The design of the 28 GHz transmission line for the EBW heating system in the TJ-II stellarator

A first harmonic electron Bernstein waves heating system is being designed to heat a dense plasma in the TJ-II stellarator. The design of the quasi-optical components and the oversized corrugated waveguide of the transmission line (28 GHz, 300 kW, 100 ms) is presented. After the gyrotron two elliptical mirrors and two polarisers conform the Gaussian beam to match into the oversized waveguide. The beam is launched into the plasma by a steerable internal mirror. The expected losses are around 9%.