• A.S. Fisher, J.C. Frisch, R.H. Iverson, H. Loos, J.J. Welch
  SLAC, Menlo Park, California

By scanning the electron beam energy in LCLS, the sharp K-edge absorption energies in nickel and yttrium were exploited to measure spectral features of x rays from a single undulator section. We show measurements obtained using a Ni foil, with beam energy tuned to scan the first harmonic across the K-edge, and similar measurements obtained using the yttrium component of a YAG screen, with the beam tuned to match the third harmonic. These spectral features allow the precise determination of the position of central ray, and provide some measure of the undulator K parameter. A refinement of this method should allow precise matching of the K parameters of multiple undulator sections after their installation in March 2009.