Design of the Upgraded TJ-II Quasi-optical Transmission Line

TJ-II plasma start-up and heating are made by electron cyclotron resonance waves at the second harmonic of the electron cyclotron frequency. Two quasi-optical transmission lines transmit the microwave power of the gyrotrons to the vacuum vessel. The first line launches the microwave power under fixed injection geometry, i.e. there is no possibility to change the launching angle and the wave polarization. The second line has a moveable mirror installed inside the TJ-II vessel. To get high absorption efficiency and a narrow energy deposition profile the internal mirror focuses the wave beam at plasma center.To get more flexibility in the experiments on heating and current drive the first transmission line needs to be upgraded. The design is presented in this paper. The new launching antenna includes an internal mirror to focus the beam and to change the injection angle. Both launchers are then symmetrical. A polarizer consisting of two corrugated mirrors is used to get any wave polarization. Two mirrors with an array of coupling holes and calorimetric measurements of the energy absorbed in the barrier window allow the estimation of the microwave power launched into the TJ-II.