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TY - CONF AU - Hori, C. AU - Aoki, T. AU - Hae, T. AU - Hiramoto, H. AU - Seki, T. ED - Conradie, Lowry ED - De Villiers, John Garrett ED - Schaa, Volker RW TI - Optical Design of AVF Weak-Focusing Accelerator J2 - Proc. of Cyclotrons2019, Cape Town, South Africa, 23-27 September 2019 CY - Cape Town, South Africa T2 - International Conference on Cyclotrons and their Applications T3 - 22 LA - english AB - A trend in proton beam therapy systems is downsizing their footprints. A larger main magnetic field for the downsizing, however, requires a septum magnet to generate a larger magnetic field for beam extraction. In order to relax the specification of the septum magnet, we consider an azimuthally varying field (AVF) weak-focusing accelerator. The magnetic fields of its hills and valleys can be designed while maintaining the average magnetic fields over the design orbits. Thus, by locating the septum magnet near one of the valleys, the specification is relaxed while keeping the footprint of the accelerator. In this study, we show an optical design of an AVF weak-focusing accelerator with cotangential orbits. The magnetic field in the valleys is smaller than the average magnetic field over the maximum energy orbit by 0.2 T. We evaluate gradient magnetic fields required for beam extraction and find the possibility of variable energy extraction by the static gradient fields. PB - JACoW Publishing CP - Geneva, Switzerland SP - 242 EP - 244 KW - extraction KW - septum KW - focusing KW - cyclotron KW - resonance DA - 2020/06 PY - 2020 SN - 978-3-95450-205-9 DO - doi:10.18429/JACoW-Cyclotrons2019-TUP036 UR - http://jacow.org/cyclotrons2019/papers/tup036.pdf ER -