N. Bonanomi, C. Angioni, G. D. Conway, T. Happel, U. Plank, P. Schneider, G. Staebler
This work combines experimental observations from the ASDEX Upgrade tokamak with related gyrokinetic simulations of the turbulence moving from L-mode toward, and beyond, the L–H transition. Dedicated experiments have been performed with slow steps of increasing electron cyclotron heating power. Gyrokinetic simulations of the edge turbulence of these plasmas highlight the key roles of the non-linear electromagnetic effects and the external flow shear (E × B shear), both related to the evolution of the plasma pressure profile with increasing heating power. The increase in the plasma βe destabilizes turbulence at low toroidal mode numbers, that, in turn, is strongly suppressed by the external flow shear. This allows the plasma pressure profiles to evolve without a sharp rise in the turbulent fluxes. When all the experimentally measured plasma parameters are consistently included as inputs of the local gyrokinetic simulations, both the experimental electron and ion heat fluxes are quantitatively reproduced on the whole L-mode phase of the selected discharge. Simulations carried out with edge parameters of an ELM-free H-mode phase still show the importance of the mechanisms discussed earlier while also indicating possible limitations of the local approach.
这项工作将 ASDEX 升级型托卡马克的实验观测结果与湍流从 L 模式向 L-H 过渡和超越 L-H 过渡的相关陀螺动力学模拟相结合。专门的实验是在电子回旋加速器加热功率缓慢增加的情况下进行的。这些等离子体边缘湍流的陀螺动力学模拟突出了非线性电磁效应和外部流剪切（E × B 剪切）的关键作用，两者都与等离子体压力剖面随加热功率增加而演变有关。等离子体 βe 的增加会破坏低环模数湍流的稳定性，而湍流又会受到外部流剪切的强烈抑制。这使得等离子体压力剖面在湍流通量没有急剧上升的情况下发生演变。当所有实验测量到的等离子体参数都作为局部陀螺动能模拟的输入时，实验中的电子和离子热通量在所选放电的整个 L 模式阶段都得到了定量再现。利用不含 ELM 的 H 模式相的边缘参数进行的模拟仍然显示了前面讨论的机制的重要性，同时也说明了局部方法可能存在的局限性。
{"title":"From L-mode to the L–H transition, experiments on ASDEX upgrade and related gyrokinetic simulations","authors":"N. Bonanomi, C. Angioni, G. D. Conway, T. Happel, U. Plank, P. Schneider, G. Staebler","doi":"10.1063/5.0202867","DOIUrl":"https://doi.org/10.1063/5.0202867","url":null,"abstract":"This work combines experimental observations from the ASDEX Upgrade tokamak with related gyrokinetic simulations of the turbulence moving from L-mode toward, and beyond, the L–H transition. Dedicated experiments have been performed with slow steps of increasing electron cyclotron heating power. Gyrokinetic simulations of the edge turbulence of these plasmas highlight the key roles of the non-linear electromagnetic effects and the external flow shear (E × B shear), both related to the evolution of the plasma pressure profile with increasing heating power. The increase in the plasma βe destabilizes turbulence at low toroidal mode numbers, that, in turn, is strongly suppressed by the external flow shear. This allows the plasma pressure profiles to evolve without a sharp rise in the turbulent fluxes. When all the experimentally measured plasma parameters are consistently included as inputs of the local gyrokinetic simulations, both the experimental electron and ion heat fluxes are quantitatively reproduced on the whole L-mode phase of the selected discharge. Simulations carried out with edge parameters of an ELM-free H-mode phase still show the importance of the mechanisms discussed earlier while also indicating possible limitations of the local approach.","PeriodicalId":510396,"journal":{"name":"Physics of Plasmas","volume":"8 31","pages":""},"PeriodicalIF":0.0,"publicationDate":"2024-07-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141696384","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. Mariscal, B. Djordjević, R. Anirudh, J. Jayaraman-Thiagarajan, E. Grace, R. Simpson, K. Swanson, T. C. Galvin, D. Mittelberger, J. Heebner, R. Muir, E. Folsom, M. P. Hill, S. Feister, E. Ito, K. Valdez-Sereno, J. J. Rocca, J. Park, S. Wang, R. Hollinger, R. Nedbailo, B. Sullivan, G. Zeraouli, A. Shukla, P. Turaga, A. Sarkar, B. Van Essen, S. Liu, B. Spears, P.-T. Bremer, T. Ma
