【作者】 何莹；

【导师】 丁永华； 王能超；

【作者基本信息】 华中科技大学 ， 电气工程， 2023， 博士

【摘要】 等离子体大破裂会对装置造成严重损坏,是托卡马克安全稳定运行面临的重大威胁和首要难题。多种不同模数的磁流体不稳定性(magnetohydrodynamic instability,MHD)模式相互环耦合(简称多模耦合)会使磁流体不稳定性幅度快速增长,进而诱发等离子体破裂。因此,研究多模耦合的物理机制,同时寻求多模耦合的有效控制手段,对于避免等离子体大破裂具有重要意义。本论文在J-TEXT托卡马克上开展了多模耦合过程及其机理研究,同时基于外加磁扰动发展了多种有效控制多模耦合的方案。通过对J-TEXT托卡马克上多模耦合及其演化过程的实验研究,发现了多模耦合的演化规律及其内在机制。在J-TEXT等离子体中,通过缓慢降低边界安全因子q_a接近于3,观测到了2/1与3/1模发生相位锁定,随后幅度快速增长的耦合过程。定性上给出了多模耦合的作用机理与物理图像:不同频率的多模之间因环效应发生电磁相互作用,降低3/1模频率,最终发生频率匹配;耦合后的两支模式在低场侧中平面保持相位差为0,进而导致多模相互解稳,甚至诱发破裂。本文进一步研究了耦合模式幅度演化与q_a的依赖关系,研究表明3/1模幅度演化对q_a非常敏感,q_a越接近3时,3/1模幅度增长越快;同时3/1模的增长会进一步解稳2/1模,2/1模幅度的演化与3/1模幅度及两支模式之间的相位差相关,获得了耦合模式相互解稳并诱发大破裂的演化规律。基于对多模耦合物理机制的理解,本文提出利用外加共振扰动场(resonant magnetic perturbations,RMPs)控制多模耦合的方案,实现了对多模耦合的抑制或避免,同时避免了等离子体大破裂。本文首先利用混合模式RMPs(2/1与3/1共振分量幅度相当)对2/1与3/1模耦合进行控制。研究发现混合模式RMPs幅值越大,2/1与3/1模耦合的时间越早,同时混合模式RMPs对耦合模式的增长存在抑制作用,当幅度增长到一定阈值时甚至可以完全抑制耦合模式的增长,从而避免大破裂的发生。本文深入研究了外加混合模式RMPs时多模频率锁定及其幅度增长的过程,给出了混合模式RMPs控制2/1与3/1模耦合的作用机制:一方面,混合模式RMPs中3/1 RMP分量减速3/1模,降低2/1与3/1模之间的频差,导致2/1与3/1模更快耦合的不利影响;另一方面,混合模式RMPs对2/1与3/1模均存在抑制作用,两种作用相互竞争从而影响最后的作用效果。考虑到混合模式RMPs控制多模耦合的复杂性,本文还提出了利用单一模式RMP控制多模耦合的方案。实验研究表明利用2/1 RMP抑制2/1小磁扰动可以避免多模耦合;通过对不同幅度的2/1 RMP作用效果的研究,获得了2/1 RMP避免多模耦合的适用区间;相较于混合模式RMPs,2/1 RMP适用区间更宽,作用效果更优。此外,利用3/1 RMP激发3/1锁模磁岛,显著提升2/1与3/1模之间的频率差,也可以实现多模耦合的避免。两种单一分量主导的RMPs均通过破坏多模之间的耦合条件来避免多模耦合。本论文还探索了利用非共振扰动场(non-resonant magnetic perturbations,NRMP)控制多模耦合的新方案。基于J-TEXT托卡马克上现有的扰动场系统,通过调节扰动场线圈电流大小及方向来产生NRMP。实验研究发现n=2外加扰动场可以有效控制多模耦合,经过对比研究排除了其中共振分量的影响,证实了n=2 NRMP控制多模耦合的有效性。同时由于-1/1 NRMP总是伴随着3/1共振分量的存在,为了排除3/1共振分量的影响,将等离子体运行在q_a远小于3的区间,探索性地研究了-1/1NRMP对低q极限破裂的影响,初步拓展了J-TEXT上的低q极限。本论文以多模耦合控制为研究主体,揭示了多模之间通过电磁相互作用的耦合过程,获得了耦合模式的演化规律。在J-TEXT上利用混合模式RMPs和单一模式RMP实现了对多模耦合的抑制和避免,探索了NRMP对多模耦合的控制方案。本文利用外加磁扰动对多模耦合进行控制,实现了对等离子体破裂的避免,对未来聚变堆多模耦合的控制及大破裂的避免具有参考价值。更多还原

