Core Electron Temperature Fluctuation Measurements via CECE in the HSX Stellarator

A 16-channel radial correlation electron cyclotron emission (CECE) radiometer is used to study core (ρ < 0.5) electron temperature fluctuations in the Helically Symmetric Experiment (HSX) stellarator. Fluctuation amplitudes on the high field side and outside the region near the magnetic axis generally increase with increasing ECRH power. Near the magnetic axis (ρ < 0.1), fluctuation amplitudes are below the radiometer noise floor (δT/T < 0.1%), consistent with low gradient drive and dominant core neoclassical transport. An extended radial structure is identified in the high electron temperature gradient region for on-axis ECRH discharges. A comparison of temperature fluctuation amplitude and spectra from CECE with experimentally relevant nonlinear GENE simulations will be presented.