Effects of resonant magnetic perturbation on the instability of single tearing mode with non-shear flow

Non-shear flow can change the O-point position of a magnetic island, and thus it may play an important role in the effects of resonant magnetic perturbation(RMP) on the single tearing mode. We employ the nonlinear magnetohydrodynamics model in a slab geometry to investigate how RMP affects the single tearing mode instability with non-shear flow. It is found that the driving and suppressing effects of RMP on single tearing mode instability will appear alternately. When the flow velocity is small, the suppressing effect plays a major role through the development of the mode, and the tearing mode instability will be suppressed. With the flow velocity increasing, the driving effect will increase, while the suppressing effect will decrease. When the two effects reach equilibrium, the tearing mode will become stable.     

J-TEXT 装置静态扰动场电源系统结构分析及实现

研制了一种基于电容储能的脉冲电源系统用于J-TEXT 装置扰动磁场线圈的运行,介绍了J-TEXT 装置静态扰动磁场线圈(SRMP),对静态扰动磁场电源系统进行了原理分析,并给出了电源的运行结果。实验运行效果表明,输出电流最大能达到8kA,最大电流上升率为200A.ms^-1,静态扰动场电源系可以稳定地工作,可以产生足够的扰动磁场并开展相关物理实验。     

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研制了一种基于电容储能的脉冲电源系统用于J-TEXT 装置扰动磁场线圈的运行,介绍了J-TEXT 装置静态扰动磁场线圈(SRMP),对静态扰动磁场电源系统进行了原理分析,并给出了电源的运行结果。实验运行效果表明,输出电流最大能达到8kA,最大电流上升率为200A.ms-1,静态扰动场电源系可以稳定地工作,可以产生足够的扰动磁场并开展相关物理实验。     

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研究了电漂移对通行高能离子与新经典撕裂模(NTM)共振相互作用的影响。利用漂移动力论方法,在求解共振相互作用产生的作用在磁岛上的环向力矩的过程中重新考虑了电漂移的作用。结果表明,在与磁岛运动相关的环向动量平衡中v>0的通行高能离子与v<0的通行高能离子作用恰好相反,当磁岛沿电子抗磁漂移方向传播时,前者趋向于使磁岛传播频率减小,后者趋向于使磁岛传播频率增大,通行高能离子产生的总的环向力矩几乎为零。仅将v>0的通行高能离子所产生的环向力矩带入由环向动量平衡方程和修正的卢瑟福方程所组成的方程组中,数值计算结果表明,描述磁岛旋转频率与宽度随时间做非线性振荡的稳定极限环并不存在。     

外部驱动电流抑制双撕裂模的发展

在Hall MHD方程组中引入外部驱动电流项,数值模拟外部驱动电流对双撕裂模不稳定性的影响.结果表明,在x点加入反向外部驱动电流对撕裂模的发展有抑制作用,周期性的外部驱动电流对双撕裂模不稳定性的抑制效果较好,能控制磁岛的尺度在相互驱动的临界尺度以下,避免发生双撕裂模非线性磁场重联的爆发,随着驱动电流周期变大抑制效果变坏,在一定限度内随着驱动电流强度增大抑制效果变好,在一定范围内随着驱动电流宽度变小抑制效果变好.     

EAST装置RMP线圈电源的优化设计

对EAST装置中边界局域模等相关物理现象研究的要求,RMP线圈电源需要有更大的承载电流能力,同时提高响应速度和减小输出电压纹波。对于一期RMP线圈电源的拓扑结构、主回路参数进行了优化设计,结合理论计算、MATLAB仿真和实际测试验证了设计方案的可行性,实验结果表明二期RMP线圈电源在响应速度、承载电流能力和电压纹波方面相比一期均表现得更好,达到优化的目的。     

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对EAST装置中边界局域模等相关物理现象研究的要求,RMP线圈电源需要有更大的承载电流能力,同时提高响应速度和减小输出电压纹波.对于一期RMP线圈电源的拓扑结构、主回路参数进行了优化设计,结合理论计算、MATLAB仿真和实际测试验证了设计方案的可行性,实验结果表明二期RMP线圈电源在响应速度、承载电流能力和电压纹波方面相比一期均表现得更好,达到优化的目的.     

Nonambipolar magnetic-fluctuation-induced particle transport and plasma flow in the MST reversed-field pinch

First direct measurements of nonambipolar magnetic fluctuation-induced charge transport in the interior of a high-temperature plasma are reported. Global resistive tearing modes drive the charge transport which is measured in the vicinity of the resonant surface for the dominant core resonant mode. Finite charge transport has two important consequences. First, it generates a potential well along with locally strong electric field and electric field shear at the resonant surface. Second, this electric field induces a spontaneous E x B driven zonal flow.     

Nonlinear evolution of q=1 triple tearing modes in a tokamak plasma

In magnetic configurations with two or three q=1 (with q being the safety factor) resonant surfaces in a tokamak plasma, resistive magnetohydrodynamic modes with poloidal mode numbers m much larger than 1 are found to be linearly unstable. It is found that these high-m double or triple tearing modes significantly enhance through nonlinear interactions the growth of the m=1 mode. This may account for the sudden onset of the internal resistive kink, i.e., the fast sawtooth trigger. Based on the subsequent reconnection dynamics that can proceed without formation of the m=1 islands, it is proposed that high-m triple tearing modes are a possible mechanism for precursor-free partial collapses during sawtooth oscillations.     