【Abstract】 Plasma disruption is an urgent problem to be solved for the safe and stable operation of tokamak.The coupling of magnetohydrodynamic(MHD)instability(mode coupling)lead to mutual destabilization and ultimately to confinement degradation and even major disruption.Therefore,it is of great significance to study physical mechanism and the effective control scheme of mode coupling for the avoidance of plasma disruption.In this thesis,J-TEXT tokamak is used as the experimental platform to reveal the mode coupling process and interaction mechanism,and a variety of effective control schemes for mode coupling are developed based on the external magnetic perturbations.Through the experimental study on the mode coupling and its evolution process on the J-TEXT tokamak,the evolution and the interaction mechanism of mode coupling are found.In J-TEXT plasma,it is found that mode coupling often occurs when the edge safety factor q_a is close to 3.The mutual destabilization and growth process of coupled modes are observed.The interaction mechanism and physical image of mode coupling are given qualitatively.The electromagnetic interaction between multiple modes of different frequencies lead to frequency coupling.The phase difference between coupled modes is 0in low-field side(LFS),which leads to the mutual destabilization and even induces the disruption.This thesis further studies the dependency between the evolution of coupled modes and q_a.It is found that the evolution of 3/1 mode amplitude is very sensitive to q_a.Specifically,the 3/1 mode is more unstable when q_a is close to 3.Meanwhile,the growth of the 3/1 mode will further destabilize the 2/1 mode.The evolution of the 2/1 mode is related to the 3/1 mode amplitude and the phase difference between the two modes.The above experimental results reveal the evolution law of the mutual destabilization of coupled modes and inducing disruption.Based on the comprehend of mode coupling,a scheme of controlling mode coupling by external resonant magnetic perturbations(RMPs)is proposed in this thesis.The mode coupling can be suppressed or avoided,and the plasma disruption can be avoided.This thesis first investigates the effect of mixed RMPs(the amplitude of 2/1 RMP and 3/1 RMP is comparable)on the mode coupling.It is found that with the increase in mixed RMPs amplitude,the onset of mode frequency coupling appears earlier.Meanwhile,the coupled modes can be suppressed by mixed RMPs.When the amplitude of mixed RMPs increase to a certain threshold,the growth of the coupled modes can be completely suppressed and even avoid disruption.The underlying mechanism of the impact of mixed RMPs on coupled modes is related to two effects:On the one hand,the mixed RMPs contributes to the braking of mode because of the 3/1 RMP decelerating the 3/1 mode;On the other hand,the mixed RMP contributes to the suppression effect on both the 2/1 and 3/1 modes.These two effects compete to influence the final effect.Considering the complexity of mixed RMPs on mode coupling control,this thesis presents a new scheme to avoid mode coupling by pure 2/1 RMP or pure 3/1 RMP.Experimental results demonstrate that the 2/1 RMP with a moderate amplitude can prevent the mode coupling by suppressing the 2/1 mode.The applicable interval of pure 2/1 RMP is wider than that of the mixed RMP.Moreover,the prevention of mode coupling is also achieved by exciting a 3/1 locked mode at 0 k Hz via a pure 3/1 RMP,which can increase the frequency difference between 2/1 and 3/1 modes.Both pure RMPs avoid large MHD by breaking the coupling conditions of 2/1 and 3/1 modes.In addition,the controlling mode coupling using non-resonant magnetic perturbations(NRMP)is also explored.Based on the existing RMP system on the J-TEXT,NRMP is generated by adjusting the amplitude and direction of coils current.The experimental results show that n=2 magnetic perturbations can avoid mode coupling,and the comparison with RMPs shows that n=2 NRMP has a beneficial effect on controlling the mode coupling.The-1/1 component is always accompanied by the 3/1 RMP.In order to exclude the effect of3/1 RMP,the plasma operate in a range where q_a much less 3.The influence of the-1/1NRMP on the low q limit disruption is explored.The low q limit of J-TEXT tokamak is extended preliminary.This thesis focuses on the control of mode coupling,reveals the coupling process through the electromagnetic torque interaction,and obtains the evolution law of the coupled modes.The coupled modes are suppressed by mixed RMPs or avoided by pure RMPs on J-TEXT,and the influence of NRMP on mode coupling is explored.In this thesis,the mode coupling is controlled by external magnetic perturbations and the disruption is avoided,which might provide valuable reference for future mode coupling control in fusion reactor.更多还原