The application of traveling magnetic fields for communication blackout mitigation introduces significant temporal variations in plasma magnetization characteristics. However, the traditional electromagnetic propagation model does not consider this time-varying magnetization effect, which leads to calculation errors. To address this challenge, this paper presents an enhanced current density convolution finite-difference time-domain algorithm that incorporates two critical advancements: the influence of traveling-wave magnetic fields on the electron density distribution and time-dependent magnetization effects in plasma. The improved methodology enables the comprehensive simulation of oblique electromagnetic wave incidence and wave-plasma interactions under traveling magnetic field excitation. Using the electron-density distribution model of plasma under a traveling magnetic field, an electromagnetic wave propagation model is constructed for scenarios where electromagnetic waves are obliquely incident on plasma influenced by a traveling magnetic field. The electromagnetic propagation characteristics of such electromagnetic waves are calculated. The results indicate that the transmission coefficient of the electromagnetic waves exhibits periodic variation over time. In addition, the transmission coefficient of the electromagnetic waves decreases as the angle of incidence increases.

The energetic electron (EE) excitation of beta-induced Alfven eigenmodes is investigated by using the newly developed global eigenvalue code MAS, which is based on a hybrid model that consists of Landau fluid bulk plasma and drift kinetic EE. Specifically, the bulk plasma kinetic effects such as finite Larmor radius, diamagnetic drifts and Landau dampings, and the EE adiabatic fluid response of convection and non-adiabatic kinetic response of precessional drift resonance are incorporated in the simulations. The global eigenmode equation is solved for e-BAE mode structure and linear dispersion relation in tokamak non-perturbatively. The radial width of e-BAE mode structure becomes narrower as the toroidal mode number increases, which can be explained by the change of Alfven continuous spectra that interact with kinetic Alfven waves for corresponding eigenmode formation. The e-BAE growth rate exhibits a non-monotonic variation with toroidal mode number for precessional drift resonance destabilization, while the e-BAE real frequency is close to the continuum accumulation point that almost remains the same. The parametric dependence of e-BAE stability on EE density and that on temperature are analyzed by MAS non-perturbative simulations, which shows that the EE density can affect e-BAE real frequency and thus changes the resonance condition, resulting in e-BAE stabilization in the strong EE drive regime. Further, the EE non-perturbative effect on the symmetry breaking of e-BAE mode structure is reported. The poloidal symmetry breaking characterized by the 'boomerang' shape two-dimensional (2D) structure can be greatly enhanced by increasing EE temperature, together with the large radial variation of the poloidal phase angle of dominant principal poloidal harmonic. The radial symmetry breaking of e-BAE mode structure arises when EE density/temperature drive is not symmetric with respect to corresponding rational surface, which can lead to a net volume-averaged value of e-BAE parallel wave number which drives plasma intrinsic rotation. These results are helpful in understanding the e-BAE dynamics observed in recent experiments.

Collision process is crucial to the transport in magnetized plasmas. This article reviews the three typical approaches, i.e. the Fokker-Planck (FP) approach, the Bogoliubov-Born-Green-Kirwood-Yvon (BBGKY) approach, and the quasilinear (QL) approach, to deriving the kinetic equation for weakly coupled uniformly magnetized plasmas. The collision terms derived based on these three approaches are shown to be identical and satisfy the conservation laws and H theorem. Relatively speaking, the BBGKY and QL approaches are more systematic and readily to be generalized from weakly magnetized plasmas to strongly magnetized plasmas. The FP approach is pretty simple for weakly magnetized plasmas and has the advantage that the collision term derived based on it can be naturally separated into two parts, one part arising from the polarization and the other from the correlation of the fluctuating electrostatic field. However, the usual form of the FP equation is not suitable for strongly magnetized plasmas. To derive the magnetized collision term based on the FP approach, a general form of the FP equation for magnetized plasmas has to be found first.

The nonlinear interaction between the m / n = 2 / 1 beta-induced Alfvén eigenmode (BAE) and the m / n = 2 / 1 tearing mode (TM) observed in the HL-2A experiment is systematically studied with the hybrid kinetic-magnetohydrodynamic code M3D-K. It is found that the nonlinear growth of TM can lead to a gradient buildup on the magnetic island (MI) edge, and then triggers the destabilization of the linearly-stable BAE. Then, the triggered BAE together with TM can produce a significant redistribution of energetic particles. For BAE linearly-dominant-unstable case, the TM activity results in the inward motion of BAE mode structure, and the BAE can have a delay effect on the MI saturation. Furthermore, a high-frequency axisymmetric m / n = 0 / 0 ‘breathing’ mode is generated by the mode coupling of BAE and TM, agreeing well with the experimental observation, and causes the synchronized periodic oscillation of MI width.

