• W. Singer, S. Aderhold, J. Iversen, G. Kreps, L. Lilje, A. Matheisen, X. Singer, H. Weise
  DESY, Hamburg
• M. Pekeler, J.Sch. Schwellenbach
  ACCEL, Bergisch Gladbach
• F. Schoelz, B. Spaniol, E. Stiedl
  W.C. Heraeus GmbH, Materials Technology Dept., Hanau

A test program of 1.3 GHz TESLA shape 9-cell large grain (LG) resonators for the European XFEL project was started at DESY. The main aim is to find out whether or not the choice of LG material could be an option for the fabrication of approx. 800 XFEL resonators. Several aspects are under investigation and will be compared with the conventional polycrystalline material option. One of the aspects is the material issue: could the required amount of LG niobium be produced at industry in a cost effective and reliable manner? The second issue is the fabrication of cavities: could the series production of resonators be done on the level of required accuracy and costs? The third one is the performance issue: what is the appropriate treatment for reproducibly achieving the specified XFEL accelerating gradients? Development of the LG disc production was done within the framework of the R&D program of DESY and W. C. HERAEUS. Eleven resonators are produced at the company ACCEL. Up to now three resonators are RF-tested vertically. The He-vessel was welded onto one of the resonators which passed the horizontal RF-test. The data and perspectives of the LG cavity application are discussed.

• X. Singer, I. Jelezov, A. Matheisen, W. Singer
  DESY, Hamburg
• P. Kneisel
  JLAB, Newport News, Virginia

Technological aspects of seamless tube fabrication and multi-cell cavity production by hydroforming will be discussed. Problems related to the fabrication of seamless cavities from bulk niobium are mainly solved. Several two cell- and three cell- niobium cavities have been produced by hydroforming at DESY. A 9-cell cavity of the TESLA shape has been completed from three sub-sections at company ZANON. The cavity was treated by electropolishing (EP) and successfully RF-tested. Two 3-cell units equipped with niobium beam pipes are being RF-tested after BCP surface treatment. The temperature mapping method with Jlab’s two-cell thermometry system is applied for performance analysis. It is of particular interest to compare the seamless cavity quench locations to those from standard cavities. The cryogenic test results and the T-mapping findings will be discussed. Of special interest is the combination of the seamless technique with NbCu cladding, i.e. the fabrication of cavity from bimetallic clad NbCu tube by hydroforming. Fabrication of single-cell and multi-cell NbCu clad cavities by hydroforming from bimetallic tubes is proven. Some test results will be presented.