Energy confinement at high density in the FT tokamak

Abstract

The energy confinement of plasma in FT (Frascati Tokamak) has been studied in a wide range of plasma currents (I_p up to 550 kA) and densities ( up to 4.5 × 10¹⁴ cm⁻³). The Lawson parameter τE has reached a value of 4 × 10¹³ cm⁻³ s. The main objective was to investigate the limits of validity of the linear relationship between confinement time and density. The ion heat flux has been found to be consistent with neoclassical ion transport. The electron heat diffusion coefficient has been found to increase with plasma current. Indeed, the electron thermal diffusion coefficient has been shown to be approximately proportional to the electron drift parameter (v_D/v_th). Thus the linear relationship of the electron energy confinement time with density holds only for discharges with the same current. – The deviation from a linear dependence of the totalenergy confinement time on density is due to ion transport and, therefore, appears to be a neoclassical effect.