Speaker
Description
After successful tests of Cs2Te photocathodes at the SwissFEL Test Injector Facility (SITF) in 2014, decision was made to use these types of semiconductor photocathodes for SwissFEL operation, rather than copper. Since SwissFEL first beam in winter 2016, only two photocathodes were used. Quantum efficiency (QE) degradation of 40 % has been observed after 6 months of operation or after 15 mC of charge extraction in a 5.0e-10 mbar pressure environment and with 100 MV/m peak electric field. Bunch slice emittance is similar to what it was for copper cathodes. The slower response time of Cs2Te also helps to smooth out the noise ripple of the illuminating laser profile. However, it is still not clear how much it affects the microbunching instabilities at Swiss FEL. Even if Cs2Te is compatible with Swiss FEL operation, a new deposition chamber has been assembled to produce Cs3Sb coatings, capable of emitting electron bunches under illumination with green laser light. Indeed laser shaping (longitudinally and transversally) is easier in the visible wavelength range providing potential improvements in the electron beam quality. The lifetime in the lab of first samples were however still much too short.
