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Kinetic theory of geodesic acoustic modes in toroidal plasmas:a brief review

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Plasma Science and Technology 2018年第9期20卷 24-49页

作者： Zhiyong QIU Liu CHEN Fulvio ZONCA institute for fusion theory and simulation and department of physics Zhejiang University department of physics and Astronomy University of California ENEA Fusion and Nuclear Safety Department

Geodesic acoustic modes（GAM） are oscillating zonal structures unique to toroidal plasmas,and have been extensively studied in the past decades due to their potential capabilities of regulating microscopic turbulences and associated anomalous transport.This article reviews linear and nonlinear theories of GAM;with emphases on kinetic treatment,system nonuniformity and realistic magnetic geometry,in order to reflect the realistic experimental conditions.Specifically,in the linear physics,the resonant wave-particle interactions are discussed,with the application to resonant excitation by energetic particles（EPs）.The theory of EP-induced GAM（EGAM） is applied to realistic devices for the interpretation of experimental observations,and global effects due to coupling to GAM continuum are also discussed.Meanwhile,in the nonlinear physics,the spontaneous GAM excitation by microscale turbulences is reviewed,including the effects of various system nonuniformities.A unified theoretical framework of GAM/EGAM is then constructed based on our present understandings.The first-principle-based GAM/EGAM theories reviewed here,thus,provide the tools needed for the understanding and interpretation of experimental/numerical results.

关键词： geodesic acoustic mode kinetic theory nonlinear physics energetic particle physics

Dynamics of oscillatory plasma flows prior to the H-mode in the HL-2A tokamak

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Plasma Science and Technology 2017年第7期19卷 1-6页

作者：钟武律邹晓岚石中兵段旭如许敏杨曾辰施培万蒋敏肖国梁宋显明董家齐丁玄同刘永 HL-2A团队 Southwestern institute of physics CEA IRFM institute for fusion theory and simulation Zhejiang University

This paper discusses edge oscillatory plasma flows, geodesic acoustic mode （GAM） and limit cycle oscillations （LCOs）, which have been measured by Doppler reflectometry prior to the high confinement mode （H-mode） in the HL-2A tokamak. The complex relations between the flows and background turbulence have been analyzed. It was observed that the GAM and LCO coexist, and these two flows and turbulence have strong nonlinear interactions during the intermediate confinement phase （I-phase）. Dynamics of the shear flows and turbulence prior to the H-mode shows that the oscillatory flows quench the turbulence along with the increase of the mean E x B flow at the early stage of the I-phase, then the oscillatory flows are damped and the further increased mean flow takes over the role in turbulence suppression. The reduced turbulent transport results in the formation of a steep edge transport barrier. It suggests that the oscillatory flows can initiate the L-H transition through providing a positive feedback for the increase of the mean E × B flow strength.

关键词： plasma shear flow turbulence L-H transition H-mode microwave reflectometry

The dynamics of an ion acting on two monochromatic obliquely propagating Alfvén waves

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Plasma Science and Technology 2017年第7期19卷 12-25页

作者：虞立敏盛正卯张先梅薛二兵 department of physics East China University of Science and Technology department of physics and institute for fusion theory and simulation Zhejiang University

The interaction between a magnetized ion and two monochromatic shear Alfvtn waves propagating obliquely to an ambient magnetic field is investigated both analytically and numerically. According to the Hamiltonian of this system, the invariant of motion at the lowest order and the half-island widths at the corresponding resonances are obtained analytically using the Lie transformation method. It is shown that these theoretical results agree with the numerical ones from the Poincare surface of section. The regular motions from the invariant and the transition to stochasticity due to resonance overlapping are demonstrated. Compared to the case of a single wave, there may be a lower stochastic threshold in the multiple-wave problem.

关键词： Alfven waves Lie transformation Poincare section stochastic heating

Solving Poisson equation with slowing-down equilibrium distribution for global gyrokinetic simulation

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Plasma Science and Technology 2023年第2期25卷 11-19页

作者：钟奇肖湧 institute for fusion theory and simulation Department of PhysicsZhejiang UniversityHangzhou 310027People's Republic of China

fusion-born alpha particles in burning plasmas are usually regarded as have a slowing-down distribution,which differs significantly from the Maxwellian distribution of thermal particles in velocity space.A generalized multi-point average method has been developed for gyrokinetic Poisson equation with slowing-down equilibrium distribution using optimization in Fourier space.Its accuracy is verified in both long and short wavelength limits.The influence of changing equilibrium distribution from Maxwellian to slowing-down on gyrokinetic Poisson equation is analyzed to illustrate the significance of the new method.The effect of critical speed in the slowingdown distribution on the field solver is also presented.This method forms an important basis for global gyrokinetic simulation of low-frequency drift Alfvénic turbulence in burning plasmas.

关键词： gyrokinetics Poisson solver slowing-down distribution

Self-Organization of Charged Particulates in the Presence of External Force

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Chinese physics Letters 2017年第3期34卷 90-94页

作者：汪友梅陈琦郁明阳 department of physics School of ScienceHangzhou Dianzi University institute for fusion theory and simulation and department of physics Zhejiang University institute for Theoretical physics I Ruhr University

Evolution of spatial distribution of charged particulates under the action of an external force is investigated. It is found that starting from a homogeneous Maxwellian distribution of particulates, clusters can form and aggregate. The evolution process, as well as the asymptotic number and configuration of the clusters formed, depends strongly on the strength of the external force. The particulates in most of the final clusters are in the crystal state, as can also be deduced from the corresponding velocity and auto-correlation functions.

