Two-dimensional structure and particle pinch in tokamak H mode

Two-dimensional structures of the electrostatic potential, density, and flow velocity near the edge of a tokamak plasma are investigated. The model includes the nonlinearity in bulk-ion viscosity and turbulence-driven shear viscosity. For the case with the strong radial electric field (H mode), a two-dimensional structure in a transport barrier is obtained, giving a poloidal shock with a solitary radial electric field profile. The inward particle pinch is induced from this poloidal asymmetric electric field, and increases as the radial electric field becomes stronger. The abrupt increase of this inward ion and electron flux at the onset of L- to H-mode transition explains the rapid establishment of the density pedestal, which is responsible for the observed spontaneous self-reorganization into an improved confinement regime.     

HL-1M托卡马克边缘参数和雷诺胁强的径向分布

利用多组马赫/郎缪尔探针测量了HL-1M装置刮离层和边缘静电雷诺胁强，等离子体极向旋转，径向和极向电场的径向分布，在低杂波电流驱动，超声分子束注入，多发弹丸注入和中性束注入实验中，给出了雷诺胁强和极向流的关系。结果表明，由于雷诺胁强的径向变化，托卡马克等离子体可以自发地产生剪切极向流。     

Two-Chamber Model for Divertors with Plasma Recycling

To model particle and heat-loss terms at the edge of a tokamak with a divertor or pumped limiter, a simple two-chamber formuluation of the scrapeoff has been constructed by integrating the fluid equations, including sources, along open field lines. The model is then solved for a wide range of density and temperature conditions in the scrapeoff, using geometrical parameters typical of the poloidal divertor in the poloidal divertor experiment (PDX). The solutions characterize four divertor operating conditions for beam-heated plasmas: plugged, unplugged, blowthrough, and blowback.     

TEMPEST simulations of collisionless damping of the geodesic-acoustic mode in edge-plasma pedestals

The fully nonlinear (full-f) four-dimensional TEMPEST gyrokinetic continuum code correctly produces the frequency and collisionless damping of geodesic-acoustic modes (GAMs) and zonal flow, with fully nonlinear Boltzmann electrons for the inverse aspect ratio scan and the tokamak safety factor q scan in homogeneous plasmas. TEMPEST simulations show that the GAMs exist in the edge pedestal for steep density and temperature gradients in the form of outgoing waves. The enhanced GAM damping may explain experimental beam emission spectroscopy measurements on the edge q scaling of the GAM amplitude.     

Density Asymmetry and Marfe Localization in Tokamak Edge

The effect of tokamak toroidal geometry on producing edge density and parallel flow asymmetries and its influence on Marfe localization are studied. In the presence of a large poloidal rotation, the density asymmetry is peaked at the high field side of tokamak edge and this becomes the seed of a condensation process, which triggers a Marfe there finally.     

低混杂波高N‖分量对EAST等离子体电流驱动的影响

EAST等离子体高约束模运行条件下，在等离子体边缘区域观测到明显的等离子体电流带.在EAST托卡马克装置非圆截面平衡位形下，使用射线追踪方法研究低混杂波高平行折射率N_‖分量对电流驱动的影响.结果表明：当-8≤N_‖≤-6时，平行折射率分量能够在小半径（0.7 < r/a < 1）区域驱动kA量级的等离子体电流.对于具有台基区、等离子体边缘温度更高的电子温度剖面，驱动电流的位置r/a>0.9.低混杂波朗道阻尼的理论分析与数值模拟结果一致.另外，高N_‖低混杂波在等离子体边缘的功率沉积和电流驱动与电子温度分布和发射谱分布相关.     

HL-1M装置边缘参数测量

在HL－1M装置上利用马赫／郎缪尔探针分别在欧姆放电,低杂波注入,中性束注入,离子回旋加热和电子回旋加热等情况下测量下刮离层和等离子体边缘的极向流速度和电场,得到了它们的径向分布,研究了LHW,NBI,ICRH和ECRH对改善等离子体约束性能,边缘粒子的径向传输的影响。     

