Gyro-Landau-fluid simulations of impurity effects on ion temperature gradient driven turbulence transport

The effects of impurities on ion temperature gradient(ITG)driven turbulence transport in tokamak core plasmas are investigated numerically via global simulations of microturbulence with carbon impurities and adiabatic electrons.The simulations use an extended fluid code(ExFC)based on a four-field gyro-Landau-fluid(GLF)model.The multispecies form of the normalized GLF equations is presented,which guarantees the self-consistent evolution of both bulk ions and impurities.With parametric profiles of the cyclone base case,well-benchmarked ExFC is employed to perform simulations focusing on different impurity density profiles.For a fixed temperature profile,it is found that the turbulent heat diffusivity of bulk ions in a quasi-steady state is usually lower than that without impurities,which is contrary to the linear and quasilinear predictions.The evolutions of the temperature gradient and heat diffusivity exhibit a fast relaxation process,indicating that the destabilization of the outwardly peaked impurity profile is a transient state response.Furthermore,the impurity effects from different profiles can obviously influence the nonlinear critical temperature gradient,which is likely to be dominated by linear effects.These results suggest that the improvement in plasma confinement could be attributed to the impurities,most likely through adjusting both heat diffusivity and the critical temperature gradient.

Dynamics of Secondary Large-Scale Structures in ETG Turbulence Simulations

The dynamics of secondary large-scale structures in electron-temperature-gradient （ETG） turbulence is investigated based on gyrofluid simulations in sheared slab geometry. It is found that structural bifurcation to zonal flow dominated or streamer-like states depends on the spectral anisotropy of turbulent ETG fluctuation, which is governed by the magnetic shear. The turbulent electron transport is suppressed by enhanced zonal flows. However, it is still low even if the streamer is formed in ETG turbulence with strong shears. It is shown that the low transport may be related to the secondary excitation of poloidal long-wavelength mode due to the beat wave of the most unstable components or a modulation instability. This large-scale structure with a low frequency and a long wavelength may saturate, or at least contribute to the saturation of ETG fluctuations through a poloidal mode coupling. The result suggests a low fluctuation level in ETG turbulence.

Evolution of edge turbulent transport induced by L-mode detachment in the HL-2A tokamak

This paper presents the characteristics of L-mode detachment,together with the behavior of edge turbulent transport and plasma confinement on the HL-2A tokamak.Partially detached and pronounced detached states have been achieved in L-mode plasma.Stored energy was maintained before and after detachment.Edge turbulence and its transport have increased obviously in the partially detached state.In the pronounced detached state,redistribution of the density and temperature profiles due to detachment leads to low amplitude of electron temperature and pressure,as well as very weak edge turbulence and transport.Despite strong plasma radiation in the pronounced detached state,reduced edge turbulent transport contributes to maintaining stored energy in detached L-mode plasma in HL-2A.Different detachment states play an important role in the redistribution of density and temperature profiles,which requires further study.

Verification of Gyrokinetic Particle of Turbulent Simulation of Device Size Scaling Transport

Verification and historical perspective are presented on the gyrokinetic particle simulations that discovered the device size scaling of turbulent transport and indentified the geometry model as the source of the long-standing disagreement between gyrokinetic particle and continuum simulations.

Gyrofluid Simulation of Ion-Scale Turbulence in Tokamak Plasmas

An improved three-field gyrofluid model is proposed to numerically simulate ion-scale turbulence in tokamak plasmas,which includes the nonlinear evolution of perturbed electrostatic potential,parallel ion velocity and ion pressure with adiabatic electron response.It is benchmarked through advancing a gyrofluid toroidal global(GFT G)code as well as the local version(GFT L),with the emphasis of the collisionless damping of zonal flows.The nonlinear equations are solved by using Fourier decomposition in poloidal and toroidal directions and semi-implicit finite difference method along radial direction.The numerical implementation is briefly explained,especially on the periodic boundary condition in GFT L version.As a numerical test and also practical application,the nonlinear excitation of geodesic acoustic mode(GAM),as well as its radial structure,is investigated in tokamak plasma turbulence.

