Physical processes determining plasma confinement in tokamaks with transport barriers from the point of view of self-organization

Abstract

The goal of this article is to describe processes linked to energy confinement in tokamak plasmas from the perspective of self-organization—the main process that determines the behavior of turbulent plasmas. In the paper Razumova et al 2020 Plasma Phys. Rep. 46 337, such an analysis was performed for regimes without transport barriers. The present paper extends this approach to regimes with barriers and magnetic islands. In a shorter version, it was presented in Razumova et al 2020 Entropy 22 53, which showed that the appearance of islands in the inner part of the barrier is directly related to the formation of the barrier and limits its growth. We discuss the structure of the radial heat flux that carries energy from the plasma in such a way that the pressure profile remains close to the self-consistent profile (as observed in the experiment).

Physical Processes That Occur in Self-Organized Tokamak Plasma

“…On the contrary, in experiments on TEXTOR [13] and KSTAR [16], the island m/n = 2/1 was generated and the formation of a barrier was observed. Figure 7 shows the result obtained by M. Kantor [17], who used multi-pulse Thomsom Scattering diagnostics with high spatial and temporal resolution. The structure of the magnetic island is shown in isotherms, lines of constant density, and isobars.…”

Analysis of the highest energy confinement in tokamaks based on thermodynamic approach

“…When the input power is inconsistent with the self-consistent pressure profile, it results in a deviation of the pressure profile from the self-consistent profile and accordingly in the increase in the free energy F. The free energy increase results in the increase in the disturbed flux Γ 1 and of the coefficient κ = θ•(χ 0 + χ 1 ). The resulting flux Γ 1 aims to bring the pressure profile closer to the self-consistent pressure profile [4,16,17].…”

“…It was shown in [3,4,16,17] that the experimentally observed self-consistent pressure profiles in a tokamak can be described within the framework of the nonequilibrium thermodynamics approach. This approach is successfully used to describe complex nonequilibrium systems in other fields of science, when the desired stable states correspond to the minimum free energy and represent the solution of the equation δF = δ(−θ•S + E) = 0, where S and E are entropy and energy respectively, and θ is some effective turbulent temperature.…”