【作者】 吴彦斌；

【导师】 钟方川；

【作者基本信息】 东华大学 ， 等离子体物理， 2010， 硕士

【摘要】 球形托卡马克是环径比A(A=R/a,R和a分别是等离子体的大环半径和小环半径)接近1的非传统托卡马克装置,其由于结构紧凑,更易实现高β(β=2μ0<P>/B~2,等离子体的热能与磁能之比)值,更好的磁流体稳定性(magnetohydrodynamic stabilities,简称MHD稳定性)等优势,近20多年来得到了广泛的重视和研究。实验研究表明球形托卡马克仍然发生各种MHD不稳定性,如垂直位移不稳定性(vertical displacement event, VDE),锯齿振荡(sawtooth),扭曲不稳定性(kink modes),新经典撕裂模(neoclassical tearing mode, NTM),边界定位模(ELM),内部重联事件(IRE)及各种微观不稳定性等。因此研究MHD不稳定性发生的基本条件和物理机制,探索避免或控制MHD不稳定性的可行途径,提高球形托卡马克运行参数,是球形托卡马克研究中一个重要而基础的问题。SUNIST是我国建立的第一个球形托卡马克装置,自2002年放电以来,已经观察到了丰富的MHD不稳定性现象,如Mirnov振动,内部重联事件(IRE)等。然而对扰动基本特征,如扰动的模数,频率未有系统的分析和研究。本文利用磁探针诊断对SUNIST球形托卡马克上的Mirnov扰动进行了测量和分析,利用奇异值分解(SVD)方法对扰动的环向和极向模数进行了分辨,并给出了放电过程中的模数时间演化过程。理论和实验研究表明适当的等离子体旋转和剪切流的存在将改善球形托卡马克上的MHD不稳定性。我们通过在真空室内部加带偏压的电极来实现等离子体粒子运动的改变。偏压电极用来产生一个径向方向的电场Er,然后通过E×B漂移来改变粒子运动。由于外加电场在高温等离子体中渗透长度的有限性,此法对比较靠近等离子体边界的扰动有较好的结果。更多还原

【Abstract】 Spherical tokamak is different from traditional toakamak as its aspect ratio A (A=R/a, R and a are the major and minor radius of device) is closed to 1. In last 20 years, it has attracted a more and more attention and has been widely studied owing to its advantage of compact construction, easily accessed high P, better magnetohydrodynamic (MHD) stabilities. Results of experiments show that MHD instabilities still happen in spherical tokamak, such as vertical displacement event (VDE), sawtooth, kink mode, neoclassical tearing mode (NTM), ELM, internal reconnection events (IRE) and microscope instabilities. It is primary and significant that to study the conditions and mechanism of MHD instabilities, explore the the possible method to avoid or suppress the occurrence of the MHD instabilities and improve the operation parameters of spherical tokamak..SUNIST is the first spherical tokamak build in China. Various MHD instabilities events have been observed on it since the first discharging in 2002, such as Mirov fluctuations and IRE. However, the detail investigation of the instabilities features, such as the mode numbers and the frequency is lacke up to now. The Mirnov fluctuations are measured and analysed by magnetic measurement system on SUNIST Spherical Tokamak. The toroidal and poloidal numbers of Mirnov fluctuations are distinguished by using singular value decomposition (SVD), and the time evolution of the mode numbers during a discharge is presented.The theoretical and experimental research indicated that proper plasma rotation and shear flow will improve MHD instabilities on spherical tokamak. The change of plasma movements is realized by a biased electrode. The electrode produces a electric filed through the radius direction Er, and changes the movements of the grain by ExB drift. As the electric filed can penetrate only a limit length in the high temperature plasma, it is found that the biased electrode has a better result for fluctuations close to plasma boundary.更多还原