Study of the phase difference between turbulent density and electrostatic potential fluctuations in the TJ-II stellarator

Minimizing turbulence in plasmas is necessary for good confinement in tokamaks and stellarators. To predict conductive and convective losses (transport), neoclassical models are used. These models neglect turbulence and disagree with experiments. However, when transport models that take into account the turbulent particle flux driven by out of phase fluctuations of the density and electrostatic potential, the disagreement between theory and experiment is reduced [see Thienpondt et al. 2023 Phys. Rev. Research 5 L022053]. In this work we experimentally study the phase difference between the density and electrostatic potential in the TJ-II stellarator with the heavy ion beam probe diagnostic and compare the observations with gyrokinetic simulations of particle transport.