Research Projects

Relativistic electron beam flows are considered to be one of the biggest challenges that needs to be addressed for the successfull operation of a tokamak device for fusion power generation. The issue even assumes urgency in the case of the upcoming ITER tokamak in which India is an important partner. Such high energy electron beams are generated when the hot plasma undergoes a thermal quench due to disruptive magnetohydrodynamic instabilities. Robust solutions to avoid or mitigate the problem requires a sound physical understanding of the dynamics of the interaction between relativistic electrons and the background plasma magnetohydrodynamics. While significant inroads have been made in this regard, there are important open issues that are very little understood. Two most critical aspects are aimed to be addressed in this project: i) Linear and non-linear stability of the plasma including relativistic electrons drift-orbit shifts, and ii) Full lifecycle evolution of the relativistic electron beams in mitgated ITER disruptions. Equilibrium in the presence of relativistic electrons has a special feature of having a radial shift between the electron drift orbits and the magentic flux surfaces. The relative shift can be comparable to the tearing-mode width, due to which the fundamental nature of the instability can be drastically different. Existing studies of plasma fluid instabilites with relativistic electrons have always used the classical plasma equilibrium, and hence the effect is not captured. Novel reduced equilibrium formulations recently derived by the author enables studying this effect. This is basis for the part i) of the proposed study. Furthermore, only certain phases of the co-evolution of the relativistic beams with the background plasma have been studied until now, due to which a fully consistent picture and full dynamics of the phenomena has been missing. This is due to the shortcomings of the existing models to address all phases of the lifecycle. Relativistic electron fluid model coupled with plasma MHD, developed and tested by the author would enable such a study (after development and implementation of a new hot-tail model) which is the aim of part ii). The proposed work involves model development as well as large scale simulations that will be performed using the massively parallel non-linear magnetohydrodynamics code JOREK. The aforementioned models will be implemented and tested in the updated JOREK framework before carrying out the computations. Physical insights into the non-linear dynamics will be the main focus along with quantitative predictions for the relatistic electron impact heat loads in ITER. The predictions will form a solid basis upon which further mitigation strategies can be devised for ITER. In addition, the developed physics also applies in general to all the upcoming and future power-plant-grade tokamak devices.