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(EX/P1-03) Role of Magnetic Flux Perturbations in Confinement Bifurcations in the TUMAN-3M

S.V. Lebedev1), M.V. Andreiko1), L.G. Askinazi1), V.E. Golant1), V.A. Kornev1), S.V. Krikunov1), G.T. Razdobarin1), V.A. Rozhansky2), V.V. Rozhdestvensky1), E.A. Shevkin1), A.I. Smirnov1), M. Tendler3), A.S. Tukachinsky1), M.I. Vildjunas1), S.P. Voskoboynikov2), N.A. Zhubr1)
1) Ioffe Physico-Technical Institute, St.-Petersburg, Russia
2) St.-Petersburg State Polytechnical University, St.-Petersburg, Russia
3) Alfven Laboratory, EURATOM-NFR Association, Stockholm, Sweden

Abstract.  Poloidal magnetic flux variations allowed observation of transitions between different confinement modes in the TUMAN-3M tokamak. The possibility of switching on/off the ohmic H-mode by edge poloidal magnetic flux perturbations has been found. The flux perturbations were created by fast current ramp up/down or by magnetic compression/decompression. Various mechanisms involved in the L-H and H-L transition physics in the flux perturbation experiments were analyzed. The transitions might be understood in the terms of a model of a sheared radial electric field generation. In a separate set of experiments the core electron confinement improvement was observed. Variation of the rates of current ramp up and working gas puffing in the beginning of a discharge resulted in a fast increase in the electron temperature near the axis. The confinement improvement is apparently connected with the rate of current ramp. Deviation from the optimal rate results in disappearance of the observed phenomenon. Possible explanation of the core electron confinement improvement is the formation of magnetic shear profile favourable for turbulence damping.

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IAEA 2003