  In a diffraction-limited storage ring (DLSR), the momentum acceptance (MA)
might be limited by the half integer resonances (HIRs) excited by focusing
errors, associated with the large detuning terms from the strong focusing and
strong sextupoles required for an ultralow emittance. Taking the High Energy
Photon Source (HEPS) as an example and through statistical analysis, we found
that the horizontal HIRs have stronger impact on dynamics than the vertical
ones; and the probability of MA reduction caused by a HIR is closely correlated
with the level of the beta beats at the same plane, but independent of the
error sources. For the HEPS design, to reach a small MA-reduction probability
of about 1%, the rms amplitude of the beta beats at the nominal tunes should be
kept below 1.5% horizontally and 2.5% vertically. The presented analysis can
provide useful reference for other DLSR designs.
