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The SOLEIL II storage ring will be equipped with many in-vacuum undulators (IVUs) and superbends, which are vulnerable to gas scattering–induced beam losses considering their small vertical gaps. In this paper, gas scattering–induced beam losses in SOLEIL II are studied with tracking simulations. The results show that, without vertical scrapers, 53% of elastic scattering–induced losses happen at IVUs with 4 mm vertical gaps, which may be a risk of damage to their magnets over 15 years of operation. Detailed tracking finds that most of these losses originate from scattering events in short range, e.g., within half a turn. This suggests that one vertical scraper located upstream of each IVU group could provide optimal collimation, protecting the IVUs while maintaining the beam lifetime. However, this scheme is not allowed due to space constraints. A second optimal vertical collimation scheme is proposed with 2 scrapers, which reduces the beam losses at IVUs by a factor of 0.4 while maintaining an elastic scattering lifetime of 40 hours. In contrast to elastic scattering, inelastic scattering leads to only minor beam losses and remains acceptable.
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