• M. M. Dehler, A. Citterio, A. Falone, J.-Y. Raguin
  PSI, Villigen
• G. D'Auria, M.M. El-Ashmawy
  ELETTRA, Basovizza
• A. Grudiev, D. Gudkov, G. Riddone, A. Samoshkin, W. Wuensch, R. Zennaro
  CERN, Geneva

Currently a X band traveling wave accelerator structure is fabricated in a collaboration between CERN and PSI. It will compensate nonlinearities in the longitudinal phase space at the injector prototype of the PSI-XFEL, whereas CERN will use it to test break down limits and rates in the high gradient regime. Due to the modest beam energies, the operation in the PSI-XFEL injector is quite sensitive to transverse wakes destroying the beam emittance. In that respect, the structure will use an active monitoring of the beam to structure alignment and include two wake field monitors coupling to the transverse higher order modes. These allow steering the beam to the structure axis giving a higher precision than mechanical alignment strategies. Localized offsets due to bends or tilts have individual signatures in the frequency spectrum, which in turn are correlated with different delays in the signal envelope. By taking advantage of this combined with the single bunch mode at the PSI-XFEL, the use of a relatively simple detector type RF front end should be possible, which will not only show beam offsets, but also higher order misalignments as tilts in the structure.