Research on magnetic center measurement of quadrupole and sextupole using vibrating wire alignment technique in HEPS-TF

Purpose In order to meet the extremely low emittance requirement, the magnets in the storage ring of high-energy photon source (HEPS) need to have a stable support and precise positioning. In HEPS-TF, the key and difficult technologies of HEPS should be researched and developed. Vibrating wire alignment technique is one important project of HEPS-TF. It can be used to pre-align the quadrupoles and sextupoles on one girder with high precision. A vibrating wire measurement system was set up and tested to verify the magnetic center measurement precision and the magnet adjustment error. Methods There are one sextupole and one quadrupole installed on a multipole girder. Vibrating wire is stretched through mechanical center of the magnet apertures and supported by the test benches on the two sides. A single conducting wire is stretched through the magnet aperture and electrified by alternating current. The wire will vibrate for a period of Lorentz force. By matching the current frequency to one mode of natural frequency of the wire, the vibrating amplitude will be enhanced. And by measuring the vibrating amplitude, the magnetic field at the wire position can be got. Moving the wire across the magnet aperture in the transversal or vertical direction, the distribution of magnetic field and magnetic center position can be measured. According to the magnetic center position error to adjust the magnet. Measure the magnetic center of all magnets installed on the multipole girder one by one, and adjust their magnetic center to a line. Results The magnetic center measurement precision is better than ±3 μm, and the magnet adjustment error is less than 6 μm. Conclusion The vibrating wire system design and a series of magnetic center measurement experiments have gained good achievements. It has been proved the vibrating wire system is designed reasonable and using the vibrating wire to align the magnets installed on a multipole girder is feasible and can reach a high precision.