Shancai Zhang

An upgrade proposal of injection bump system for HLS

The current injection bump system in HLS storage ring, which is designed 8 years ago, has been operated 5 years up to the present with acceptable performance. Due to inherent limitation of HLS (Hefei Light Source) storage ring, there are some deficiencies of the design. For the potential of full energy injection, reasonable design objective was summed up. Then, physical design of new bump system was brought forward. Using simple formula, the acceptance to injected beam and perturbation on stored beam were estimated approximately. Finally, the ELEGANT software was used to simulate the injection process with new designed bump system. The simulation results showed that, the injection efficiency would be higher than 90% and perturbation on stored beam would be small enough, which are very essential to full energy injection and top-up operation of HLS.

A low emittance lattice design for hls storage ring

Reducing beam emittance is the most effective measure to enhance brilliance of light source. HLS (Hefei light source) is a second generation synchrotron light source, whose emittance is relatively large. To improve the performance of HLS, a new low emittance lattice, whose circumference is similar to that of current storage ring but the focusing structure was different, was studied and presented in this paper. The new ring can be set upon current ground settlement of HLS, while all magnets would be reconstructed. The new designed lattice has two operation modes, the low emittance mode, whose purpose is to reduce beam emittance and to increase the number of straight section, and the low momentum compaction mode, whose purpose is to adjust bunch length for the production of coherent THz radiation. After optimization, beam emittance was reduced to several nmmiddotrad, and the dynamic aperture for on-momentum and off-momentum particle is large enough. It is conceivable that, with the new lattice, the brilliance of HLS should be increased two orders.

Calculations and design of a third harmonic cavity for increasing the beam lifetime

Higher harmonic cavities are used widely in light sources to increase the bunch length and decrease the charge density. This approach may be adopted to increase the beam lifetime in HLS-II. The beam dynamics and bunch lengthening with a passive harmonic cavity are presented in this paper. The result shows the charge density is decreased greatly. A third harmonic cavity similar to the KEK-PF RF cavity for HLS-II is designed, in which the higher order modes are absorbed by SiC ducts and three couplers with rodshaped antenna.

The nonlinear effects of fringe fields in HLS

The main body of HLS (Hefei Light Source) is an 800 MeV electron storage ring, whose circumference is about 66 m. As a typical small ring, although the sextupole fields for correction of chromaticities are relatively weak, there still exist strong nonlinear fields coming from fringe fields of dipole and quadrupole magnets. In this paper, the effects of fringe fields on chromaticities and tune shifts with amplitude were discussed and calculated for HLS storage ring. Under the low injection energy, the tune shifts with amplitude coming from fringe fields are one of important sources of transverse Landau damping, which is main stabilizing mechanism for HLS ring.

The operation status of hls (hefei light source)

HLS (Hefei light source) is a dedicated synchrotron radiation research facility, spectrally strongest in VUV and soft X-ray, designed and constructed in 1980s, accepted to regular service in 1991. From 1999 to 2004, the National Synchrotron Radiation Laboratory carried out Phase II Project, in which quite a few sub-systems in HLS were upgraded and 8 new beamlines were constructed. After Phase II Project, the operation reliability and performance of HLS is improved considerably, for example, the operation beam current is above 250 mA, beam lifetime is longer than 8 hours, orbit stability met the requirement of users, and fault time of machine operation is much less than before. The capability of HLS to serve synchrotron radiation users is enhanced significantly. The main tasks of machine study in HLS are introduced briefly.