The Study On The MHD Instabilities And Their Control In Toroidal Configuration

In the exploration process of toroidal magnetic confinement experimental devices,the instability of plasma and its control has always been a central issue in plasma physics research.This instability,manifested primarily as resistive wall modes and tearing modes,constitutes the primary challenge inhibiting high-performance operation of toroidal devices such as tokamaks and reversed field pinches.Issues instigated by these two modes include energy loss,particle transport,and potential plasma quenching,making their resolution critically important.As such,researchers are committed to developing effective active control strategies for magnetically confined plasma,aiming to address core scientific issues in the steady-state operation of these devices,which is a key pursuit in this field.In the divertor tokamak devices,the existence of the axisymmetric mode(n=0)greatly increases the operation risk of the device and seriously restricts the realization of high-performance plasma states.Indeed,when considering the resonance effects at X-points,these instabilities exhibit significant similarities with tearing and resistive wall modes,further exacerbating the difficulty of steady-state operation of toroidal magnetic confinement fusion devices.Therefore,conducting an in-depth study of the instability and its control in these two types of toroidal devices is of great theoretical and practical significance for a comprehensive understanding and resolution of common problems in toroidal magnetic confinement fusion devices.This thesis consists of two parts,each focusing on the instability and its control in two different types of magnetic confinement fusion devices.In the first part,we focus on the study of magnetohydrodynamic instability and its active control in the KTX reversed field pinch magnetic confinement fusion device.We provide a detailed introduction to the composition and main features of the active magnetic field control system at the boundary of the KTX device,involving various techniques such as magnetic field measurement,power management,real-time feedback control,and the establishment of active control simulation software for magnetohydrodynamic instability in the geometric environment of the KTX device.Based on this,we conducted practical experimental research and detailed analysis of the results.The study shows that by using eddy current magnetic probes as feedback input,we can significantly improve the operating stability of the KTX device,enabling the magnetohydrodynamic modes generated in the KTX device to be effectively suppressed.In the second part,we extensively investigate the theoretical model of vertical instability in divertor tokamak devices and develop a new control strategy for vertical instability.Due to the resonant effect of the X-point on the n=0 mode,a disturbance current sheet with a peak at the X-point is formed along the magnetic separatrix,which can suppress the vertical instability.First,we qualitatively present the image of vertical instability in various scenarios using a simple current filament model,and quantitatively calculate the growth rate of the mode.Next,we construct a relatively simple elliptically elongated cross-section equilibrium configuration with two symmetric X-points and discuss in detail the analytic theory of vertical instability when the plasma density does not extend to the X-points under this configuration.The research results from this part not only contribute to solving the problem of vertical instability in divertor tokamak devices,but also provide strong theoretical support for understanding the dynamic behavior of plasma under complex magnetic field structures.In this study,we deeply investigate the instability and its control strategies in two types of toroidal magnetic confinement fusion devices,based on theoretical models.Through this process,we offer a novel theoretical perspective and potential solutions for understanding common problems in toroidal magnetic confinement fusion devices.The findings from this research could possibly aid the progression of steady-state operation research of toroidal magnetic confinement fusion devices and might have an impact on other related fields in plasma physics.However,we recognize that while our research contributes to theoretical advancement,further research and experimental verification might be required for practical applications.The objective of this study is to provide a potential theoretical foundation and research direction for the steady-state operation of toroidal magnetic confinement fusion devices and a deeper understanding of plasma physics.Nonetheless,we acknowledge that scientific research is a process of continual iteration and deepening,and our research is just one part of this journey.There are still many unknown areas waiting for our exploration and study.