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

Ceramic RF 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. A new MgTi-oxide ceramic with loss tangent in the 10-5 range and conductivity 2-3 orders of magnitude larger than traditional ceramics at room temperature was developed. A beam charging test of both conductive and non-conductive MgTi-oxide was performed. A box furnace with tightly controlled gas mixtures and flows was installed and commissioned at Euclid Techlabs for window production. Windows made of this conductive ceramic were fabricated for use in 1.5 GHz and 650 MHz RF couplers at JLab and FNAL. Fabrication of four RF couplers (two for JLab and two for FNAL) has commenced. 1.5 GHz and 650 MHz RF couplers made of this new ceramic will be tested at high power at JLab and FNAL. Multiple couplers at each lab will be tested to determine the maximum safe operating conditions. Additional couplers will be fabricated to accommodate this. The window production and coupler brazing process will be formalized, leveraging Euclid’s furnace commissioned during Phase II. Prototypes of RF coupler windows for the EIC at JLab and LHC at CERN will be designed, produced and tested. This technology will be applied to normal conducting cavity couplers for wider use in industry. 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.