Comparison of 3-D Modeling With Experimental Results on Fast Wave Antenna Loading in DIII-D

In DIII-D and other tokamaks, with a fixed system voltage limit, the parameter that limits the ICRF power that can be coupled to H-mode plasmas is the antenna loading resistance $R_L$. For a fixed antenna geometry and excitation (phasing), $R_L$ is determined by the electron density profile in the antenna near-field region. Quantitative understanding of the coupling physics is obtained by comparing the resistive ($R_L$) and reactive components of the antenna loading, without and with plasma, to predictions of 3-D models of the antenna and the edge plasma (Microwave Studio and TOPICA). When measured density profiles from reflectometers are used, good agreement between predicted and measured values of $R_L$ is obtained without any adjustable parameters in the model. The improved understanding is applied to enhancement of $R_L$ in advanced scenarios in DIII-D to increase the coupled fast wave power.