47 Boine-Frankenheim, Oliver Kornilov, Vladimir APH 14th International Particle Accelerator Conference JACoW Publishing Geneva, Switzerland Venice, Italy 10.18429/JACOW-IPAC2023-WEPA015 English 2673 - 2676 Octupole magnets are a central mitigation method against the transverse collective instabilities expected for the high-intensity operation of the SIS18 and SIS100 synchrotrons in the FAIR project. For these beam parameters, the self-field space-charge effect dominates the betatron footprint, and strongly modifies the instability drive and the Landau damping properties. The space-charge tune shifts are related to all three incoherent amplitudes, and is an intrinsic interaction. We consider all these effects and study Landau damping of head-tail modes due to the combination of octupoles and space-charge. Using the data from experimental instability observations, and particle tracking simulations, we provide estimations for the expected high-intensity operation of the SIS synchrotrons. Published by JACoW Publishing under the terms of the Creative Commons Attribution 4.0 license. ; 33, ; PUB:(DE-HGF)8, ; Accelerator Physics mc5-beam-dynamics-and-em-fields - MC5: Beam Dynamics and EM Fields mc5-d06-coherent-and-incoherent-instabilities-measurements-and-countermeasures - MC5.D06: Coherent and Incoherent Instabilities Measurements and Countermeasures Contribution to a conference proceedings 2023 2023-05-07 - 2023-05-12 GSI-2025-00522 2023-05-07 - 2023-05-12 2023 https://repository.gsi.de/record/358338 https://doi.org/10.18429/JACOW-IPAC2023-WEPA015