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。     

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.     

用电子迴旋共振加热抑制托卡马克中的撕裂模

利用电子迴旋共振加热的定域性,改善等离子体电流分布,从而改善撕裂模的稳定条件,只要电子迴旋共振加热的吸收区能覆盖住撕裂模的共振层,就有很好的稳定效应;而不一定要求电子迴旋共振面与撕裂模的共振面重合,在迴旋加热期间,撕裂模被有效地抑制住。 关键词：     

First Observation of Neoclassical Tearing Modes in the HL-2A Tokamak

The m/n = 2/1 neoclassical tearing modes are first observed in HL-2A low density, low beta plasma with central electron cyclotron resonance heating. The neoclassical tearing modes （NTMs） are triggered by a sawtooth crash with m/n = 1/1 precursors, which are toroidal coupled with a small scale m/n = 2/1 mode. The time history of the island width is compared with the prediction of the NTM theory, showing a good agreement between theory and experiment.     

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.     

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The synergy current drive by combining electron cyclotron wave (ECW) with lower hybrid wave (LHW) can be used to either increase the noninductive current drive efficiency or shape the plasma current profile. In this paper, the synergy current drive by ECW and LHW is studied with numerical simulation. The nonlinear relationship between the wave powers and the synergy current of ECW and LHW is revealed. When the LHW power is small, the synergy current reduces as the ECW power increases, and the synergy current is even reduced to lower than zero, which is referred as negative synergy in the this context. Research shows that the mechanism of the negative synergy is the peaking effect of LHW power profile and the trapped electrons effect. The present research is helpful for understanding the physics of synergy between electron cyclotron current drive and lower hybrid current drive, it can also instruct the design of experiments.     

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。     

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.     

HL-2A装置等离子体可见光成像系统

在HL-2A装置上研制了等离子体可见光成像系统,用于孔栏、偏滤器位形放电的诊断。该成像系统由彩色摄像机、观察窗和转向镜、广角收集和准直透镜组、采集卡和计算机组成。本文描述了系统的布局和各部件参数的匹配,报道了观测到的实验结果。等离子体成像系统能监视放电的整个过程,实时显示可见光辐射图形,特别在识别孔栏与偏滤器位形放电的诊断中发挥了重要作用,成为HL-2A装置放电的重要诊断手段。     

Design of the Upgraded TJ-II Quasi-optical Transmission Line

TJ-II plasma start-up and heating are made by electron cyclotron resonance waves at the second harmonic of the electron cyclotron frequency. Two quasi-optical transmission lines transmit the microwave power of the gyrotrons to the vacuum vessel. The first line launches the microwave power under fixed injection geometry, i.e. there is no possibility to change the launching angle and the wave polarization. The second line has a moveable mirror installed inside the TJ-II vessel. To get high absorption efficiency and a narrow energy deposition profile the internal mirror focuses the wave beam at plasma center.To get more flexibility in the experiments on heating and current drive the first transmission line needs to be upgraded. The design is presented in this paper. The new launching antenna includes an internal mirror to focus the beam and to change the injection angle. Both launchers are then symmetrical. A polarizer consisting of two corrugated mirrors is used to get any wave polarization. Two mirrors with an array of coupling holes and calorimetric measurements of the energy absorbed in the barrier window allow the estimation of the microwave power launched into the TJ-II.