反常输运与非线性自持磁岛的自洽分析

从沿磁力线的等离子体电流与粒子径向输运相关的新经典ＭＨＤ型的广义欧姆定律出发，提出了分析反常输运与非线性自持磁岛的自洽理论模型，基于该模型导出了反常扩散系数及反常电子热导。结果表明，非线性磁岛链可由磁岛调制的反常输动维持，反过来又通过磁岛短路效应维持反常输运。     

粘滞效应对非线性电阻撕裂模的影响

本文研究粘滞效应对非线性电阻撕裂模的影响。利用准环坐标将具有标量电阻率和粘滞系数的MHD方程简化为一组无量纲的非线性方程。并对这组方程采用二步交替隐式差分格式进行数值计算。结果给出了2/1模的演变过程对无量纲粘滞系数的依赖关系和电流密度的分布。发现粘滞效应对饱和磁岛宽度的修正大约为5％(此时R=10~(-5)),同时发现由于粘滞效应的引入导致电流分布在奇异面附近的涨落明显减小。     

电流驱动对磁岛的稳定化

大破裂限定了托卡马克的运行。实验指出，撕裂模或者说磁岛的发展是这种大破裂的主要原因。考虑到无感电流驱动效应，我们重新推导了电阻撕裂模的三维非线性方程组?数值计算表明，跟随磁岛旋转的ＲＦ波电流驱动有效地抑制磁岛的发展。     

输运与撕裂模相互作用下等离子体的时空结构

本文应用等离子体一维输运模型与撕裂模理论,对于不同的输运模型和托卡马克放电参数下撕裂模的演变进行了数值研究。结果表明,能量过程是影响等离子体宏观稳定性行为的一个不可低估的重要因素,它们与磁流体稳定性的相互影响,会使其磁流体形态构成多种时间或空间结构,等离子体温度、密度等宏观参量也将表现出不同的时空特征。 关键词：     

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利用离子香蕉轨道中心坐标和香蕉轨道平均算符,讨论了磁岛转动引起的沿磁力线电流分布及其对新经典撕裂模演进的影响.结果显示,考虑此电流的影响,当磁岛旋转频率ω=ω*i时,被离子香蕉轨道宽度效应削弱的自举电流驱动项基本恢复;当ω=ω*e时,离子香蕉轨道宽度效应对自举电流驱动项的削弱则加剧.这意味着磁岛转动方向不同时,此沿力线电流能显著增大或减弱离子香蕉轨道宽度效应对自举电流驱动项的削弱作用.     

局域热源对磁岛热输运的影响

研究托卡马克等离子体磁岛内的热输运行为.应用局域高斯热源对磁岛加热来模拟电子回旋共振加热.对同时存在背景热源与局域高斯热源的情况,观察局域高斯热源对径向电子温度分布及热输运产生的变化,分析局域高斯热源对温度扰动及磁岛约束能量的影响.     

小磁岛转动引起的沿磁力线电流对撕裂模的影响

利用离子香蕉轨道中心坐标和香蕉轨道平均算符,讨论了磁岛转动引起的沿磁力线电流分布及其对新经典撕裂模演进的影响。结果显示,考虑此电流的影响,当磁岛旋转频率ω=ω_*i 时,被离子香蕉轨道宽度效应削弱的自举电流驱动项基本恢复;当ω=ω_*e时,离子香蕉轨道宽度效应对自举电流驱动项的削弱则加剧。这意味着磁岛转动方向不同时,此沿力线电流能显著增大或减弱离子香蕉轨道宽度效应对自举电流驱动项的削弱作用。     

Stabilization of tearing mode by current drive

The major disruption limits the operation of present tokamaks. Experimental evidences point out that the growth of tearing modes or the magnetic islands is primarily responsible for the occurrence. Taking the non-inductive current drive effects into account, a set of 3D nonlinear equation is derived. It is shown from simulation that the growth of the magnetic island is suppressed effectively by RF current drive. It is consistent with recent experiments on the HL-1 tokamak in which the plasma is stabilized by an RF current drive.     

磁转变对La0.7Ca0.3MnO3在Tc附近的输运性质的影响

测量了Ｌａ０．７Ｃａ０．３ＭｎＯ３的热导和电阻，温度范围为７７－３００Ｋ，在２６０Ｋ，观察到电阻曲线上的金属－半导体转变上的，热导曲线上有一个不大的斜率的变化。同时不发现在热导单调光滑下降曲线上２２０－２６０Ｋ热导有增加，电阻在２４０Ｋ有斜率的变化，我们讨论了这两种输运性质，认为这与材料在ＴＣ附近复杂的磁行为相联系。     

Observation of reduced heat transport inside the magnetic island O point in the large helical device

Evidence for a reduction of heat transport inside the magnetic island O point is observed from the propagation of a cold pulse produced by a tracer encapsulated solid pellet in the Large Helical Device. A small peak and slow propagation of the cold pulse are observed inside the island. A significant result is that electron heat diffusivity inside the island is estimated to be 0.2 m(2)/s which is smaller than that outside the island by an order of magnitude.     