托卡马克高约束模边缘等离子体不稳定性研究

托卡马克高约束模运行可大幅提高磁约束核聚变等离子体约束品质,该模式下的等离子体不稳定性研究对于控制约束和保护装置有重要意义。本文主要介绍了高约束模及其边缘等离子体不稳定性的研究概况,并重点介绍了中国环流器二号A托卡马克装置上关于高约束模转换、边缘局域模特征和控制方法、台基区不稳定性和台基饱和机制等方面的研究进展。研究结果表明,实验上有望通过粒子和射频波注入等外部激励的方法,影响台基区等离子体湍流,进行控制台基动力学演化以及ELM,实现既保持高约束又降低高热负荷的等离子体稳态运行。     

Toroidicity and shape dependence of peeling mode growth rates in axisymmetric toroidal plasmas

The growth rate of the peeling mode instability with large toroidal mode number is calculated for general axisymmetric toroidal plasmas, including tokamaks and the spherical torus(ST) equilibia by using formalism presented by Connor et al.Analytic equilibia with non-zero edge current density and quasi-uniform current profiles are assumed. It is found that in sharp D-shape tokamak plasma, the derivative of the safety factor with respect to the poloidal flux becomes very large,making the perturbed poloidal motion very large, in turn making a significant reduction of the growth rate of the peeling mode, similar to the X-point effect in diverted plasma. The large aspect ratio effect is also studied, which reduces the growth rate further.     

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基于Hasegawa-Wakatani湍流模型,数值模拟了托卡马克边缘等离子体中漂移波湍流和相关的反常粒子输运.从等离子体动量守恒方程出发导出了不采用常规的布辛涅斯克近似的带状流方程,论证了大振幅密度扰动和湍性粒子流对激发带状流的贡献可等效地对应于低阶负粘滞阻尼效果.数值模拟表明,大振幅密度扰动的非线性大大增强了带状流饱和振幅,从而有效抑制了湍性粒子输运.研究结果阐明了托卡马克边缘等离子体大振幅密度扰动的非线性对驱动等离子体旋转、动量输运和带状流的重要性.     

托卡马克边缘湍流中带状流的负粘滞阻尼

基于Hasegawa-Wakatani湍流模型,数值模拟了托卡马克边缘等离子体中漂移波湍流和相关的反常粒子输运。从等离子体动量守恒方程出发导出了不采用常规的布辛涅斯克近似的带状流方程,论证了大振幅密度扰动和湍性粒子流对激发带状流的贡献可等效地对应于低阶负粘滞阻尼效果。数值模拟表明,大振幅密度扰动的非线性大大增强了带状流饱和振幅,从而有效抑制了湍性粒子输运。研究结果阐明了托卡马克边缘等离子体大振幅密度扰动的非线性对驱动等离子体旋转、动量输运和带状流的重要性。     

DESTABILIZATION OF THE POLOIDAL ROTATION IN A MULTIPLE ION SPECIES TOKAMAK PLASMA

The destabilization of the poloidal rotation for the species of ions with the poloidally inhomogeneous sources or sinks is studied in multiple ion species tokamak plasmas. Based on the fluid equations, the evolution equation of the poloidal ion rotation speed is derived analytically. The magnitude of the inhomogeneous sources or sinks needed to destabilize the rotation is shown to be proportional to the ion density. It is suggested that the poloidal plasma rotation can be generated by destabilizing the rotation of the minority ions.     

Analyses of edge plasma characteristics in HL-2A

The edge plasma characteristics are studied by both a movable array of Mach/Reynolds stress/Langmuir 10-probes in the boundary region and the fixed flush probe arrays on the 4 divertor neutralization plates at the same toroidal cross-section in the HL-2A tokamak. The dependence of the Reynolds stress on poloidal flow in the edge plasma is analysed. The result indicates that the sheared poloidal flow in tokamak plasma can be induced by the radial gradient of Reynolds stress. In the divertor experiments of HL-2A, the profiles of the electron temperature, density and floating potential on divertor plates are measured by the flush probe arrays. The edge electron temperature in divertor configuration is higher than that in limiter configuration. The temperature asymmetry between outer and inner target plates is observed. The result of magnetic surface reconstructed from 18 Mirnov coils signals is presented. Both the particle recycling and the impurity flux in the bulk plasma during divertor discharges are discussed. Neutral gas pressure in divertor chamber, measured by fast ionization gauge during divertor discharge, is given.     