We present progress in utilizing a machine learning (ML) assisted optimization framework to study the trends in a parameter space defined by spectrally shaped, high-intensity, petawatt-class (8 J, 45 fs) laser pulses interacting with solid targets and give the first simulation-based overview of predicted trends. A neural network (NN) incorporating uncertainty quantification is trained to predict the number of hot electrons generated by the laser–target interaction as a function of pulse shaping parameters. The predictions of this NN serve as the basis function for a Bayesian optimization framework to navigate this space. For post-experimental evaluation, we compare two separate neural network (NN) models. One is based solely on data from experiments, and the other is trained only on ensemble particle-in-cell simulations. Reviewing the predicted and observed trends across the experiment-capable laser parameter search space, we find that both ML models predict a maximal increase in hot electron generation at a level of approximately 12%–18%; however, no statistically significant enhancement was observed in experiments. On direct comparison of the NN models, the average discrepancy is 8.5%, with a maximum of 30%. Since shot-to-shot fluctuations in experiments affect the observations, we evaluate the behavior of our optimization framework by performing virtual experiments that vary the number of repeated observations and the noise levels. Here, we discuss the implications of such a framework for future autonomous exploration platforms in high-repetition-rate experiments.
我们介绍了利用机器学习（ML）辅助优化框架研究参数空间趋势的进展，该参数空间由光谱成形、高强度、小功率级（8 J，45 fs）激光脉冲与固体靶相互作用所定义，并首次对预测趋势进行了基于模拟的概述。我们训练了一个包含不确定性量化的神经网络（NN），以预测激光与目标相互作用产生的热电子数量与脉冲整形参数的函数关系。该神经网络的预测结果可作为贝叶斯优化框架的基础函数，用于导航该空间。为了进行实验后评估，我们比较了两个独立的神经网络（NN）模型。其中一个完全基于实验数据，而另一个则仅在粒子入胞模拟中进行训练。回顾整个实验激光参数搜索空间的预测和观察趋势，我们发现两个 ML 模型都预测热电子生成的最大增幅约为 12%-18%；但在实验中并未观察到统计意义上的显著增强。直接比较 NN 模型，平均差异为 8.5%，最大差异为 30%。由于实验中镜头间的波动会影响观测结果，我们通过执行虚拟实验来评估优化框架的行为，这些虚拟实验改变了重复观测的数量和噪声水平。在此，我们讨论了这种框架对未来高重复率实验中自主探索平台的影响。
{"title":"Toward machine-learning-assisted PW-class high-repetition-rate experiments with solid targets","authors":"D. Mariscal, B. Djordjević, R. Anirudh, J. Jayaraman-Thiagarajan, E. Grace, R. Simpson, K. Swanson, T. C. Galvin, D. Mittelberger, J. Heebner, R. Muir, E. Folsom, M. P. Hill, S. Feister, E. Ito, K. Valdez-Sereno, J. J. Rocca, J. Park, S. Wang, R. Hollinger, R. Nedbailo, B. Sullivan, G. Zeraouli, A. Shukla, P. Turaga, A. Sarkar, B. Van Essen, S. Liu, B. Spears, P.-T. Bremer, T. Ma","doi":"10.1063/5.0190553","DOIUrl":"https://doi.org/10.1063/5.0190553","url":null,"abstract":"We present progress in utilizing a machine learning (ML) assisted optimization framework to study the trends in a parameter space defined by spectrally shaped, high-intensity, petawatt-class (8 J, 45 fs) laser pulses interacting with solid targets and give the first simulation-based overview of predicted trends. A neural network (NN) incorporating uncertainty quantification is trained to predict the number of hot electrons generated by the laser–target interaction as a function of pulse shaping parameters. The