Speaker
Description
Beam-induced backgrounds present critical challenges for high-luminosity e⁺e⁻ colliders such as SuperKEKB. Significant beam loss near the interaction point risks quenching superconducting magnets and limits luminosity. While narrow-gap collimators protect these magnets, their small apertures generate high inductive impedance and are vulnerable to beam damage, which further increases impedance. A nonlinear collimation scheme using skew-sextupoles was recently implemented at SuperKEKB, reducing impedance while maintaining collimation. However, this method has two drawbacks: (1) collimation uses only one side of collimator jaw, restricting the allowable beam current due to possible damage; (2) symmetric collimation of top and bottom beam halos requires a phase advance near π/2 between the first sextupole and the collimator, which is not optimal for collimation efficiency. In this paper, we propose a novel nonlinear collimation method based on anti-symmetric skew-sextupole fields, which effectively addresses both drawbacks. This approach collimates the top and bottom halos on different jaw sides, effectively doubling the tolerable beam current. Additionally, since the two halo sides are separately collimated, the phase advance between the first anti‑symmetric skew-sextupole and the collimator can be optimized to maximize collimation efficiency. Theoretical analysis and multi‑particle simulations confirm the effectiveness and improved performance of the proposed scheme.
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