Synchrotron radiation intensity and energy of runaway electrons in EAST tokamak

A detailed analysis of the synchrotron radiation intensity and energy of runaway electrons is presented for the Experimental Advanced Superconducting Tokamak(EAST). In order to make the energy of the calculated runaway electrons more accurate, we take the Shafranov shift into account. The results of the analysis show that the synchrotron radiation intensity and energy of runaway electrons did not reach the maximum at the same time. The energy of the runaway electrons reached the maximum first, and then the synchrotron radiation intensity of the runaway electrons reached the maximum.We also analyze the runaway electrons density, and find that the density of runaway electrons continuously increased. For this reason, although the energy of the runaway electrons dropped but the synchrotron radiation intensity of the runaway electrons would continue rising for a while.     

EAST快速极紫外光谱仪绝对强度的原位标定

磁约束等离子体中杂质(特别是高Z杂质)的存在将大大增强等离子体辐射功率损失，破坏等离子体的约束性能。杂质行为的定量研究首先要求对杂质测量的光谱诊断系统进行绝对强度标定，获得灵敏度响应曲线。介绍了EAST托卡马克上的快速极紫外光谱仪系统绝对强度的原位标定方法。在波长范围20～150Å内，通过对比极紫外(EUV)波段连续轫致辐射强度的计算值和测量值得到光谱仪的绝对强度标定。在此过程中，首先由(523±1) nm范围内可见连续轫致辐射强度的绝对测量值计算出有效电荷数Z_eff，进而结合电子温度和密度分布计算EUV波段连续轫致辐射强度；EUV波段连续轫致辐射强度的测量值即为不同波长处探测器的连续本底计数扣除背景噪声计数值。对于较长波段范围130～280Å，通过对比等离子体中类锂杂质离子(Fe23+，Cr21+，Ar15+)和类钠杂质离子(Mo31+，Fe15+)发出的共振谱线对(跃迁分别为1s22s 2S_1/2-1s22p 2P_{1/2, 3/2}及2p63s 2S_1/2-2p63p 2P_{1/2, 3/2})强度比的理论和实验值进行相对强度标定。其中共振谱线对强度比的理论值由辐射碰撞模型计算得到，模型中处在各个能级的离子数主要由电子碰撞激发，去激发以及辐射衰变三个过程决定。两种方法相结合，实现了光谱仪20～280Å范围的绝对强度标定。考虑轫致辐射、电子温度及电子密度的测量误差，绝对标定误差约为30%。在绝对标定的基础上，我们对杂质特征谱线强度进行绝对测量，并将测量结果与杂质输运程序结合ADAS(Atomic Data and Analysis Structure)原子数据库计算得到的模拟值进行比较，进而估算等离子体中的杂质浓度。     

HT-7托卡马克slide-away放电充气对等离子体行为的影响

本文研究了slide-away放电条件下的等离子体约束性能;分析了充气对等离子体约束性能以及反常多普勒共振不稳定性的影响.研究了等离子体密度的提升对slide-away放电过程中逃逸电子辐射行为的影响.研究结果发现:slide-away放电充气可以抑制逃逸电子反常多普勒不稳定性,但是使得等离子体约束状态变差,逃逸电子辐射增强.     

DNB引出束流功率及剖面分布测量

 利用束流截止板热量计原理，测量了诊断中性束(DNB)注入托卡马克的束流功率及束流剖面分布。基于热量截止板上正交分布的13只K型热电偶探针测量出DNB引出束流，在加速极电源49 kV，6 A，100 ms的脉冲放电时，采样铜靶上的最高温升为14 ℃，从而计算出注入束流功率达到160 kW并得到束剖面分布。同时通过对热量截止板冷却循环水温升测量值在时间上的积分数值计算，也获得了注入束流总功率，为130 kW。分析了两种测量结果存在差异的原因，实验结果表明惯性束截止板热量计方法是测量粒子束流功率及剖面分布的有效手段。     

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.     

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HT-7中性束诊断电源系统的计算机控制系统由PLC、工控机、逻辑控制和定时单元等组成。对起弧、束流引出等实验进行了研究。在多种参数下,通过调节弧压、进气量等观察了其对弧流的影响。初步实验结果表明,在高压35kV、弧流80A的情况下,束电流可以达到3.6A,引出的中性束流功率可以稳定地达到50kW以上。     

Ohmic Radio-Frequency Synergy Current Drive and Transformer Recharging Experiments in the HT-7 Tokamak

Lower hybrid current drive (LHCD) experiments for investigating the interaction between lower hybrid (LH) wave and residual dc electric field were performed in extensive plasma parameter ranges in the HT-7 superconducting tokamak. The experimental results are well fitted to the Karney-Fisch theory on the efficiency of LH waves energy converted to poloidal magnetic field energy. The fraction of absorbed LH power is about 0.75 for the HT-7 machine, and the upshift of the LH-wave parallel refraction index during LHCD experiments have been derived by the optimizing fitting parameters. The LH wave is also used for the transformer recharging when the plasma current is maintained unchanged. The highest efficiency about 7% has been achieved in HT-7 machine.     

HT-7电子加热实验的软X射线能谱诊断

介绍了HT-7装置上软X射线能谱诊断系统,用软X射线能谱对HT-7托卡马克上电子温度进行了测量。在离子伯恩斯坦波和低杂波协同实验中,观察到了对等离子体的较好的加热效果。     

EAST 装置固有杂质驱动蛇形振荡行为研究

利用多阵列高时空分辨的软X 射线阵列成像系统对EAST 芯部固有杂质驱动的蛇形振荡进行时间动态演化和空间结构反演研究,研究了实验上发现的两种时空行为明显不同的两类蛇形振荡,一类具有字母V 或W形状的动态频谱,空间上为理想近圆状热芯结构;另外一类蛇形振荡和锯齿崩塌共存,振荡的频谱呈现手掌状,空间上为很大的电阻性月牙形磁岛结构。结果表明,锯齿共存的蛇形振荡的饱和径向扰动位移通常比无锯齿的蛇形振荡大,并且会触发边界的新经典撕裂模。     

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).