Radial Distributions of Quasi-Coherent Mode in T-10 Ohmic and ECR-heated plasmas

One of the most important problems in magnetic confinement fusion is the anomalous level of the energy and particle losses caused by the plasma turbulence. It has been shown that, at the T-10 tokamak (R = 1.5 m, a = 0.3 m), the major contribution to the turbulent particle flux is given by the density oscillations in the 50-150 kHz frequency range corresponding to the Quasi-Coherent mode (QC-mode). In this study radial distributions of the QC-mode in the Ohmic and ECR-heated plasmas are presented (B0 = 2.2 T, Ipl = 230 kA, and ne ≈ 1·1019 m3, PECRH ≤ 2.2 MW). The measurements were carried out in the wide radial range 0.3 < ρmeas. < 1 using Heavy Ion Beam Probe (HIBP) diagnostic which is capable of detecting mid-scale (kpol < 3 cm-1) plasma potential and density fluctuations. The most pronounced changes of QC-mode during ECRH appear in the core plasma region with ρ < 0.5. ECR heating causes the gradual decrease of the QC-mode frequency from f = 90±50 kHz in the OH stage to f = 20±10 kHz in the 2.2 MW ECRH stage. The direction of the QC-mode poloidal rotation remains the same during both Ohmic and ECR-heated stages despite the radial electric field change from Er = -80 V/cm in the OH stage to Er = +20 V/cm in the ECRH stage.