平行速度剪切驱动湍流引起的粒子输运

通过离子温度梯度及平行速度剪切的准线性湍流理论,得到了由杂质离子及抵频E×B湍流所驱动的径向离子流及相应的输运系数．理论分析表明,主要离子和杂质离子的径向离子流具有相反的方向,并随着平衡流速剪切以及杂质离子的密度梯度的变化而改变．增强平行速度剪切对主要离子的约束可产生有利影响关键词：     

HL-1M装置弹丸和分子束加料的粒子输运研究

研究了IL-1M装置上弹丸和分子束加料的粒子输运。在研究粒子输运时拟合了粒子源分布,利用调制送气模型研究了分子束送气时的粒子输运。由弹丸注入后较长时间内密度的自然衰减研究了粒子输运,给出了一种简单的研究弹丸注入后粒子输运的方法。计算表明,分子束和弹丸注入改善了等离子体的粒子输运特性。将计算结果与实验测量进行了比较。     

HL-2A装置上ECRH实验的初步结果和电子热输运分析

电子回旋共振加热（ECRH）是托卡马克等离子体一种最常用的辅助加热手段，也是进行等离子体电子热输运和约束性能研究的一种有效手段。本文介绍了HL-2A装置上ECRH实验的初步结果，分析了在ECRH实验期间的电子热输运特征和约束情况。     

HL-2A装置边缘静电湍流谱特征研究

利用具有极向和径向结构的三探针在HL-2A装置等离子体边缘最后闭合磁分界面以内5cm左右，对静电湍流的谱特征进行了实验研究。空间二级关联分析指出，静电湍流主要是由具有低频和长波长的波胞组成，波胞以内都是相关结构；波在极向的传播主要是沿电子逆磁漂移方向，偶尔也会由于多谱勒频移造成在离子逆磁漂移方向的频率分量。静电波在径向向外传播，其速度的大小与极向相速度相当，这个特征意味着径向模对横越磁场的输运有重要的影响。     

在HT-7托卡马克上密度扫描实验中的边界湍流和输运

在HT-7托卡马克上密度扫描实验中使用一个快速扫描气动朗缪尔探针来研究边界湍流和输运。随着中心弦平均等离子体密度的增加,在等离子体边界观察到径向电场剪切增强,径向电场的增强能够解释边界输运的减小和全局粒子约束的改善。粒子约束时间的增加和垂直扩散系数的减小证明粒子输运降低了。在等离子体边界区域发现电离和辐射驱动湍流的特征,表明电离和辐射在湍流驱动过程中具有重要性。     

托卡马克实验与工程——HL-2A装置上芯部弹丸加料中的电子热输运研究

从80年代中期开始，在许多聚变装置上观察到了用弹丸注入改善的等离子体能量约束。在JET和一些大型托卡马克上实现了弹丸增强约束模（PEP）。PEP模的机制也已在理论上做了分析。分析表明，有多种机制在减小反常输运中起作用，而这些机制的作用依赖于实验的条件。本文将报道在HL-2A装置上无辅助加热条件下的弹丸加料实验结果。该工作的着重点是研究在中心加料欧姆放电中的电子热输运。     

旋转槽道湍流标量场输运特性数值模拟研究

展向旋转槽道湍流中的标量场输运过程是与众多工程流动直接相关的模型问题。基于直接数值模拟工作对该问题开展系统性的研究。由壁面摩擦速度定义的流动Reynolds数固定在180, 重点考察Schmidt数和旋转数的影响。结果表明, 较弱旋转强度即可对主导流动结构形态产生明显的影响: 此时槽道不稳定侧产生流向大尺度结构, 由此导致标量场出现条带状结构。强旋转时不稳定侧出现被湍流充分混合的区域, 而在稳定侧流动层流化并出现近似传导区。平均标量剖面在湍流区和层流区呈现斜率不同的线性分布。Schmidt数小于1时, 湍流区标量场脉动和湍流输运随旋转数出现非单调变化, 而Schmidt数大于等于1时两者都随旋转数单调下降。由此导致总标量传输率在Schmidt数小于1时随旋转数先上升后下降, 而当Schmidt数大于1时单调下降且在弱旋转区域下降趋势最快。     

Active and passive scalar intermittent statistics in turbulent atmospheric convection

We study the small-scale statistics of active and passive scalar fields, obtained from 3D large-eddy simulations of the atmospheric boundary layer turbulence. The velocity field is anisotropic and inhomogeneous, due to the action of both buoyancy and shear. We focus on scalar field rare fluctuations dominated by the so-called fronts. Temperature, coupled to the velocity field by the Boussinesq equations, exhibits anomalous scaling and saturation of the scaling exponents to a constant value, due to the presence of thermal fronts. Although qualitatively similar, the small-scale statistics of a passive tracer advected by the convective flow shows quantitative differences: the large fluctuations of the tracer concentration field distribute differently and appear to be less intermittent than the temperature ones. To better understand these results, the role of boundaries in this problem is discussed.     

