• 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.

• P. Pierini, S. Barbanotti, A. Bosotti, P.M. Michelato, L. Monaco, R. Paparella
  INFN/LASA, Segrate (MI)

Funding: Work partially supported by the FP6 EU programs EUROTRANS (Contract FI6KW-CT-2004-516520) and CARE/HIPPI (Contract RII3-CT-2003-506395).

The two TRASCO elliptical superconducting cavities for low energy (100-200 MeV) protons have been completed with equipping them with cold tuner and a magnetic shield internal to the helium tank. One of the two structures is now available for significative tests of Lorentz Force Detuning control of these low beta structures under pulsed conditions for future high intensity linac programs, as SPL or the ESS. The second structure will be integrated in a single cavity cryomodule under fabrication for the prototypical activities of the EUROTRANS program for nuclear waste trasmutation in accelerator driven systems.

• M.W. McGee
  Fermilab, Batavia
• R. Amirikas, M. Boehnert, C. Engling, D. Hoppe, K. Jensch, D. Kostin, C. Mueller, H. Remde, O. Sawlanski, J. Wojtkiewicz
  DESY, Hamburg
• S. Barbanotti, A. Bosotti, M. Fusetti, P.M. Michelato
  INFN/LASA, Segrate (MI)
• S. Berry, M. Dorlot, O. Napoly, C.G. Thomas-Madec
  CEA, Gif-sur-Yvette
• A. Bertolini
  Albert Einstein, Leibniz Universität, Hannover

With a view to the series production of one hundred, 12 m long XFEL 1.3 GHz cryomodules and their transportation from the assembly site at CEA Saclay (F) to the installation site at DESY Hamburg (D) a test transportation of a FLASH cryomodule has been performed, in the condition foreseen for the mass transportation. The present study examines the stresses induced on the module and verify the damping capabilities of the transport frame in order to minimize risk of damage to the most critical components. During the transportation, acceleration and vibration have been monitored as well as coupler antenna contacts and vacuum performances. This paper describes the analysis performed and compares those results to the data of a similar transportation study at Fermilab for the CM1 cryomodule.