Author: Baboi, N.
Paper Title Page
MOPWA055 Status of Higher Order Mode Beam Position Monitors in 3.9 GHz Superconducting Accelerating Cavities at FLASH 798
  • P. Zhang, R.M. Jones, I.R.R. Shinton
    UMAN, Manchester, United Kingdom
  • N. Baboi, P. Zhang
    DESY, Hamburg, Germany
  • T. Flisgen, U. van Rienen
    Rostock University, Faculty of Computer Science and Electrical Engineering, Rostock, Germany
  Funding: This work was partially funded by the European Commission under the FP7 Research Infrastructures grant agreement No.227579.
Higher order mode (HOM) beam position monitors (BPM) are being developed for the 3.9GHz third harmonic superconducting accelerating cavities at FLASH. The transverse beam position in a cavity can be determined utilizing beam-excited HOMs based on dipole components. The existing couplers used for HOM suppression provide the necessary signals. The diagnostics principle is similar to a cavity BPM, but requires no additional vacuum instruments on the linac. The challenges lie in the dense HOM spectrum arising from couplings of the majority HOMs amongst the four cavities in the cryo-module. HOMs with particularly promising diagnostics features were evaluated using various devices with various analysis methods. After careful theoretical and experimental assessment of HOMs, multi-cavity modes at ~5GHz were chosen to provide a global position over the complete module with superior resolution (~20μm) while trapped modes at ~9GHz provide local position in each cavity with comparable resolution (~50μm). A similar HOM-BPM system is planned for the European XFEL 3.9GHz module with 8 cavities. This paper reviews both the current status and the future prospects of HOM-BPMs in 3.9GHz cavities.