The recent advances in radiofrequency (RF) heating have led to the use of substantial amounts of RF power for startup and heating. The RF heating system requires a number of ceramics for coaxial feedthrough insulation, antenna radomes, windows, and ceramic-filled waveguides. These dielectric materials should maintain electrical and structural integrity in a severe radiation and thermal environment. It is becoming more evident that the ceramic materials could be the weak point in the performance of the RF system, unless they are properly chosen.