Recent results of Ohmic H mode studies in Tuman-3

In recent experiments the Ohmic H mode was found in shots with a higher plasma current than in earlier experiments. Plasma parameters in this regime are as follows: Ip = 0.115 MA, qcyl = 2.45, n-bar = (2-3.5) x 1019 m-3, Te0 = 0.4-0.6 keV, Ti0 ≅ 0.12 keV. The longest confinement time in the Ohmic H mode is 9.0 ms, whereas in the ordinary Ohmic regime it s <3.8 ms. The enhancement factor above τE ∝ n-bar Ohmic scaling is 1.3-1.5. Maximum βT values reach 4% at the centre and 1% volume averaged (the Troyon limit is equal to 3.4%, assuming the Troyon factor 3.5). In contrast to auxiliary heated H modes, in the case of the Ohmic H mode the density increase after the transition is accompanied by a transitory decrease of the boundary electron temperature. Transport analysis showed that the effective diffusion coefficient at r = 0.9a decreased by a factor of 7 after the transition. In the bulk plasma anomalous inward convection plays a dominant role in the particle transport. A pronounced reduction of the electron thermal conductivity was found in the gradient region (r = 0.7a). The possibility was found of initiating an improved confinement regime after a single LiD pellet injection. This improved confinement mode looks similar to the H mode and was termed the pellet caused H mode (PCH mode). The PCH mode is characterized by suppression of the density fluctuations in the entire plasma region compared with the Ohmic H mode. Transport reduction appears to be stronger than in the Ohmic H mode. (author). 10 refs, 8 figs