Predictive analysis of EC wave propagation and absorption in the ADITYA-U tokamak

This work presents a detailed investigation of Electron Cyclotron (EC) wave propagation and absorption in the ADITYA-U tokamak using the GENRAY ray-tracing code under conditions relevant to the 42 GHz Electron Cyclotron Resonance Heating (ECRH) system. The 42 GHz ECRH system, designed for plasma breakdown and heating at on-axis magnetic fields up to 1.4 T, is analyzed for its single-pass absorption (SPA) efficiency under various launching configurations. For O1 mode launched from the low-field side (LFS), the SPA is limited to ∼30% at a core density of 1 × 1019 m−3 and temperature of 500 eV for B0 = 1.4 T. In contrast, X2 mode launching from the LFS at B0 = 0.75 T yields ∼84% SPA. Complete EC wave absorption is obtained either with X1 mode launching from the high-field side or with X2 mode launching from the top at B0 = 1.4 and 0.75 T, respectively. Parametric density scans indicate that SPA is more effective at sub-cutoff densities with elevated electron temperatures above 1 keV. Furthermore, a shaped plasma configuration exhibits slightly improved absorption compared to limiter-based circular plasmas. GENRAY results are benchmarked against the GRAY beam-tracing code, providing validation for ADITYA-U experimental scenarios. In addition, a case study on EC wave propagation during ITER start-up conditions with a slightly reduced magnetic field is presented. These results offer significant insights for optimizing future ECRH experiments in ADITYA-U, enabling improved wave coupling and enhanced core electron heating.