Neumann, A.; Anders, W.; Kugeler, O.; Knobloch, J.: Analysis and active compensation of microphonics in continuous wave narrow-bandwidth superconducting cavities. Physical Review Accelerators and Beams 13 (2010), p. 082001/1-15
10.1103/PhysRevSTAB.13.082001
Abstract:
Many proposals for next generation light sources based on single pass free electron lasers or energy recovery linac facilities require a continuous wave (cw) driven superconducting linac. The effective beam loading in such machines is very small and in principle the cavities can be operated at a bandwidth of a few Hz and with less than a few kW of rf power. However, a power reserve is required to ensure field stability. A major error source is the mechanical microphonics detuning of the niobium cavities. To understand the influence of cavity detuning on longitudinal beam stability, a measurement program has been started at the horizontal cavity test facility HoBiCaT at HZB to study TESLA-type cavities. The microphonics detuning spectral content, peak detuning values, and the driving terms for these mechanical oscillations have been analyzed. In combination with the characterization of cw-adapted fast tuning systems based on the piezoelectric effect this information has been used to design a detuning compensation algorithm. It has been shown that a compensation factor between 2–7 is achievable, reducing the typical detuning of 2–3 Hz rms to below 0.5 Hz rms. These results were included in rf-control simulations of the cavities, and it was demonstrated that a phase stability below 0.02 can be achieved. DOI: 10.1103/PhysRevSTAB.13.082001 PACS numbers: 29.20.Ej, 07.10.Fq, 85.25.Am