Identification of m=2 competent mode of complex magneto-hydro-dynamics activities during internal soft disruption based on singular value decomposition and tomography of soft-X-ray emission on the HT-7 tokamak

In this paper,the singular value decomposition(SVD) method as a filter is applied before the tomographic inversion of soft-X-ray emission.Series of ’filtered’ signals including specific chronos and topos are obtained.(Here,chronos and topos are the decomposed spatial vectors and the decomposed temporal vectors,respectively).Given specific magnetic flux function with coupling m = 1 and m = 2 modes,the line-integrated soft-X-ray signals at all chords have been obtained.Then m = 1 and m = 2 modes have been identified by tomography of simulated ’filtered’ signals extracted by the SVD method.Finaly,using the experimental line-integrated soft-X-ray signals,m = 2 competent mode of complex magnetohydrodynamics(MHD) activities during internal soft disruption is observed.This result demonstrates that m = 2 mode plays an important role in internal disruption(Here,m is the poloidal mode number).     

基于激光二极管的软X射线相机信号的自检设计

介绍了在ITER装置中使用激光二极管实现软X射线相机自检的设计。利用漫反射板进行光路设计,基于FPGA完成驱动模块设计和基于LABVIEW软件完成上位机设计。实现了激光二极管的远程实时开关和激光功率的调控,控制精度达到10^-3量级。在FPGA代码中预留了发出窄脉冲电流信号的功能,最窄脉冲达到100ns以内,能用于探测系统响应速率的测量,并对探测系统的本底噪声和基线偏移进行测量。     

Compound sawtooth in EAST LHCD plasma:An experimental study

A compound sawtooth with an incomplete relaxation was observed in EAST’s lower hybrid current drive(LHCD)plasma. The sub-crash phase of the compound sawtooth corresponds to a longer-lasting and slower-growing 1/1 mode.Based on the two-dimensional(2D) SXR tomography, the time-dependent 2D image of a compound sawtooth crash is obtained. The island produced during a resistive internal kink mode is observed in the all crash phases of the compound sawtooth. The destabilization of 1/1 long-lasting saturated 1/1 mode is related to the current driven by the LHCD near the q = 1 surface.     

HT-7装置软X射线诊断系统及锯齿行为研究

利用HT-7装置上建立的多阵列软X射线诊断系统对等离子体放电中的锯齿不稳定性进行研究,发现锯齿的出现及其行为特点与等离子体电子密度N_e、电子温度T_e、边界安全因子q_α、壁条件等放电参数有密切关系。在低杂波电流驱动等离子体放电条件下,观察到m/n=1/1的中间模振荡出现在锯齿的上升阶段,并迅速发展、饱和、衰减,在锯齿塌陷或先兆振荡出现以前消失。分析和讨论了欧姆加热条件下和低杂波加热条件下的锯齿行为。     

通过软X射线信号研究芯部等离子体的结构

介绍了如何从软X射线原始信号上分析等离子体芯部磁场结构的方法. 在HT-7托卡马克上,通过分析一炮典型的放电数据,直接从软X射线原始信号上分析了磁岛的位置和旋转方向. 通过软X射线图像反演的结果和Mirnov信号上观察到的m=2模的走向验证了磁岛旋转的方向和位置. 关键词： 软X射线 MHD不稳定性 磁岛     

AC operation and runaway electron behaviour in HT-7 tokamak

Operation of HT-7 tokamak in a multicycle alternating square wave plasma current regime is reported. A set of AC operation experiments, including LHW heating to enhance plasma ionization during the current transition and current sustainment, is described. The behaviour of runaway electrons is analysed by four HXR detectors tangentially viewing the plasma in the equatorial plane, within energy ranges 0.3--1.2~MeV and 0.3--7~MeV, separately. High energy runaway electrons (\sim MeV) are found to circulate predominantly in the opposite direction to the plasma current, while the number of low energy runaway electrons (\sim tens to hundreds of keV) circulating along the plasma current is comparable to that in the direction opposite to the plasma current. AC operation with lower hybrid current drive (LHCD) is observed to have an additional benefit of suppressing the runaway electrons if the drop of the loop voltage is large enough.     

Repetitive ＇Snakes＇ and Their Damping Effect on Core Toroidal Rotation in EAST Plasmas with Multiple H-L-H Transitions

Repetitive impurity snake modes are observed after H-L mode transitions （high to low confinement modes） in EAST plasmas exhibiting multiple H-L-H transitions. Such snake modes are observed to lower the core plasma toroidal rotation. A critical impurity strength factor associated with snake-mode formation is estimated to be as high as αz,c = nz,cZ^2/ne - 0.75. These observations have implications for ITER H-mode sustainability when the heating power is only slightly above the H-mode power threshold.     

小波变换在HT-7 Tokamak磁流体动力学振荡动态频谱分析中的应用

将Gauss复小波变换方法成功地应用于HT-7Tokamak磁流体动力学振荡动态频谱分析中.研究结果表明,这种方法具有较好的时间分辨率和空间分辨率,比较适用做动态频谱分析.对典型放电数据的分析结果表明, m=1模的振荡频率与等离子体压强梯度有着密切的关系.