Experimental Study Of Lattice Calibration And Magnet Hysteresis Effects At Duke Storage Ring

Gaining precise understanding of the magnetic optics (lattice) of the real accelerators is critical for a storage ring based light source to achieve its maximum performance. In the first part of this dissertation, we will introduce our work on the lattice charac-terization and compensation on the Duke storage ring. Since the Linear Optics from Closed Orbit (LOCO) cannot be employed in any straight forward manner on the Duke storage ring which employs combined function quadru-sextupoles, to character-ize the storage ring lattice. Beta-functions are directly determined by measuring the betatron tune shifts while varying quadrupole strengths. This beta-function measure-ment technique is systematically studied and optimized. Five sets of beta-function measurements for all 78 quadrupoles are carried out with optimized parameters, and the results show that the beta-functions can be measured with extremely high reso-lution and reproducibility. A lattice model for the real storage ring is constructed by minimizing the relative beta-function differences between the measured values from the storage ring and those from using a lattice model. Quadrupoles in the Duke storage ring are tuned according to this model, and the beta beating in the real machine is significantly reduced.The magnetic hysteresis effects in the Duke storage ring are experimentally stud-ied using the transverse feedback based precision tune measurement system to un-derstand the impacts on the electron beam energy and lattice focusing. The major magnet hysteresis effects associated with magnet normalization cycles and lattice ramping are carefully studied to determine an effective procedure for lattice prepara-tion while maintaining a high degree of reproducibility of lattice focusing. The local hysteresis effects are also studied by measuring the betatron tune shifts resulted from adjusting the setting of a quadrupole. A new technique has been developed to precisely recover the focusing strength of the quadrupole by returning it to a proper setting to overcome the local hysteresis effect, and it has been successfully implemented in the afore mentioned beta-function measurement technique for lattice char act erization.Orbit stability is critical for the gamma-ray operation in the Duke storage ring. It is observed that the beam orbit in the storage ring is significantly altered by the nearby booster dipoles, which can be a significant problem for gamma-ray production. To overcome this problem, we have developed an orbit compensation scheme for the booster leakage field using a beam based technique with two orbit correctors. The compensation scheme is implemented as a feedforward and operated transparently together with the slow orbit feedback system.