Multiscaling dynamics of impurity transport in drift-wave turbulence

Intermittency effects and the associated multiscaling spectrum of exponents are investigated for impurities advection in tokamak edge plasmas. The two-dimensional Hasagawa-Wakatani model of resistive drift-wave turbulence is used as a paradigm to describe edge tokamak turbulence. Impurities are considered as a passive scalar advected by the plasma turbulent flow. The use of the extended self-similarity technique shows that the structure function relative scaling exponent of impurity density and vorticity follows the She-Leveque model. This confirms the intermittent character of the impurities advection in the turbulent plasma flow and suggests that impurities are advected by vorticity filaments.     

Detection of zero-mean-frequency zonal flows in the core of a high-temperature tokamak plasma

A low-frequency, spectrally broad (Deltaf approximately 10 kHz) poloidal flow structure that peaks near zero frequency is observed in time-resolved measurements of the turbulence velocity field in the core region (r/a approximately 0.6-0.9) of DIII-D tokamak plasmas. These flows exhibit a long poloidal wavelength (low m) and a short radial coherence length comparable to the ambient turbulence decorrelation length. Characteristics of these observed poloidal flows are consistent with the theoretically predicted residual or zero-mean-frequency zonal flows.     

实验物理与工业控制系统平台在HL-2A主机测控系统中的应用

描述了利用实验物理与工业控制系统(EPICS)平台对HL-2A主机运行参数进行的集中测控系统开发。系统采用s7nodave设备驱动模块,实现了SoftIOC与各PLC的通讯,将各子系统的PLC集成到了EPICS控制系统中。通过对关系型数据库和应用层软件CSS中数据归档及报警等组件的扩展与配置,实现OPI层与各个子系统的实时通信。测控系统成功地将HL-2A主机参数集中在EPICS平台下运行,为下一代装置的主机集中测控系统设计打下了基础。     

HL-2A等离子体边缘极向剩余胁强的研究

首次报导了托卡马克等离子体边缘与湍流相关的极向剩余胁强剖面的测量结果。采用外中平面往复式静电探针阵列对HL-2A托卡马克边缘的极向湍流动量输运进行研究。在没有外部动量注入的欧姆放电下,剩余胁强为有限值、且其空间剖面在等离子体边缘具有明显的径向梯度,表明托卡马克等离子体边缘存在极向动量源。由动量源产生的动量主要以扩散形式向与剩余胁强相反的方向传播,最终的结果是等离子体边缘存在有限的雷诺胁强。在最后闭合磁面以内0.5~2cm区域,剩余胁强的梯度提供自发旋转的力矩,由该力矩引起的动量产生与由速度梯度引起的动量扩散共同导致了雷诺胁强出现负梯度,造成动量沉积,从而驱动极向平衡流。     

Study of density and potential fluctuations in the TEXT tokamakwith a heavy ion beam probe

A heavy ion beam probe was used to study the characteristics of density and potential fluctuations in the TEXT tokamak. Fluctuations of density and space potential are nearly Boltzmann like, n˜/n~φ˜/kT_e, near the edge of the plasma (0.80.9). The turbulent E&oarr;×B&oarr; radial particle flux is sufficient to account for all of the particle loss from the tokamak. No poloidal asymmetries, within a poloidal angle range of about 70°, are observed in the fluctuation levels. The fluctuation spectral shape, the density potential phase angle, and the fluctuation propagation speed show a strong radial dependence     

EDGE REYNOLDS STRESS STRUCTURE OF LOWER HYBRID WAVE INJECTION IN THE HL—1M PLASMA

The radial profiles of electrostatic Reynolds stress,plasma poloidal rotations,radial and poloidal electric fields have been measured in the plasma boundary region on the HL-1M tokamak using a multi-array of Mach/Langmuir probes.During experiments of lower hybrid wave current drive,the variations in LHW drive power xill cause changes in the edge electric field,poloidal rotation veloity and Reynolds stress.The results indicate that sheared poloidal flow can be generated in the edge plasma due to radially varied Reynolds stress.     

HL-2A 装置的边缘参数测量

HL-2A 装置中平面边缘的等离子体特性通过磁力传动的马赫/ 雷诺协强/ 朗缪尔10 探针组进行了研究。10 探针组安装在可径向向里和向外移动, 并可绕轴旋转360^o 的传动杆上, 用于测量主等离子体边缘的温度、密度、悬浮电位、空间电位、径向和极向电场、湍流的雷诺协强、径向和极向等离子体流速及其径向分布。HL- 2A 装置的实验结果表明, 边缘等离子体扰动诱发的雷诺协强产生了边缘极向流; 雷诺协强的径向梯度驱动带状流抑制了湍流输运。