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TY - UNPB AU - Li, J.T. ED - Schaa, Volker RW ED - Huang, Wenhui ED - Yan, Xueqing ED - Tang, Chuanxiang ED - Li, Lu TI - Damping Trapped Modes in Vacuum Chamber of Heps in-Air Undulators J2 - presented at SAP2023, Xichang, China, 10-12 July 2023 CY - Xichang, China T2 - Symposium on Accelerator Physics T3 - 14 LA - english AB - The HEPS is the fourth-generation light source under construction. For the requirements for high-brightness, a large number of in-air undulators with small gaps will be installed in the storage ring and become one of the important impedance contributors. Photon absorbers will be commonly used in the vacuum chamber of the in-air undulators to shielding the vacuum components downstream which are sensitive to the synchrotron radiations. Due to the existence of photon absorbers, some trapped modes in the transverse planes will be excited by the beam passage. In this paper, a series of numerical simulations are performed to investigate the detailed properties of the trapped modes. In addition, according to electromagnetic field distribution of the trapped modes, damping strategies are investigated to mitigate their influence to the beam instabilities. ER -