• R. Paparella, A. Bosotti, C. Pagani, N. Panzeri
  INFN/LASA, Segrate (MI)
• C. Albrecht, R. Lange, L. Lilje
  DESY, Hamburg
• J. Knobloch, O. Kugeler, A. Neumann
  BESSY GmbH, Berlin

Cavity tuners are needed to precisely tune the narrow-band resonant frequency of superconducting cavities. The Blade Tuner presented is installed coaxially to the cavity and changes the resonator frequency by varying its length. Piezoceramic actuators add dynamic tuning capabilities, allowing fast compensation of main dynamic instabilities as Lorentz Forces, under pulsed operations, and microphonic noise. A prototype piezo Blade Tuner has been assembled on a TESLA cavity and extensively cold tested inside the horizontal cryostats CHECHIA (DESY) and HoBiCaT (BESSY). Then, as suggested by results, a few minor modifications have been implemented thus achieving the current Blade Tuner design. The introduction of thicker blades re-distributed along the circumference allows to increase its stiffness and fulfill European and American pressure vessel codes, while ensuring requested performances and cost. The paper will present the successful characterization tests performed on the prototype, the extensive mechanical analyses made to validate the final model and the results from qualification tests of first revised Blade Tuner produced, to be installed in the second module of ILCTA at FNAL.

• P. Pierini, A. Bosotti, N. Panzeri, D. Sertore
  INFN/LASA, Segrate (MI)
• H.T. Edwards, M.H. Foley, E.R. Harms, D.V. Mitchell
  Fermilab, Batavia
• J. Iversen, W. Singer, E. Vogel
  DESY, Hamburg

The third harmonic cavities that will be used at the injector stage in the XFEL to linearize the rf curvature distortions and minimize beam tails in the bunch compressor are based on the rf structures developed at FNAL for the DESY FLASH linac. The design and fabrication procedures have been modified in order to match the slightly different interfaces of XFEL linac modules and the procedures followed by the industrial production of the main (1.3 GHz) XFEL cavities. A revision of the helium vessel design has been required to match the layout of the cryomodule strings, and a lighter version of the tuner has been designed (derived from the 1.3 GHz ILC blade tuner activities). The main changes introduced in the design of the XFEL cavities and the preliminary experience of the fabrication of three industrially produced and processed third harmonic rf structures are described here.