Abstract:The LCLS hard x-ray Free Electron Laser at SLAC reported first lasing in April of 2009. Since then two successful user runs have been completed at the two soft x-ray stations. The first hard x-ray station has started commissioning in July of 2010. Beam diagnostics play an essential role for tuning the machine and delivering the requested beam properties to the users. An overview of the LCLS photon diagnostics will be presented including some selected commissioning results. Plans for future improvements and upgrades will be briefly discussed.

The Ramp Rate Limitation phenomena were studied using local field sensors to observe the intrinsic processes within the cable. Sensitive miniature Hall sensors and small pick-up coils placed around Cable-in-Conduit Conductor were used to measure local magnetic fields and field derivatives associated with currents in the cable. Using this method both fast jumps and slow changes in local magnetic fields at different conditions were observed. Fast jumps occured during ramping background magnetic field and may indicate a fast current redistribution processes. Slow changing of local fields may be associated with current loops closed through the current lead joints. Such current loops may also indicate the non-uniformity of current distribution in the cable strands. The new method is a promising tool for future investigations of stability of multistrand cables.

The Linac Coherent Light Source is an x-ray free-electron laser that recently demonstrated lasing in the 1.5-15 Å wavelength range. We report on luminescence measurements of a molecular nitrogen gas irradiated by ∼2  mJ, 80 fs x-ray pulses at energies of 0.83, 2.7, and 8.3 keV. These results provide a direct test of our current understanding of photoabsorption, electron dynamics, and fluorescence processes for such intense, ultrashort x-ray pulses. At 0.83 keV, the duration of the fluorescence signal depends strongly on space-charge effects. At 8.3 keV, space-charge effects are weak, and the signal duration is determined by the Auger electron dynamics.

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