Processes Determining the Energy Confinement in Tokamak Plasmas

Abstract

In a brief review, we discuss the processes associated with plasma self-organization in tokamaks, and the model of the self-consistent pressure profiles formation used in the energy and particle balance equations. Plasma self-organization can be interpreted as the formation of a structure consisting from chain of magnetic islands, each of which can form a self-consistent pressure profile. The convergence of island chains leads to anomalous transport, and their divergence leads to the formation of transport barriers. In the proposed model, the total energy flux Γ consists of two main parts: Γ₀ and Γ₁, where Γ₀ corresponds to a self-consistent pressure profile, and the anomalous turbulent flux Γ₁ appears, when the pressure profile is distorted by additional heating/cooling, as well as the neoclassical flux Γ_neo. The electron pressure profiles obtained by Thomson scattering in plasmas with magnetic islands and the effect of sawtooth oscillations on the anomalous Γ₁ flux are analyzed. We present examples of the plasma confinement deterioration due to the nonoptimal deposition of additional heating power, and the confinement improvement due to increased radiation losses at the edge, leading to diminishing the level of magnetic fluctuations, which can be associated with the divergence of the chain of magnetic islands or with a decrease in the size of the islands.