Abstract
Top-up injection is an essential ingredient for the future circular lepton collider (FCC-ee) to maximize the integrated luminosity and it determines the design performance. In ttbar operation mode, with a beam energy of 175 GeV, the design lifetime of ∼1 h is the shortest of the four anticipated operational modes, and the beam lifetime may be even shorter in actual operation. A highly robust top-up injection scheme is consequently imperative. Various top-up methods are investigated and a number of suitable schemes are considered in developing alternative designs for the injection straight section of the collider ring. For the first time, we consider multipole-kicker off-energy injection, for minimizing detector background in top-up operation, and the use of a thin wire septum in a lepton storage ring, for maximizing the luminosity.
Highlights
The future circular lepton collider (FCC-ee) is conceived as a double ring storing electron and positron beams
The design lifetime is shortest in the ttbar operation mode, ∼1 h, and it may be even shorter in actual operation, e.g., due to beam–beam effects
We investigated various top-up injection schemes listed in Table 2 and concluded that both conventional injection and multipole-kicker injection are suitable for FCC-ee
Summary
The FCC-ee is conceived as a double ring storing electron and positron beams. The two beams collide with a crossing angle at two (or four) interaction points, where the physics detectors are installed. Four operation modes are planned, and the stored beam energy is varied from 45.6 GeV (Z pole) to 175 GeV (ttbar threshold). The collider ring is under active study, and recent design parameters are found in Ref. Beam particles are continuously lost due to radiative Bhabha scattering in the collision. The design lifetime is shortest in the ttbar operation mode, ∼1 h, and it may be even shorter in actual operation, e.g., due to beam–beam effects. Top-up injection is essential to maximize the integrated luminosity, and at the same time, it is of importance to establish a highly robust injection scheme because of the necessary frequent topping up
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