【作者】 陈伟；

【导师】 虞清泉； 庄革；

【作者基本信息】 华中科技大学 ， 脉冲功率与等离子体， 2015， 博士

【摘要】 为实现经济而持续的核聚变反应,需要提高等离子体密度和温度,并对能量和粒子约束足够的时间,这一目标的实现建立在对基本输运过程深入理解的基础上,因此等离子体输运一直是磁约束聚变的一个主要研究方向。目前世界上几乎所有的托卡马克装置都开展了输运方面的研究,并取得了丰硕的成果,但是距离理解输运的物理机制还有一定的距离。因此,研究粒子输运是一项重要性和挑战性十足的工作。研究粒子输运的方法有很多,其中最直接的是测量粒子输运系数。实验上测量粒子输运系数最常用的手段是对等离子体密度进行周期性调制。通过密度调制实验研究粒子输运,需要1)拥有足够测量精度、测量道数的密度诊断；2)得到等离子体密度随时间的剖面演化关系;3)可控的加料手段,实现满足要求的密度扰动；4)建立一套密度调制实验的数据分析方法,实现测量粒子输运系数的目的。高精度的密度测量系统是粒子输运研究的前提,而现有的J-TEXT干涉仪并不满足粒子输运研究的要求。为此,对干涉仪进行如下升级：1)大幅提升激光器的输出特性,实现了输出功率提升2.4倍,功率稳定性时间提升2.3倍的跃变。2)通过升级光路布局和机械结构,优化探头,将密度信号中振动分量由50%以上抑制到信号噪声水平,同时大幅提升中频信号信噪比。最终建成了等离子体密度测量精度为1017m-3量级,时间分辨率为0.1ms,空间分辨率为50mm,测量道数为7道的非对称分布的远红外(FIR)氰化氢(HCN)干涉仪。其次,发展了成功率达97%的密度翻转算法,设计了基于快速傅里叶变换的软件相位差计,相比硬件相位差计,进一步提高了密度信号的信噪比。在高精度密度测量数据的基础上,编写了一套采用了基于三次样条函数的Abel反演算法,得到等离子体电子密度剖面的时空演化。接着,基于粒子输运方程发展了三套不同的粒子输运系数算法,并验证他们可行性与正确性。通过初步开展密度调制实验,对可能影响密度调制实验和输运系数的参量(送气波形、调制频率和调制幅度)进行了系统的研究,分析了它们对输运的影响,最终确定了符合J-TEXT粒子输运研究的实验方案。最后,对比了两种密度调制手段——超声分子束注入和普通送气,总结出了J-TEXT典型参数下的输运系数。1)通过螺旋场产生的密度泵出,确定了密度峰化影响粒子约束的机制为扩散系数减小一半以上,对流速度增大一倍以上,粒子约束时间增加50%。2)研究了密度极限破裂下的粒子输运行为,发现了破裂前扩散系数不断减小,对流速度基本不变,总体增强径向向内的粒子流,使等离子密度剖面不断峰化。破裂时对流速度显著增强(-25%),与等离子体电流箍缩效应一致。3)给出了J-TEXT上输运系数与等离子体参数的定标关系,如扩散系数D与密度的对数具有很好的线性关系。为粒子输运更为深入的研究奠定了坚实的基础。更多还原

【Abstract】 To achieve economic and continuous nuclear fusion, a high enough plasma density and temperature and the same as energy confinement time is needed. In order to achieve this goal, the transport process should be understood hardly. Therefore, transport in plasma has always been a main research direction. Now, almost all the tokamak device in the world has carried out research about transport, and fruitful results are achieved. But there still has a long way to understand the physical mechanism of transport. Therefore, particle transport research is an important and challenging work.There are many ways to study the particle transport, but the most direct method is measuring particle transport coefficients. The most common means to mearsure the particle coefficients is density modulation experiment. To measure the particle transport coefficients, the most common way is density modulation. To study particle transport by the density modulation experiment, one need:1) a density diagnostic with sufficient accuracy, sufficient number of measuring channels.2) To obtain the time evolution of the profile of the plasma electron density.3) A controlled fuelling system, which to realize the added disturbance to the equilibrium (steady) state.4) To establish a set of data processing method for the data of perturbed density, which could obtain the particle transport coefficients from the data of density modulation experiment.Density measurement diagnostic with high accuracy is the base of the particle transport research, but the original J-TEXT interferometer does not meet the requirements. Based on those, this paper firstly upgrade the original interferometer from following parts.1) A sharp improvement on the output characteristic of the laser is achieved. The output power increases2.4times, the power stability time increases2.3times.2) By upgrading the light path layout and the mechanical structure, optimizing the probe, the vibration ingredient in signal intensity is suppressed from more than50%to signal to noise level, a sharp rise in the signal-to-noise ratio (S/N) of IF signal is achieved. Finally, the upgraded seven channels far-infrared (FIR) hydrogen cyanide (HCN) interferometer with asymmetric distribution has following parameters:the accuracy of plasma density measurement is1017m-3orders of magnitude, the time resolution is0.1ms, and spatial resolution is up to50mm.Second, to observe of the changes of plasma density profile, a density inversion algorithm should be set up. In this paper, the high precision density signal is obtained by processing from two aspects:software and hardware. Based on this, an Abel inversion procedure based on cubic spline function is written to get the space-time evolution of the plasma electron density profile and its correctness is verified while its calculation error is evaluated.Thirdly, a density overturned algorithm with the success rate of97%is developed. The software phase-meter based on fast Fourier transformation is designed. Compared with the hardware phase-meter, it has a higher S/N of density signal. Based on high measurement density data, a set of Abel inversion algorithm based on cubic spline function is written. And the space-time evolution of the plasma electron density profile is obtained.Fourthly, based on the particle transport equations, three sets of algorithms which calculating particle transport coefficients are developed, and their feasibility and correctness are recognized. Through developing density modulation experiment preliminary, the systematical studies on the parameters (plenum waveform, frequency modulation and amplitude modulation), which may affect the density modulation experiment or transport coefficient, is achieved. The analyzation of their effect on transport is executed. The final experiment scheme of particle transport research, which is accord with the characteristic of J-TEXT is determined.Finally, the similarities and differences of two kinds of density modulation technology, supersonic molecular beam injection and gas puff, are compared. For the first time, the particle transport coefficients under typical discharge parameters on J-TEXT Tokamak is shown.1. The effect of density peak on particle confinement is achieved by externally applied resonant magnetic perturbations (RMPs) on density modulation experiment With a peaking density, the diffusion coefficient is decreased one half, the the inward convective velocity is increased more than doubled, the particle confinement time is increased50%.2. The research about particle transport under high density rupture is executed. The author find that the diffusion coefficient is decreased while the convective velocity remains unchanged before plasma disruption, the convective velocity is increased significantly (-25%) during plasma disruption which is consistent with plasma current pinch effect.3. The scaling of transport coefficients with plasma discharge parameters is gives, for example, the diffusion coefficient D and the logarithm of density has a good linear relationship. All those lay a solid foundation for further study of particle transport.更多还原