J-TEXT achievements in turbulence and transport in support of future device/reactor

Following the reconstruction of the TEXT tokamak at Huazhong University of Science and Technology in China, renamed as J-TEXT, a plethora of experimental and theoretical investigations has been conducted to elucidate the intricacies of turbulent transport within the tokamak configuration. These endeavors encompass not only the J-TEXT device's experimental advancements but also delve into critical issues pertinent to the optimization of future fusion devices and reactors. The research includes topics on the suppression of turbulence, flow drive and damping, density limit, non-local transport, intrinsic toroidal flow, turbulence and flow with magnetic islands, turbulent transport in the stochastic layer, and turbulence and zonal flow with energetic particles or helium ash. Several important achievements have been made in the last few years, which will be further elaborated upon in this comprehensive review.

Progress of microwave diagnostics development on the HL-2A tokamak

Sets of powerful microwave diagnostic systems have been developed on the HL-2 A tokamak,including 18 subsystems with high spatial and temporal resolutions.These systems have been applied in the HL-2 A tokamak experiments to investigate the core plasma transport,turbulence,MHD,energetic particle physics and so on.In this paper,the microwave diagnostics and their applications are reviewed.Some new technologies,including GHz sampling digital correlation electron cyclotron emission（DCECE）,multi-channel correlation reflectometers,and solid state terahertz interferometers,are also presented in the paper.

Dynamical evolution of cross phase of edge fluctuations and transport bifurcation

The dynamical evolution of edge turbulence during a transport bifurcation is explored using a flux-driven nonlinear fluid model with a geometry relevant to the plasma edge region.The simulations show that the self-generated mean shear flows can dramatically modify the phase angle between turbulent fluctuations.The changes in phase differences and amplitudes of edge fluctuations give rise to the modifications of turbulent edge transport.The statistical properties of flux and fluctuations are also investigated before and after edge shear flow generation.

LARGE EDDY SIMULATION OF PARTICLE TRANSPORT IN FULLY DEVELOPED VERTICAL TURBULENT CHANNEL FLOW

Fully developed vertical turbulent channel flow with particle transport wasinvestigated by use of Large Eddy Simulation (LES) approach coupled with dynamic the Sub-Grid Scale(SGS) model. It was assumed that the motion of each particle is followed in a Lagrangian frame ofreference driven by the forces exerted by fluid motion and gravity under the condition of one-waycoupling. The goal of this study is to investigate the effectiveness of the LES technique forpredicting particle transport in turbulent flow and the behavior of particle-laden turbulent channelflow for three kinds of particles at different Stokes numbers. To depict the behavior ofparticle-laden turbulent channel flow, statistical quantities including particle fluctuation andfluid-particle velocity correlation, and visualization of the particle number density field wereanalyzed.

Heat transport mechanisms of low Mach number turbulent channel flow with spanwise wall oscillation

Large eddy simulation （LES） of low Mach num- ber compressible turbulent channel flow with spanwise wall oscillation （SWO） is carried out. The flow field is analyzed with emphases laid on the heat transport as well as its rela- tion with momentum transport. When turbulent coherent structures are suppressed by SWO, the turbulent transports are significantly changed, however the momentum and heat transports change in the same manner, which gives the evi- dence of inherently consistent transport mechanisms between momentum and heat in turbulent boundary layers. The Reynolds analogies of all the flow cases are quite good, which confirms again the fact that the transport mechanisms of momentum and heat are consistent, which gives theoreti- cal support for controlling the wall heat flux control by using the drag reducing techniques.

