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 (Ip up to 550 kA) and densities (n̄ up to 4.5 × 1014 cm−3). The Lawson parameter n̂τE 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 (vD/vth). 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.

Anomalous thermal confinement in ohmically heated tokamaks

“…In machines with higher fields the change in the scaling of TE with density was found to be less dramatic. Nevertheless, while the results from Alcator A [ 14] and FT [9] were found to be in agreement with the prediction of saturation associated with ion neoclassical theory, the Alcator C data [7] showed an apparent disagreement.…”

“…This has involved comparisons of results from different experiments and also confinement studies carried out on a single machine [4][5][6][7][8][9]. The data base from these studies, which have been recently summarized in Refs.…”

“…In particular, the experimental observation that the energy confinement time rg increases linearly with the average density [ 1 ] has stimulated attempts to explain this trend, and there were further investigations of possible scalings of rg with other key plasma parameters and with the size of the device [2,3]. This has involved comparisons of results from different experiments and also confinement studies carried out on a single machine [4][5][6][7][8][9]. The database from these studies, which have been summarized in Refs [10,11], indicates that at low density in Ohmic discharges, TE is rather well described by the 'Neo-Alcator' scaling, rg a n a 1 0 4 R 2 0 4 , where n is the line average density, a is the minor radius and R is the major radius.…”

Understanding LOC/SOC phenomenology in tokamaks

“…[3] were in the SOC regime. It can similarly be argued that the FT [12] and TEXT [96] observations were also completely in the SOC regime. As for the negative slopes in Fig.…”

Theoretical interpretation of experimental dibaryon resonance data

“…(16b)] provide the transport in the core itself. It probably applies to the high-density Alcator and FT discharges, where sawtooth oscillations are not seen or have a negligible amplitude [46,47]. Horton and Estes [48] have argued that this scenario is consistent with plasma discharges in the TFR, ORMAK, ATC, ST, and Alcator tokamaks.…”