Drift-wave fluctuation in an inviscid tokamak plasma

In order to describe the characterization of resistive drift-wave fluctuation in a tokamak plasma,a coupled inviscid two-dimensional Hasegawa–Wakatani model is investigated.Two groups of new analytic solutions with and without phase shift between the fluctuant density and the fluctuant potential are obtained by using the special function transformation method.It is demonstrated that the fluctuant potential shares similar spatio–temporal variations with the density.It is found from the solutions without phase shift that the effect of the diffusion and adiabaticity on the fluctuant density is quite complex,and that the fluctuation may be controlled through the adiabaticity and diffusion.By using the typical parameters in the quasi-adiabatic regime in the solutions with phase shift,it is shown that the density gradient becomes larger as the contours become dense toward the plasma edge and the contours have irregular structures,which reveal the nonuniform distribution in the tokamak edge.     

Observation of intermittency in edge plasma of SUNIST tokamak

The temporal intermittency of the fluctuation-driven particle transport fluxes is analysed by using data obtained from Langmuir probe array in the edge of the Sino-United Spherical Tokamak (SUNIST). The conditional statistics analysis indicates that the intermittent structures have a characteristic time width of about 30μs, which is the typical fluctuation time scaling. It is also found that the transport fluxes have a multifractal character over the fluctuation time scales, and exhibit a long-time-range correlation character with self-similar parameter H>0.5 in the plasma confinement time scales. Furthermore, the analyses show that the level of the intermittency and the long-range correlation of the fluxes vary with increasing plasma density. These observations are consistent with the prediction of the avalanche-like model.     

HL-2A等离子体垂直振荡缓解边缘局域模实验观测

在HL-2A 装置实验中，通过对水平场加入方波扰动，实现了等离子体垂直运动。当等离子体向上垂直运动时，观察到了边缘局域模(ELM)缓解现象。研究发现，等离子体向上运动过程中边缘不断形成新的闭合磁面，导致等离子体体积膨胀，进而使台基宽度增加。此外，ELM 缓解期间杂质和工作气体再循环有所增加。等离子体向上运动过程中体积膨胀、工作气体再循环及杂质增加可能是导致ELM 缓解的主要物理因素。该实验可为未来聚变实验装置ELM 的控制提供一些参考。     

超声分子束在HL-1M托卡马克等离子体中的消融和穿透

讨论并研究了超声分子束在托卡马克等离子体中的消融和穿透问题，其中包括了分子束的绝热膨胀，团簇的形成和解离，束的静电屏蔽效应和冷通道效应.研究结果表明，在考虑了这些效应以后数值得到的结果与实验结果相近.这些研究对于更好地理解超声分子束与等离子体的相互作用和优化设计加料系统有一定作用. 关键词： 超声分子束 加料 托卡马克等离子体 消融和穿透     

First results of movable limiter experiments and its effects on the tokamak plasma confinement

Limiters play a number of roles in the tokamak operation. It serves primarily to protect the wall from the plasma when there are disruptions, runaway electrons, or other instabilities and also the limiters localize the plasma–surface interaction. In this research, we presented the first results of movable limiter experiments and its effects on the tokamak plasma confinement. For this purpose, we designed, constructed, and installed a movable localized poloidal limiter, and then measured the effects of limiter position on the time intervals of plasma parameters such as plasma density, temperature, and energy confinement time. The results of effects of the movable limiter experiments on plasma confinement.     

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通过出气率测量装置评价了SUNIST装置的内部磁探针出气特性,实验结果表明其出气量和出气气体成分不足以影响SUNIST真空特性。其后的放电实验验证了这一结论。     

SUNIST装置中磁探针出气率测量

通过出气率测量装置评价了SUNIST装置的内部磁探针出气特性,实验结果表明其出气量和出气气体成分不足以影响SUNIST真空特性。其后的放电实验验证了这一结论。     

Poloidal inhomogenity of the particle fluctuation induced fluxes near the LCFS at lower hybrid heating and improved confinement transition at the FT-2 tokamak

