Author: Flisgen, T.
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.
WEPWO010 BERLinPro Seven-cell SRF Cavity Optimization and HOMs External Quality Factors Estimation 2331
  • T. Galek, K. Brackebusch, T. Flisgen, U. van Rienen
    Rostock University, Faculty of Computer Science and Electrical Engineering, Rostock, Germany
  • J. Knobloch, A. Neumann
    HZB, Berlin, Germany
  • B. Riemann, T. Weis
    DELTA, Dortmund, Germany
  Funding: Work funded by EU FP7 Research Infrastructure Grant No. 227579 and by German Federal Ministry of Research and Education, Project: 05K10HRC.
The main scope of this work is the optimization of the superconducting radio frequency (SRF) accelerating cavity design for the Berlin Energy Recovery Linac Project (BERLinPro)*. BERLinPro shall serve as a demonstrator for 100-mA-class ERLs with CW LINAC technology. High-current operation requires an effective damping of higher-order modes (HOMs) of the 1.3 GHz main-linac cavities. Consequently it is important, at the SRF cavity design optimization stage, to calculate the external quality factors of HOMs to avoid beam break up (BBU) instabilities. The optimization of the SRF cavity design consists of two steps. In the first step the cavities' end half-cells are tuned with respect to field flatness, effective shunt impedance and geometrical factor of the fundamental accelerating mode using robust eigenmode simulations. The second step involves frequency domain simulations and the extraction of external quality factors of HOMs from transmission S-parameter spectra using vector fitting procedure and an automated scheme to remove non-static poles **. The eigenmode,as well as the frequency domain simulations are performed using CST Microwave Studio ***.
* A. Neumann et al., Proc. of ICAP2012, pp. 278–280.
** T. Galek et al., Proc. of ICAP2012, pp. 152–154.
*** CST AG,