Phimsen, T. Boonsuya, S. Chaichuay, S. Chitthaisong, S. Juntong, N. Klysubun, P. Prawanta, S. Pulampong, T. Sittisard, K. Srichan, S. Sudmuang, P. Sunwong, P. JACoW Publishing Geneva, Switzerland 2673-5520 978-3-95450-250-9 10.18429/JACoW-MEDSI2023-FROAM02 English 363-367 vacuum simulation photon synchrotron storage-ring Contribution to a conference proceedings 2024 2024-07 https://doi.org/10.18429/JACoW-MEDSI2023-FROAM02 https://jacow.org/medsi2023/papers/froam02.pdf Siam Photon Source II (SPS-II) is the first Thailand¿s 4th generation synchrotron light source. It not only provides high-energy and high-brightness synchrotron radiation for both academic and industrial research after its completion, but it is also strategically aimed to build up a stronger Thai industrial community during the design and construction period. Vacuum system is one of the systems expected to play a key role in leveling up the local manufacturing capability of the country. Most of the main components in the system are planned to domestically fabricate through technology transfer. Instead of NEG coating technology, this vacuum system design of SPS-II storage ring is based on the conventional technology which involves Thai industry potential and expertise. This paper reviews the challenges and adaptation of conservative design in dense DTBA magnet lattice with magnet aperture limitation. The vacuum chambers and bending magnets have been modified to accommodate IR beamlines which are included in the second phase plan. Pressure profile of the vacuum system in storage ring is evaluated. Then, the progress of overall vacuum system of SPS-II is described.