ECH Ray Propagation and Deposition in Under- and Over-Dense Plasmas on DIII-D

The electron cyclotron heating (ECH) deposition profile and location has been examined by modulating the power from a single gyrotron on the DIII-D tokamak. These measurements are compared to theoretical calculations from the TORAY-GA ray tracing code to check the deposition width in low density cases and refraction of EC waves out of the plasma in high density cases. In under-dense plasmas, the modulations in electron temperature measured by electron cyclotron emission (ECE) are fitted to the linearized energy conservation equation to find the best-fit transport coefficients and ECH source profile. If an anomalously wide ECH source profile is found, the reasons for this will be investigated. As the density is increased and the right-hand cutoff is approached, the ECE analysis will look for the expected shift in deposition location and a sudden drop in absorbed ECH power. In a novel experiment, an IR camera was used to image the carbon tiles in the outer wall to observe any heat deposition from unabsorbed EC waves after their first pass through the plasma. Modulation analysis of the IR camera data will compare the measured heat flux on the outer wall to TORAY-GA predictions.