托卡马克旋转等离子体中阿尔芬波电流驱动

随着托卡马克实验的发展，人们正在寻求和研究多种更适合先进托卡马克高约束性能等离子体的电流驱动方法，然后加以比较和选择。尽管达到兆安量级的低杂波电流驱动已经在许多托卡马克上取得成功，但低杂波不能渗透到反应堆尺寸的托卡马克等离子体密度增加而降低，使得在反应堆尺寸的托卡马克等离子体中使用低杂波驱动电流受到限制。有人预计在反应堆托卡马克中采用电子回旋波驱动电流比低杂波驱动更有效，不幸的是，直到目前还没有足够的实验证明这个预言的正确性。阿尔芬波电流方式，它具有在等离子体中传播不存在密度极限问题等优点，也许更适合未来的反应堆托卡马克。     

HL－1M感应与低杂波组合电流驱动研究

本文结合ＨＬ－１Ｍ的基本参数，利用准线性的低杂波电流驱动理论和等离子体的电回路方程．研究了在控制等离子体总电流不变情形下欧姆感应和低杂波注入组合驱动电流的问题。结果表明，这一组合驱动方案对ＨＬ－１Ｍ装置的运行是可行的，其驱动电流分布可以通过改变低杂波注入功率、波谱形状、等离子体电子温度、密度以及总等离子体电流等加以控制。组合驱动的电流分布将优于欧姆驱动的电流分布，并可能抑制诸如锯齿振荡等一些ＭＨＤ不稳定性。     

HT-6B托卡马克参数下低杂波驱动电流的密度窗口

在简晰的物理模型下,采用数值方法,研究了HT-6B托卡马克参数下的低杂波射线轨迹,波谱移动,功率吸收和驱动电流分布。结果表明,存在着驱动电流的密度窗口,即仅在一定的等离子体密度范围内才能驱动电流(通常在理论和实验上仅注意到驱动电流的密度上限)。文中对这种密度窗口的存在给予了物理解释,并进而讨论了影响驱动电流效率的主要因素。 关键词：     

关于HL－1托卡马克的低杂波电流驱动效率

在一些ＨＬ－１托卡马克的低杂波电流驱动（ＬＨＣＤ）实验中，驱动效率对低杂波注入功率和等离子体电子密度等参数的依赖关系很分散。分析表明，其可能原因是驱动电流的计算不够精确，携带电流的快电子的相当部分逃离等离子体后损失到孔栏或真空室壁上以及放电的重复性差等。本文对这些问题进行了仔细的讨论     

HL—1M感应与低杂波组合电流驱动研究

本文结合ＨＬ－１Ｍ的基本参数，利用准线性的低杂波电流驱动理论和等离子体的电回路方程，研究了在控制等离子体总电流不变情形下欧姆感应和低杂洲入组合驱动电流的问题。结果表明，这一组合驱动方案对ＨＬ－１Ｍ装置的运行是可行的，其驱动电流分布可以通过发迹低杂流注入功率、波谱形状、等离子体电子温度、密度以及总等离子体电流等加以控制。     

关于HL—1托卡马克的低杂波电流驱动效率

在一些ＨＬ－１托卡马克的低杂波电流驱动实验中，驱动效率对低杂波注入功率和等离子体电子密度等参数的依赖关系很分散。分析表明，其可能原因是驱动电流的计算不够精确，携带电流的快是电子相当的部分逃离等体后损失到也栏或真空室壁上，以及放电的重复性差等。本文对这些问题进行了仔细的讨论。     

低杂波控制电流分布与改善约束研究

在HT-7超导托卡马克装置上利用低杂波电流驱动有效地控制了等离子体电流分布,并使等离子体约束性能改善。数值模拟与硬X射线测量结果均表明,低杂波的发射功率谱、纵场和等离子体密度对改变等离子体电流分布有明显的影响。在优化低杂波电流驱动实验参数的条件下,等离子体密度、温度分布发生了理想的变化。在电子和离子温度分布上出现了内部输运垒,同时等离子体的能量约束时间和粒子约束时间均有提高。     

HT-7托卡马克中低杂波和离子波恩斯坦波协同作用的数值研究

用隐含5点模式对二维Fokker-Planck方程进行离散化,调用NAG程序库中子函数D03UAF求解该方程,并将求解二维Fokker-Planck方程的code与波的射线轨迹code相结合,根据HT-7托卡马克装置参数,分别对有或没有IBW情况下的等离子体电流的全波驱动和在低杂波和离子伯恩斯坦波协同作用下低杂波的功率沉积分布、驱动电流分布等进行数值模拟研究.结果显示:有IBW情况下的全波驱动电流分布比没有IBW时全波驱动的电流分布区域要广一些,而且驱动的总电流也大一点;在双波协同作用下,全波驱动的等离子体电流空间分布随IBW的频率和n_//谱的变化而变化;在两波协同作用下低杂波驱动非感应电流的效率得到了很大的改善.     

低杂波电流驱动的数值模拟

通过求解二维FokkerPlanck方程,得到了HT7托卡马克低杂波驱动电流随时间的演化关系及其空间分布,理论值与实验结果基本符合,为HT7托卡马克实验提供了理论依据.通过解电流扩散方程,考虑了快电子的径向扩散效应对驱动电流的影响 关键词： 低杂波电流驱动 数值模拟 径向扩散     

低杂波驱动的共振电子径向能量输运

在低杂波驱动电流的托卡马克中,可出现波驱动的共振电子径向能流,由定向能流和传导型能流两部分组成,其效应可能与碰撞效应可比,从而改变了驱动电流的基本图象。 关键词：     

捕获电子对低杂波与电子回旋波的协同效应的影响

电子回旋波和低杂波的协同效应可有效地提高两只波的电流驱动效率.本文数值研究了捕获电子效应对电子回旋波和低杂波协同的影响.结果显示,随着捕获角的增大,双波协同驱动电流会减小,且协同因子也会明显减小,即捕获角对两只波协同驱动流的影响要比其对单独驱动电流的影响更加敏感.通过加宽低杂波共振区可减弱电子回旋波电流驱动对捕获角的依赖,同时发现随着电子回旋波功率的增加,捕获角对电子回旋波电流驱动的影响也会变小.     

