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.     

托卡马克等离子体中的电子回旋波电流驱动

通过将波迹方程与相对论情况下的完全Fokker-Planck方程联合进行求解,研究了寻常波基频电子回旋波从托卡马克等离子体中平面弱场侧发射时的电流驱动。数值结果表明:随着等离子体电子密度、温度的提高, 功率沉积和电流分布的位置将向等离子体的边缘方向偏移,并且产生的总的驱动电流随之减小;入射波极向发射角和环向发射角度的改变对功率沉积、电流分布及其大小产生明显的影响。     

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.     

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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。     

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。     

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.      

Optimized calculation of the synergy conditions between electron cyclotron current drive and lower hybrid current drive on EAST

The optimized synergy conditions between electron cyclotron current drive(ECCD) and lower hybrid current drive(LHCD) with normal parameters of the EAST tokamak are studied by using the C3PO/LUKE code based on the understanding of the synergy mechanisms so as to obtain a higher synergistic current and provide theoretical reference for the synergistic effect in the EAST experiment. The dependences of the synergistic effect on the parameters of two waves(lower hybrid wave(LHW) and electron cyclotron wave(ECW)), including the radial position of the power deposition, the power value of the LH and EC waves, and the parallel refractive indices of the LHW(N) are presented and discussed.     

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以磁流体理论为基础,采用基于有限体积法的通量差分分裂格式数值求解具有双曲保守律形式的电阻磁流体方程组.编写C++程序对平板几何位形下的等离子体双撕裂模进行了长时间数值模拟,得到双撕裂模不稳定性的演化图景,捕捉到了双撕裂模非线性发展过程中磁场重联的几个典型阶段,讨论了等离子体电阻和两个有理面之间的距离对双撕裂模不稳定性非线性发展的影响.为研究磁流体动力学提供了一种可行的高精度数值算法.     

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.     

基于有限体积法数值模拟双撕裂模非线性演化

以磁流体理论为基础,采用基于有限体积法的通量差分分裂格式数值求解具有双曲保守律形式的电阻磁流体方程组。编写C++程序对平板几何位形下的等离子体双撕裂模进行了长时间数值模拟,得到双撕裂模不稳定性的演化图景,捕捉到了双撕裂模非线性发展过程中磁场重联的几个典型阶段,讨论了等离子体电阻和两个有理面之间的距离对双撕裂模不稳定性非线性发展的影响。为研究磁流体动力学提供了一种可行的高精度数值算法。     

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     

电子回旋共振离子源等离子体的密度测量

 诊断电子回旋共振离子源等离子体的传统方法是采用传统的单探针无发射时测量伏安曲线,并根据曲线的拐点由理论公式计算出的等离子体密度。本文设计并研制了等离子体密度的测量装置。采用单根朗缪尔探针（该探针可以用来发射电子）测量等离子体的伏安特性。在探针有发射和无发射两种状态下测量得到两条伏安曲线,根据这两条曲线的"分叉点"得到等离子体电位,然后根据该电位直接由计算机计算出电子温度、电子密度。采用该新方法,测量得到的等离子体参量空间电位约为17 V,悬浮电位约为-5 V,电子温度约为4.4 eV,离子密度为1.10×10¹¹cm^-3,与传统方法计算出的等离子体1.12×10¹¹cm^-3相比,两者相差仅1.8％,但新方法效率和精度更高。     

The effects of a shear flow on nonlinear evolutions of double tearing mode in Hall magnetohydrodynamics

The effects of a shear flow on nonlinear evolution of double tearing mode in Hall magnetohydrodynamics are investigated. The parallel shear flow displays a suppressing effect on the double tearing mode. Due to the effect of the shear flow, the relative displacements between the magnetic islands are changed, and therefore their mutual interactions become weak. Furthermore, the nonlinear impulsive growth phase of the double tearing mode is delayed with increasing the shear flow velocity. When the magnetic islands are pushing against each other, the width of current sheets decreases drastically, and therefore the Hall effects are dominant and the magnetic reconnection enhances greatly.     

EAST 电子回旋共振加热效果的数值模拟和分析

为了给EAST 电子回旋共振加热物理实验提供理论依据和模拟预测,从电子热输运方程出发,运用 CRONOS 输运程序对不同等离子体和波参数下,电子回旋加热效果进行了数值模拟计算。给出不同电子回旋波功率、入射角、电子密度和纵场等参数对电子回旋加热效果的影响,预测在不同参数下,电子温度、等离子体总内能和能量约束时间的变化,分析了其原因,并与实验结果进行了初步的比较。     

Numerical analysis of the optimized performance of the electron cyclotron wave system in a HL-2M tokamak

The capabilities of current drive, neoclassical tearing mode(NTM) stabilization, and sawtooth control are analyzed for the electron–cyclotron wave(ECW) system in a HL-2M tokamak. Better performance of the upper launcher is demonstrated in comparison with that of a dropped upper launcher, in terms of J_(EC)/J_(bs) for NTM stabilization and I_(ECCD)/(?ρtor)~2 for sawtooth control. 1-MW ECW power is enough for the 3/2 NTM stabilization, and 1.8-MW ECW power is required to suppress 2/1 NTM in a single null divertor equilibrium with 1.2-MA toroidal current with the upper launcher. Optimization simulation of electron–cyclotron current drive(ECCD) is carried out for three mirrors in an equatorial port, indicating that the middle mirror has a good performance compared with the top and bottom mirrors. The results for balanced co- and counter-ECCD in an equatorial port are also presented.     

CFETR低杂波电流驱动数值模拟研究

利用射线追踪和福克-普朗克方程,研究了CFETR上驱动电流和功率沉积对低杂波注入位置和耦合波谱的依赖关系,讨论了边界非线性效应对电流驱动与功率沉积的影响,给出了低杂波平行折射率和低杂波注入位置的一个优化值。初步数值计算表明：边界非线性效应会导致驱动电流降低;不考虑低杂波非线性效应时,驱动电流的差异约为6%左右,小于考虑该效应时的差异(~25%)。     

Investigation of lower hybrid current drive during H-mode in EAST tokamak

H-mode discharges with lower hybrid current drive (LHCD) alone are achieved in EAST divertor plasma over a wide parameter range. These H-mode discharges are characterized by a sudden drop in D_α emission and a spontaneous rise in main plasma density. Good lower hybrid (LH) coupling during H-mode is obtained by putting the plasma close to the antenna and by injecting D₂ gas from a pipe near the grill mouse. The analysis of lower hybrid current drive properties shows that the LH deposition profile shifts off axis during H-mode, and current drive (CD) efficiency decreases due to the increase in density. Modeling results of H-mode discharges with a general ray tracing code GENRAY are reported.     

2cm电子回旋共振离子推力器离子源中磁场对等离子体特性与壁面电流影响的数值模拟

电子回旋共振离子推力器(electron cyclotron resonance ion thruster,ECRIT)离子源内等离子体分布会影响束流引出,而磁场结构决定的ECR区与天线的相对位置共同影响了等离子体分布.在鞘层作用下,等离子体中的离子或电子被加速对壁面产生溅射,形成壁面离子或电子电流,造成壁面磨损和等离...