Nitrogen infusion R&D at DESY a case study on cavity cut-outs

A first series of nitrogen infusion runs of 1.3 GHz single-cell cavities at DESY resulted in an unexpected and severe deterioration observed during the vertical cold test. To investigate the origin of the deterioration, one of the cavities underwent extensive radio-frequency measurements and a temperature- and magnetic field-mapping was performed in collaboration with the Helmholtz-Zentrum Berlin. After combining all results, regions of interests were identified and cut-out of the cavity. Subsequent surface analysis techniques (EBSD, PALS, PIXE, SEM/EDX, SIMS, XPS) were applied in order to identify the microscopic origin of the deterioration and especially the differences between hot and cold spots as well as quench spots. An excess of niobium carbides, reducing the thermal conductivity, was identified as the probable cause for the deterioration, and the size- and density-distributions were observed to be crucial for the resulting performance reduction. The origin for the local differences in the niobium carbide formation between hot and cold spots is an effect of preexisting variations of the crystal structure.BMBF, 05H18GURB1, Verbundprojekt 05H2018 - R&D BESCHLEUNIGER (STenCiL): Optimierung der Hochfrequenzeigenschaften supraleitender Resonatoren durch Oberflächenbehandlun

Measurement Manual for OBACHT

OBACHT is an instrument developed for optical inspection of SRF cavities. This manual contains the description of a complete measurement cycle with OBACHT in section 2. The user shall be enabled to take pictures of welding seams at cavity equators and irides. In addition, beforehand needed cavity installation (cf. section 1) and calibration work (cf. section 2.3) is described as well as further information about the steering GUIs in section 3. Afterwards the safety components light tower and light curtain are shortly mentioned, while section 5 describes possible occurring errors and hopefully their elimination. The last part is only meant for experts and includes information for additional features of the system