We have developed a new global eigenvalue code, multiscale analysis for plasma stabilities (MAS), for studying plasma problems with wave toroidal mode number ( n ) and frequency ( ω ) in a broad range of interest in general tokamak geometry, based on a five-field Landau-fluid description of thermal plasmas. Beyond keeping the necessary plasma fluid response, we further retain the important kinetic effects including diamagnetic drift, ion finite Larmor radius, finite parallel electric field ( E | | ), ion and electron Landau resonances in a self-consistent and non-perturbative manner without sacrificing the attractive efficiency in computation. The physical capabilities of the code are evaluated and examined in terms of both theory and simulation. In theory, the comprehensive Landau-fluid model implemented in MAS can be reduced to the well-known ideal magnetohydrodynamic (MHD) model, electrostatic ion-fluid model, and drift-kinetic model in various limits, which clearly delineates the physics validity regime. In simulation, MAS has been well benchmarked with theory and other gyrokinetic and kinetic-MHD hybrid codes in a manner of adopting the unified physical and numerical framework, which covers the kinetic Alfvén wave, ion sound wave, low- n kink, high- n ion temperature gradient mode and kinetic ballooning mode. Moreover, MAS is successfully applied to model the Alfvén eigenmode (AE) activities in DIII-D discharge #159243, which faithfully captures the frequency sweeping of reversed shear AE, the tunneling damping of toroidal AE, as well as the polarization characteristics of kinetic beta-induced AE and beta-induced Alfvén-acoustic eigenmode being consistent with former gyrokinetic theory and simulation. With respect to the key progress contributed to the community, MAS has the advantage of combining rich physics ingredients, realistic global geometry and high computation efficiency together for plasma stability analysis in the linear regime.

Based on first-principles nonlinear gyrokinetic simulations, the electrostatic turbulence properties in the internal transport barrier (ITB) region of an Experimental Advanced Superconducting Tokamak discharge (#93890) are investigated. Specifically, ITBs with steep density and temperature gradients are located in the weakly negative magnetic shear region at the plasma center. In the linear stage, the growth rate and frequency of the ion temperature gradient (ITG) mode increase significantly due to resonant excitation by trapped electrons. That is, the resonance between trapped electrons and the ITG becomes strong due to the precession drift reversal of trapped electrons by the negative magnetic shear and Shafranov shift. Meanwhile, the trapped electron mode is stable in the ITB region due to only a very small fraction of electrons precessing in the direction of the electron diamagnetic drift. Nonlinear simulations show that, after considering the non-adiabatic effect of trapped electrons, the heat conductivity of ions and the turbulence intensity increase by at least a factor of 7 compared with the results only considering the adiabatic effect of electrons. The zonal charge density of trapped electrons can partially cancel that of ions, which weakens the intensity of the zonal flow, and consequently reduces the zonal flow regulation and enhances the turbulent transport.

The dynamics of energetic particles and tearing modes and the interactions between them are of great significance for magnetically confined fusion plasmas. In this review, we focus on these issues in the context of tokamak plasmas. The interaction between energetic particles and tearing modes is considered from two perspectives:（i） the influence of energetic particles on tearing modes and（ii） the transport of energetic particles by tearing modes. The influence of energetic particles on tearing modes is described on the basis of a general dispersion relation for tearing modes. The effects of energetic particles are considered separately in the outer region and the island region of a tearing mode. The physics mainly results from the modification of the perturbed parallel current by energetic particles without wave–particle resonance. In addition, the resonance between energetic particles and tearing modes is also reviewed. For the transport of energetic particles, transport of both circulating and trapped energetic particles by tearing mode is reviewed. Our descriptions of physical phenomena here are based on an analytical approach, while the experiments and simulations are used to illustrate and confirm our results. Finally, a number of open issues are discussed.

Understanding and modeling fast-ion stabilization of ion-temperature-gradient (ITG) driven microturbulence have profound implications for designing and optimizing future fusion reactors. In this work, an analytic model is presented, which describes the effect of fast ions on ITG mode. This model is derived from a bounce-average gyro-kinetic equation for trapped fast ions and ballooning transformation for ITG mode. In addition to dilution, strong wave-fast-ion resonant interaction is involved in this model. Based on numerical calculations, the effects of the main physical parameters are studied. The increasing density of fast ions will strengthen the effects of fast ions. The effect of wave-particle resonance strongly depends on the temperature of fast ions. Furthermore, both increasing density gradient and the ratio of the temperature and density gradients can strengthen the stabilization of fast ions in ITG mode. Finally, the influence of resonance broadening of wave-particle interaction is discussed.