关键词： Self-Organization of Charged Particulates in the Presence of External Force

Sawtooth-like oscillations and steady states caused by the m/n=2/1 double tearing mode

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Plasma Science and Technology 2022年第3期24卷 89-97页

作者：张威马志为张豪伟王鑫 institute for fusion theory and simulation Department of PhysicsZhejiang UniversityHangzhou 310027People's Republic of China

The sawtooth-like oscillations resulting from the m/n=2/1 double tearing mode(DTM)are numerically investigated through the three-dimensional,toroidal,nonlinear resistive-MHD code(CLT).We find that the nonlinear evolution of the m/n=2/1 DTM can lead to sawtooth-like oscillations,which are similar to those driven by the kink mode.The perpendicular thermal conductivity and the external heating rate can significantly alter the behaviors of the DTM driven sawtooth-like oscillations.With a high perpendicular thermal conductivity,the system quickly evolves into a steady state with m/n=2/1 magnetic islands and helical flow.However,with a low perpendicular thermal conductivity,the system tends to exhibit sawtooth-like oscillations.With a sufficiently high or low heating rate,the system exhibits sawtooth-like oscillations,while with an intermediate heating rate,the system quickly evolves into a steady state.At the steady state,there exist the non-axisymmetric magnetic field and strong radial flow,and both are with helicity of m/n=2/1.Like the steady state with m/n=1/1 radial flow,which is beneficial for preventing the helium ash accumulation in the core,the steady state with m/n=2/1 radial flow might also be a good candidate for the advanced steady state operations in future fusion reactors.We also find that the behaviors of the sawtooth-like oscillations are almost independent of tokamak geometry,which implies that the steady state with saturated m/n=2/1 islands might exist in different tokamaks.

关键词： DTM reversed magnetic shear pressure crash sawteeth sawtooth double tearing mode steady state advanced scenario

MHD Equilibrium Configuration Reconstructions for HL-2A Tokamak

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Plasma Science and Technology 2011年第4期13卷 424-430页

作者：何志雄董家齐何宏达蒋海滨高喆张锦华 Southwestern institute of physics department of Engineering physics Tsinghua University institute for fusion theory and simulation Zhejiang University department of Engineering physics Tsinghua University

The EFIT （Equilibrium Fitting） code is modified for the equilibrium configuration reconstruction in HL-2A. Signals from Langmuir probe （LP） at the divertor target plates are employed in the reconstruction of divertor configurations. The results show that discharge #2895 starts with a limiter configuration and develops gradually into a divertor configuration after t = 230 ms. This transition process is clearly demonstrated by the LP signals for the reconstruction. The profiles of plasma parameters such as safety factor q, pressure and current density as well as the evolution of major shape parameters of plasma, such as the boundary magnetic fluxes, the positions of both x-point and magnetic axis, are calculated from the reconstructed configurations. The possibility to apply the method to the swing of strike point on the target plate is discussed.

关键词： equilibrium reconstruction MHD equilibrium LP signals HL-2A tokamak

Validation of the current and pressure coupling schemes with nonlinear simulations of TAE and analysis on the linear stability of tearing mode in the presence of energetic particles

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Plasma Science and Technology 2023年第4期25卷 39-50页

作者：张豪伟马志为 institute for fusion theory and simulation School of PhysicsZhejiang UniversityHangzhou 310027People’s Republic of China

Both current and pressure coupling schemes have been adopted in the hybrid kinetic–magnetohydrodynamic code CLT-K recently.Numerical equivalences between these two coupling schemes are strictly verified under different approximations.First,when considering only the perturbed distribution function of energetic particles(EPs),the equivalence can be proved analytically.Second,when both the variations of the magnetic field and the EP distribution function are included,the current and pressure coupling schemes numerically produce the same result in the nonlinear simulations.On this basis,the influences of co-/counter-passing and trapped EPs on the linear stabilities of the m/n=2/1 tearing mode(TM)have been investigated(where m and n represent the poloidal and toroidal mode numbers,respectively).The results of scanningβh of EPs show that the co-passing and trapped EPs are found to stabilize the TM,while the counter-passing EPs tend to destabilize the TM.The behind(de)stabilization mechanisms of the TM by EPs are carefully analyzed.Furthermore,after exceeding critical EP betas,the same branch of the high-frequency mode is excited by co-/counterpassing and trapped EPs,which is identified as the m/n=2/1 energetic particle mode.

关键词： hybrid kinetic–magnetohydrodynamic simulation tearing mode energetic particle

simulation of electron cyclotron current drive and electron cyclotron resonant heating for the HL-2A tokamak

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Chinese physics B 2013年第9期22卷 490-493页

作者：王中天龙永兴董家齐何志雄 Southwestern institute of physics College of Physical Science and Technology Sichuan University institute for fusion theory and simulation Zhejiang University

A quasi-linear formalism is developed for relativistic particles. It is self-consistent including spatial diffusion. An attempt is made to simulate the process of electron cyclotron resonant heating (ECRH) and electron cyclotron current drive (ECCD) for the HL-2A tokamak. Temperature oscillating regimes in Tore Supra diagnosed by MHD activity seem to be reproduced in the simulation. The special feature in this paper is to see the resonance in the long time scale for relativistic plasma.

关键词： relativistic particles quasi-linear formalism three-dimensional diffusion