title: Design and performance of the APPLE-Knot undulator.
abstract: Along with the development of accelerator technology, synchrotron emittance has continuously decreased. This results in increased brightness, but also causes a heavy heat load on beamline optics. Recently, optical surfaces with 0.1 nm micro-roughness and 0.05 µrad slope error (r.m.s.) have become commercially available and surface distortions due to heat load have become a key factor in determining beamline performance, and heat load has become a serious problem at modern synchrotron radiation facilities. Here, APPLE-Knot undulators which can generate photons with arbitrary polarization, with low on-axis heat load, are reported.
authors.affiliation: Department of Physics, State Key Laboratory of Surface Physics, and Laboratory of Advanced Materials, Fudan University, 2005 Songhu Road, Shanghai 200438, People's Republic of China.
authors.forename: Fuhao
authors.initials: F
authors.lastname: Ji
authors.affiliation: State Key Laboratory of Functional Materials for Informatics, Shanghai Institute of Microsystem and Information Technology, Chinese Academy of Sciences, 865 Changning Road, Shanghai 200050, People's Republic of China.
authors.forename: Rui
authors.initials: R
authors.lastname: Chang
authors.affiliation: Shanghai Synchrotron Radiation Facility, Shanghai Institute of Applied Physics, Chinese Academy of Sciences, 239 Zhangheng Road, Shanghai 201204, People's Republic of China.
authors.forename: Qiaogen
authors.initials: Q
authors.lastname: Zhou
authors.affiliation: Shanghai Synchrotron Radiation Facility, Shanghai Institute of Applied Physics, Chinese Academy of Sciences, 239 Zhangheng Road, Shanghai 201204, People's Republic of China.
authors.forename: Wei
authors.initials: W
authors.lastname: Zhang
authors.affiliation: State Key Laboratory of Functional Materials for Informatics, Shanghai Institute of Microsystem and Information Technology, Chinese Academy of Sciences, 865 Changning Road, Shanghai 200050, People's Republic of China.
authors.forename: Mao
authors.initials: M
authors.lastname: Ye
authors.affiliation: Hiroshima Synchrotron Radiation Center, Hiroshima University, 2-313 Kagamiyama, Hiroshima 739-0046, Japan.
authors.forename: Shigemi
authors.initials: S
authors.lastname: Sasaki
authors.affiliation: State Key Laboratory of Functional Materials for Informatics, Shanghai Institute of Microsystem and Information Technology, Chinese Academy of Sciences, 865 Changning Road, Shanghai 200050, People's Republic of China.
authors.forename: Shan
authors.initials: S
authors.lastname: Qiao
keywords: APPLE undulator; APPLE-8 undulator; Apple-Knot undulator; Knot undulator; figure-8 undulator; undulator