Влияние электродной поляризации и динамического эргодического дивертора на характеристики прерывистых всплесков плотности плазмы в токамаке

Abstract

Intermittent bursts of plasma density measured by Langmuir probes at the edge of TEXTOR tokamak are studied. These bursts appear as a result of turbulent plasma transport processes involving the formation and propagation of various coherent turbulent structures. Such processes impede controlled thermonuclear fusion: they degrade plasma confinement and entail increased heat load on the vacuum chamber walls and other components located near plasma; they also entail strong erosion of these components along with unwanted capture of tritium. Therefore, investigation of turbulent plasma transport processes and dynamics of coherent turbulent structures is one of the most important tasks to be solved for implementing controlled thermonuclear fusion. This is especially important in the context of elaborating and improving the methods for externally controlling the turbulent plasma transport processes. The electrode biasing method and a dynamic ergodic divertor are frequently used for externally influencing thermonuclear plasma and controlling turbulent transport processes. It should be noted that by studying the temporal characteristics of plasma density bursts together with their radial dependence it becomes possible to get better understanding of and deeper insight into the physical nature of turbulent plasma transport processes and dynamics of coherent turbulent structures. In this article, the temporal characteristics of plasma density bursts and their radial dependence are studied in two different modes: with electrode biasing and with a dynamic ergodic divertor. Conformable changes in the characteristics of intermittent bursts are observed in both cases. Namely, the average burst rate increases, and the average burst duration decreases in comparison with the ohmic regime. This is due to the fact that electrode biasing and certain regimes of the dynamic ergodic divertor cause changes in the radial electric field. This has a conformable effect on the dynamics of coherent turbulent structures and plasma transport processes through a shear poloidal flow, which emerges as a consequence of electric drift due to nonuniform radial electric field and toroidal magnetic field, which are perpendicular to each other. After detailed investigations and refinement, it should become possible to use certain regimes of the dynamic ergodic divertor as a means of contactless biasing for externally controlling the turbulent plasma transport in thermonuclear installations.