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. How the problem is being addressed: 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. What was done in Phase I: In Phase I, we synthesized ceramic material based on Mg,Ti oxides having a very low dielectric loss at microwave frequencies and exhibiting two orders (100 times) of magnitude increased conductivity. We developed a set of MgTi ceramic elements for high power 650 MHz RF coupler windows. In addition to the Phase I plan, we also carried out a beam-charging test of the developed ceramic. Excellent performance of the vacuum part of the 650 MHz high power couplers equipped with the MgTi based RF windows was demonstrated with the Multiphysics modeling.What will be done in Phase II: In Phase II of this project, 650 MHz high-power RF windows made of this new ceramic will be fabricated and tested at high power at BNL and FNAL. The MgTi-oxide based ceramic components with improved quality will be fabricated and characterized, the brazing technology will be developed, four high power 650 MHz RF windows will be manufactured and tested as a key component of the high power coupler.Applications and 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.