predictions of this NN serve as the basis function for a Bayesian optimization framework to navigate this space. For post-experimental evaluation, we compare two separate neural network (NN) models. One is based solely on data from experiments, and the other is trained only on ensemble particle-in-cell simulations. Reviewing the predicted and observed trends across the experiment-capable laser parameter search space, we find that both ML models predict a maximal increase in hot electron generation at a level of approximately 12%–18%; however, no statistically significant enhancement was observed in experiments. On direct comparison of the NN models, the average discrepancy is 8.5%, with a maximum of 30%. Since shot-to-shot fluctuations in experiments affect the observations, we evaluate the behavior of our optimization framework by performing virtual experiments that vary the number of repeated observations and the noise levels. Here, we discuss the implications of such a framework for future autonomous exploration platforms in high-repetition-rate experiments.","PeriodicalId":510396,"journal":{"name":"Physics of Plasmas","volume":"1 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2024-07-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141690659","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":"Foreword to Special Issue: Papers from the 65th Annual Meeting of the APS Division of Plasma Physics, October 30–November 3, 2023","authors":"E. Thomas, Michael Mauel","doi":"10.1063/5.0223942","DOIUrl":"https://doi.org/10.1063/5.0223942","url":null,"abstract":"","PeriodicalId":510396,"journal":{"name":"Physics of Plasmas","volume":"3 3","pages":""},"PeriodicalIF":0.0,"publicationDate":"2024-07-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141698303","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}
In direct-current (DC) discharge, it is well known that hysteresis is observed between the Townsend (gas breakdown) and glow regimes. Forward and backward voltage sweep is performed using a one-dimensional particle-in-cell Monte Carlo collision (PIC-MCC) model considering a ballast resistor. When increasing the applied voltage after reaching the breakdown voltage (Vb), transition from Townsend to glow discharges is observed. When decreasing the applied voltage from the glow regime, the discharge voltage (Vd) between the anode–cathode gap can be smaller than the breakdown voltage, resulting in a hysteresis, which is consistent with experimental observations. Next, the PIC-MCC model is used to investigate the self-sustaining voltage (Vs) in the presence of finite initial plasma densities between the anode and cathode gap. It is observed that the self-sustaining voltage coincides with the discharge voltage obtained from the backward voltage sweep. In addition, the self-sustaining voltage decreases with increased initial plasma density and saturates above a certain initial plasma density, which indicates a change in plasma resistivity. The decrease in self-sustaining voltage is associated with the electron heat loss at the anode for the low pd (rarefied) regime. In the high pd (collisional) regime, the ion energy loss toward the cathode due to the cathode fall and the inelastic collision loss of electrons in the bulk discharge balance out. Finally, it is demonstrated that the self-sustaining voltage collapses to a singular value, despite the presence of a initial plasma, for microgaps when field emission is dominant, which is also consistent with experimental observations.
