Asp, E.

Goodman, T.P.

Sauter, O.

Turri, G.

Udintsev, V.S.

Infoscience - École polytechnique fédérale de Lausanne

Control of Global Plasma Oscillations in TCV  V.S. Udintsev, E. Asp, T.P. Goodman, O. Sauter, G. Turri and TCV Team  Association Euratom-Confédération Suisse, EPFL/SB/CRPP, Station 13,  CH-1015 Lausanne, Switzerland  In the Tokamak à Configuration Variable (TCV; R/a = 0.88 m/ 0.24 m, BT < 1.54 T), global plasma oscillations have been discovered in fully non-inductively driven plasmas featuring Electron Internal Transport Barriers (eITBs) with strong Electron Cyclotron Resonance Heating and Current Drive (ECRH/ECCD). This phenomenon is akin to the so-called Oscillatory, or O-regime, first observed in Lower Hybrid (LH) driven plasmas on Tore Supra [1]. In TCV, the O-regime is closely linked to the evolution of the mag-netohydrodynamic (MHD) modes in the reversed magnetic shear plasmas [2]. It is dem-onstrated that the O-regime can be effectively suppressed by ECCD-induced local cur-rent density perturbation or by adding an Ohmic current perturbation. In these experi-ments MHD activity is modified through current density profile tailoring rather than local deposition within an island. The suppression of the O-regime usually leads to im-proved energy confinement, which is characterized by exceeding the TCV L-mode scal-ing (the Rebut-Lallia-Watkins scaling), to obtain HRLW above 3.5. The detection of the MHD modes by various diagnostics (Electron Cyclotron Emission, soft X-ray, Mirnov coils etc) has aided in the correct identification of rational q-surfaces and in the under-standing their role in the evolution of the O-regime. The evolution of the safety factor during the O-regime has been studied by means of combined CQL3D/ASTRA simula-tions. High-frequency modes, most likely electron fishbones, and broadband tempera-ture fluctuations in plasmas with global oscillations have been observed by means of recently installed correlation ECE diagnostic [2]. Their influence on the confinement properties will be discussed in the paper.  [1] G. Giruzzi et al., Phys. Rev. Lett. 91, 135001 (2003) [2] V.S. Udintsev et al., Fusion Sci. Technol. 52, Special Issue (2007)    

Control of Global Plasma Oscillations in TCV

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Control of Global Plasma Oscillations in TCV

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Infoscience - École polytechnique fédérale de Lausanne