Welding a Helium Vessel to a 1.3 GHz 9-Cell Nitrogen Doped Cavity at Fermilab for LCLS-II

Fermilab has developed a TIG welding procedure that is used attach a nitrogen doped 1.3 GHz 9-cell niobium (Nb) cavity to a titanium (Ti) helium vessel. These cavities will be used in the two prototype cryomodules for the Linac Coherent Light Source (LCLS-II) upgrade at SLAC National Accelerator Laboratory. Discussion in further detail will include setting up TIG welding parameters and tooling requirements for assembly and alignment of the cavity to the helium vessel. The weld designs and glovebox environment produce the best quality TIG welds that meet ASME Boiler and Pressure Vessel Code. The cavity temperature was monitored to assure the nitrogen doping is preserved, and RF measurements are taken throughout the process to monitor the cavity for excessive cell deformation due to heat loads from welding.