{"title":"Hysteresis between gas breakdown and plasma discharge","authors":"Yusuke Yamashita, K. Hara, S. Sriraman","doi":"10.1063/5.0198151","DOIUrl":"https://doi.org/10.1063/5.0198151","url":null,"abstract":"In direct-current (DC) discharge, it is well known that hysteresis is observed between the Townsend (gas breakdown) and glow regimes. Forward and backward voltage sweep is performed using a one-dimensional particle-in-cell Monte Carlo collision (PIC-MCC) model considering a ballast resistor. When increasing the applied voltage after reaching the breakdown voltage (Vb), transition from Townsend to glow discharges is observed. When decreasing the applied voltage from the glow regime, the discharge voltage (Vd) between the anode–cathode gap can be smaller than the breakdown voltage, resulting in a hysteresis, which is consistent with experimental observations. Next, the PIC-MCC model is used to investigate the self-sustaining voltage (Vs) in the presence of finite initial plasma densities between the anode and cathode gap. It is observed that the self-sustaining voltage coincides with the discharge voltage obtained from the backward voltage sweep. In addition, the self-sustaining voltage decreases with increased initial plasma density and saturates above a certain initial plasma density, which indicates a change in plasma resistivity. The decrease in self-sustaining voltage is associated with the electron heat loss at the anode for the low pd (rarefied) regime. In the high pd (collisional) regime, the ion energy loss toward the cathode due to the cathode fall and the inelastic collision loss of electrons in the bulk discharge balance out. Finally, it is demonstrated that the self-sustaining voltage collapses to a singular value, despite the presence of a initial plasma, for microgaps when field emission is dominant, which is also consistent with experimental observations.","PeriodicalId":510396,"journal":{"name":"Physics of Plasmas","volume":"30 3","pages":""},"PeriodicalIF":0.0,"publicationDate":"2024-07-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141697992","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}
De-Sheng Zhang, Xue-Ren Hong, Xiao-Bo Zhang, R. Tang, Bai-Song Xie
The generation of vortex terahertz (THz) radiation by the interaction of a two-color Laguerre–Gaussian (LG) laser with plasmas under an external magnetic field is investigated theoretically and numerically. It is found that the vortex THz radiation with good monoenergetic properties can be generated successfully, and the orbital angular momentum of the LG lasers can be transferred to the radiation. In this scheme, the external magnetic field can not only enhance the intensity but can also break the spatial distribution symmetry of the vortex THz radiation. With the increase in the initial plasma density, the intensity of the vortex THz radiation increases significantly before reaching saturation and the spatial period of the radiation decreases, which indicates the monoenergetic peak of the vortex THz radiation can be well controlled through the initial plasma density. The relevant conclusions are verified by two-dimensional particle-in-cell simulations.
本文从理论和数值上研究了外磁场下双色拉盖尔-高斯（LG）激光器与等离子体相互作用产生涡旋太赫兹（THz）辐射的问题。研究发现，可以成功产生具有良好单能特性的涡旋太赫兹辐射，并且 LG 激光的轨道角动量可以转移到辐射中。在该方案中，外磁场不仅能增强强度，还能打破涡旋太赫兹辐射的空间分布对称性。随着初始等离子体密度的增加，涡旋太赫兹辐射的强度在达到饱和之前显著增加，辐射的空间周期减小，这表明通过初始等离子体密度可以很好地控制涡旋太赫兹辐射的单能峰。相关结论通过二维粒子入胞模拟得到了验证。
{"title":"Generation of the vortex terahertz radiation by the interaction of two-color Laguerre–Gaussian laser with plasmas in the presence of a static magnetic field","authors":"De-Sheng Zhang, Xue-Ren Hong, Xiao-Bo Zhang, R. Tang, Bai-Song Xie","doi":"10.1063/5.0207570","DOIUrl":"https://doi.org/10.1063/5.0207570","url":null,"abstract":"The generation of vortex terahertz (THz) radiation by the interaction of a two-color Laguerre–Gaussian (LG) laser with plasmas under an external magnetic field is investigated theoretically and numerically. It is found that the vortex THz radiation with good monoenergetic properties can be generated successfully, and the orbital angular momentum of the LG lasers can be transferred to the radiation. In this scheme, the external magnetic field can not only enhance the intensity but can also break the spatial distribution symmetry of the vortex THz radiation. With the increase in the initial plasma density, the intensity of the vortex THz radiation increases significantly before reaching saturation and the spatial period of the radiation decreases, which indicates the monoenergetic peak of the vortex THz radiation can be well controlled through the initial plasma density. The relevant conclusions are verified by two-dimensional particle-in-cell simulations.","PeriodicalId":510396,"journal":{"name":"Physics of Plasmas","volume":"24 3","pages":""},"PeriodicalIF":0.0,"publicationDate":"2024-07-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141710644","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. Lazerson, David Kulla, P. McNeely, N. Rust, Lucas van Ham, D. Hartmann
