Alfvén-wave character oscillations in tokamak COMPASS plasma T. Markoviˇ c 1,2 , J. Seidl 1 , A. Melnikov 3,4 , P. Hᡠcek 1,2 , J. Havlicek 1,2 , A. Havránek 1,5 , M. Hron 1 , O. Hronova 1 . M. Imríšek 1,2 , F. Janky 1 , K. Kovaˇrík 1,2 , O. Mikulín 1 , R. Pánek 1 , R. Papˇrok 1,2 , J. Pipek 1 , P. Vondrᡠcek 1,2 , V. Weinzettl 1 1 Institute of Plasma Physics CAS, Prague, Czech Republic 2 Faculty of Mathematics and Physics, Charles University in Prague, Prague, Czech Republic 3 National Research Centre ’Kurchatov Institute’, Moscow, Russian Federation 4 National Research Nuclear University MEPhI, Moscow, Russian Federation 5 Faculty of Electrical Engineering, Czech Technical University in Prague, Prague, Czech Republic In magnetic confinement fusion devices, high-energy particles originating e.g. from auxiliary- heating systems can drive instabilities by channeling the free energy (typically pressure gra- dients) to otherwise stable plasma eigenmode via resonance of particle velocity with plasma Alfvén velocity [1]. Consequently, the confinement of these particles is degraded by their in- teraction with the resulting shear Alfvén waves. Toroidal Alfvén Eigenmodes (TAE), caused by an interference of two counter-propagating Alfvén continuum waves [2], are of the most concern due to their low damping rate. In the recent work from the COMPASS tokamak [3], observations of possible TAE and BAE (Beta-induced Alfvén Eigenmodes) in H-mode plasmas in the spectral range of 50-250 kHz were reported. The present work introduces further observa- tions of plasma fluctuations in the spectral range of 150-2500 kHz in both L-mode and H-mode plasmas showing their Alfvén-wave character. Experimental arrangement The COMPASS tokamak is a device with an ITER-like plasma geometry, having major radius R 0 = 0.57 m and minor radius about 0.2 m. In discharges described in this work, plasma cur- rent was I p < 0.3 MA, toroidal magnetic field B 0 = 1.15 T and pulse duration Δt < 0.4 s. The tokamak is capable of H-mode plasma generation, either ohmic or NBI assisted (2 × 300 kW deuterium beams, energy up to 40 keV). It is also equipped with a Resonant Magnetic Pertur- bation (RMP) system of variable spatial configuration [4]. Plasma eigenmode fluctuations are detected by two sets of Mirnov Coils (MC, 24 coils each) located at different toroidal positions measuring poloidal magnetic field fluctuations across the whole poloidal cross section (specifi- cally, as coherence between two coils at the same poloidal position from different toroidal sets). Other detection coils are mounted on the U-probe manipulator [7] located in the bottom part of the chamber on Low-Field Side (LFS). The maximal detectable frequency is given by f Nyquist 42 nd EPS Conference on Plasma Physics P4.104