Cryogenic Testing Of The 2.1 Ghz Five-Cell Superconducting Rf Cavity With A Photonic Band Gap Coupler Cell

We present results from cryogenic tests of the multi-cell superconducting radio frequency (SRF) cavity with a photonic band gap (PBG) coupler cell. Achieving high average beam currents is particularly desirable for future light sources and particle colliders based on SRF energy-recovery-linacs (ERLs). Beam current in ERLs is limited by the beam break-up instability, caused by parasitic higher order modes (HOMs) interacting with the beam in accelerating cavities. A PBG cell incorporated in an accelerating cavity can reduce the negative effect of HOMs by providing a frequency selective damping mechanism, thus allowing significantly higher beam currents. The multi-cell cavity was designed and fabricated of niobium. Two cryogenic (vertical) tests were conducted. The high unloaded Q-factor was demonstrated at a temperature of 4.2K at accelerating gradients up to 3 MV/m. The measured value of the unloaded Q-factor was 1.55 x 10(8), in agreement with prediction. Published by AIP Publishing.