Abstract
The Z-pole option of FCC-ee is an Ampere class machine with a beam current of 1.39 A. Due to high HOM power and strong HOM damping requirements, the present baseline of FCC-ee considers a single-cell cavity at 400 MHz. In this paper, different HOM damping schemes are compared for the Z-pole operating scenario with the aim of lowering the parasitic longitudinal and transverse impedance. The HOM power for each damping scheme is also calculated.
Highlights
The FCC-ee provides collisions in a wide beam energy spectrum, ranging from Z-pole (45.6 GeV) to tt (182.5 GeV)
In order to calculate the propagation of higher-order mode (HOM) power into the couplers, the power couplers (FPC), HOM couplers and beam pipes (BP) are terminated with ports accounting for multiple modes
The amount of power absorbed by the rectangular WG and quad-ridged WG (QRWG) is of the same order, but the QRWG has the advantage that it can efficiently damp the modes in the first dipole band at the cost of a more complicated geometry
Summary
The FCC-ee provides collisions in a wide beam energy spectrum, ranging from Z-pole (45.6 GeV) to tt (182.5 GeV). The present baseline of the FCC-ee considers a single-cell superconducting cavity for the Z-pole to mitigate the challenges created by the high beam current [1,2,3]. First, we design a single-cell cavity with a focus on its fundamental mode (FM) and higher-order mode (HOM) spectrum at the same time. In the HOM power calculation, usually the total power deposited into the cavity by the traversing beam is calculated. This does not specify the absorption of power by each HOM coupler. We use a spectral weighting method to approximate the amount of power that propagates into the HOM couplers
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