恒定非均匀磁场调控下的强制对流传热数值研究

分别对雷诺数、磁场强度和磁纳米流体浓度进行了讨论,并将数字高程模型(DEM)应用到梯度磁场模型的建立,分析了磁场梯度大小和方向对传热效果的影响。结果表明：雷诺数、磁场强度和梯度与传热效果呈正相关,在磁场介入的情况下,磁纳米流体浓度对传热效果的影响存在一个最佳值;磁场梯度方向垂直于流动方向时对传热的强化效果最显著。以平均努塞尔数和压降为目标参数,利用正交试验设计的方法研究了各变量对传热效果影响的权重大小,得到各变量取值范围内的最佳组合。     

Electron heat transport measured in a stochastic magnetic field

New profile measurements have allowed the electron thermal diffusivity profile to be estimated from power balance in the Madison Symmetric Torus where magnetic islands overlap and field lines are stochastic. The measurements show that (1) the electron energy transport is conductive not convective, (2) the measured thermal diffusivities are in good agreement with numerical simulations of stochastic transport, and (3) transport is greatly reduced near the reversal surface where magnetic diffusion is small.     

Time-dependent plasma transport simulation for the study of edge impurity radiation dynamics with magnetic island in large helical device

The dynamics of impurity radiation distribution during detachment transition with edge magnetic island induced by the application of resonant magnetic perturbation (RMP) is studied numerically by solving time-dependent plasma fluid equations together with impurity and neutral transports in a 2D grid system. Computations provide the appearance of a macroscopic structure in the heat transfer along the island separatrix and outside the island. The resultant parallel temperature gradient generates the plasma flow and the density gradient according to the parallel momentum balance. The resulting plasma flow effectively transports impurity towards the X-point region. As a result, the impurity radiation is more intense near the X-point than in the vicinity of the O-point. This leads to the predominant cooling of the region around the X-point. These results are in agreement with experimental observation with RMP application in the large helical device (LHD). The time scale of the thermal condensation instability is found to be of the order of 10 ms.     

Magnetically-driven heat transport device using a binary temperature-sensitive magnetic fluid

The magnetic body force in boiling two-phase temperature-sensitive magnetic fluid (TSMF) flow is known to effectively increase the driving force of magnetic fluid in a non-uniform magnetic field. Based on this mechanism, in the present study, a binary TSMF, which is a mixture of the TSMF and a low-boiling-saturation-temperature organic solution, is proposed to be used in a heat transport device to enhance its circulation. In order to see its performance in the heat transport device, the pressure difference at different heated temperatures, magnetic fields and inclination angles of the heating section are investigated experimentally and theoretically. Results showed that the driving force increases remarkably due to more gas phase appearing in the test fluid and the magnetization of it decreasing. At low magnetic field the driving force is enhanced greatly when the inclination angle is close to 60°, while at high magnetic field the driving force is remarkably enhanced due to the effect of the magnetic force in the inclination angle range from 0° to 30° and 60° to 90°.     

Local and nonlocal parallel heat transport in general magnetic fields

A novel approach for the study of parallel transport in magnetized plasmas is presented. The method avoids numerical pollution issues of grid-based formulations and applies to integrable and chaotic magnetic fields with local or nonlocal parallel closures. In weakly chaotic fields, the method gives the fractal structure of the devil's staircase radial temperature profile. In fully chaotic fields, the temperature exhibits self-similar spatiotemporal evolution with a stretched-exponential scaling function for local closures and an algebraically decaying one for nonlocal closures. It is shown that, for both closures, the effective radial heat transport is incompatible with the quasilinear diffusion model.     

Analytical study of non-linear transport across a semiconductor-metal junction

In this paper we study analytically a one-dimensional model for a semiconductor-metal junction. We study the formation of Tamm states and how they evolve when the semi-infinite semiconductor and metal are coupled together. The non-linear current, as a function of the bias voltage, is studied using the non-equilibrium Green’s function method and the density matrix of the interface is given. The electronic occupation of the sites defining the interface has strong non-linearities as a function of the bias voltage due to strong resonances present in the Green’s functions of the junction sites. The surface Green’s function is computed analytically by solving a quadratic matrix equation, which does not require adding a small imaginary constant to the energy. The wave function for the surface states is given.     

单层有机器件的电子传输特性的数值模拟

在漂移扩散模型的基础上建立了单层有机器件的模型,包括了电荷注入、传输、空间电荷效应和陷阱的影响.电荷注入考虑了热电子发射电流和隧道电流.模拟得到的结果和文献中报道的实验测试数据一致.模拟研究了各个因素对器件J-V曲线的影响,电流和器件长度成反比,电流随着空穴注入势垒的减小而增加.电子注入势垒从1.7 eV减少到0.5 eV时,电流随着电子注入势垒的减小而减小,这主要是因为有机材料中电子迁移率太小,电子注入电流的增加可以忽略,而电子注入势垒的减小使内建势增加,在同样的电压下,场强 关键词： 有机器件 传输特性 数值模拟     

Electronic contribution to the heat transfer across metal single crystal-He II boundaries

Measurements of the Kapitza conductance by the ac technique are reported for oriented gallium and copper single crystal discs. The data show convincing evidence that conduction electrons participate in the transmission of heat across the metal-He II interfaces for both metals. Measurements of the Kapitza conductance as a function of transverse and longitudinal fields and the influence of temperature, sample thickness and impurities allow a qualitative understanding of the total heat transfer across the sample.     

Electron transport across a microconstriction in an arbitrarily oriented homogeneous magnetic field

An analysis is made of ballistic electron transport in three-dimensional microconstrictions of elliptic cross section located in an arbitrarily oriented magnetic field. The model of a parabolic confinement potential is used to obtain and analyze the dependence of hybrid frequencies on the magnitude and direction of the magnetic field. An expansion of the conductance as a Fourier series is obtained and used to study Aharonov-Bohm and Shubnikov-de Haas oscillations as a function of the field and the stepped quantization structure of the conductance. A possible explanation is given for the experimentally observed effect of conductance quantization at fairly high temperatures.