Booster Free From Spin Resonance For Future 100~km-scale Circular e$^{+}$e$^{-}$ Colliders

TL;DR

This paper investigates spin depolarization resonances in a 100 km scale collider booster, demonstrating that polarization can be maintained at certain energies without Siberian snakes, enabling future high-energy polarized beam applications.

Contribution

The study provides a detailed analysis of spin resonance structures in a large-scale collider booster, showing potential for polarization preservation at high energies without Siberian snakes.

Findings

Weak resonance strengths at lower energies allow polarization maintenance.

Severe depolarization occurs at energies above 80 GeV.

Coherent addition of resonance contributions influences depolarization behavior.

Abstract

Acceleration of polarized electron~(positron) beams in a booster synchrotron may suffer from depolarization due to crossings of many spin depolarization resonances, which could limit its applications. We have studied the spin depolarization resonance structure of a 100~km scale booster lattice of the Circular Electron Positron Collider~(CEPC). The lattice has 8 arc regions with hundreds of FODO cells, interleaved with straight sections, which leads to a high periodicity. Our analysis shows the contributions to the strength of intrinsic and imperfection spin resonances add up coherently near the super strong resonances beyond 120 GeV, but mostly cancel out and result in generally weak resonance strengths at lower beam energies. Detailed simulations confirm that beam polarization can be mostly maintained in the fast acceleration to 45.6 GeV and 80 GeV, but severe depolarization may occur at even higher energies. This study suggests the possibility of acceleration of polarized electron~(positron) beams to ultra-high beam energies without the help of Siberian snakes, and supports injecting highly polarized beams into the collider rings as an attractive solution for resonant depolarization measurements and longitudinal polarized colliding beam experiments for future 100~km scale circular e$^{+}$e$^{-}$ colliders.