DESY, Hamburg
INFN/LASA, Segrate (MI)
BESSY GmbH, Berlin
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.
DESY, Hamburg
Diamond, Oxfordshire
DESY Zeuthen, Zeuthen
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.
DESY, Hamburg
Uni HH, Hamburg
The free-electron laser user facility FLASH at DESY, Germany is the world-wide leading SASE-FEL operating in the VUV and the soft X-ray wavelengths range. At present, FLASH provides fully coherent femtosecond laser radiation from 47 nm down to 6.5 nm and higher harmonics. Late 2009, FLASH will be upgraded with an additional superconducting TESLA type accelerating module boosting its beam energy to 1.2 GeV. This will allow lasing with a wavelength below 5 nm. In addition, a 3rd harmonic accelerating cavity will be installed. It allows to flatten and to a certain extend shape the longitudinal phase space improving the overall performance of the facility.
DESY, Hamburg
ANL, Argonne
Fermilab, Batavia
KEK, Ibaraki
Funding: Work at Argonne supported by U.S. Department of Energy, Office of Science, office of Basic Energy, Sciences, under Contract No. DE-AC02-06CH11357
XFEL and ILC both intend to accelerate long beam pulses of a few thousand bunches and high average current. It is expected that the superconducting accelerating cavities will eventually be operated close to their respective gradient limits as they are pushed to higher energies. In addition, a relative energy stability of <10-4 must be maintained across all bunches. These parameters will ultimately push the limits of several sub systems including the low-level rf control, which must properly compensate for the heavy beam loading while avoiding problems from running the cavities close to their quench limits. An international collaboration led by DESY has begun a program of study to demonstrate such ILC-like conditions at FLASH, which serves as a prototype for both XFEL and ILC. The objective is to achieve reliable operation with pulses of 2400 3-nC bunches spaced by 330 ns (a current of 9 mA) while meeting the required energy stability and while operating accelerating cavities close to their quench limits. Other goals include measurement of cryoload from HOM heating and evaluation of rf power overhead for the ILC. The paper will describe the program and report recent results.
DESY Zeuthen, Zeuthen
DESY, Hamburg
MBI, Berlin
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
DESY, Hamburg
The free-electron laser facility FLASH at DESY, Germany is the world-wide unique SASE-FEL operating in the VUV and the soft X-ray wavelengths range. Since Summer 2005, FLASH operates as a user facility providing fully coherent 10 to 50 femtosecond long laser radiation in the wavelength range from 47 nm to 6.5 nm and with an unprecedented brilliance - many orders of magnitude higher than any other facility. The SASE radiation contains also higher harmonics. Several experiments have successfully used the third and fifth harmonics, in the latter case with a wavelength down to 1.59 nm. In addition, FLASH serves as a pilot facility for the European XFEL. Part of the beam time is reserved for general accelerator studies which also includes ILC related studies.
