2020同步年報

094 ACTIVITY REPORT 2020 effective field. The EPU has a narrow horizontal range of uniform field producing strong dynamic multipole errors. In the case of EPU66, the dynamic field integral of the VL mode extends to 210 G cm. To address the inherent prob- lems of the EPU, the magnet group investigated both pas- sive and active approaches. They first experimented with the use of iron shims (L-shim) attached to the corners of the magnets; this approach improved beam dynamics issues. It should be noted that the passive method is convenient but inaccurate for an inclined mode of an EPU and opera- tion of the storage ring at varied energies. To be stable for universal operation, a prototype flat wire was installed on Fig. 3 : Photographs of the EPU and flat wire installed in the TPS storage ring this year. From left to right are EPU66, EPU168 and flat wire on EPU chamber. EPU66 EPU168 Flat wire the chamber within the gap of the EPU56 at TLS during the 2017 summer shutdown. The improved ring stability be- came experimentally evident. Installation of a Phase-II EPU and Flat Wire According to the experimental results and experience, both EPU66 and EPU168 of TPS phase II have been completed and installed with flat wire on October 2020, as seen in Fig. 3 . After that, the EPU will be commissioned according to the construction schedule of the front end and the beam line. (Reported by Ting-Yi Chung) Global Tune Feedback in TPS T aiwan Photon Source (TPS) is a 3-GeV dedicated synchrotron light source, consisting of 24 double bend achromat that provide six long straights and 18 short straights to accommodate insertion devices including in-vacuum undulators (IU) and elliptical polarization undulators (EPU). The side effects of the insertion devices on the storage ring are betatron tune shift, lattice function distortion, closed-orbit distortion, variation of emittance and an energy spread. These effects deterio- rate the quality of the synchrotron light source. Many actions are taken to cure these undesired effects, among which a global tune feedback system has been implemented to compensate the tune shift caused by the insertion devices. Introduction There are two EPU48, one EPU46 and six IU operating in the TPS storage ring. To compensate the tune shift due to the vari- ation of gap and/or phase of these insertion devices, MATLAB was used to develop a global tune feedback system that uses two-family quadrupole magnets (36 defocusing quadrupoles QD1S and 36 focusing quadrupoles QF2S) located besides 18 short straights to maintain the betatron tune at the desired working point. Algorithm The correction currents to be applied to the quadrupoles of QD1S and QF2S families are calculated with the model tune response matrix M and the tune difference ∆ν. The accuracy of the tune response matrix and tune difference determines whether the betatron tunes can be well controlled. The storage ring lattice is well calibrated with Linear Optics from Closed Orbit; the tune response matrix is hence calculated from the model lattice. The tune difference is the difference between the target tune ν 0 and measured tune ν m from the bunch-by-bunch feedback system (BBF). Before correcting betatron tunes, 2,000 data points of the BBF tunes were collected within about three minutes when all IDs’ gaps or phases were at rest; the