A new neutral beamline (OPTEMIST) uniquely capable of exploring the predicted improvement of fast ion confinement in Wendelstein 7-X (W7-X), which comes with increasing plasma beta, is proposed. As the plasma beta increases in the W7-X device, the high mirror magnetic configuration has drift orbits that begin to close, enhancing the confinement of the deeply trapped particles. The existing neutral beam system is found to produce particle populations that do not adequately probe the deeply trapped orbits. Fast tritons generated by thermal deuterium–deuterium fusion reactions are found to probe the necessary conditions for demonstrating this effect. However, it is found that diagnostically measuring this effect will be difficult. A scoping study of a neutral beamline that directly populates the trapped orbits is performed. It is found that a monoenergetic population of 120 kV injected protons provides the largest confinement enhancement in the fast ion population as the plasma beta is increased. The necessity to raise plasma density to increase plasma beta results in blinding of spectroscopic beam measurements by bremsstrahlung. An array of novel fast ion loss detectors that would adequately assess the confinement of these particles is proposed.
{"title":"OPTEMIST: A neutral beam for measuring quasi-omnigenity in Wendelstein 7-X","authors":"S. Lazerson, David Kulla, P. McNeely, N. Rust, Lucas van Ham, D. Hartmann","doi":"10.1063/5.0218670","DOIUrl":"https://doi.org/10.1063/5.0218670","url":null,"abstract":"A new neutral beamline (OPTEMIST) uniquely capable of exploring the predicted improvement of fast ion confinement in Wendelstein 7-X (W7-X), which comes with increasing plasma beta, is proposed. As the plasma beta increases in the W7-X device, the high mirror magnetic configuration has drift orbits that begin to close, enhancing the confinement of the deeply trapped particles. The existing neutral beam system is found to produce particle populations that do not adequately probe the deeply trapped orbits. Fast tritons generated by thermal deuterium–deuterium fusion reactions are found to probe the necessary conditions for demonstrating this effect. However, it is found that diagnostically measuring this effect will be difficult. A scoping study of a neutral beamline that directly populates the trapped orbits is performed. It is found that a monoenergetic population of 120 kV injected protons provides the largest confinement enhancement in the fast ion population as the plasma beta is increased. The necessity to raise plasma density to increase plasma beta results in blinding of spectroscopic beam measurements by bremsstrahlung. An array of novel fast ion loss detectors that would adequately assess the confinement of these particles is proposed.","PeriodicalId":510396,"journal":{"name":"Physics of Plasmas","volume":"79 4","pages":""},"PeriodicalIF":0.0,"publicationDate":"2024-07-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141702023","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 present the generation of well-collimated gamma photons and pairs with extrinsic transverse orbital angular momentum (TOAM) through the head-on collision of an intense spatiotemporal optical vortex (STOV) pulse carrying intrinsic TOAM and a high-energy electron beam. It is found that the TOAM of STOV pulse remains almost unchanged, and the TOAM is conserved in the center-of-mass frame. Moreover, there exhibits a duality for particles TOAM in the CMF and laboratory frame when the initial location of high-energy electron beam is different. Furthermore, the TOAM of gamma photons in the CMF increases while that of positrons decreases as the topological charge of STOV pulse increases, whereas in the LF, the TOAM of both gamma photons and positrons decreases. The result under the same pulse intensity is better than that under the same pulse energy. The increase in the initial energy of high-energy electrons leads to an enhancement of the TOAM of both gamma photons and positrons in both frames. Gamma photons and electrons/positrons with TOAM as a new degree of freedom may have extensive applications in optical communication, astrophysics, nanomaterials, and other fields.
