Abstract
We propose a method for numerical calculation of driving and detuning transverse beam coupling impedances of an asymmetric cavity. The method relies on eigenmode simulations and can be viewed as an alternative to time domain wakefield simulations. A similar procedure is well-established for symmetric cavities, and this paper extends it to the case of an asymmetric cavity. The method is benchmarked with time-domain wakefield simulations and its practical implementation is discussed.
Highlights
The interaction of the particle beam with its surrounding is a source of coherent beam instabilities that may limit the performance of the machine
We developed a method to separately compute the driving and the detuning geometrical transverse impedances of an asymmetric cavity
For practical implementation of the method, we investigated how numerical noise in the input eigenmode data affects the end results
Summary
The interaction of the particle beam with its surrounding is a source of coherent beam instabilities that may limit the performance of the machine. This interaction can be described by the wake function WðtÞ in the time domain, or, alternatively, by the impedance function ZðωÞ in the frequency domain (t is the time and ω is the angular frequency). The total transverse impedance ZxðωÞ (measured in Ω) is a function of both the driving charge offset ðxd; ydÞ and the trailing charge offset ðxt; ytÞ, with y being the second transverse coordinate. The expansion of the total impedance around a point of interest ðx0; y0Þ can be written as
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