Validation of global gyrokinetic simulations in stellarator configurations

In this paper, recent simulations carried out with the global gyrokinetic code EUTERPE in configurations of the TJ-II stellarator are presented. The simulations are compared with experimental measurements from the Doppler reflectometry (DR) system in dedicated experiments carried out in TJ-II. Electron-driven modes are found to be unstable in the plasma edge region in linear simulations. The range of unstable wavenumbers and the radial location of maximum instability found in simulations are consistent with the experimental density fluctuations spectra and their variation with the radius. A qualitative agreement is found between the poloidal propagation of unstable modes found in simulations and the perpendicular velocities measured by the DR system. No dependency of the power spectra with the bulk ion mass is observed in simulations or experimentally, which is consistent with the electron-driven modes found unstable in the simulations. Instabilities are localized toroidally and poloidally in the simulations, the location of maximum instability being affected by the rotational transform. A systematic difference is found between the density fluctuation spectra measured by the DR system at poloidally separated positions on the same flux-surface, which is also affected by the rotational transform. However, a discrepancy between the location of maximum fluctuations in simulations and experiments is found so far. (paper)