托卡马克中共振螺旋场对撕裂模的影响

本文在共振螺旋场(RHF)条件下,对撕裂模的时间演化过程进行了数值计算。在等离子体内部磁扰动与外加RHF的相位差不同时,分析了撕裂模的不同发展过程和结果。认为RHF可以最终改变托卡马克中的饱和磁岛宽度。     

Effect of resonant magnetic perturbations on edge plasma parameters in the STOR-M tokamak

Edge plasma properties have been modified in the Saskatchewan Torus-Modified tokamak by means of resonant magnetic perturbations (RMP). It has been found that the radial profiles of ion saturation current and floating potential in the edge region can be modified by an externally applied static (m?=?2, n?=?1) RMP field. An increase in the pedestal plasma density (n) and more negative electric field (E_r) have been observed in the plasma edge region. It is believed that the RMP field altered the plasma transport in the edge and scrape-off layer regions, leading to a higher density pedestal and a potential drop in some cases. During the enhanced confinement phase, it is possible to identify a region where intermittent transport events, the so-called blobs, are created and the holes of lower density left behind.     

A New Criterion for Disruption Prediction on HL-2A

A new criterion has been proposed to predict the major disruptions caused by tearing mode instabilities. According to the HL-2A experimental results, the statistical analyses are employed to investigate the relationships between MHD activities and the plasma disruptions. Two kinds of the tearing mode activities can finally cause the disruption on HL-2A operations. By introducing a new parameter, i.e. an integral of poloidal magnetic field over time, as the criterion of disruption precursor, almost all of the disruptions can be predicted.     

First EMC3-EIRENE modelling of JT-60SA edge plasmas with/without resonant magnetic perturbation field

The first EMC3-EIRENE modelling for the JT-60SA edge plasmas with/without the resonant magnetic perturbation field (RMP) was conducted. Both core degradation in the vacuum approximation and strike-point splitting were observed due to the application of the RMP, as in previous studies in other devices. Toroidally averaged divertor heat fluxes with and without the RMP were fitted by using a one-dimensional diffusive model function, showing similar profiles. To extract the modulation components of the divertor heat flux profile, the proper orthogonal decomposition (POD) method was applied. By using the POD outputs, a modulation ratio with respect to the toroidally averaged profile was quantitatively calculated.     

撕裂模实时主动控制系统

在HL-2A装置上发展了一套撕裂模实时主动控制系统。该系统在放电期间用电子回旋发射/软X射线诊断实时确定撕裂模的几何位置,结合实时剖面重建和电子回旋波沉积计算,得到电子回旋波反射镜的控制角度值。通过电机实时驱动电子回旋波反射镜到达指定角度,使得电子回旋波功率沉积在撕裂模的有理磁面附近,改变当地局部的电流剖面,从而控制撕裂模,改善等离子体约束。该系统已经在2015年以后的实验中投入使用,并取得了良好的控制效果。它不仅能够实时发现并控制经典撕裂模,并且具有控制新经典撕裂模的潜力。     

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Tearing mode real-time active control system has been developed on HL-2A tokamak. During the plasma discharge, electron cyclotron emission and soft X-ray diagnostic signals are used to get the geometric location where tearing modes emerge, combined with the real time profile reconstruction and electron cyclotron wave (ECW) deposition algorithm, the target angle of ECW steering mirror can be obtained. Then the mirror angle is set by the motor so that the ECW power deposit at the position of tearing modes finally. Consequently the tearing modes can be controlled, owing to the change of local current profile, and the plasma confinement is improved. This system has been deployed in HL-2A campaigns after 2015, and the good control effect is obtained. It has been proved that the system can discover and control not only the classical tearing modes in real time, but also has the potential to control the neoclassical tearing mode in the future.     

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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.     

Plasma Response to Resonant Perturbations at Tokamak Edge

In certain circumstances, plasma response suppresses magnetic islands expected at perturbed resonant magnetic surfaces. We investigate the plasma response to the resonant magnetic perturbations in a large aspect ratio tokamak perturbed by external resonant helical windings, considering polar toroidal coordinates for which analytical toroidal equilibrium solutions and perturbing fields are available. We apply an empirical approach to mimic the plasma screening effects by introducing presumed plasma current sheets on the resonance surfaces to cancel the RMP effects. Numerical examples show the effect of plasma response reducing magnetic islands at the plasma edge and also regularizing field lines around the resonant surface. The distribution of connection lengths along the plasma cross section indicates that the plasma response increases the connection lengths since more toroidal turns are performed until a field line reaches the tokamak wall.     

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。     

导体壳对电阻磁流体不稳定性的影响

结合HL-1装置的条件,采用撕裂模的准线性理论,研究了托克马克中导体壁对m=2/n=1扰动模的稳定作用。着重研究了导体壁位置,等离子体电流分布,等离子体位形对这种稳定效应的影响。结果表明,共振面的位置与壁的稳定作用有密切关系,存q_a接近于2的位形中,m=2的撕裂模扰动可以被靠近等离子体的导体壁完全抑制。导体壁的稳定效应与等离子体电流分布相联系,在一些现实的电流分布中,只要适当地压低等离子体边界区的电流密度,壁的稳定效应会更加显现出来。     

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From the point of view of resistive MHD theory, the linear resistive tearing mode model in the low β plasma with macroscopic axial motion of plasma was deduced in a cylindrical geometry. Numerical study shows that the axial velocity of the plasma itself has a stable effect on tearing mode and the axial velocity shear role is not obvious. Analyses indicate that the axial motion reduces the tearing mode growth rate by changing the phase difference between the plasma potential perturbation and magnetic flux perturbation (deviating from π/2), and results in a lower tearing mode frequency.