicationDate":"2024-04-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140788079","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}
S. C. Molesworth, J. Boedo, C. Tsui, R. Perillo, D. Rudakov
Measured filament velocities in the DIII-D tokamak are compared against theoretical scalings, finding that the latter often represents an upper limit on experimental velocity distributions with most filaments possessing lower velocity. Filament spin from internal E × B drift is experimentally demonstrated to alter filament radial velocity. A critical spin velocity, where filament radial velocity peaks, is observed and corresponds to approximately 5 km/s. This transition is corroborated using a less direct measure of filament spin in the form of a temperature ratio. These techniques are combined to find that the critical spin velocity closely aligns with transport times along and across filaments becoming comparable. The normalized filament size distribution is consistent with the most stable size as dictated by Kelvin–Helmholtz and curvature-driven instabilities. Overall, the findings suggest filament stability and spin alter filamentary transport that may threaten the integrity of first walls in fusion devices.
将在 DIII-D 托卡马克中测量到的灯丝速度与理论标度进行了比较，发现后者往往代表了实验速度分布的上限，大多数灯丝的速度较低。实验证明，内部 E × B 漂移产生的灯丝自旋改变了灯丝的径向速度。观测到了一个临界自旋速度，在这个速度下灯丝的径向速度达到峰值，大约相当于 5 公里/秒。利用温度比的形式对灯丝自旋进行了不太直接的测量，从而证实了这一转变。将这些技术结合起来可以发现，临界自旋速度与沿灯丝和跨灯丝的传输时间密切相关。归一化细丝尺寸分布与开尔文-赫尔姆霍兹不稳定性和曲率驱动不稳定性决定的最稳定尺寸一致。总之，研究结果表明，丝状稳定性和自旋改变了丝状传输，这可能会威胁到聚变装置第一壁的完整性。
{"title":"Filamentary velocity scaling validation and spin dynamics in the DIII-D tokamak","authors":"S. C. Molesworth, J. Boedo, C. Tsui, R. Perillo, D. Rudakov","doi":"10.1063/5.0195025","DOIUrl":"https://doi.org/10.1063/5.0195025","url":null,"abstract":"Measured filament velocities in the DIII-D tokamak are compared against theoretical scalings, finding that the latter often represents an upper limit on experimental velocity distributions with most filaments possessing lower velocity. Filament spin from internal E × B drift is experimentally demonstrated to alter filament radial velocity. A critical spin velocity, where filament radial velocity peaks, is observed and corresponds to approximately 5 km/s. This transition is corroborated using a less direct measure of filament spin in the form of a temperature ratio. These techniques are combined to find that the critical spin velocity closely aligns with transport times along and across filaments becoming comparable. The normalized filament size distribution is consistent with the most stable size as dictated by Kelvin–Helmholtz and curvature-driven instabilities. Overall, the findings suggest filament stability and spin alter filamentary transport that may threaten the integrity of first walls in fusion devices.","PeriodicalId":510396,"journal":{"name":"Physics of Plasmas","volume":"954 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2024-04-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140774662","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}
Yimeng Li, L. Ang, Bing Xiao, F. Djurabekova, Yonghong Cheng, G. Meng
With the continual miniaturization of electronic devices, there is an urgent need to understand the electron emission and the mechanism of electrical breakdown at nanoscale. For a nanogap, the complete process of the electrical breakdown includes the nano-protrusion growth, electron emission and thermal runaway of the nano-protrusion, and plasma formation. This review summarizes recent theories, experiments, and advanced atomistic simulation related to this breakdown process. First, the electron emission mechanisms in nanogaps and their transitions between different mechanisms are emphatically discussed, such as the effects of image potential (of different electrode's configurations), anode screening, electron space-charge potential, and electron exchange-correlation potential. The corresponding experimental results on electron emission and electrical breakdown are discussed for fixed nanogaps on substrate and adjustable nanogaps, including space-charge effects, electrode deformation, and electrical breakdown characteristics. Advanced atomistic simulations about the nano-protrusion growth and the nanoelectrode or nano-protrusion thermal runaway under high electric field are discussed. Finally, we conclude and outline the key challenges for and perspectives on future theoretical, experimental, and atomistic simulation studies of nanoscale electrical breakdown processes.
