The Magnetic Performance of an Exotic APPLE-Knot Undulator Developed at SSRF

An exotic pure permanent magnet (PPM) undulator that consists of eight rows of PPMs is developed at the Shanghai Synchrotron Radiation Facility. With the four quasiperiodic magnet arrays of APPLE-II type and four additional arrays of Knot type with the different period length, the undulator can produce various polarized light with very low radiation power on the axis and low higher harmonics radiation. The magnet design of the undulator and the simulations of the spectrum and the power distribution are described in this paper.