Radial electrostatic flux inferred from core measurements of potential and density fluctuations

Abstract

Broadband potential fluctuations and electrostatic fluctuation induced particle flux have been measured in the core of a medium size tokamak plasma for the first time. Density fluctuations and wave numbers were simultaneously measured. Measurements indicate that radial electrostatic fluctuation induced particle flux in the core region, at the normalized radii of 0.17<ρ<0.38, due to modes with wave numbers less than 4 cm−1 is small in magnitude, is likely directed inward, and cannot account for particle flux predicted by the continuity equation and particle source codes. Estimates of electrostatic energy flux are also significantly less than values predicted via power balance analysis. Asymmetries in coherent density and potential fluctuation levels on closed flux surfaces are evident. Relative fluctuation levels ñ/n and φ̃ tend to increase with radius, and the fluctuations are Boltzmann-like in the region 0.17⩽ρ⩽0.38. The direction of mode propagation is in the electron diamagnetic drift direction. Corresponding phase velocities, vph∼3.5×105 cm/s, are similar to drift wave velocities.