Asp, E.

Coda, S.

Falchetto, G.

Goodman, T.P.

Llobet, X.

Madeira, T.I.

Marmillod, Ph.

Sauter, O.

Shidara, H.

Turco, F.

Turri, G.

Udintsev, V.S.

Weisen, H.

Infoscience - École polytechnique fédérale de Lausanne

Control of the Oscillatory Regime by Local Current Perturbation in ECCD Plasmas on TCVV.S. Udintsev, E. Asp, O. Sauter, H. Shidara, F. Turco1, G. Turri, S. Coda, G. Falchetto1, T.P. Goodman, X. Llobet, T.I. Madeira2, Ph. Marmillod, H. WeisenAssociation EURATOM-Confédération Suisse, CRPP/EPFL, CH-1015, Lausanne, Switzerland1Association EURATOM-CEA, DRFC/SCCP/CEA Cadarache, F-13108 France2Associação EURATOM-IST, Centro de Fusão Nuclear, P-1049-001, Lisboa, Portugal Introduction Global plasma oscillations (10 – 15 Hz; the O-regime) in fully non-inductive eITB discharges1 Reversed magnetic shear and MHD modes are key requirements for the O-regime to occur in TCV The O-regime can be suppressed by adding ECCD-driven localized current perturbation Transition from the ideal (infernal2) to the resistive(NTM-like) MHD can be demonstrated during the oscillation cycle Co-ECCD (1 MW) off-axis (w.r.t. total Ip direction which has negative sign for plasmas discussed here), Vloop ~ 0 Confinement improvement: HRLW up to 4 Oscillations: m/n = 0/0; MHD: m/n = 2/1 or 3/11Suppression of the O-regime by central ECRH/ECCD Co-ECCD/ECH on-axis: 0.25 MW constant; co-ECCD off-axis constant Cntr-ECCD/ECH on-axis: 0.25 MW constant; co-ECCD off-axis power ramp down (1 MW  0.75 MW)j(r) less hollow weaker barrier MHD remainsbut the O-regime suppressesBarrier strength preserves  q(r) rises  MHD mode stabilizes together with the O-regime at 1.7 s(marked as 4 on the plot)Transition to the infernal modeExcitation of the O-regime by modulated ECRHHigh-frequency modes in the O-regime Conclusions Effective suppression of the O-regime and recovering the barrierby local ECCD (with and without MHD stabilization) Transition from resistive to ideal MHD by influencing the strength of a barrier and, thus, the pressure profile Observation of high-frequency modes (more analysis ahead)References: 1V.S.Udintsev et al., FS&T 8, at press (2007); 2G. Zhuang, EPS, P2-143 (2004); 3P. Maget, Nucl. Fusion 46, 797 (2006)• Broadband fluctuations(correlation ECE): 30 – 200 kHz during full-power ECCD/ECH phases (see numbers in the figure above)• 35-37 kHz mode: possibly e-fishbone3?More ECH/cntr-ECCD inside eITB  HRLW rises  steeper pressure gradients  transition to the ideal (infernal) mode with q=3 crashes instead of oscillations (caused by NTM-like MHD) • Modulated ECH (10 Hz) 1.4 – 1.8 s); MHD mode follows modulation• After modulation stops, “natural” oscillations continue with the same frequencyE-fishbone: requires reversed q(r) and barely trapped fast electrons with 13 keV -> feasible for these plasmas1!

CONTROL OF THE OSCILLATORY REGIME BY LOCAL CURRENT PERTURBATION IN ECCD PLASMAS ON TCV

http://infoscience.epfl.ch/record/124626/files/075010602.pdf

CONTROL OF THE OSCILLATORY REGIME BY LOCAL CURRENT PERTURBATION IN ECCD PLASMAS ON TCV

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Infoscience - École polytechnique fédérale de Lausanne