Machine learning of turbulent transport in fusion plasmas with neural network

Turbulent transport resulting from drift waves,typically,the ion temperature gradient(ITG)mode and trapped electron mode(TEM),is of great significance in magnetic confinement fusion.It is also well known that turbulence simulation is a challenging issue in both the complex physical model and huge CPU cost as well as long computation time.In this work,a credible turbulence transport prediction model,extended fluid code(ExFC-NN),based on a neural network(NN)approach is established using simulation data by performing an ExFC,in which multi-scale multi-mode fluctuations,such as ITG and TEM turbulence are involved.Results show that the characteristics of turbulent transport can be successfully predicted including the type of dominant turbulence and the radial averaged fluxes under any set of local gradient parameters.Furthermore,a global NN model can well reproduce the radial profiles of turbulence perturbation intensities and fluxes much faster than existing codes.A large number of comparative predictions show that the newly constructed NN model can realize rapid experimental analysis and provide reference data for experimental parameter design in the future.

Numerical simulation of tritium behavior under a postulated accident condition for CFETR TEP system

China Fusion Engineering Test Reactor(CFETR)is China's self-designed and ongoing next-generation fusion reactor project.Tritium confinement systems in CFETR guarantee that the radiation level remains below the safety limit during tritium handling and operation in the fuel cycle system.Our tritium technology team is responsible for studying tritium transport behavior in the CFETR tritium safety confinement systems of the National Key R&D Program of China launched in 2017,and we are conducting CFETR tritium plant safety analysis by using CFD software.In this paper,the tritium migration and removal behavior were studied under a postulated accident condition for the Tokamak Exhaust Processing system of CFETR.The quantitative results of the transport behavior of tritium in the process room and glove box during the whole accident sequence(e.g.,tritium release,alarm,isolation,and tritium removal)have been presented.The results support the detailed design and engineering demonstration-related research of CFETR tritium plant.

BITS: an efficient transport solver based on a collocation method with B-spline basis

A B-spline Interpolation Transport Solver(BITS) based on a collocation method is developed. It solves transport equations as a generalized interpolation problem, taking the first-order accuracy in time and the second-order accuracy in space along with a predictor–corrector or under-relaxation iteration method. Numerical tests show that BITS can solve one-dimensional transport equations for tokamak plasma more accurately without additional computation cost, compared to the finite difference method transport solver which is widely used in existing tokamak transport codes.

Reynolds number dependence of particle transport in a 90°bend with electrostatic effects

In this work,particle transport in a fully developed turbulent 90°bend flow at the"electrostatic equi-librium"state is simulated using large eddy simulation coupled with Lagrangian particle tracking technique.The flow Reynolds numbers(based on bulk velocity)considered is from 34000 to 58000.Three particle size 5,10 and 50μm are considered and their corresponding St number are from 2.2 to 547.Simulation results of the bend flow agree well with experimental data.The electrostatic field formed in the bend is symmetric in the spanwise direction but asymmetric in the vertical direction and radial direction,which is independent of Reynolds number.The minimum electrostatic field strength occurs at r/ra=0.25 near the inner wall of the bend.Particles transported in a bend gradually accumulate near the wall due to turbophoresis,such trend is improved by electrostatics.In addition,under the effect of electrostatics,the plume pattern of particle distribution disappeared.Particle concentration at the inner wall of the bend is higher than that at the outer wall,which depends on the combined effect of elec-trostatics and Dean vortices in the bend.

Transport of particles in an atmospheric turbulent boundary layer

A program incorporating the parallel code of large eddy simulation （LES） and particle transportation model is developed to simulate the motion of particles in an atmospheric turbulent boundary layer （ATBL）. A model of particles of 100-micrometer order coupling with large scale ATBL is proposed. Two typical cases are studied, one focuses on the evolution of particle profile in the ATBL and the landing displacement of particles, whereas the other on the motion of particle stream.

HL-2A 装置边缘湍流与带状流相互作用的实验研究

利用组合静电探针阵列研究了HL-2A装置中湍流与带状流相互作用的动力学过程。实验结果表明,在粒子注入后的等离子体恢复阶段,边界区径向电场剖面逐渐变陡,湍流相干尺度和带状流幅度相应增加,而湍流强度随之降低。这些实验提供了带状流与边缘湍流相互作用的直接实验证据,暗示了能量转移是引起带状流增长的主要原因。

