Explanation of Experimentally Observed Phenomena in Hot Tokamak Plasmas from the Nonequilibrium Thermodynamics Position

Abstract

In studying the hot plasma behavior in tokamak devices, the classical approach for collisional processes is traditionally used. This approach leaves unexplained a number of phenomena observed in experiments related to plasma energy confinement. Further, it is well known that tokamak plasma is always turbulent and self-organized. In the present paper, we show that the nonequilibrium thermodynamics approach allows us to explain many observed dependences and paradoxes; for example, puffing of impurities results in confinement improvement if zones of plasma cooling by impurities and additional plasma heating are not overlapped. The analysis of the experimental results shows the important role of radiation losses at the plasma edge in the processes determining its total energy confinement. It is shown that the generally accepted dependence of energy confinement on plasma density is not quite adequate because it is a consequence of dependence on radiation losses. The phenomenon of the appearance of internal transport barriers and magnetic islands can also be explained by plasma self-organization. The obtained results may be taken into account when calculating the operation of a future tokamak reactor.

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.…”

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

“…When the energy deposited is inconsistent with the pressure profile, it destroys the self-consistent pressure, and leads to an increase in the free energy F, an increase in the level of turbulence and flux Γ 1 , and as a consequence, an increase in the transport coefficient κ = θ(χ 0 + χ 1 ). Here, the coefficient χ 1 depends on the value of Γ 1 , the part of the total flux Γ that smooths out the pressure profile distortion [11,12].…”

“…In papers [10][11][12] it was shown that in regimes without transport barriers, the conservation of the normalized pressure profile p N (ρ) in tokamaks with different heating powers can be explained within the framework of the approach of nonequilibrium thermodynamics.…”

“…In papers [10][11][12] it was shown that the confinement of plasma energy is determined not by the density but by the power of radiation losses at the periphery. It turned out that the thermodynamic approach also explains energy confinement in tokamak plasmas in the linear ohmic confinement (LOC) and saturated ohmic confinement (SOC) regimes.…”