Bridge coupler thermal/structural analysis and frequency shift studies for the coupled cavity linear accelerator of the Spallation Neutron Source

The Spallation Neutron Source (sns) is an accelerator-based neutron scattering research facility. The linear accelerator (linac) is the principal accelerating structure and divided into a room-temperature linac and a superconducting linac. The normal conducting linac system that consists of a Drift Tube Linac (DTL) and a Coupled Cavity Linac (CCL) is to be built by Los Alamos National Laboratory. The CCL structure is over 55 meters long. It accelerates H^- beam from 86.8 MeV to 185.6 MeV at operating frequency of 805 MHz. This side coupled cavity structure has 8 cells per segment, 12 segments per module, and 4 modules total. The bridge coupler with length of 2.5 βλis a three-cell structure and located between the segments and allows power flow through the module. The center cell of each bridge coupler is excited during normal operation. There is total 44 bridge couplers included 8 of them used as the RF feed locations. To obtain a uniform electromagnetic field and meet the resonant frequency shift, the RF induced heat must be removed. Thus, the thermal deformation and frequency shift studies are performed via numerical simulations in order to have an appropriate cooling design and predict the frequency shift under operation. The center cell of the bridge coupler also contains a slug tuner and a post tuner that used to provide bulk frequency adjustment and field intensity adjustment, so that produce the proper total field distribution in the module assembly. Thermal analyses and estimate of frequency-adjusted levels to help guide the cooling design are also proceeded