金盆水库上游降雨径流二维泥沙输移沉积模拟

为了探究降雨径流在不同流量、含沙量下对西安市金盆水库水体的影响规律,基于湍流流动模型,对2022年10月降雨径流时期西安市金盆水库上游的泥沙输移和沉积进行了数值模拟,并对所建立模型的可靠性进行了验证。通过对不同流量、含沙量下的径流进行模拟计算,表明在沿程前部断面处,流速越大底部含沙量越小;在沿程后部断面处,流速越大断面含沙量越高;径流含沙量越大,断面含沙量越大,泥沙分布厚度越大。因此,可以根据降雨径流时期来水的流量及含沙量分析泥沙输移沉积的过程,为水库的运行维护提供参考。

基于LES的射流火焰湍流辐射交互作用研究

在大涡模拟中,研究了亚格子湍流辐射交互作用(SGS-TRI)对Sandia Flame D和Flame 4D(Scaled Sandia flame D)辐射源项的影响。模拟中,采用概率密度函数输运方程(TPDF)湍流燃烧模型模拟湍流燃烧过程,球谐函数(P1近似)法、灰气体加权和模型(WSGGM)模拟辐射换热。采用湍流涡团光学薄脉动近似(OTFA)处理滤波吸收项,分别采用考虑和忽略SGS-TRI的方法求解滤波发射项。结果显示,SGS-TRI仅在辐射源项本身数值较小的区域对时均辐射源项有相对较大的影响(最大为25%);考虑和忽略SGS-TRI计算得到的时均温度以及CO_(2)浓度等径向分布基本重合(相对差别小于3%)。因此,亚格子湍流辐射交互作用对无碳烟湍流射流火焰(Flame D和Flame 4D)的影响较小。

HL-2M装置内部输运垒湍流输运的GTC模拟研究

HL-2M托卡马克是我国新一代磁约束聚变等离子体装置,目前已经实现了等离子体电流1 MA的高参数运行模式。本文采用回旋动理学GTC(Gyrokinetic Toroidal Code)程序,研究了具有双输运垒结构的先进运行模式下该装置内部输运垒(Internal Transport Barrier,ITB)的湍流输运。研究结果表明:ITB湍流输运呈现两次连续饱和过程,计算获得的平均离子热扩散系数约为首次饱和水平的两倍。对湍流发展的极向谱和线性色散关系的研究表明,第一次饱和湍流输运由波长kθρi~2.15的短波模式主导,而第二次饱和以kθρi~0.49的长波模式主导;同时,体系湍流的能量由短波模式反向级联到长波模式,湍流饱和阶段径向热扩散系数在输运垒位置处呈现“M”形分布。考虑等离子体带状流结构,数值模拟结果表明:该运行模式下带状流对湍流输运饱和水平没有明显的影响。此外,输运垒等离子体温度和密度梯度最大处对应的湍流饱和期的径向离子热扩散系数最低,极大地增强了对等离子体的约束。

滑溜水压裂主裂缝内支撑剂输送规律实验及数值模拟

滑溜水压裂时通过泵送大排量压裂液在储层中形成主裂缝为主干的裂缝网络,主裂缝内支撑剂的铺置状况直接影响油气井的产能。采用自主设计的大型可视化平板裂缝装置来研究大排量泵送时主裂缝内支撑剂的输送规律,建立了相应的数值模型模拟了砂堤在不同时刻的铺置形态,并分析了湍流对支撑剂铺置的影响规律,为滑溜水压裂时主裂缝内支撑剂的有效铺置提供一定的理论指导。研究表明,滑溜水压裂时支撑剂在主裂缝内的铺置规律与小排量压裂时不同:支撑剂首先在主裂缝入口处形成一个较低的砂堤,而在距入口较远处形成一个较高的砂堤,之后才一层一层周期性的覆盖在两处砂堤之上,直到达到最终的平衡高度;大排量压裂时易引起湍流,将主裂缝进口端暂时沉降的支撑剂重新卷入裂缝深处,形成类似"卷云状"的沉降结构;数值模拟与物理实验模拟得到的支撑剂铺置结果相似,证明了研究的数值模型具有一定的实用性。