3D structure of density fluctuations in the T-10 tokamak and new approach for current profile estimation

Abstract

The paper is focused on the new systematic measurements of the 3D spatial distributions of the amplitudes, the radial correlation lengths and the long-range correlations along the magnetic field lines for the different turbulence types. The density fluctuations were measured by the heterodyne correlation reflectometry (CR) using the plasma probing with ordinary mode. CR data was supported by recent experiments with the measurements of the perturbation properties using an heavy ion beam probe (HIBP). The new reflectometer antenna array in T-10 tokamak consists of sets of horns distributed at four places toroidally and poloidally over the torus. The experiments confirmed previously found strong poloidal asymmetry of the amplitude for the broadband (BB) and quasi-coherent (QC) fluctuations. It was found that amplitude of density fluctuations is uniform poloidally for the stochastic low frequency (SLF) fluctuations. The radial correlation were measured at four poloidal angles to reveal the poloidal dependence of the radial correlation length for the different fluctuation types. The significant decrease of the radial correlation lengths towards the high magnetic field side was observed for the QC and the SLF fluctuations. The long-range correlations along the field lines were measured by the reflectometers in two cross-sections separated by 1/4 of the torus. The reflectometers had the same probing frequency thus provide reflection from the same magnetic surface. The measurements were carried out at the low and the high field sides with two currents and two magnetic configurations with simultaneous reversal of the toroidal field and plasma current. The positions of the resonance radius were calculated also using 3D tracing of the magnetic field line and demonstrated good agreement with experiment ones. These results allow to propose the new approach for the current profile measurements in tokamaks.