DESY, Hamburg
The structure, properties and welding parameters of Nb55%Ti -Ti and Nb55%Ti-Nb connection of cavities for XFEL are investigated. These are for example the welding connections of conical disc with helium tank rings (bellow unit and reduction ring) and of conical disc with reference ring. Several samples have been prepared using the electron beam welding equipment of DESY and Lufthansa Technik AG. The metallographic structure analysis, EDX, measurement of gas content, Vickers hardness HV, RRR and electrical resistance measurement have been done. Properties of the welding connection Nb55%Ti-Nb present mainly the bcc body-centered cubic ß-phase according the phase diagram of NbTi alloy. The HV changes rather uniformly, annealing at 1400°C does not lead to changes of the behaviour. The small maximum of the critical superconducting temperature Tc in agreement with the element distribution in the welding connection is observed. Properties of the welding connection Nb55%Ti-Ti present the mixture of the bcc ß-phase and the hexagonal α-phase. Maximum of the HV and increased hydrogen content in the welding connection was observed.
DESY, Hamburg
Super conducting resonators are cooled by liquid helium. For the application in accelerator modules most superconducting resonators are equipped with individual helium containers. During the welding of the helium tank to the super conducting resonator special care has to be taken not to change the resonator specific data like acceleration gradient, resonance frequency and the cell to cell distribution of the accelerating field. At DESY a tank welding process and an in situ field profile control system on the basis of the bead pull field profile measurements (FMS) is set up. We report on the experiences and results of the welding procedures and the application of the FMS at DESY.