Statistical Analysis of Similarity of Profiles of Plasma Parameters at Quasi-Stationary Stage of Discharges in Globus-M2 Tokamak

Abstract

The similarity of spatial profiles of electron temperature T_e and electron density n_e at the quasi-stationary stage of electric current in plasma in 21 discharges in the Globus-M2 tokamak have been statistically analyzed. The analysis is similar to that carried out earlier with JET tokamak data. The existence of universal profiles of T_e and n_e depending on the normalized minor radius of the plasma column ρ has been shown. The discharge universal profiles (DUPs) are obtained by dividing the space-time-dependent profile by the space-averaged value of this parameter in the region ρ ≤ ρ_max = 0.5–1 and subsequent averaging over time at the quasi-stationary stage of each discharge. The machine universal profiles (MUPs) are obtained by additional averaging over time of all discharges. It has been shown that, in all considered discharges, the time-averaged \({{{{\tilde {\sigma }}}}_{{{{T}_{{\text{e}}}}}}}\), the relative root-mean-square deviations of the T_e profile from the DUP and MUP, at ρ_max = 0.8 on radii of ρ = 0.1–0.7 do not exceed 10%, and at ρ = 0.9, accuracy decreases. Similar values of spatially averaged \({{{{\tilde {\sigma }}}}_{{{{T}_{{\text{e}}}}}}}\) exceed 10% only at one of 136 time points of all considered discharges. A similar picture has been observed for n_e profiles. A comparison of the MUP for T_e in JET and Globus-M2 has shown some difference in profiles, maximal at small ρ. Using the SvF method of balanced identification, the accuracy of the representation of T_e(ρ, t) as the product of two functions of only one variable, time and coordinate, has been found. The results illustrate the high degree of plasma self-organization in tokamaks.