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.
DESY, Hamburg
Within the last decade the production and preparation of superconducting resonators became more and more stable at DESY. Two cycles for the final surface preparation, the final surface removal by electro polishing (EP) and the final surface removal by a short buffered chemical polishing (BCP flash) are the baseline of cavity surface preparation at DESY. Basing on the positive development overtime and in view of industrialization of the processes for the XFEL project, a proposal for a reduced number of work steps was presented on the SRF 2007 workshop in Beijing [1]. Two parallel preparation lines, the final EP and BCP flash line, are tested on 15 cavities, for each line since. The cavities were produced by two different suppliers and randomly distributed to the preparation lines. In addition two industrial suppliers started industrialized electro polishing facilities for the main surface removal by electro polishing (main EP.) We present the cavity test results for the two preparation cycles.
DESY, Hamburg
In 2007 a new High Pressure Rinsing (HPR) system was developed at DESY and is operational since 2008. Beside implementations of improvements on high pressure rinsing systems lay out, one goal of the design is to set up a prototype high pressure rinsing stand applicable in industry and in an industrial production line. After commissioning, the new high pressure rinsing stand became a standard hardware in use for the cavity preparation processes at DESY. We report on design specialities and experiences gained so far in more than 300 rinsing processes of about 2 hours length.
DESY, Hamburg
Henkel, Neustadt-Glewe
Electro-polishing has become one of the leading surface preparation processes to reach high gradients in superconducting cavities. For industrialization and for reproducible results in the electro-polishing process a study on acid quality control and quality management was launched under the scope of the European investigations under the CARE. First results of this acid management studies were presented at the TTC meeting 2006 and the JRI-SRF summary reports 2008. A second study with experimental results on the quality control methods proposed was launched where the different methods and instrumentations for acid quality control are studied in detail. We present the results of this following up investigations made on acid quality control for the electro-polishing mixture applied at DESY.