Experimental and Analytical Study of Heating in RF Accelerator Windows

Radio Frequency (RF) windows are one of the most likely places for a failure to occur in input power couplers for accelerators. In order to gain a better understanding of the failure mechanism of RF windows, bulk heating from electric fields in the window was examined both experimentally and analytically. Experiments were performed to measure the heating in the RF window using an infrared imaging camera. The tests used varying duty factors, from 0.2% to 0.6%, and varying average power, from 600 Watts to 6000 Watts. An analytical model was built to predict the temperatures of the RF window. The electromagnetic solution was obtained using an electromagnetic finite element code called High Frequency Structure Simulator (HFSS). A FORTRAN program was developed as a translator between the electromagnetic code and the thermal code, and then ABAQUS, a finite element thermal structural code, was used to determine the temperatures of the RF window. The experimental temperature increase vs. power was correlated with the analytical results. The experimentally observed heating was greater than the predictions of the analytical model.