Experimental Observations Related To The Thermodynamic Properties Of The Tokamak Plasmas

The enormous complexity of the description of the plasma in reactor relevant conditions suggests that insights coming from global approaches complementary to the microscopic dynamic description are useful as well, as much as their basic assumptions are physically meaningful and widely applicable. In this frame, the coarse-grained tokamak plasma description derived from the magnetic entropy concept presents appealing features as it involves a simple mathematics and it identifies a limited set of characteristic parameters of the macroscopic equilibrium. The aim of this paper is to provide a comprehensive review of the work done in order to check the reliability of the SME predictions against experimental data collected from different tokamaks (FTU, JET, TS, AUG), plasma regimes (L and H modes, advanced scenarios) and heating methods (Ohmic, ECH, ICRH, NBI). The SME analysis so far performed provides a satisfactory description of the current density and derived quantities (safety factor, electron temperature if the Ohmic relaxation can be assumed) in all the machines and in L and H confinement modes. Results preliminary obtained in advanced tokamak scenario indicate a similar capability. The restrictions on the pressure profile provided by the SME theory are consistent with the experiments, showing that the normalised experimental pressure can be reasonably reproduced assuming its zero order moment only. The electron heat flux calculated with the SME shows a good agreement with the experimental data for L mode plasmas both in terms of radial profile and in terms of electron temperature gradient. The situation is more difficult in H mode and in the advanced scenarios, where the assumption of Ohmic relaxation is little or not at all verified. In these cases the calculated heat flux profile is still comparable with the experimental data, but the calculated electron temperature gradient is generally not satisfactory.