Simulations of polarization levels and spin tune biases in high energy leptons storage rings The use of resonant depolarization has been suggested for precise beam energy measurements in the 100 km long Future Circular Collider e⁺e⁻. The principle behind resonant depolarization is that a vertically polarized beam excited through an oscillating horizontal magnetic field gets depolarized when the excitation frequency is in a given relationship with the beam energy. In this paper the possibility

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... self-polarized leptons at 45 and 80 GeV is investigated. Preliminary results of simulations in presence of quadrupole misalignments and beam position monitors (BPMs) errors for a simplified ring are presented. Even in presence of errors a level of polarization useful for energy calibration seems not out of reach. However it is crucial to demonstrate that a energy measurement precision better than 100 KeV can be actually obtained. The last ring layout with 1 mm vertical beta at the IPs has been also considered. The large vertical beta in the IR quadrupoles makes the closed orbit very sensitive to their vertical misalignment and the orbit correction procedure challenging.