Design and multiphysics analysis of a high power RF window for LHCD system of tokamaks

An RF window is used in microwave systems where it is required to isolate pressurized and ultra-high vacuum (UHV) regions of transmission lines. One area of application is in the plasma heating systems of the tokamak, in which several MW's of Continuous Wave (CW) RF power, is launched into the plasma. As the tokamak is in UHV environment and the transmission lines are pressurized to sustain high RF power, an RF window is required. This window has to withstand several MW's of RF power for longer durations with acceptable RF performance and without experiencing any physical deformity to maintain the pressure difference between both the sides. This paper presents the RF design of such a window. Further, its multiphysics analysis is carried out to determine its structural stability. Several ceramic materials were considered for the RF window design of which BeO exhibited the best results like low insertion loss (0.008 dB) and high return loss (44 dB) at the desired frequency of 3.7 GHz. The peak temperature rise in the window was 9.1°C for an input power of 500kW/CW. Cooling channels were employed with a flow rate of 120 lpm for efficient thermal management thereby limiting the overall thermal stress to 54 MPa.