Mini-Workshop on Commissioning of
X-Ray Free-Electron Lasers
April 18-22, 2005, DESY Zeuthen, Germany

Work Package 2: Linac Commissioning

1. Layout a detailed plan for the initial set up of the proper bunch compression parameters, including method for precise setting of RF phases, beam energy, and chicane strengths, and back this plan up with realistic simulations starting from a very scrambled initial parameter set. Indicate what measurements are needed, how they are performed, their required resolutions, and what correction 'knobs' are adjusted in order to produce the final desired peak current and energy spread.
2. Simulate the measurement of projected, and or time-sliced emittances starting with x-y beam images. Measured and simulated images are provided from three sources:

   Measured x-y images from TTF-II at DESY. Simulated x-y 3-screen images from LCLS at SLAC. Simulated x-y streaked images from LCLS BC1 at SLAC.

   The first case (TTF-II data) is a set of 4 screens just beyond the BC2 (1st) chicane taken in various conditions of beam quality. The second case (LCLS 3-screen data) is a simuation with three screens in a drift just after the BC1 (1st) chicane. The last case (LCLS streaked image) is a simulation taken on one screen in the center of the BC1 chicane, where the horizontal beam profile is streaked in time due to the chirped energy spread. This streak is used to time-slice the vertical profiles and therefore reconstruct the vertical slice emittance. Seven images are provided, each taken with a different upstream quadrupole setting (quad-scan). In each of the above cases a 'descriptions' file details the layout so that the participants can reconstruct the emittance, or slice-emittance, using their favorite method.
3. The study will focus on three issues: 1) converting the image to an rms beam size value, 2) using the rms values to predict the projected emittance and Twiss parameters, and possibly 3) using the time steak to calculate the time-sliced values of all parameters.
4. Describe the method and provide supporting simulations for empirical emittance minimization and Twiss parameter matching in the accelerator. Emittance degradation should arise through magnet field errors, misaligned components inducing transverse wakefields and anomalous dispersion, and limited trajectory corrections. Identify what parameters are measured, how and where they are measured, what resolution is required, and what specific correction 'knobs' are available in each main area.