{"title":"Review of electron emission and electrical breakdown in nanogaps","authors":"Yimeng Li, L. Ang, Bing Xiao, F. Djurabekova, Yonghong Cheng, G. Meng","doi":"10.1063/5.0202607","DOIUrl":"https://doi.org/10.1063/5.0202607","url":null,"abstract":"With the continual miniaturization of electronic devices, there is an urgent need to understand the electron emission and the mechanism of electrical breakdown at nanoscale. For a nanogap, the complete process of the electrical breakdown includes the nano-protrusion growth, electron emission and thermal runaway of the nano-protrusion, and plasma formation. This review summarizes recent theories, experiments, and advanced atomistic simulation related to this breakdown process. First, the electron emission mechanisms in nanogaps and their transitions between different mechanisms are emphatically discussed, such as the effects of image potential (of different electrode's configurations), anode screening, electron space-charge potential, and electron exchange-correlation potential. The corresponding experimental results on electron emission and electrical breakdown are discussed for fixed nanogaps on substrate and adjustable nanogaps, including space-charge effects, electrode deformation, and electrical breakdown characteristics. Advanced atomistic simulations about the nano-protrusion growth and the nanoelectrode or nano-protrusion thermal runaway under high electric field are discussed. Finally, we conclude and outline the key challenges for and perspectives on future theoretical, experimental, and atomistic simulation studies of nanoscale electrical breakdown processes.","PeriodicalId":510396,"journal":{"name":"Physics of Plasmas","volume":"157 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2024-04-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140758528","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}
D. Silvagni, M. Dunne, T. Luda, A. Bock, A. Burckhart, R. Fischer, M. Griener, R. M. McDermott, U. Plank, T. Pütterich, M. Reisner, J. Stober, B. Tal, G. Tardini, H. Zohm
Over previous campaigns, an intense experimental program on advanced tokamak (AT) scenarios, has been carried out at the ASDEX Upgrade tokamak with full-tungsten wall. These discharges have been executed shortly after the boronization of the first wall to reduce the density and the impurity influx. The confinement level of such AT discharges was found to vary considerably, even when discharges with similar, if not identical, engineering parameters were carried out. This work investigates the causes of such confinement variations. Among all plasma quantities analyzed, confinement quality of AT scenarios correlates best with divertor neutral pressure, highlighting the key role of edge and scrape-off layer physics in determining global plasma confinement. In particular, it is found that the main cause of confinement degradation is the reduction of pedestal stability, which is in turn caused by the outward shift of the maximum density gradient position typically observed when the divertor neutral pressure increases. Owing to the low density of AT discharges under analysis, the movement of the maximum density gradient position can be caused entirely by changes in deuterium outgassing from the wall, which is strongly influenced by the boron layer deposited on the plasma-facing components and by the deuterium wall inventory. Finally, the predictive capability of confinement quality with the integrated model IMEP [Luda et al., Nucl. Fusion 60, 036023 (2020)] is tested on these discharges and shows promising results.
在以往的活动中，ASDEX 升级版全钨壁托卡马克已经开展了一项针对先进托卡马克（AT）方案的密集实验计划。这些放电是在第一壁硼化后不久进行的，目的是降低密度和杂质流入。研究发现，即使在工程参数相似（甚至不完全相同）的情况下进行放电，这种 AT 放电的约束水平也会有很大差异。这项工作研究了造成这种约束变化的原因。在分析的所有等离子体量中，AT 方案的束缚质量与分流器中性压力的相关性最好，突出了边缘和刮除层物理在决定全局等离子体束缚中的关键作用。特别是，研究发现，约束性下降的主要原因是基座稳定性的降低，而基座稳定性的降低又是由最大密度梯度位置的外移造成的，而最大密度梯度位置的外移通常是在分流器中性压力增加时观察到的。由于所分析的 AT 放电密度较低，最大密度梯度位置的移动可能完全是由壁面氘排出量的变化引起的，而氘排出量受沉积在面向等离子体部件上的硼层和壁面氘存量的影响很大。最后，利用综合模型 IMEP [Luda 等人，Nucl. Fusion 60, 036023 (2020)]对约束质量的预测能力在这些放电中进行了测试，结果很有希望。
{"title":"Impact of divertor neutral pressure on confinement degradation of advanced tokamak scenarios at ASDEX Upgrade","authors":"D. Silvagni, M. Dunne, T. Luda, A. Bock, A. Burckhart, R. Fischer, M. Griener, R. M. McDermott, U. Plank, T. Pütterich, M. Reisner, J. Stober, B. Tal, G. Tardini, H. Zohm","doi":"10.1063/5.0184405","DOIUrl":"https://doi.org/10.1063/5.0184405","url":null,"abstract":"Over previous campaigns, an intense experimental program on advanced tokamak (AT) scenarios, has been carried out at the ASDEX Upgrade tokamak with full-tungsten wall. These discharges have been executed shortly after the boronization of the first wall to reduce the density and the impurity influx. The confinement level of such AT discharges