托卡马克等离子体不同平衡位形下的电子回旋波电流驱动

在给定的等离子体总电流和中心电流密度条件下,数值求解平衡方程,求出不同拉长比和三角形变因子的托卡马克等离子体温度、密度、磁场分布,然后通过求解波迹方程和Fokker-Planck方程,分别计算这些位形下的电子回旋波波迹和电流驱动.结果表明：电子回旋波X模从顶部发射时,随着拉长比的增大,波迹会向弱场侧偏移.电子回旋波X模从弱场侧发射时,电子回旋波在等离子体中传播沉积的功率份额随着拉长比的增大而增加,驱动电流位置随着三角形变因子的增大向等离子体中心移动.驱动电流位置随环向和极向发射角的减小向中心移动,对应的电流密度峰值也变大.     

发射波功率密度对电子回旋波电流驱动的影响

采用高斯光束的研究方法,结合Fokker-Planck方程,在堆级等离子体条件下模拟了发射波功率密度的改变对电子回旋波功率沉积以及电流驱动的影响。结果表明,高功率密度的波束会拓宽功率沉积剖面,使功率沉积的位置略有外移,电流驱动效率略有降低。     

托卡马克等离子体不同运行模式下的电子回旋波电流驱动

在给定等离子体密度分布下，从电子、离子的能量方程出发，根据不同运行模式下等离子体的热传导率不同，分别求出了中心负剪切模式，常规剪切H模式和L模式下的等离子体温度分布，然后通过求解波迹方程与相对论情况下的Fokker-Planck方程，分别计算了这些模式下的电子回旋波电流驱动和波功率沉积.得到在中心负剪切下，驱动电流最大，驱动效率最高，功率沉积和电流分布区间跨度大；在常规剪切H模式下，驱动电流较小，分布区间跨度比较窄，驱动效率相对较低；在常规剪切L模式，驱动电流效率最低，分布区间跨度也非常集中. 关键词： 托卡马克 电子回旋波电流驱动 中心负剪切 常规剪切     

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.     

基于三维Fokker-Planck方程的电子回旋波加热与电流驱动模拟

利用反弹平均的三维Fokker-Planck方程,对电子回旋波加热和电流驱动进行数值模拟.考虑超热电子径向扩散对电流驱动的影响,在方程中加入径向扩散输运项,采用九点格式的中心差分对方程进行数值离散得到系数矩阵,采用不完全LU分解对系数矩阵进行预处理,利用双共轭梯度稳定法求解得到分布函数.在不考虑电子径向扩散输运条件下,得到电子回旋波驱动电流密度与功率沉积密度的分布;考虑径向扩散输运的计算结果与BANDIT3D进行比较,驱动电流分布的趋势基本一致.     

电子回旋波驱动的托卡马克芯部等离子体极向旋转

提出了一个驱动托卡马克芯部等离子体极向旋转的新途径：用电子回旋波产生芯部等离子体极向旋转.物理机制如下：在高功率的电子回旋波加热的托卡马克等离子体中，共振局域化现象将产生极向电场从而形成极向外高内低的离子密度分布；这个极向离子的积累可以克服来自磁泵的阻尼而使等离子体极向旋转退稳定.从流体力学方程和漂移动力学方程中，得到了等离子体旋转退稳的判别式.结果表明现有的电子回旋波加热功率水平可以驱动芯部等离子体的极向旋转. 关键词：     

托卡马克中快波电流驱动下全波方程的数值求解

用全波方法研究环形对称托卡马克等离子体中离子回旋频率范围内(ICRF)的快波电流驱动(FWCD)问题,考虑有限拉莫尔半径(FLR)效应和平行色散,建立全波计算的物理模型—全波方程,通过对全波方程的数值求解得到快波在等离子体中激发的电场强度分布.结果表明:快波可以传播到高温高密度等离子体的中心;快波在磁轴附近发生了模式转换;快波可以驱动中心的等离子体电流以改善等离子体的平衡位型;平行电场比垂直电场小三个数量级,通过垂直方向的回旋共振和平行方向的穿越期磁泵效应达到驱动电流的目的.     