The impact of magnetic field (MF) on the parallel resistivity η_{∥} is studied for strongly magnetized plasmas with the electron thermal gyroradius ρ_{the} smaller than the Debye length λ_{D} but much larger than the Landau length λ_{L}. Two previous papers [P. Ghendrih et al., Phys. Lett. A 119, 354 (1987)10.1016/0375-9601(87)90614-1; S. D. Baalrud and T. Lafleur, Phys. Plasmas 28, 102107 (2021)10.1063/5.0054113] found η_{∥} to increase monotonically with MF. Unfortunately, both works used predetermined electron distribution functions and are thus not self-consistent. In this paper, we analyze the MF dependence of η_{∥} self-consistently by solving the electron magnetized kinetic equation in a Lorentz gaslike approximation. It is found η_{∥} decreases monotonically with MF, with λ_{D} in the usual Coulomb logarithm lnΛ=ln(λ_{D}/λ_{L}) being replaced by ρ_{the}. The underlying physics is that the electrons affected only by the collisions with impact parameters between λ_{L} and ρ_{the} carry almost all the parallel current.

Based on the experimental parameters in the HL-2A tokamak, hybrid simulations have been carried out to investigate the linear stability and nonlinear dynamics of the beta-induced Alfvén eigenmode (BAE). It is found that the ( m / n = 3/2) BAE is excited by co-passing energetic ions with q min = 1.5 in linear simulation, and the mode frequency is consistent with the experimental measurement. The simulation results show that the energetic ions β h , the injection velocity v 0 , and orbit width parameter ρ h of energetic ions are important parameters determining the drive of BAE. Furthermore, the effect of q min (with the fixed shape of the q profile) is studied, and it is found that when q min ⩽ 1.5, the excited modes are BAEs, which are located near q = 1.5 rational surfaces; when q min > 1.5, the excited modes are similar to the reversed-shear Alfvén eigenmodes, which are mainly localized around q = q min surfaces. Nonlinear simulation results show that the nonlinear dynamics of BAE are sensitive to the EP drive. For the strongly driven case, firstly, redistribution and transport of energetic ions are trigged by 3/2 BAE, which raised the radial gradient of the distibution function of energetic ions near the q = 2 rational surface, and then an energetic particle mode (EPM) ( m / n = 4/2) is driven in the nonlinear phase. Finally, these two instabilities triggered a significant redistribution of energetic ions, which results in the twice-repeated and mostlydownward frequency chirping of 3/2 BAE. For the weakly driven case, there are no 4/2 EPM being driven nor twice-repeated chirping in the nonlinear phase, since the radial gradient near q = 2 rational surface is small and almost unchanged.

Rutherford scattering formula plays an important role in plasma classical transport. It is urgent to need a magnetized Rutherford scattering formula since the magnetic field increases significantly in different fusion areas (e.g. tokamak magnetic field, self-generated magnetic field, and compressed magnetic field). The electron-ion Coulomb collisions perpendicular to the external magnetic field are studied in this paper. The scattering angle is defined according to the electron trajectory and asymptotic line (without magnetic field). A magnetized Rutherford scattering formula is obtained analytically under the weak magnetic field approximation. It is found that the scattering angle decreases as external magnetic field increases. It is easy to find the scattering angle decreasing significantly as incident distance, and incident velocity increasing. It is shown that the theoretical results agree well with numerical calculation by checking the dependence of scattering angle on external magnetic field.

In group activity recognition, hierarchical framework is widely adopted to represent the relationships between individuals and their corresponding group, and has achieved promising performance. However, the existing methods simply employed max/average pooling in this framework, which ignored the distinct contributions of different individuals to the group activity recognition. In this paper, we propose a new contextual pooling scheme, named attentive pooling, which enables the weighted information transition from individual actions to group activity. By utilizing the attention mechanism, the attentive pooling is intrinsically interpretable and able to embed member context into the existing hierarchical model. In order to verify the effectiveness of the proposed scheme, two specific attentive pooling methods, i.e., global attentive pooling (GAP) and hierarchical attentive pooling (HAP) are designed. GAP rewards the individuals that are significant to group activity, while HAP further considers the hierarchical division by introducing subgroup structure. The experimental results on the benchmark dataset demonstrate that our proposal is significantly superior beyond the baseline and is comparable to the state-of-the-art methods.

利用射频激励电容耦合等离子体放电装置产生等离子体,分别采用氧、空气、氩、氖等离子体对Ta2O5/Al2O3激光陀螺反射镜进行处理,试验研究了等离子体气压和等离子体种类对Ta2O5/Al2O3激光陀螺反射镜光学损耗的影响.通过比对实验、能谱、光电子能谱分析测试等技术手段,对Ta2O5/Al2O3激光陀螺反射镜在等离子体环境下出现的损耗变化现象、机理进行了探讨.Ta2O5/Al2O3激光陀螺反射镜经氧等离子体处理后的损耗变化量最大,达到了15 ppm(1 ppm=1×10-6),为另3种等离子体处理后损耗变化量的2-4倍.定位出了Ta2O5/Al2O3激光陀螺反射镜等离子体环境下产生吸收具体膜层为最外层2LAl2O3,发现了2LAl2O3在氧、氩等离子体作用下吸收损耗在一定程度上产生可逆变化的现象,结合XPS分析,对这一可逆现象从薄膜中游离O、Ar与等离子体中粒子之间相互作用产生缺陷等角度进行了探讨.提出了进一步提升Ta2O5/Al2O3激光陀螺反射镜等离子体环境稳定性的技术措施.

