High precision superconducting cavity diagnostics with higher order mode measurements

Stephen Molloy; Josef Frisch; Doug McCormick; Justin May; Marc Ross; Tonee Smith; Nicoleta Baboi; Olaf Hensler; Lyudvig Petrosyan; Olivier Napoly; Rita C. Paparella; Claire Simon; Nathan Eddy; Sergei Nagaitsev; Manfred Wendt

doi:10.1103/PhysRevSTAB.9.112802

High precision superconducting cavity diagnostics with higher order mode measurements

Stephen Molloy, Josef Frisch, Doug McCormick, Justin May, Marc Ross, Tonee Smith, Nicoleta Baboi, Olaf Hensler, Lyudvig Petrosyan, Olivier Napoly, Rita C. Paparella, Claire Simon, Nathan Eddy, Sergei Nagaitsev, Manfred Wendt

DOI 10.1103/PhysRevSTAB.9.112802 · Physical Review Special Topics - Accelerators and Beams

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Abstract

Experiments at the FLASH facility at DESY have demonstrated that the higher order modes induced in superconducting cavities can be used to provide a variety of beam and cavity diagnostics. The axes of the modes can be determined from the beam orbit that produces minimum power in the dipole HOM modes. The phase and amplitude of the dipole modes can be used to obtain high resolution beam position information, and the phase of the monopole modes to measure the beam phase relative to the accelerator rf. For most superconducting accelerators, the existing higher order mode couplers provide the necessary signals, and the downmix and digitizing electronics are straightforward, similar to those for a conventional beam position monitor.