This paper deals with the new spectral and microturbulence experimental data and their analysis, which show that the radial electric field E _r generated at the lower hybrid heating (LHH) in the FT-2 is high enough to form the transport barriers. The ETB is formed when LHH is switched off. The radial fluctuation-induced E × B drift flux densities near LCFS in SOL are measured at two different poloidal angles. For this purpose two Langmuir probes located at low and high field sides of the torus are used. Registration of the poloidal and radial components of the electric field and density fluctuations at the same time during one discharge permits to measure the poloidal asymmetry of the transport reduction mechanism of the radial and poloidal particle fluxes in the SOL. The absolute fluctuation levels show dependence on the sign of E _r shear. The modification of the microscale turbulence by the poloidal E _r × B rotation shear _{E × B} at the L-H transition near LCFS is also studied by X-mode fluctuation reflectometry. The new data were obtained by spatial spectroscopic technique.Presented at the Workshop Electric Fields Structures and Relaxation in Edge Plasmas, Nice, France, October 26–27, 2004.     

Modelling of nanometer scale dust grains in tokamak

Dust poses a serious threat to tokamak operation and safety. It is important to study the behaviour of dust grains under tokamak's discharge conditions, which depends heavily on their size and charge. Existing simulations mainly address issues on dust grains with radii larger than 1 μm, in which case, the drift effect due to electromagnetic fields can be safely ignored. For nanometer scale dust grains, however, the drift effect becomes significant and a new model based on guiding-centre system needs to be established. In this work, the NDS has been done under BOUT++ framework. The simulation contains two parts. Part one, NDS evaluates the charging and ablation processes of the dust grains. In the second part, the guiding-centre orbits of dust particles are tracked in tokamak plasmas, whose parameters are obtained from BOUT++, a highly desirable C++ code package for performing parallel plasma fluid simulations with an arbitrary number of equations in 3D curvilinear coordinates. The orbit of nanodust dynamics is described by guiding centre equations for simplicity, and these equations are numerically solved by conventional fourth-order Runge Kutta method. Simulations provide results such as trajectories and evolutions of dust particles with different sizes and velocities for different tokamak geometries. Results show tungsten dust grains with a radius of a few nanometers launched from outer midplane will oscillate before totally ablated in C-Mod. The oscillation in this case is driven by the ion drag force. Larger Nanodust with a radius of 100 nm, on the contrary, cannot be completely constrained by the electromagnetic field. The high plasma temperature and density in the seperatrix region causes severe dust ablation, resulting in total ablation within several ms.     

HT-7托卡马克等离子体slide-away放电研究

在HT-7托卡马克上,只在等离子体放电击穿阶段充气,击穿后关闭充气阀门,让装置内真空室器壁的出气维持放电的进行,通过密度衰减实现了slide-away放电.实验分析了不同等离子体电流平台下的slide-away放电模式的密度阈值,以及相同充气量的条件下放电等离子体电流对实现slide-away放电的影响.研究了slide-away放电模式下密度提升对等离子体放电状态的影响.结果发现,slide-away放电模式下的密度提升使得H_a线辐射强度增强,等离子体中超热电子的约束性能变差,等离子体芯部的超热电子减少,高能逃逸电子厚靶轫致辐射增加. 关键词： slide-away放电 托卡马克 等离子体 逃逸电子     

Observation of chaotic ELMs in HL-2A tokamak

The high confinement mode(H-mode) operation is recently obtained in HL-2A divertor configuration,the corresponding edge localized mode(ELM) is recognized as being of type III.Time intervals in ELM time series are analysed to obtain the information about the ELM process.Signatures of unstable periodic orbits(UPOs) are detected,which are indicators of chaos and may be used to control the big ELM events.     

