A practical design and field errors analysis of a merged APPLE-Knot undulator for High Energy Photon Source

Users of HEPS require polarization adjustable and high-flux synchrotron radiation with energy of 100-2000 eV. To achieve 100 eV photon energy at HEPS, a 6 GeV storage ring, the problem of on-axis heat load becomes a significant challenge for users. A new type of four-row merged APPLE-Knot undulator recently proposed seems to be the most effective solution to reduce on-axis power density. However, as an undulator with such complex magnetization orientation distribution of magnetic blocks, its field integrals correction and the effect of field errors on the radiation performance are different from that of conventional EPU. Whether it can realize its field integrals correction and perform as well as in theory with field errors has become a concern. Here, a set of field integrals correction schemes is reported and field errors analysis has been done. A general method for evaluating the effect of magnetization orientation deviation of the magnetic block on radiation performance is proposed. It can be used for any insertion device containing permanent magnetic magnets if necessary.