Synergy of electron-cyclotron and lower-hybrid current drive in steady-state plasmas

Improvement (up to a factor of approximately 4) of the electron-cyclotron (EC) current drive efficiency in plasmas sustained by lower-hybrid (LH) current drive has been demonstrated in stationary conditions on the Tore Supra tokamak. This was made possible by feedback controlled discharges at zero loop voltage, constant plasma current, and constant density. This effect, predicted by kinetic theory, results from a favorable interplay of the velocity space diffusions induced by the two waves: the EC wave pulling low-energy electrons out of the Maxwellian bulk, and the LH wave driving them to high parallel velocities.     

低杂波驱动的径向共振电子流

在低杂波驱动电流的托卡马克装置中,波还将驱动径向共振电子流。这种径向流由共振电子径向平均流和共振电子径向扩散流两部分组成。它们主要联系于波电场的角向分量、在驱动电流的弛豫过程中,两种径向流的强度分别以不同的方式发生显著变化,径向流对波的纵向相速度与电子热速度的比值极为敏感,在低相速情形有较高的径向通量,可对等离子体的行为发生重要影响。 关键词：     

托卡马克中电子回旋波与低杂波协同驱动的物理研究

揭示了电子回旋波与低杂波协同驱动等离子体并获得协同电流的机理. 从物理上阐述了双波协同驱动在相空间上和在电流剖面上所需满足的匹配关系. 通过计算机模拟研究展示了协同驱动的净增电流与波功率之间存在的非线性关系, 并对其给出了物理上的解释.本文工作将为相关实验的设计和分析提供物理上的支撑.     

On the Nonlinear Processes During Generation of Current Drive

The manifestations of the induced scattering effects in the generation process of current driven by lower-hybrid (LH) waves are studied taking into account the radiative-resonant interactions. The influence extent of the LH wave modulational instability on current drive is estimated. It is shown that the induced scattering of LH waves on plasma particles leads to a change of the LH waves spectrum and through this leads to an essential influence on fast electrons generation rate and the steady-state current drive. The modulational instability of LH waves can provide a “spectral gap” filling in the case of sufficiently strong LH wave pumping.     

The role of lower-hybrid-wave collapse in the auroral ionosphere

In regions where lower-hybrid solitary structures (LHSS) are observed, the character of auroral lower-hybrid turbulence (LHT) (0-20 kHz) is investigated using the amplitude probability distribution of the electric field. The observed probability distributions are accurately described by a Rayleigh distribution with two degrees of freedom. The statistics of the LHT exhibit no evidence of the global modulational instability or self-similar wave collapse. We conclude that nucleation and resonant scattering in preexisting density depletions are the processes responsible for LHSS in auroral LHT.     

Nonlinear evolution of the lower-hybrid drift instability in a current sheet

The lower-hybrid drift instability is simulated in an ion-scale current sheet using a fully kinetic approach with values of the ion to electron mass ratio up to m(i)/m(e)=1836. Although the instability is localized on the edge of the layer, the nonlinear development increases the electron flow velocity in the central region resulting in a strong bifurcation of the current density and significant anisotropic heating of the electrons. This dramatically enhances the collisionless tearing mode and may lead to the rapid onset of magnetic reconnection for current sheets near the critical scale.     

Enhanced production of runaway electrons during a disruptive termination of discharges heated with lower hybrid power in the Frascati Tokamak Upgrade

We report on the observation of a large production of runaway electrons during a disruptive termination of discharges heated with lower-hybrid waves at the Frascati Tokamak Upgrade. The runaway current plateaus, which can carry up to 80% of the predisruptive current, are observed more often than in normal Ohmic disruptions. The largest runaway currents correspond to the slowest plasma current decay rates. This trend is opposite to what is observed in most tokamaks. We attribute this anomalous behavior to the acceleration of the preexistent wave-resonant suprathermal electrons during the disruption decay phase. These results could be relevant for the operation of the ITER tokamak whenever a sizeable amount of lower-hybrid power is made available.     

Analysis of electron cyclotron emission by lower-hybrid current drive plasmas

Summary Electron cyclotron emission may be used for diagnosing non-thermal electron distribution functions generated by radio-frequency current drive. Our attention is concentrated in theX-mode-downshifted second-harmonic range of frequencies, by inspecting at the radiation collected in the horizontal low-magnetic-field side of a tokamak. The cut-off presence eliminates the thermal first-harmonic emission and the non-thermal one may be observed without other inference. The electron distribution function is modelled by a suitable sum of drifting Maxwellians for reproducing the flat tails usually obtained in the presence of lower-hybrid power injection. This model is time saving as far as the computer simulations are concerned and permits a lot of runs in order to accomplish a wide parameters exploitation. A sensitivity analysis of ECE intensity is performed with respect to the main moments of the suprathermal electrons distribution function. The analysis shown that the radiation spectra are very sensitive to the perpendicular energy and to the number of fast electrons, while only a weak dependence on the parallel energy is found.