Geometric Optimization and Experimental Validation of the Redesigned ICRF Antenna on the J-TEXT Tokamak

The ion cyclotron range of frequency (ICRF) system on the J-TEXT tokamak was commissioned in 2024, and early operation showed that the original antenna provided relatively low coupling resistance in hydrogen plasmas. To explore possible improvements, a three-dimensional curved antenna–plasma coupling model was developed and used to carry out a systematic parametric study of key geometric parameters within the practical constraints of the J-TEXT ICRF port. The modeling results reveal clear geometric trends that guided the development of a redesigned antenna configuration, which was subsequently fabricated and installed on J-TEXT. Coupling experiments with the redesigned antenna were performed in hydrogen plasmas under limiter operation. The measured coupling resistance spans a broader range of approximately 2–5 Ω, representing a systematic increase compared with the 1–3 Ω typically obtained with the previous antenna. For most operating phases, the calculated coupling resistance based on density profiles reconstructed from line-integrated polarimetry shows reasonable agreement with the experimental measurements. In addition, both experimental and simulated results exhibit an approximately exponential dependence of the coupling resistance on the parameter x c , defined as the distance between the strap front and the fast-wave cutoff layer.