{"title":"Generation of gamma photons and pairs with transverse orbital angular momentum via spatiotemporal optical vortex pulse","authors":"Cui-Wen Zhang, De-Sheng Zhang, Bai-Song Xie","doi":"10.1063/5.0214297","DOIUrl":"https://doi.org/10.1063/5.0214297","url":null,"abstract":"We present the generation of well-collimated gamma photons and pairs with extrinsic transverse orbital angular momentum (TOAM) through the head-on collision of an intense spatiotemporal optical vortex (STOV) pulse carrying intrinsic TOAM and a high-energy electron beam. It is found that the TOAM of STOV pulse remains almost unchanged, and the TOAM is conserved in the center-of-mass frame. Moreover, there exhibits a duality for particles TOAM in the CMF and laboratory frame when the initial location of high-energy electron beam is different. Furthermore, the TOAM of gamma photons in the CMF increases while that of positrons decreases as the topological charge of STOV pulse increases, whereas in the LF, the TOAM of both gamma photons and positrons decreases. The result under the same pulse intensity is better than that under the same pulse energy. The increase in the initial energy of high-energy electrons leads to an enhancement of the TOAM of both gamma photons and positrons in both frames. Gamma photons and electrons/positrons with TOAM as a new degree of freedom may have extensive applications in optical communication, astrophysics, nanomaterials, and other fields.","PeriodicalId":510396,"journal":{"name":"Physics of Plasmas","volume":"6 21","pages":""},"PeriodicalIF":0.0,"publicationDate":"2024-07-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141696394","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 ability of plasmonic optical tweezers based on metal nanostructure to stably trap and dynamically manipulate nanoscale objects at low laser power has been widely used in the fields of nanotechnology and life sciences. In particular, their plasmonic nanocavity structure can improve the local field intensity and trap depth by confining electromagnetic fields to subwavelength volumes. In this paper, the R6G dye molecules with 10−6 M were successfully trapped by using the Ag@Polydimethylsiloxane nanocavity array structure, and a R6G micro-ring was formed under the combined action of plasmonic optical force and thermophoresis. Subsequently, the theoretical investigation revealed that the trapping performance can be flexibly adjusted by changing the structural parameters of the conical nanocavity unit, and it can provide a stable potential well for polystyrene particles of RNP = 14 nm when the cavity depth is 140 nm. In addition, it is found that multiple trapping sites can be activated simultaneously in the laser irradiation area by investigating the trapping properties of the hexagonal conical nanocavity array structure. This multi-site stable trapping platform makes it possible to analyze multiple target particles contemporaneously.
{"title":"Tunable plasmonic tweezers based on nanocavity array structure for multi-site nanoscale particles trapping","authors":"Xiaoya Yan, Hongyan Shi, Pengxue Jia, Xiudong Sun","doi":"10.1063/5.0193932","DOIUrl":"https://doi.org/10.1063/5.0193932","url":null,"abstract":"The ability of plasmonic optical tweezers based on metal nanostructure to stably trap and dynamically manipulate nanoscale objects at low laser power has been widely used in the fields of nanotechnology and life sciences. In particular, their plasmonic nanocavity structure can improve the local field intensity and trap depth by confining electromagnetic fields to subwavelength volumes. In this paper, the R6G dye molecules with 10−6 M were successfully trapped by using the Ag@Polydimethylsiloxane nanocavity array structure, and a R6G micro-ring was formed under the combined action of plasmonic optical force and thermophoresis. Subsequently, the theoretical investigation revealed that the trapping performance can be flexibly adjusted by changing the structural parameters of the conical nanocavity unit, and it can provide a stable potential well for polystyrene particles of RNP = 14 nm when the cavity depth is 140 nm. In addition, it is found that multiple trapping sites can be activated simultaneously in the laser irradiation area by investigating the trapping properties of the hexagonal conical nanocavity array structure. This multi-site stable trapping platform makes it possible to analyze multiple target particles contemporaneously.","PeriodicalId":510396,"journal":{"name":"Physics of Plasmas","volume":"15 5","pages":""},"PeriodicalIF":0.0,"publicationDate":"2024-07-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141711165","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}
