(EX/P3-15) Plasma Heating by Neutral Beam Injection in the TUMAN-3M Tokamak

S.V. Lebedev1), L. G. Askinazi1), A. G. Barsukov2), F. V. Chernyshev1), V. E. Golant1), V. A. Kornev1), S. V. Krikunov1), V. V. Kuznetsov2), A. D. Melnik1), A. A. Panasenkov2), A. R. Polevoi2), D. V. Razumenko1), V. V. Rozhdestvensky1), A. I. Smirnov1), G. N. Tilinin2), A. S. Tukachinsky1), M. I. Vildjunas1), N. A. Zhubr1)
1) Ioffe Physico-Technical Institute, St Petersburg, Russian Federation
2) Nucllear Fusion Institute RRC “Kurchatov Institute”, Moscow, Russian Federation

Abstract.  Paper describes experiments on Neutral Beam Injection heating in the TUMAN-3M tokamak. A moderate ion heating was observed in the NBI experiments with the input power 330 kW. The central ion temperature Ti(0), measured by the Neutral Particle Analyzer, was increased from 180 to 350 eV in the shots performed in the nonboronized vessel. Although up to 70% of beam power was absorbed by electrons, the Te(0) increase was even smaller than the ion one. An essential increase was observed in the electron density. Thus, the major effect of NBI power absorption is the increase in the energy content due to the density increase rather than temperature rise. According to the diamagnetic measurements the increase in the perpendicular stored energy during NBI was up to factor of 2.5 as compared to the initial level. Measured energy confinement times are in good agreement with ITER98(y,2) scaling in the all regimes under consideration (ohmic H-mode, NBI H-mode: boronized/nonboronized). The SXR measurement has shown some peaking of j(r) in the co-injection NBI scenario. Seemingly, the peaking indicates appearance of noninductively driven current in the vicinity of magnetic axis. The fraction of driven current could be estimated as 10% of total plasma current, that agrees with the ASTRA transport simulation predictions. Clear peaking of the electron density profile n(r) was observed as well. Since central particle source from the NB is negligible the n(r) peaking could be attributed to Zeff(0) increase due to accumulation of impurities. Application of NB heating was found to effect MHD stability of the plasma. Practically all high density shots are terminated by disruptions, but shots with NBI were systematically longer than the ohmic ones in the similar vessel conditions. Although global stability was better in auxiliary heated shots, the level of MHD activity registered by high frequency magnetic probes was higher. Bursts of wide spectrum MHD oscillations were observed during NBI. The bursts strongly correlated with sawtooth crashes. In the experiments planned for the spring 2006 the effect of current drive by NBI will be further explored in counter-injection scenario. The increase in the input NBI power up to design value of 600 kW is planned as well.

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