• S. Lederer, S. Schreiber
  DESY, Hamburg
• P.M. Michelato, L. Monaco, C. Pagani, D. Sertore
  INFN/LASA, Segrate (MI)
• R. Ovsyannikov, M. Sperling, A. Vollmer
  BESSY GmbH, Berlin
• F. Stephan
  DESY Zeuthen, Zeuthen

Caesium telluride (Cs2Te) photocathodes are used as sources for electron beams because of their high quantum efficiency (QE) and their ability to release high peak current electron bunches in a high gradient RF-gun. A rapid unexpected decrease of the initial QE, from 10% to values below 0.5% in only a few weeks of operation, was observed. In XPS measurements we identify a peak of Fluorine possibly originating from Teflon. After identification and removal of this specific contaminant, the life time of the cathodes increased to several months. In addition we have investigated the response of fully functional photocathodes to extensive usage, bad vacuum conditions, and oxidation by means of XPS measurements. The experiments - carried out at the ISISS and the PM3 beam lines at the synchrotron facility BESSY – compare the chemical composition and electronic structure of freshly prepared, contaminated, used, and oxidised Cs2Te cathodes.

• S. Lederer, S. Schreiber
  DESY, Hamburg
• J.H. Han
  Diamond, Oxfordshire
• M. Hänel, F. Stephan
  DESY Zeuthen, Zeuthen
• P.M. Michelato, L. Monaco, C. Pagani, D. Sertore
  INFN/LASA, Segrate (MI)

Caesium telluride photocathodes are used as laser driven electron sources at FLASH and PITZ. FLASH is operated as user facility as well as for accelerator related studies and therefore has a constant and moderate usage of the cathodes. In contrary, PITZ is an injector R&D facility with a stronger usage of cathodes including gradients in the RF-gun of up to 60 MV/m. In the past, one concern of operating RF-guns with Cs2Te cathodes was the degradation of the quantum efficiency in a few weeks at FLASH and a couple of days at PITZ. Improved vacuum conditions and removing contaminants in both accelerators yielded an increased life time of several months. In this contribution we report on routinely performed QE measurements, investigations on the homogeneity of the electron emission, and dark current issues for both facilities.

• L. Monaco, P.M. Michelato, C. Pagani, D. Sertore
  INFN/LASA, Segrate (MI)

Funding: This work has partly been supported by the European Community, Contract Number RII3-CT-2004-506008.

Since ‘90s our laboratory is in charge of producing Cs2Te photocathodes employed as laser driven electron sources in the high brightness photoinjectors of the FLASH and PITZ facilities. The production recipe has been developed and standardized during years, fulfilling the requests for photocathode operation in the photoinjectors. Nevertheless, the growing process of the film is still not totally understood, mainly respect to the final material properties. In this paper, reflectivity and spectral response measurements, at different wavelengths, measured during the photocathode growth are presented and compared with the corresponding photocurrent behavior. The new information, together with results obtained with standard diagnostic tools, will help to improve the understanding of the growing process, of the compounds formation with different Cs/Te ratio and of the reproducibility of the Cs2Te film structure.

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

An extensive validation activity has been conducted since year 2007 for the coaxial Blade Tuner for TESLA SC cavities. During this activity, performances and limits of prototype models have been deeply investigated through detailed test sessions inside CHECHIA (DESY) and HoBiCaT (BESSY) horizontal cryostats as well as F.E. modeling and analyses. The result is an improved design for the Blade Tuner, specifically meant to satisfy the incoming ILC-level performance requirements, fulfill pressure vessels regulations and keep Ti / S.S. material compatibility. Recent Blade Tuner activities and results will be presented in this paper in view of the installation of 8 units in the second cryomodule of ILCTA facility at Fermilab, and also of our contribution to both incoming S1-Global (KEK) and ILC-HiGrade projects. The manufacturing process of the first set of 8 tuners, from production to room temperature validation for the whole series, will be also reviewed. Then results will be shown from the cold tests recently performed, where special effort has been made in evaluating the accuracy and repeatability of fast and slow tuning action at few Hz range.

• N. Ohuchi, H. Hayano, N. Higashi, H. Nakai, K. Tsuchiya, A. Yamamoto
  KEK, Ibaraki
• T.T. Arkan, H. Carter, M.S. Champion, J. Grimm, J.S. Kerby, D.V. Mitchell, T.J. Peterson, M.C. Ross
  Fermilab, Batavia
• S. Barbanotti, C. Pagani, P. Pierini
  INFN/LASA, Segrate (MI)
• L. Lilje
  DESY, Hamburg

In an attempt at demonstrating an average field gradient of 31.5 MV/m as per the design accelerating gradient for ILC, a program called S1-Global is in progress as an international research collaboration among KEK, INFN, FNAL, DESY and SLAC. The S1-Global cryomodule will contain eight superconducting cavities from FNAL, DESY and KEK. The cryomodule will be constructed by joining two half-size cryomodules, each 6 m in length. The module containing four cavities from FNAL and DESY will be constructed by INFN. The design of this module is based on an improved 3rd generation TTF design. KEK will modify the 6-meter STF cryomodule to contain four KEK cavities. The designs of the cryomodules are ongoing between these laboratories, and the operation of the system is scheduled at the KEK-STF from June 2010. In this paper, the S1-Global cryomodule plan and the module design will be presented. ‘S1-Global collaboration’ as a co-author.