Low RF loss DC conductive Ceramic for High Power Input Coupler Windows for SRF Cavities

Ceramic windows used in power couplers for superconducting cavities are prone to accumulate volume and surface charges. The electric field generated by charging builds up until it discharges, with the resultant arc damaging or destroying the window.Euclid has developed a new ceramic composition that exhibits low losses at high frequencies but is conductive at DC. This allows the charge to drain off rather than being accumulated in the material. We will synthesize ceramic samples with permittivities of 15-18 (Mg,Ti based), and of ~30 (Zn,Nb based) and figure of merit Q×f in the range of 30,000-60,000 GHz at 0.6 - 1.3 GHz frequency. We plan to test a robust electrode deposition technology for these ceramic samples. Electrical measurements at microwave and DC are also planned. Surface dc conductivity of ceramic will be increased with the magnetron sputtering (PVD) process. Commercial Applications and Other Benefits: New low-loss microwave ceramics with a small DC conductivity can eliminate the window charging problem in RF power couplers. Development of new ceramics with desired conductivity and low RF losses will significantly improve the operational reliability of power couplers in superconducting and normal conducting accelerators, and high power vacuum devices.