Plasma Potential and Turbulence Dynamics in Toroidal Devices: Survey of T-10 and TJ-II Experiments

Full text: The direct study of the electric potential and its fluctuations has been done for comparable plasma conditions in the T-10 tokamak (B =1.5 - 2.5 T, R =1.5 m, a =0.3 m, PECRH < 2.0 MW,) and TJ-II stellarator (B = 1T, (R) =1.5 m, (a) =0.22 m, PECRH < 0.6 MW, PNBI < 0.9 MW) by HIBP. In spite of the substantial differences in T-10 and TJ-II magnetic configurations, the electric potential fi has the following important similar features: (i) The scale of several hundred Volts; (ii) When ne > 1 x 1019m-3, the potential has negative sign and comparable values in spite of the different heating methods: OH and ECRH in T-10, ECRH and/or NBI in TJ-II; Er also has the same scale in both machines; (iii) The rise of ne or τE is accompanied by changes of φ and Er profiles towards the negative side. ECRH and associated Te rise and τE degradation cause the changes of φ and Er towards the positive side; (iv) Finally, negative φ and Er characterize the regimes with better confinement. In addition, Geodesic Acoustic Modes (GAM) in T-10 and Alfven Eigenmodes (AE) in TJ-II exhibit dozens Volts potential oscillations and potential-density coherence. While GAMs modulate the high-frequency turbulence, AE contribution to the bulk plasma turbulent particle flux is small in comparison with the broadband turbulence flux. (author)