HL-3装置电子回旋电流驱动的优化计算

利用托卡马克集成模拟与实验分析平台(OMFIT)开展了HL-3装置ECCD驱动效率的研究，分析了ECCD系统发射天线在等离子体环向与极向所成的角度、等离子体密度、电子温度和磁场对驱动电流大小和位置的影响。研究发现，环向角和极向角范围分别为185°～200°、85°～105°时，ECCD电流驱动效率比较高，驱动电流可以覆盖到归一化半径0.4～0.6。研究还发现，电子温度显著影响ECCD电流驱动效率，温度越高驱动电流越大；在弱场侧磁场强度(1.9～2.2T)越小，驱动电流分布归一化半径越小和驱动电流越大。     

低混杂电流驱动实验中高能电子的回旋辐射谱分析

在低混杂电流驱动实验中，研究由波驱动的快电子的行为对理解低混杂波驱动物理是十分重要的。     

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采用高斯光束的研究方法,结合Fokker-Planck方程,在堆级等离子体条件下模拟了发射波功率密度的改变对电子回旋波功率沉积以及电流驱动的影响。结果表明,高功率密度的波束会拓宽功率沉积剖面,使功率沉积的位置略有外移,电流驱动效率略有降低。     

Neoclassical tearing mode stabilization by electron cyclotron current drive for HL-2M tokamak

Investigation of neoclassical tearing mode and its suppression by electron cyclotron current drive(ECCD) has been carried out in HL-2 M tokamak. The current driving capability of the electron cyclotron wave is evaluated. It is found that the deposition location can be effectively controlled by changing the poloidal angle. The validation of electron cyclotron wave heating and current driving has been demonstrated for the upper launcher port. We show that 3.0 MW and2.5 MW modulated ECCD can completely stabilize(2,1) and(3,2) NTMs, respectively. The non-modulated ECCD, radial misalignment as well as current profile broadening have deleterious effect on the NTM stabilization. The time required for suppression of(3,2) mode is shorter than that required for the suppression of(2,1) mode. Moreover, the time needed for complete stabilization at different initial island width has been quantitatively presented and analyzed.     

Numerical simulation of electron cyclotron current drive characteristics on EAST

Electron cyclotron current drive （ECCD） will be applied in the EAST tokamak during its the new campaign. In order to provide theoretical predictions for relevant physical experiments, some numerical simulations of ECCD with the parameters of EAST have been can＇ied out by using TORAY-GA code based on the understanding of ECCD mechanisms. ECCD efficiencies achieved in different plasma and electron cyclotron （EC） wave parameters are given. The dependences of ECCD characteristics on EC wave injection angle, toroidal magnetic field, plasma density, and temperature are presented and discussed.     

Characteristics of electron cyclotron resonance plasma formed by lower hybrid current drive grill antenna

