Numerical analyses of CVD diamond windows in high power microwave applications

Nuclear fusion reactors require electron cyclotron heating and current drive (EC H&CD) systems for plasma heating and stabilization. Chemical vapor deposition (CVD) polycrystalline diamond windows on both the torus and gyrotron sides of the reactors act as confinement and/or vacuum boundaries allowing the transmission of high-power microwave beams. For example, the beam power scenarios of 1.5 MW and 2 MW are the current targets considered respectively in Wendelstein 7-X and European DEMO fusion machines. In this work, with reference to both reactors, the numerical analyses required to verify the thermal and structural performance of the windows are discussed. Experimental measurements of loss tangent in diamond provided inputs for the numerical analyses. Sensitivity studies of the windows with respect to loss tangent and other parameters were also carried out to check the temperature reserve margins of the design.