托卡马克等离子体的阿尔芬不稳定性会引起高能量粒子的输运与损失，而快电子相关的阿尔芬不稳定性研究一方面对于预测未来反应堆中阿尔法粒子行为有参考价值，另一方面也对快电子耗散过程的理解与控制有重要意义。本论文分别在SUNIST和EAST装置上开展了快电子相关的阿尔芬不稳定性研究，测量了SUNIST欧姆放电小破裂时激励的环形阿尔芬本征模（TAE）的时空演化，发现并研究了EAST欧姆放电中通行电子通过“大数相减”共振机制激发的椭圆阿尔芬本征模（EAE）。论文利用高密度分辨率、快时间响应的五通道微波干涉仪对密度扰动的测量，配合高频环向/极向磁探针阵列对磁扰动的测量，进一步确认了SUNIST小破裂阶段存在的阿尔芬不稳定性现象具有环形阿尔芬本征模（TAE）的特征。基于阿尔芬不稳定性引起的密度扰动的幅度和相位空间分布，可确定模式的径向位置和极向结构，结果与模拟结果一致。在EAST欧姆放电中，观测到了一类新的高频（400~1000 kHz）、阵发的阿尔芬不稳定性。这一阿尔芬不稳定性发生在等离子体芯部区域（归一化半径0.2~0.35范围），在低环向磁场低密度放电条件下更容易出现，在低环向磁场高等离子体电流参数下幅度更强，但在发生锯齿崩塌时会快速衰减并消失。其环向模数以n=2和n=3为主，沿离子逆磁漂移方向（电流同向）传播。模式通常呈现出多支模共存、阵发和频率啁啾的典型频谱特征，并且表现出丰富的非线性演化现象。基于实际放电中的安全因子剖面和电子密度剖面，使用MAS本征值代码计算了阿尔芬连续谱和离散本征模，确认了EAST上这一高频阵发阿尔芬不稳定性为发生在q=1有理面的EAE。使用MAS代码的测试粒子模块，考察了快电子的环向和极向运动频率ω_? 、ω_θ与EAE频率ω_EAE的共振条件：ω_EAE=nω_?-(m+l) ω_θ。结果表明，在q=1面附近，存在l=+1的共振线，使几乎所有通行电子都可以通过nω_?-(m+1) ω_θ相减的差值，与EAE频率匹配，这也称为通行电子的“大数相减”共振机制。经过分析可知，这一激发机制可以激励较高频率的EAE，但无法激励更低频率的TAE。这一实验发现是对快粒子与阿尔芬波相互作用物理图像的重要补充。
Alfvén instabilities may induce the transport and loss of energetic particles in tokamak plasma, and the studies of Alfvén instabilities driven by fast electrons are informative for predicting the behaviours of alpha particles in future reactors, and also for understanding and controlling the dissipation process of fast electrons. In this thesis, the studies of Alfvén instabilities driven by fast electrons are carried out on the SUNIST and EAST devices, respectively. The spatial and temporal evolution of perturbations caused by the toroidal Alfvén eigenmode (TAE) in the minor disruption process of SUNIST ohmic discharge are comprehensively measured, and the phenomenon of ellipticity-induced Alfvén eigenmode (EAE) driven by the passing electrons through the "large-number subtraction" resonance mechanism was found and investigated in the EAST ohmic discharges. This thesis further confirms that the Alfvén instability existing in the minor disruption of SUNIST is characterized by the toroidal Alfvén eigenmode (TAE) by the density perturbation measurement using a high-density-resolution, fast-time-response, five-channel microwave interferometer in conjunction with the magnetic perturbation measurement using high-frequency toroidal/poloidal magnetic probe arrays. Based on the spatial distribution of the amplitude and phase of the density perturbation caused by the Alfvén instability, the radial position and poloidal structure of the mode can be determined, and the results are consistent with the simulations.A kind of high-frequency (400~1000 kHz), bursty Alfvén instability is observed in EAST ohmic discharges. This Alfvén instability occurs in the plasma core (normalized radius 0.2~0.35), and it is more likely to occur under low toroidal field and low-density discharge conditions and stronger with lower toroidal field and higher plasma current, but decays rapidly and disappears when the sawtooth collapse occurs. Its toroidal mode number are mainly n=2 and n=3, and it propagates along the direction of the ions‘ diamagnetic drift (co-current). The modes usually exhibit typical spectral features of multi-branch mode coexistence, bursting and frequency chirping, and the nonlinear evolution behaviours are very rich.Based on the safety factor profiles and electron density profiles in real discharges, the Alfvén continuum and discrete eigenmodes are computed using the MAS eigenvalue code, and the high-frequency bursty Alfvén instability on the EAST is confirmed to be an EAE occurring in the q=1 rational surface. Using the MAS code‘s Test Particle Module, the resonance conditions of the fast electrons‘ toroidal and poloidal motion frequencies ω_?, ω_θ with the EAE frequency ω_EAE are examined: ω_EAE=nω_?-(m+l) ω_θ. The results show that near the q=1 surface, there exists a resonance line of l=+1 such that almost all the passing electrons can match the EAE frequency through the difference of the nω_?-(m+1) ω_θ, which is also called the "large number subtraction" resonance mechanism of the passing electrons. This resonance mechanism can excite the EAEs at higher frequencies but can not excite the TAEs at lower frequencies, and this experimental finding is an important addition to the physical picture of the interaction between fast particles and Alfvén waves.
