Physical design of a cryogenic delta-knot undulator for the high energy photon source

Abstract To supply a high flux of full adjustable polarization synchrotron radiation with low on-axis power density for users of HEPS, a new type of pure permanent magnetic (PPM) undulator structure called delta-knot has been proposed. The physical design of a prototype of a 3-period cryogenic delta-knot undulator is presented herein. It can achieve a maximum 1.6 T peak magnetic field with a periodic length of 40 mm using PrFeB material at 80 K. Specifications of the main magnetic structure as well as the field performances and radiation spectra at arbitrary polarization modes are also obtained. It is demonstrated that the on axis power density is significantly reduced in any polarization mode except the 45° incline polarization mode.