Mechanism Research Of Influences Of External Resonant Magnetic Perturbations On Tearing Mode And Particle Transport

Externally applied resonant magnetic perturbations (RMPs) have important applications in tokamak plasmas. RMPs have been shown to be a promising technique in contolling MHD instabilities, such as edge localized modes (ELMs),(neoclassical) tearing modes (NTMs), and resistive wall modes (RWM), so as to improve plasma confinement and hence maintain steady fusion plasma. On the other hand, the application of RMPs can also influence plasma confinement, especially the particle confinement. Therefore, systematically studying and understanding the interaction mechanism between RMPs and tearing mode and particle transport is important for the application of RMPs in future fusion reactor.In J-TEXT tokamak, the applied static RMPs have been applied to cause mode locking, partial and complete suppression of m/n=2/1TM. In order to understand the experimental results, numerical modeling based on single-fluids have been carried out, quantitative agreement is found, and qualitative results show the detail interaction mechanism between RMPs and TM. The interaction between RMPs and TM reveals different region, i.e. suppression region, small locked mode region and mode locking region. Detail studies show that the applied RMPs contribute a net stabilizing and decelerate effect on TM, which makes the suppression of TM and deceleration of plasma rotation is possible when parameters is suitable. Further studies found that for smaller island width, higher plasma rotation, smaller Alfven velocity and stronger plasma viscosity, the stabilizing effect is dominant and hence causes stabilization of TM with slight change in plasma rotation. Besides, small locked island (SML) is discovered firstly in numerical modeling, its width is less than linear layer width and decouples from plasma flow, and it is locked at RMPs stabilizing phase. The discovery of SML connects the relationship between TM suppression and mode penetration.Based on the understanding the mechanim of RMPs effect on TM instability, RMPs have been used to mitigate density limit disruption and control the growth of NTMs. On one hand, in J-TEXT the applied RMPs are found to successfully increase the limit density by15%and delay the time of disruption. On the other hand, numerical modeling shows that applied RMPs can effectively suppress the growth of NTMs, and there exists a stabilizing region. In the stabilizing region, the stabilizing effect contributed by RMPs is much stronger than the destabilizing effect contributed by bootstrap current, and hence suppressing the NTMs into a low saturation evel with slight change in plasma rotation. It is proposed that at the beginning of the growth of NTMs, the applied RMPs can easily suppress the NTMs.In J-TEXT, the effects of RMPs on particle transport have been studied, and the resonant feature of RMPs is verified. The resonant feature makes the applied RMPs just change the electron density within the corresponding resonant surface. Based on density modulation, the transport coefficients have been measured during the application of RMPs, it is found that the particle diffusion is increased more than doubled while the inward convective velocity is decreased one third, resulting in enhanced outward particle transport. More important, the effect of rotating RMPs on particle transport is studied in the first time. It is found that RMPs cause improved (degraded) particle confinement when its frequency is higher (lower) than the natural2/1tearing mode frequency, and the amount in density is proportional to the difference beween these two frequencies. These results reveal the important role of relative rotation between RMPs and the electron fluid in affecting the particle confinement.To understand the RMPs effects on particle transport, numerical modelings based on two-fluids have been carried and quantitative and qualitative agreement is found, and plasma rotation is found to play an important role. Numerical modeling shows the detail evolution precess of particle transport caused by RMPs, that RMPs cause change in density around its resonant surface at the first beginning, and then the change in density spreads to plasma core, resulting in density change only within the resonant surface. Systematical modelings show that the effects of RMPs on particle transport exhibit two region, the linear transport region and large island region. The density change in linear transport region is relatively slight and agrees well with analytical results. The density change in large island transport region depends on the effects of both magnetic island and RMPs. The magnetic island flattens the density profile in the inner region and hence causes density reduction within its rational surface. Further studies find that larger island width, particle diffusion and collision make the island effect more important, resulting in density reduction within rational surface.