ALIGNMENT MONITORS FOR AN X BAND ACCELERATING STRUCTURE

Currently an X band traveling wave accelerator structure is under development in a collaboration between CERN, PSI and ELETTRA. At PSI and ELETTRA, it will serve for longitudinal phase space compensation at the respec- tive FEL projects, where CERN will use it to test break down limits and rates in the high gradient regime. The de- sign employs a large iris, 5π/6 phase advance geometry, which minimizes transverse wake field effects while still retaining a good efficiency. In addition, we plan to use an active monitoring of the beam to structure alignment and to include two wake field monitors coupling to the trans- verse higher order modes. These allow steering the beam to the structure axis giving a higher precision than mechan- ical alignment strategies. Of special interest is the time do- main envelope of these monitor signals. Local offsets due to bends or tilts show up as distinct patterns, which should be easily detectable via basic measurements.