Intermittency in the atmospheric surface layer: Unresolved or slowly varying?

We present streamwise velocity structure functions 〈δv_L(τ)〉=〈|v(t+τ)−v(t)|^p〉 (with p=1:5) obtained in the near neutral atmospheric surface layer at the Utah SLTEST site at the highest terrestrial Reynolds number Re_τ=O(10⁶). We show that the occurrence of very large scale coherent oscillations in the streamwise velocity throughout the wall region, interpreted as genuine structural features of the canonical turbulent boundary layer, affects the scaling exponents of the p>3 order structure functions. This results in a slight alteration of the intermittent behavior of the velocity field. It was found that for positive (fast) large scale oscillation of the low-pass filtered velocity signal, deviations from the Kolmogorov K41 prediction (absence of multiscaling) are more marked, as compared to negative (slow) excursion. The results are discussed in terms of convergence of statistics from atmospheric boundary layer measurements.     

Intermittent dissipation and lack of universality in one-dimensional Alfvénic turbulence

The randomly driven Cohen–Kulsrud–Burgers equation is used to study the influence of viscous intermediate shocks (IS) on Alfvénic turbulence. Some of these structures are unstable and undergo gradient collapse leading, as the viscosity is reduced, to increasingly intermittent dissipation bursts. The slow decay at intermediate scales of stable IS prevents the existence of a usual inertial range. Furthermore, the dissipation is unable to adiabatically compensate for the energy injection, making the total energy sensitive to the viscosity parameter. Turbulence thus looses its universal character. Preliminary simulations extend these conclusions to magnetohydrodynamic equations with anisotropic viscosity, typical of strongly magnetized plasmas.     

Statistical properties of turbidity, oxygen and pH fluctuations in the Seine river estuary (France)

We consider here, the fluctuations of turbidity, oxygen and pH time series recorded from the MAREL system (Ifremer, France), which is based on the deployment of data buoys equipped with water analysis capabilities in an automated mode. We perform a spectral analysis (from 10 min to years) of these time series, and we estimate their probability density functions. Oxygen, turbidity and pH are important quantities for ecosystem studies and physics-biology couplings, and their fluctuations reveal the possible influence of environmental factors such as tides and turbulence. Turbidity variability is highly complex and does not appear to be directly coupled to turbulence, since no clear range is visible. On the other hand, oxygen percentage of saturation and pH data show remarkably nice scaling ranges, indicating an important coupling with turbulence, but also biological or chemical activity, since the statistics differ markedly from passive scalars. Several possible sources of this variability are discussed.     

托卡马克粒子输运快速分析方法

测量了HL 1M装置上正弦周期调制馈气方法诱发的密度扰动 ,采用了简单的数值方法求解粒子输运方程来计算密度扰动 ,并与密度扰动的测量结果进行了比较。得出欧姆加热时等离子体芯部的粒子扩散系数为0 2± 0 .1m2 ·s- 1 ,边缘粒子扩散系数为 1 0± 0 .2m2 ·s- 1 。     

Random walk particle tracking simulations of non-Fickian transport in heterogeneous media

Derivations of continuum nonlocal models of non-Fickian (anomalous) transport require assumptions that might limit their applicability. We present a particle-based algorithm, which obviates the need for many of these assumptions by allowing stochastic processes that represent spatial and temporal random increments to be correlated in space and time, be stationary or non-stationary, and to have arbitrary distributions. The approach treats a particle trajectory as a subordinated stochastic process that is described by a set of Langevin equations, which represent a continuous time random walk (CTRW). Convolution-based particle tracking (CBPT) is used to increase the computational efficiency and accuracy of these particle-based simulations. The combined CTRW–CBPT approach enables one to convert any particle tracking legacy code into a simulator capable of handling non-Fickian transport.