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TY - CONF AU - Soutome, K. AU - Shimosaki, Y. AU - Takao, M. AU - Tanaka, H. ED - Schaa, Volker RW ED - Arduini, Gianluigi ED - Pranke, Juliana ED - Seidel, Mike ED - Lindroos, Mats TI - Nonlinear Lattice Optimization for the SPring-8 Upgrade J2 - Proc. of IPAC2017, Copenhagen, Denmark, 14â19 May, 2017 C1 - Copenhagen, Denmark T2 - International Particle Accelerator Conference T3 - 8 LA - english AB - The SPring-8 upgrade project has adopted the hybrid MBA lattice to achieve the emittance of about 100 pmrad at 6 GeV with damping effects by insertion devices. This optics has two dispersion bumps in one unit cell where chromaticity-correcting sextupoles locate. The horizontal and vertical betatron phases between these bumps are tuned to be 3PI and PI, respectively, to cancel the low order contributions of nonlinear kicks due to sextupoles. However, it is not easy to obtain a sufficiently large dynamic aperture (DA) since (i) the cancellation is incomplete due to a nested arrangement, (ii) sextupoles are very strong, and (iii) the number of tuning knobs is limited. The DA is quite small due to the leakage of nonlinear kicks by nested sextupoles. We hence proposed to install additional weak sextupoles between the dispersion bumps to suppress the leakage kick further. Simulations show that this simple scheme is very effective for suppressing ADTS and for enlarging DA. We present details of this scheme and some numerical examples together with a newly developed fourth-order formula of ADTS for describing and controlling the lattice nonlinearity. PB - JACoW CP - Geneva, Switzerland SP - 3091 EP - 3094 KW - sextupole KW - lattice KW - betatron KW - injection KW - octupole DA - 2017/05 PY - 2017 SN - 978-3-95450-182-3 DO - 10.18429/JACoW-IPAC2017-WEPIK070 UR - http://jacow.org/ipac2017/papers/wepik070.pdf ER -