Simulating direct-drive inertial confinement experiments presents significant computational challenges, both due to the complexity of the codes required for such simulations and the substantial computational expense associated with target design studies. Machine learning models, and in particular, surrogate models, offer a solution by replacing simulation results with a simplified approximation. In this study, we apply surrogate modeling and optimization techniques that are well established in the existing literature to one-dimensional simulation data of a new cylindrical target design containing deuterium–tritium fuel. These models predict yields without the need for expensive simulations. We find that Bayesian optimization with Gaussian process surrogates enhances sampling efficiency in low-dimensional design spaces but becomes less efficient as dimensionality increases. Nonetheless, optimization routines within two-dimensional and five-dimensional design spaces can identify designs that maximize yield, while also aligning with established physical intuition. Optimization routines, which ignore constraints on hydrodynamic instability growth, are shown to lead to unstable designs in 2D, resulting in yield loss. However, routines that utilize 1D simulations and impose constraints on the in-flight aspect ratio converge on novel cylindrical target designs that are stable against hydrodynamic instability growth in 2D and achieve high yield.
{"title":"A Gaussian process based surrogate approach for the optimization of cylindrical targets","authors":"William Gammel, J. Sauppe, Paul Bradley","doi":"10.1063/5.0204411","DOIUrl":"https://doi.org/10.1063/5.0204411","url":null,"abstract":"Simulating direct-drive inertial confinement experiments presents significant computational challenges, both due to the complexity of the codes required for such simulations and the substantial computational expense associated with target design studies. Machine learning models, and in particular, surrogate models, offer a solution by replacing simulation results with a simplified approximation. In this study, we apply surrogate modeling and optimization techniques that are well established in the existing literature to one-dimensional simulation data of a new cylindrical target design containing deuterium–tritium fuel. These models predict yields without the need for expensive simulations. We find that Bayesian optimization with Gaussian process surrogates enhances sampling efficiency in low-dimensional design spaces but becomes less efficient as dimensionality increases. Nonetheless, optimization routines within two-dimensional and five-dimensional design spaces can identify designs that maximize yield, while also aligning with established physical intuition. Optimization routines, which ignore constraints on hydrodynamic instability growth, are shown to lead to unstable designs in 2D, resulting in yield loss. However, routines that utilize 1D simulations and impose constraints on the in-flight aspect ratio converge on novel cylindrical target designs that are stable against hydrodynamic instability growth in 2D and achieve high yield.","PeriodicalId":510396,"journal":{"name":"Physics of Plasmas","volume":"62 9","pages":""},"PeriodicalIF":0.0,"publicationDate":"2024-07-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141696569","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}
Xianglei He, Aaohua Mao, S. Apatenkov, Zhonglin Zhang, Zhibin Wang, Mengmeng Sun, Jitong Zou, Xiaogang Wang
The ground-based device, the Space Plasma Environment Research Facility (SPERF), is established for experimentally simulating magnetosphere plasma processes, with one of its major components, asymmetric reconnection experiment (AREX), for three-dimensional physics relevant to dayside asymmetric magnetopause reconnection. As an outstanding property of fast magnetic reconnection in collisionless plasmas, the Hall effect and its geometric features can be experimentally investigated in SPERF-AREX with various magnetic configurations related to different driven scenarios for simulating interplanetary magnetic field (IMF) conditions. In this work, the Hall effect and its geometric characteristics in such proposed experiments are numerically studied based on a Hall MHD model. The simulation results reveal that in the X-line geometry relevant to southward IMFs, the Hall field features in cross section perpendicular to the X-line are mostly analogous to typical two-dimensional Hall quadrupole structures, clearly an “anti-parallel reconnection” feature. In the separator (A-B null-line) geometry relevant to arbitrary IMF orientations, along the separator between magnetic nulls, the magnetic field configuration near a magnetic null also demonstrates the typical quadrupolar pattern. However, the pattern is distorted away (>10di, here di=c/ωpi is the ion inertial length) from the nulls, in a way similar to that in “component reconnection.” Furthermore, the Hall effect induces a dawn-dusk asymmetry for both the X-line and the separator geometries.
