Development of high performance passively cooled mirrors for ECH launchers

Fusion reactors and state-of-the-art tokamaks will operate at pulse lengths that require heat absorbing components to be designed for steady state operation. Electron Cyclotron Heating (ECH) power sources are approaching that goal as well. The reflecting mirrors for ECH launchers will therefore need to be designed for steady-state operation. There are still a number of ECH systems that do not operate at steady state, but at increasing pulse lengths and power levels. At these facilities, despite some advantages that would result from using actively cooled ECH launcher mirrors, operating costs and risks can be minimized by using passively cooled mirrors that are designed to be replaced with a minimum of difficulty. This paper describes the design of the most recent mirrors for the DIII-D ECH launchers. Electromagnetic and thermal stress analyses are presented, and the fatigue life of the mirrors is estimated. The costs and benefits of periodic replacement of mirrors, as compared to the use of steady-state actively cooled mirrors, are discussed.