Krejcik, P. Bowden, G.B. Condamoor, S. Ding, Y. Dolgashev, V.A. Eichner, J.P. Franzi, M.A. Haase, A.A. Lewandowski, J.R. Maxwell, T.J. Tantawi, S.G. Wang, J.W. Xiao, L. Xu, C. JACoW Geneva, Switzerland 978-3-95450-177-9 10.18429/JACoW-IBIC2016-WEPG77 English 834-836 WEPG77 cavity klystron electron operation photon Contribution to a conference proceedings 2017 2017-02 http://dx.doi.org/10.18429/JACoW-IBIC2016-WEPG77 http://jacow.org/ibic2016/papers/wepg77.pdf The successful operation of the x-band transverse deflecting cavity (XTCAV) installed downstream of the LCLS undulator has been further enhanced by the recent addition of an RF pulse compression "SLED" cavity that doubles the temporal resolving power of this powerful diagnostic system for measurement of the longitudinal profile of both the electron bunch and the x-ray FEL pulse. RF pulse compression has allowed us to use the existing SLAC X-band klystron with nominal output power of 50 MW and extend the RF pulse length by a factor 4 to give us 4 times the peak power after compression. A new, innovative SLED cavity was designed and built at SLAC to operate efficiently at X-band*. The elegant design uses a small spherical cavity combined with a polarizing mode coupler hybrid. We will report on the installation, commissioning and beam measurements demonstrating the sub-femtosecond resolution of the XTCAV system.