Formation of an internal transport barrier in the ohmic H-mode in the TUMAN-3M tokamak

In experiments on studying the ohmic H-mode in the TUMAN-3M tokamak, it is found that, in high-current (I-P similar to 120-170 kA) discharges, a regio n with high electron-temperature and density gradients is formed in the pla sma core. In this case, the energy confinement time tau(E) attains 9-18 ms, which is nearly twice as large as that predicted by the ELM-free ITER-93H scaling. This is evidence that the internal transport barrier in a plasma c an exist without auxiliary heating. Calculations of the effective thermal d iffusivity by the ASTRA transport code demonstrate a strong suppression of heat transport in the region where the temperature and density gradients ar e high. (C) 2000 MAIK "Nauka/lntelperiodica".