Koop, I. JACoW Publishing Geneva, Switzerland 978-3-95450-216-5 10.18429/JACoW-eeFACT2018-TUPBB04 English 165-168 TUPBB04 synchrotron polarization resonance ECR collider Contribution to a conference proceedings 2019 2019-04 https://doi.org/10.18429/JACoW-eeFACT2018-TUPBB04 http://jacow.org/eefact2018/papers/tupbb04.pdf Both future 100 km in circumference electron-positron colliders CEPC and FCC-ee need know beams energies with the extreme precision of 1-2 ppm. This can be done only with the help of Resonant Depolarization (RD) technique. Still, some beam parameters of these machines, like energy spread and damping decrements, are so high near 80 GeV per beam, that it is required special consideration and tricks to overcome the difficulties. The author has written simple spin tracking code, which simulates main features of the RD process in presence of continuous energy diffusion due to synchrotron radiation fluctuations. It was shown by this study, that the applicability of the RD method is limited by the effect of widening of a width of the central peak of the spin precession spectrum when the synchrotron tune is chosen too low, say below 0.05. In this case spin precession lost its resonant nature due to overlap of the wide central spectrum peak with nearby synchrotron side bands. Dependencies of the spectrum peaks width from various beam parameters and a new RD-procedure recipe are presented.