| S. Molloy, J. Frisch, L. Hendrickson, D. McCormick, J. May, M. Ross, T. Smith (SLAC), N. Baboi, O. Hensler, L. Petrosyan (DESY), N. Eddy, S. Nagaitsev, L. Piccolli, R. Rechenmacher, M. Wendt (FNAL), O. Napoly, R.C. Paparella, C. Simon (DAPNIA), K. Watanabe (KEK) |
Dipole modes have been shown to be successful diagnostics for the beam position in superconducting accelerating cavities at the Free Electron Laser in Hamburg (FLASH) facility at DESY. By help of downmixing electronics the signals from the two higher order mode (HOM) couplers mounted on each cavity are monitored. The calibration, based on sigular value decomposition, is more complicated than in standard position monitors. Position like signals based on this calibration are currently being programmed in the control system. A second setup based on directly digitizing the spectrum from the HOM couplers has been used for monitoring monopole modes. The beam phase with respect to the RF has been thus measured. The position calibration measurements and phase monitoring made at FLASH are presented. |