A 3.7 GHz system, which is meant for LHCD experiments on ADITYA tokamak, is used for producing ECR discharge. The ECR discharge is produced by setting the appropriate resonance magnetic field of 0.13 T, with hydrogen at a fill pressure of about 5 × 10⁻⁵ Torr. The RF power, up to 10 kW (of which ∼50% is reflected back), with a typical pulse length of 50 ms, is injected into the vacuum chamber of the ADITYA tokamak by a LHCD grill antenna and is used for plasma formation. The average coupled RF power density (the RF power/a typical volume of the plasma) is estimated to be ∼5 kW/m³. When the ECR appears inside the tokamak chamber for the given pumping frequency (f = 3.7 GHz) a plasma with a density (n _e) ∼ 4 × 10¹⁶ m⁻³ and electron temperature ∼8 eV is produced. The density and temperature during the RF pulse are measured by sets of Langmuir probes, located toroidally, on either side of the antenna. H_α signals are also monitored to detect ionization. An estimate of density and temperature based on simple theoretical calculation agrees well with our experimental measurements. The plasma produced by the above mechanism is further used to characterize the ECR-assisted low voltage Ohmic start-up discharges. During this part of the experiments, Ohmic plasma is formed using capacitor banks. The plasma loop voltage is gradually decreased, till the discharge ceases to form. The same is repeated in the presence of ECR-formed plasma (RF pre-ionization), formed 10 ms prior to the loop voltage. We have observed that (with LHCD-induced) ECR-assisted Ohmic start-up discharges is reliably and repeatedly obtained with reduced loop voltage requirement and breakdown time decreases substantially. The current ramp-up rates also decrease with reduced loop voltage operation. These studies established that ECR plasma formed with LHCD system exhibits similar characteristics as reported earlier by dedicated ECR systems. This experiment also addresses the issue of whether ECR plasma formed with grill antenna exhibits similar behavior as that formed by single waveguide ECR antenna. Our experimental observations suggest that the characteristics of (LHCD system-induced) ECR-assisted Ohmic start-up discharges show similar properties, reported earlier with normal ECR-assisted Ohmic start-up discharges and hence LHCD system may be used as ECR system at reduced toroidal magnetic field for other applications like wall conditioning.      

Experiment and simulation of tearing mode evolution with electron cyclotron current drive in KSTAR

The tearing mode (TM) plasma instability was observed in low confinement (L-mode) plasmas when non-axisymmetric magnetic perturbation (MP) was applied using external coils during 2011 campaign of KSTAR. Based on the collected information of the magnetic island location in a plasma, a discharge was designed for suppression of a (2,1) TM mode by adjusting electron cyclotron (EC) launcher angles to the estimated island position. Here, the (m,n) notation describes the poloidal mode number and the toroidal mode number of the TM, respectively. The discharge is analysed with experimental observations and numerical simulations. Mirnov coil (MC) arrays and electron cyclotron emission (ECE) are used for analysis of the island width and the location as well as the mode number. The EC deposition and its alignment with the island are estimated by X-ray imaging crystal spectroscopy (XICS) and ECE measurements. An integrated numerical system is employed for modelling of this discharge to analyse a temporal evolution of the mode activity by integrating plasma equilibrium, transport, heating and current drive, and the magnetic island evolution, in a self-consistent way. The effect of EC current drive is discussed by comparing with another TM discharge but without ECCD. Some possibilities for classifying this mode to neoclassical tearing mode (NTM) and stabilisation effect of ECCD are suggested based on the experimental observation and the simulation results.     

EAST低杂波电流驱动的数值模拟

应用改进后的低杂波电流驱动程序对EAST进行了低杂波电流驱动的数值模拟。通过模拟发现,波注入位置、功率谱、等离子体温度和密度对低杂波的功率沉积和电流驱动剖面分布有很大影响。通过选取合适的低杂波功率谱、等离子体温度和密度,可以实现对其功率沉积和电流驱动剖面分布的控制。     

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应用改进后的低杂波电流驱动程序对EAST进行了低杂波电流驱动的数值模拟。通过模拟发现,波注入位置、功率谱、等离子体温度和密度对低杂波的功率沉积和电流驱动剖面分布有很大影响。通过选取合适的低杂波功率谱、等离子体温度和密度,可以实现对其功率沉积和电流驱动剖面分布的控制。     

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在EAST上通过分析剩余环电压与低杂波功率之间的关系,计算得到了低杂波电流驱动效率。采用归一化功率,即功率对等离子体电流、电子密度、等离子体大半径以及有效电荷数归一化,将所有数据绘制在同一曲线中,这样可以得到不同等离子体参数下的低杂波电流驱动效率。实验得到低杂波电流驱动效率η0=(0.5~1.3)×1019 A.m-2.W-1,在等离子体电流Ip=277kA、低杂波功率PLH=681kW条件下,实验得到长达3s的低杂波全波驱动。