Design of the electron cyclotron emission diagnostic on EXL-50 spherical torus

The electron cyclotron emission (ECE) diagnostic system has been developed on the ENN spherical torus (EXL-50). The ECE system is designed to detect radiation emitted by energetic electrons, rather than conventional 1D electron temperature profile measurement, in the frequency range of 4−40 GHz. The system is composed of five subsystems, each covering a different frequency band, including the C-band (4−8 GHz), X-band (8−12 GHz), Ku-band (12−18 GHz), K-band (18−26.5 GHz) and K\textα-band (26.4−40 GHz). The system uses heterodyne detection to analyze the received signals. The K-band and K \textα -band subsystems are located horizontally in the equatorial plane of the EXL-50, while the C-band, X-band and Ku-band subsystems are located under the vacuum vessel of the EXL-50. To direct the microwaves from the plasma to the antennas for the horizontal detection subsystems, a quasi-optical system has been developed. For the vertical detection subsystems, the antennas are directly attached to the port located beneath the torus at R = 700 mm, which is also the magnetic axis of the torus. The system integration, bench testing and initial experimental results will be thoroughly discussed, providing a comprehensive understanding of the ECE system’s performance and capabilities.