EAST中n=4共振磁扰动下等离子体的环向旋转制动

在EAST中n=4的共振磁扰动下观察到明显的等离子体旋转制动效应，其分布具有全局性，且峰值靠近等离子体中心。利用模拟得到的新经典环向粘滞(NTV)力矩来反演等离子体环向角速度的变化，结果表明在大部分径向区域与实验测量的速度变化符合得较好，量值上相差约1~2倍。     

Effect of passive plates on vertical instability in the EAST tokamak

The effect of passive plates on vertical displacement control in the EAST tokamak is investigated by open loop experiments and numerical simulations based on a rigid displacement model.The experiments and simulations indicate that the vertical instability growth rate is reduced by a factor of about 2 in the presence of the passive plates,where the adjacent segments are not connected to each other.The simulations also show that the vertical instability growth rate is reduced by a factor of about 10 if all adjacent segments on each passive plate loop are connected to each other.The operational window is greatly enlarged with the passive plates.     

Tomographic analysis of the central magnetohydrodynamic oscillations on the HT-7 tokamak

Multi-channel soft x-ray (SX) detectors are applied to generate images of magnetohydrodynamic (MHD) oscillation on the HT-7 tokamak, and the data from SX cameras are analysed by using the Fourier--Bessel harmonic reconstruction method and the singular value decomposition. The image reconstruction of SX emissivity is obtained on the assumption of plasma rigid rotation. One of the important phenomena in the HT-7 discharge is the transition from the sawtooth oscillations to the MHD oscillations when the plasma density grows higher. The MHD structure observed in the SX tomography is featured as follows: the magnetic surface of MHD structure is made up of the crescent-shaped ``hot core' and the circular ``cold bubble'. The structure of the magnetic surface is relatively stable. It rotates in the direction of the electron diamagnetic drift at a frequency being the oscillation frequency of the MHD oscillations.     

Observation and analysis of halo current in EAST

Plasma in a typically elongated cross-section tokamak （for example, EAST） is inherently unstable against vertical displacement. When plasma loses the vertical position control, it moves downward or upward, leading to disruption, and a large halo current is generated helically in EAST typically in the scrape-off layer. When flowing into the vacuum vessel through in-vessel components, the halo current will give rise to a large J × B force acting on the vessel and the in-vessel components. In EAST VDE experiment, part of the eddy current is measured in halo sensors, due to the large loop voltage. Primary experimental data demonstrate that the halo current first lands on the outer plate and then flows clockwise, and the analysis of the information indicates that the maximum halo current estimated in EAST is about 0.4 times the plasma current and the maximum value of TPF × Ih/Ip0 is 0.65, furthermore Ih/Ipo and TPF × Ih/Ipo tend to increase with the increase of Ip0. The test of the strong gas injection system shows good success in increasing the radiated power, which may be effective in reducing the halo current.     

Study of sawtooth oscillations on the HT-7 tokamak using 2D tomography of soft x-ray signal

It is the first time so far as we know that two arrays of multi-channel soft x-ray detectors are used to generate twodimensional （2D） images of sawtooth oscillation on the HT-7 tokamak using the Fourier-Bessel harmonic reconstruction method, and using the singular value decomposition to analyse the data from soft x-ray cameras. By these two arrays, 2D image reconstruction of soft x-ray emissivity can be obtained without assumption of plasma rigid rotation. Tomographic reconstruction of the m=1 mode structure is obtained during the precursor oscillation of the sawtooth crash. The crescent-shaped mode structure appearing on the contour map of the soft x-ray emissivity is consistent with the quasiinterchange mode. The characteristics of the m=1/n=1 mode structure observed in the soft x-ray tomography are as follows： the magnetic surface is made up of the crescent-shaped “hot core” and the circular “cold bubble”. The structure of the magnetic surface rotates in the direction of the electron diamagnetic drift and the rotation frequency is the oscillation frequency of soft x-ray signals.     

Effect of passive structure and toroidal rotation on resistive wall mode stability in the EAST tokamak

If βN exceeds no-wallβN, the plasma will be unstable because of external kink and resistive wall mode(RWM). In this article, the effect of the passive structure and the toroidal rotation on the RWM stability in the experimental advanced superconducting tokamak(EAST) are simulated with CHEASE and MARS codes. A model using a one-dimensional(1D)surface to present the effect of the passive plate is proved to be credible. The no wall βN limit is about 3li, and the ideal wall βN limit is about 4.5li on EAST. It is found that the rotation near the q = 2 surface and the plasma edge affects the RWM more.     

EAST托卡马克上共振磁扰动对锯齿行为的影响

锯齿振荡是托卡马克装置上常见的磁流体不稳定性之一.先进实验超导托卡马克(experimental advanced superconducting Tokamak,EAST)装置放电中观察到外加共振磁扰动(resonant magnetic perturbation,RMP)会影响锯齿振荡行为.本文研究了环向模数n=2的RMP对锯齿周期的影响.通过RMP线圈相位差扫描实验发现,当RMP上下线圈(n=2)相位差Δφ_UL发生变化时,扰动场的谱型发生变化,锯齿周期和崩塌幅度也随之发生明显的改变.单流体电阻磁流体力学(MARS-F)程序分析表明,在相同实验条件下,当RMP上下线圈(n=2)相位差为Δφ_UL=270°时,等离子体芯部区域的响应最强,此时锯齿周期和幅度最小.锯齿行为的改变可能与RMP引起的快离子损失相关.该研究利用RMP上下线圈(n=2)实现对锯齿行为的有效调控,有利于未来EAST发展高比压放电条件下的大锯齿自动控制技术.     

Numerical study of fast ion behavior in the presence of magnetic islands and toroidal field ripple in the EAST tokamak

A peculiar first orbit loss type was found apart from the normal ones when we use ORBIT code to simulate fast ion orbits in the EAST tokamak. Fast ion orbits were studied in the presence of toroidal field （TF） ripple and magnetohydro- dynamic （MHD） perturbations. We analyzed the properties of the drifted orbits in detail and compared their differences, finding that the combined effects of ripple and magnetic islands are much greater than the effects of either one of them alone. Then we investigated the orbitdeviations as a function of pitch angle in different radial positions. The modeling results demonstrate that the loss of trapped particles is mainly caused by the ripple, while MHD＇perturbation mainly plays an important role in the passing particles. Furthermore we modeled the loss rate using different equilibriums. Results prove that a higher beta can indeed improve the confinement of fast ions, while a little change in the q profile can make the topologies of magnetic islands become quite different and results in quite different total particle losses.     

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通过求解椭圆积分,计算了EAST极向场系统的磁场分布,从而计算出极向场线圈在等离子体放电过程中的热负荷。并根据磁体运行的热工水力条件估算出极向场线圈在等离子体放电过程中的最高温升。     

EAST 磁探针 NS 值标定

为了获得精准的磁场测量数据,基于磁探针测量磁场的基本原理,构建了由长螺线管、交流电源、标准探针和数据采集系统组成的长螺线管标定系统,对EAST 磁探针垂直于磁感应强度方向的总有效面积(NS 值) 进行了精确的标定,并对标定数据进行了分析处理。获得的结果符合预期的误差要求,为磁探针精确测量托卡马克中的磁场提供了前提条件。