Speaker
Description
The Super Tau-Charm Facility (STCF), proposed in China, is a new-generation high-luminosity electron-positron collider operating in the low-energy range of 1-3.5 GeV. To achieve the target luminosity exceeding $5×10^{34}\ \text{cm}^{−2}\text{s}^{−1}$, a collision scheme combining a large Piwinski angle and crab-waist correction is adopted. However, the required high beam current, low emittance, and an extremely low vertical beta function ($\beta_y^*$ < 1 mm) lead to a very short Touschek lifetime. In particular, the strong nonlinear chromaticity induced by the sub-millimeter $\beta_y^*$ constitutes a major limitation on the momentum aperture of the collider rings. To improve the Touschek lifetime, a momentum aperture of 1.5% is essential. This necessitates local correction of the nonlinear chromaticity originating from the final focus quadrupoles. In this paper, we derive the theoretical origin of the nonlinear chromaticity and identify dedicated measures to systematically mitigate these nonlinearities order by order. Specifically, we design a modular linear lattice for the interaction region to facilitate the optimization of nonlinear chromaticity. The dispersion invariant is constrained to enhance the local momentum aperture. By implementing a local chromaticity correction scheme up to the third order, the momentum aperture of 1.5% is obtained.
Funding Agency
This work is supported by the National Natural Science Foundation of China (Project No.
12341501, No. 12405174)
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