Investigations of Beam Characteristics in High-Power Millimeter-Wave Transmission Line for ECRH System

The millimeter-wave beam characteristics in the oversized circular corrugated waveguides transmission lines (TLs), approximately 40 m, for electron cyclotron resonance heating (ECRH) system on HL-3 tokamak were studied. The irradiance moments were calculated and the phase retrieval, also mode analysis was finished according to the wave amplitude profiles obtained by taking temperature using an infrared (IR) camera on paper target placed in front of the waveguide outlet. As results, the wave beam is radiated from the waveguide aperture with about 0.44° and less than 0.05° tilt angles inx-andy-directions, and expanses faster than LP01mode, and the phase profile is inclined along thex-axis and flat along the$y$-axis. The proportion of LP01mode is about 94%, and it is about 4.6% for the LP11(even) mode. All results agree well with the assumed theoretical calculations that 95% LP01mode and 5%${}_{\mathrm { }}$LP11(even) mode with relative phase$- 0.75\pi $in the waveguide, verifying their reliability. These results suggest that the wave beam coupling efficiency between waveguides and the initial coupling efficiency at matching output unit are important, and they are good enough for the experimental system.