H-mode studies on TUMAN-3 and TUMAN-3M

Abstract

The focus of the TUMAN-3 and TUMAN-3M tokamaks programme is on issues of improved confinement. The transition from an ordinary ohmic regime into improved confinement mode has been found in circular limiter configuration in a vessel with all-metallic walls and limiters. The signatures of the H-mode in auxiliary heated tokamaks have been observed in this regime. The crucial role of the radial electric field was found in experiments with internal probe biasing. Other techniques were demonstrated to trigger H-mode: short increase of the working gas puffing rate, minor radius magnetic compression and pellet injection. The scaling of the energy confinement time in ohmic H-mode was obtained, which differs dramatically from the scaling for the ordinary ohmic regime. A strong dependence of on plasma current was found. The scaling for the ohmic H-mode is consistent with the scaling proposed for devices with powerful auxiliary heating (JET/DIII-D H-mode scaling). The result shows that H-mode physics is universal in tokamaks with different geometries and heating methods. In 1994 a new vacuum vessel was installed in the TUMAN-3 tokamak. The modified device, TUMAN-3M, is able to produce higher and , up to 2 T and 0.2 MA, respectively. During the first operational period a plasma current of 0.15 MA was achieved at T, which corresponded to . The impact of the quality of wall coating on confinement was asserted. The longest energy confinement time (30 ms) was observed under the conditions of best boronization.