空间等离子体环境研究设施（Space Plasma Environment Research Facility，SPERF）是为实验模拟磁层等离子体过程而建立的地面装置，其主要组成部分之一是非对称再连接实验（AREX），用于与日侧非对称磁层顶再连接相关的三维物理学。霍尔效应及其几何特征是无碰撞等离子体中快速磁性再连接的一个突出特性，可在 SPERF-AREX 中通过与不同驱动情景相关的各种磁性配置进行实验研究，以模拟行星际磁场（IMF）条件。在这项工作中，基于霍尔 MHD 模型，对拟议实验中的霍尔效应及其几何特征进行了数值研究。模拟结果表明，在与南向 IMF 有关的 X 线几何中，与 X 线垂直的横截面上的霍尔场特征大多类似于典型的二维霍尔四极结构，显然是一种 "反平行再连接 "特征。在与任意 IMF 方向相关的分离器（A-B 空线）几何中，沿着磁空之间的分离器，磁空附近的磁场配置也显示出典型的四极模式。然而，该模式在远离磁极（>10di，此处 di=c/ωpi 为离子惯性长度）的地方发生了扭曲，其方式与 "分量再连接 "类似。此外，霍尔效应还导致 X 线和分离器的几何形状出现黎明-黄昏不对称现象。
{"title":"Numerical analysis of three-dimensional magnetopause-like reconnection properties by Hall MHD simulation for SPERF-AREX","authors":"Xianglei He, Aaohua Mao, S. Apatenkov, Zhonglin Zhang, Zhibin Wang, Mengmeng Sun, Jitong Zou, Xiaogang Wang","doi":"10.1063/5.0213566","DOIUrl":"https://doi.org/10.1063/5.0213566","url":null,"abstract":"The ground-based device, the Space Plasma Environment Research Facility (SPERF), is established for experimentally simulating magnetosphere plasma processes, with one of its major components, asymmetric reconnection experiment (AREX), for three-dimensional physics relevant to dayside asymmetric magnetopause reconnection. As an outstanding property of fast magnetic reconnection in collisionless plasmas, the Hall effect and its geometric features can be experimentally investigated in SPERF-AREX with various magnetic configurations related to different driven scenarios for simulating interplanetary magnetic field (IMF) conditions. In this work, the Hall effect and its geometric characteristics in such proposed experiments are numerically studied based on a Hall MHD model. The simulation results reveal that in the X-line geometry relevant to southward IMFs, the Hall field features in cross section perpendicular to the X-line are mostly analogous to typical two-dimensional Hall quadrupole structures, clearly an “anti-parallel reconnection” feature. In the separator (A-B null-line) geometry relevant to arbitrary IMF orientations, along the separator between magnetic nulls, the magnetic field configuration near a magnetic null also demonstrates the typical quadrupolar pattern. However, the pattern is distorted away (>10di, here di=c/ωpi is the ion inertial length) from the nulls, in a way similar to that in “component reconnection.” Furthermore, the Hall effect induces a dawn-dusk asymmetry for both the X-line and the separator geometries.","PeriodicalId":510396,"journal":{"name":"Physics of Plasmas","volume":"313 3","pages":""},"PeriodicalIF":0.0,"publicationDate":"2024-07-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141692080","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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