Recent Development of Transmission Systems for ECRH in the GAMMA 10 Tandem Mirror

In the tandem mirror GAMMA 10, a 500 kW gyrotron was newly equipped in the central-cell ECRH system, following the plug ECRH systems. Then, the transmission system for the central-cell ECRH, including a taper, mirrors and a polarizer, has been designed correspondingly. The guidelines to design the transmission system are to make the beam cross section axisymmetrical on the resonance surface with a high power transmission rate and high heating efficiency. According to the guidelines, mirrors in the launcher systems have been designed with our electromagnetic code. Controlling polarization of the incident microwave is achieved with a polarizer for raising heating efficiency.