• 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.

• M. Krasilnikov, G. Asova, J.W. Bähr, C.H. Boulware, U. Gensch, H.-J. Grabosch, L. Hakobyan, M. Hänel, Ye. Ivanisenko, M.A. Khojoyan, M. Otevrel, B. Petrosyan, S. Riemann, S. Rimjaem, J. Rönsch-Schulenburg, A. Shapovalov, R. Spesyvtsev, L. Staykov, F. Stephan, G. Vashchenko
  DESY Zeuthen, Zeuthen
• K. Flöttmann, S. Lederer, S. Schreiber
  DESY, Hamburg
• G. Klemz, I. Will
  MBI, Berlin
• D. Richter
  BESSY GmbH, Berlin

The Photo Injector Test facility at DESY, Zeuthen site, (PITZ*) aims to develop and optimize electron sources for frontiers linac based FELs such as FLASH and the European XFEL. A new laser system has been commissioned at PITZ in autumn 2008. It is capable to deliver laser pulses with challenging temporal shape: a flat-top profile with ~20 ps FWHM and rise and fall times of ≤2 ps. This laser system, being a significant step towards the European XFEL photo injector specifications, has been used in a 1.6-cell L-band rf gun with ~60MV/m electric field at the cathode to produce high brightness electron beams. A major part of the PITZ measurement program is the optimizing of the transverse phase space. Recent electron beam measurements at PITZ will be presented.

*for the PITZ team