was found to vary considerably, even when discharges with similar, if not identical, engineering parameters were carried out. This work investigates the causes of such confinement variations. Among all plasma quantities analyzed, confinement quality of AT scenarios correlates best with divertor neutral pressure, highlighting the key role of edge and scrape-off layer physics in determining global plasma confinement. In particular, it is found that the main cause of confinement degradation is the reduction of pedestal stability, which is in turn caused by the outward shift of the maximum density gradient position typically observed when the divertor neutral pressure increases. Owing to the low density of AT discharges under analysis, the movement of the maximum density gradient position can be caused entirely by changes in deuterium outgassing from the wall, which is strongly influenced by the boron layer deposited on the plasma-facing components and by the deuterium wall inventory. Finally, the predictive capability of confinement quality with the integrated model IMEP [Luda et al., Nucl. Fusion 60, 036023 (2020)] is tested on these discharges and shows promising results.","PeriodicalId":510396,"journal":{"name":"Physics of Plasmas","volume":"149 ","pages":""},"PeriodicalIF":0.0,"publicationDate":"2024-02-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"139821129","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}
C. Tsui, J. Boedo, J. Myra, D. Galassi, C. Wüthrich
The relative importance of divertor radial turbulent particle fluxes is considered by comparing it against the fluxes in the main-chamber outer midplane (OMP) in a variety of conditions and divertor geometries in the tokamak à configuration variable. Within the first power falloff length, the radial turbulent fluxes in the leg of the outer divertor are consistently found to be small, and about 1/5th the magnitude measured at the OMP. In a low-density single null divertor, magnetic shear is found to play a strong role in isolating the main-chamber turbulence from the divertor. The snowflake divertor is purported to have turbulence-enhancing properties in the volume between the two X-points but was instead found to further reduce the divertor turbulent fluxes compared to the single null. Depending on the collisionality, the electric field fluctuations and radial turbulent fluxes were higher near the X-point than at the outer midplane, which is likely due to the binormal compression of the flux bundles consistent with analytical models of the resistive X-point mode. Density and potential fluctuation amplitudes decrease monotonically with distance from the OMP with a slope that depends on collisionality.
在托卡马克 à 配置变量中的各种条件和分流器几何形状下，通过将分流器径向湍流粒子通量与主腔外中面（OMP）的通量进行比较，考虑了分流器径向湍流粒子通量的相对重要性。在第一功率衰减长度范围内，外侧分流器腿部的径向湍流通量一直很小，约为 OMP 测量值的 1/5。在低密度单空分流器中，发现磁剪切在将主腔湍流从分流器中隔离出来方面发挥了很大作用。雪花分流器被认为在两个 X 点之间的空间具有增强湍流的特性，但与单空分流器相比，它反而进一步降低了分流器的湍流通量。根据碰撞性的不同，X 点附近的电场波动和径向湍流通量比外中面高，这可能是由于通量束的双法压缩与阻力 X 点模式的分析模型一致。密度和势能波动幅度随距离 OMP 的远近而单调减小，斜率取决于碰撞性。
{"title":"Divertor turbulent transport in the single null and snowflake in the TCV tokamak","authors":"C. Tsui, J. Boedo, J. Myra, D. Galassi, C. Wüthrich","doi":"10.1063/5.0175437","DOIUrl":"https://doi.org/10.1063/5.0175437","url":null,"abstract":"The relative importance of divertor radial turbulent particle fluxes is considered by comparing it against the fluxes in the main-chamber outer midplane (OMP) in a variety of conditions and divertor geometries in the tokamak à configuration variable. Within the first power falloff length, the radial turbulent fluxes in the leg of the outer divertor are consistently found to be small, and about 1/5th the magnitude measured at the OMP. In a low-density single null divertor, magnetic shear is found to play a strong role in isolating the main-chamber turbulence from the divertor. The snowflake divertor is purported to have turbulence-enhancing properties in the volume between the two X-points but was instead found to further reduce the divertor turbulent fluxes compared to the single null. Depending on the collisionality, the electric field fluctuations and radial turbulent fluxes were higher near the X-point than at the outer midplane, which is likely due to the binormal compression of the flux bundles consistent with analytical models of the resistive X-point mode. Density and potential fluctuation amplitudes decrease monotonically with distance from the OMP with a slope that depends on collisionality.","PeriodicalId":510396,"journal":{"name":"Physics of Plasmas","volume":"38 8","pages":""},"PeriodicalIF":0.0,"publicationDate":"2024-02-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"139965461","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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