Mirror development for the 140 GHz ECRH system of the stellarator W7-X

For the future stellarator W7-X in Greifswald, a powerful electron cyclotron resonance heating (ECRH) system at 140 GHz with a total RF power of 10 MW CW is under construction. The transmission of the radiation from the gyrotron hall to the machine will be realized via a fully optical system consisting of more than 160 water cooled mirrors. This paper describes the design of the mirrors and presents results of calculations of the thermo-mechanical properties. Experimental verification of the calculations showed that mirror deformation under application of a heat load equivalent to the absorbed power from a 1 MW mm-wave beam is in the tolerable range. Water cooled mirrors of the single-beam type have been used successfully during conditioning of a prototype gyrotron with a mm-wave power of 850 kW and a pulse length of up to 180 s. To test and optimize in-situ measurements of beam parameters and power of the CW ECRH system on W7-X, these mirrors are equipped with different diagnostics. (C) 2003 Elsevier Science B.V. All rights reserved.