OPTIMIZATION OF THE SRF CAVITY DESIGN FOR THE CEBAF 12 GEV UPGRADE

Abstract

Based on initial testing of the “HG” and “LL” 7-cell cavities in the prototype cryomodule Renascence, several opportunities for improved optimization were identified. The HOM damping configuration was refined so as to meet the requirements for damping key dipole modes while simultaneously dramatically reducing risk of HOM pickup probe heating and also creating beamline clearance for mounting the tuner to stainless steel helium vessel endplates (rather than NbTi/Ti transitions to a titanium helium vessel). Code modeling and bench measurements were performed. The new design maintains the 7-cell LL cells and incorporates a brazed transition between Nb and the SS helium vessel. The resulting configuration is now called the “C100” design. Cavity design details as well as vertical dewar and horizontal test bed performance are presented.