Multi-field/multi-scale turbulence response to electron cyclotron heating of DIII-D ohmic plasmas

Abstract

The multi-field/multi-scale core (ρ ∼ 0.5–0.8) turbulence response to electron cyclotron heating (ECH) of DIII-D Ohmic plasmas is reported for the first time. Long wavelength (low-k) electron temperature (T̃e/Te) and high-k density turbulence levels (ñe/ne) are observed to strongly increase during ECH. In contrast, low-k and intermediate-k ñe/ne showed little change, whereas the cross-phase between local low-k electron temperature and density fluctuations (αneTe) was significantly modified. The increase in the electron thermal diffusivity determined from power balance is consistent with the increased turbulent transport correlated with the measured increases in low-k T̃e/Te and high-k ñe/ne. Linear stability analysis using the trapped gyro-Landau fluid (TGLF) model indicates an enhanced growth rate for electron modes [e.g., trapped electron mode (TEM)] at low-k consistent with the observed modifications in T̃e/Te and αneTe. TGLF also predicts an increase in high-k electron mode growth rates for normalized wavenumbers kθρs > 7, where electron temperature gradient (ETG) modes exist, which is consistent with the observed increase in high-kñe/ne turbulence