Measurement and Modeling of Radiation Temperature Fluctuations in the HSX Stellarator

Download or read book Measurement and Modeling of Radiation Temperature Fluctuations in the HSX Stellarator written by Luquant Singh and published by . This book was released on 2024 with total page 0 pages. Available in PDF, EPUB and Kindle. Book excerpt: The Helically Symmetric Experiment (HSX) stellarator has been optimized for low neoclassical transport. Anomalous transport attributed to drift-wave turbulence remains an important loss channel. High-resolution plasma diagnostics can be used to study fluctuations in equilibrium plasma parameters, such as plasma density and temperature, which are sensitive quantities of the underlying turbulence. In this work, core radiation temperature fluctuations were measured in the HSX stellarator using a correlation electron cyclotron emission radiometer. The experimental measurements have been compared with gyrokinetic simulations of plasma turbulence. The HSX correlation electron cyclotron emission diagnostic measures radiation temperature fluctuations from second harmonic X-mode wave emission in optically semi-transparent plasmas. Multiple pass raytracing calculations indicate reinforcement of single pass emission on the high-field side of the magnetic axis, permitting localized measurements. Interpretation of radiation temperature fluctuations as electron temperature fluctuations is within reasonable uncertainty, based on modeling of density fluctuation effects. It is found that long-wavelength radiation temperature fluctuations increase with the inverse scale length of electron temperature. This is consistent with linear gyrokinetic simulations of trapped electron mode turbulence, which show enhanced dominant linear growth rates at higher inverse scale length of electron temperature, and nonlinear gyrokinetic simulations, which when coupled with a synthetic diagnostic, reproduce the experimental trend in fluctuation amplitude. A synthetic frequency spectrum derived from a simulation of the trapped electron mode is similar in shape to the experimental frequency spectrum. The experimental observations and gyrokinetic predictions indicate that electron-temperature-gradient-driven trapped electron modes are destabilized in the core of HSX plasmas. These results improve the understanding of core turbulence in an optimized stellarator and inform optimization strategies for future devices.