Design of dual-frequency transmission lines for the ECRH system on HL-2M

To carry out research related to electron cyclotron waves, 6 MW ECRH system including four 105 GHz/1 MW/2s and two 140 GHz/1 MW/3s units will be developed on the HL-2M tokamak being built in the first stage. Dual-frequency transmission lines with same components for the 105 GHz and 140 GHz systems are designed to make the fabrication easier. The corrugated waveguides are used to ensure the bandwidth of the transmission systems. In addition, the parameters of polarizers are specially considered to obtain the required polarizations at the two different frequencies. The transmission efficiency is analyzed with the multimode propagation model, and also the polarization characteristics of polarizers are calculated for the two different frequencies. The results indicate that both the transmission efficiency and the polarization characteristics can meet the requirements of ECRH system on HL-2M.