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利用电流丝模型对SUNIST球形托卡马克等离子体边界重构进行了模拟计算。结果表明,用电流丝模型能够比较好地对等离子体自由边界进行快速识别,与EFIT平衡计算的边界径向平均误差小于6mm。     

Linear analysis of plasma pressure-driven mode in reversed shear cylindrical tokamak plasmas

The linear behavior of the dominant unstable mode ($m=2$, $n=1$) and its high order harmonics ($m=2n$, $nge 2$) are numerically investigated in a reversed magnetic shear cylindrical plasma with two $q=2$ rational surfaces on the basis of the non-reduced magnetohydrodynamics (MHD) equations. The results show that with low beta (beta is defined as the ratio of plasma pressure to magnetic field pressure), the dominant mode is a classical double tearing mode (DTM). However, when the beta is sufficiently large, the mode is driven mainly by plasma pressure. In such a case, both the linear growth rate and mode structures are strongly affected by pressure, while almost independent of the resistivity. This means that the dominant mode undergoes a transition from DTM to pressure-driven mode with the increase of pressure, which is consistent with the experimental result in ASDEX Upgrade. The simulations also show that the distance between two rational surfaces has an important influence on the pressure needed in mode transition. The larger the distance between two rational surfaces, the larger the pressure for driving the mode transition is. Motivated by the phenomena that the high-$m$ modes may dominate over low-$m$ modes at small inter-resonance distance, the high-$m$ modes with different pressures and $q$ profiles are studied too.     

东方超环(EAST)装置中等离子体边界锂杂质的碰撞-辐射模型

在东方超环(EAST)装置中,由于大量锂化壁处理的使用,切向可见光摄像机拍摄到等离子体边界通常存在一条由锂(Li)杂质形成的绿色发光带.本文基于EAST边界等离子体参数条件,基于碰撞-辐射模型给出由已知边界等离子体状态推算Li绿光光强的空间分布的具体方法,并针对简化后的一维径向分布问题,收集、处理OPEN-ADAS数据库的数据,采用软件Mathematica 10.4.1编写相应的数值计算程序,分别输入EAST工作于低约束(L)与高约束(H)模时获得的两组边界电子温度、密度分布数据,给出并分析比较了利用该模型的计算结果.此项工作对于未来建立通过测量及反演边界锂杂质特征谱线强度的空间分布来重构边界等离子体状态的全新技术和研究存在三维磁场扰动条件下的边界等离子体行为均具有重要的理论参考价值.     

Non-steady interaction of plasma with aircraft in its near wake region

Non-steady interactions between plasmas and aircraft in its near wake region are investigated in detail. Under the non-static limit, a set of equations that describe these interactions are obtained. The results of the numerical simulation show that the cavitons of transverse plasmas are excited and density cavitons appear when the envelope of plasma becomes sufficiently intensive. This is very important for detecting the moving body that has a `stealth' characteristic.     

HL-1M装置上MHD不稳定性磁扰动模的传播

对在HL-1M装置放电实验中发现的宏观MHD不稳定性磁扰动模的传播现象进行了研究。通过对实验中发现的各种极向模数m值的MHD磁扰动模特征的观察,以及在不同放电条件,特别是在偏压H模放电下传播方向不同的分析,深入研究了MHD模传播与等离子体旋转的定性关系。     

Measurement of density fluctuations on the JIPP T-IIU tokamak via an HCN laser scattering

Observation of density fluctuations in tokamak plasmas is important to study the plasma confinement and to perform high power heating of the plasma. We observed the density fluctuations by means of an HCN laser scattering method during rf heating in the ion-cyclotron range of frequency on a tokamak plasma.The density fluctuations at the drift wave frequency are not enhanced so much by the heating, but the frequency spectrum is shifted to higher frequency. The increase of the density fluctuation level during the heating has been observed only in low-frequency region owing to MHD activity.     

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.     

Measurements of Reynolds stress and turbulence in the boundary plasma of the HT-7 tokamak

Measurements of electric field fluctuations, Reynolds stress and poloidal flow have been performed in the boundary region of the HT-7 tokamak using a Langmuir probe array.Sheared radial electric field and poloidal flow have been found in the vicinity of the limiter and the turbulence has been clearly modified in this region. Furthermore,the electrostatic Reynolds stress component shows a radial gradient close to the velocity shear layer location.All results here indicate that the radial gradient of Reynolds stress may play an important role in the driving of poloidal flows in the plasma boundary region.