Flux coordinates and field-line coordinates are ubiquitous in magnetically confined plasma research. Most of these coordinates are essentially non-orthogonal curvilinear coordinates, in which the differential operators are rather complicated. This article reports an automatic tool, OpGen, for generating a finite difference coefficient matrix for field solvers by using a computer symbolic computation system. This tool is suitable for, but is not limited to, code development for toroidally confined plasmas.

For an electron-electron collision with characteristic scale length larger than the relative gyro-radius of the two colliding electrons, when the initial relative parallel kinetic energy cannot surmount the Coulomb repulsive potential, reflection will occur with interchange of the parallel velocities of the two electrons after the collision. The Fokker–Planck approach is employed to derive the electron collision term C R describing parallel velocity scattering due to the reflections for a magnetized plasma where the average electron gyro-radius is much smaller than the Debye length but much larger than the Landau length. The electron parallel velocity friction and diffusion coefficients due to the reflections are evaluated, which are found not to depend on the electron perpendicular velocity. By studying the temporal evolution of the H quantity due to C R , it is found that C R eventually makes the system relax to a state in which the electron parallel velocity distribution is decoupled from the perpendicular velocity distribution.

The drift-tearing instability due to diamagnetic drift effects is verified using the Gyrokinetic Toroidal Code (GTC). First, the classical (2,1) resistive tearing mode is verified in a cylindrical geometry with a fluid model. The dependence of the growth rate of the resistive tearing mode on the beta value of the plasma is obtained and is found to qualitatively agree with the theoretical prediction. A drift-tearing mode is subsequently generated when the equilibrium pressure gradient is significant. In this mode, diamagnetic drift effects result in a reduced growth rate and a real frequency equal to the electron diamagnetic frequency. The scaling relation between the diamagnetic frequency and the growth rate of the drift-tearing mode has been calculated. This relation shows good agreement with the theoretical prediction for a relatively small resistivity; however, an obvious deviation arises when the resistivity is large.

We analytically investigate nonlinear tearing modes with the anomalous electron viscosity or, as it is normally called, hyper-resistivity. In contrast to the flux average method used by previous work, we employ the standard singular perturbation technique and a quasilinear method to obtain the time evolution equation of tearing modes. The result that the magnetic flux grows with time in a scaling as t(2/3) demonstrates that nonlinear tearing modes with the hyper-resistivity effect alone have a weaker dependence on time than that of the corresponding resistive case.

A new finite element (FE) field solver has been implemented in the gyrokinetic toroidal code (GTC) in attempt to extend the simulation domain to magnetic axis and beyond the last closed flux surface, which will enhance the capability the GTC code since the original finite difference (FD) solver will lose its capability in such circumstances. A method of manufactured solution is employed in the unit fidelity test for the new FE field solver, which is then further verified through integrated tests with three typical physical cases for the comparison between the new FE field solver and the original finite difference field solver. The results by the newly implemented FE field solver are in great accord with the original solver.

We give theoretical analyses of the Magneto-Rayleigh-Taylor instability driven by a rotating magnetic field. Both slab and liner configurations with finite thicknesses are dealt with in the WKB and the non-WKB approximations. Results show that instabilities for all modes (combinations of wave vectors) are alleviated. We further discuss the potential application of the alternant/nested configurations of a theta and a Z pinch to the Theta-Z Liner Inertia Fusion (Theta-Z-LIF) concept.

The analytical approaches for nonlinear tearing mode have been reviewed. It is shown that Rutherford's model has triggered numerous studies on the nonlinear tearing mode. Its physical picture is clear meanwhile its mathematical method is ingenious but still puzzling to understand. It is trying to find how the 'nonlinear behavior' resulted from the linear equation by a nonlinear transform. It is indicated that Li's model for the tearing mode includes the linear growth, Rutherford's behavior and the new behavior. It was found that the quasilinear modification of magnetic field provided a new damping mechanism for nonlinear growth. The new behavior w similar to t(1/2) becomes dominant if the mode is weakly unstable. It is shown that many analytical methods have been developed to calculate the criterion parameter Delta' of the tearing mode. Li's instability criterion can cover the previous results in the limit cases.