Development Of Digital Bunch-by-Bunch Feedback Systems For The Storage Ring Of HLS Ⅱ

The development of the Hefei Light Source has never stopped during the operation. And the aim we pursue has remained the same, summarized as follows:let the light source "brighter, stronger and more stable". In order to obtain the higher current and brightness, the HLS requires the storage of intense electron beam with many bunches, but the interaction between the adjacent bunches by the wake field can give rise to collective effects called "coupled-bunch instabilities". The coupled-bunch instabilities produce the growth of the beam oscillation. If the growth is stronger than the damping the oscillation becomes unstable. The severe coupled-bunch instabilities can reduce the brightness, degrade the beam quality and even’cause beam loss. The beam feedback system is the most effective approach to suppress the coupled-bunch instabilities. With the rapid development of electronic technique, the digital feedback systems have more and more advantages like flexible, efficient, simple and programmable, and gradually replace analog feedback systems to become the new trend.From2010to2014, the Hefei Light Source undergoes a great maintenance and upgrade project (HLS II). In order to improve the stability of the beam orbit to operate steadily at high current situation, we develop a set of longitudinal and transverse digital bunch-by-bunch feedback systems which is an important part of the HLS II to cure the transverse and longitudinal coupled-bunch instabilitiesFirstly, we briefly introduce some basic knowledge of the beam transverse and longitudinal movements in the storage ring. Then we analyze the spectrum characteristics of the beam signal when the coupled-bunch instabilities occur. In the following part of the paper, we give an account of the theory and the composition of the digital bunch-by-bunch feedback system. At the end, we respectively describe the longitudinal and transverse digital feedback system and experiments at HLS II in detail.The severe longitudinal coupled-bunch instabilities also exist in the HLS II storage ring, and we have no effective action to suppress them before the implementation of the longitudinal digital bunch-by-bunch feedback system. The longitudinal feedback kicker used in this system is the first longitudinal cavity-type feedback kicker which is carried out by the domestic independent design and used in the actual storage ring. This paper detailedly describes the design and the test measurements of the longitudinal kicker and the commissioning and experiments of the whole longitudinal feedback system.In the old storage ring of the HLS, two sets of transverse bunch-by-bunch feedback systems have been developed by our researchers, one of them is an analogy system and another one is a digital system. But in the HLS II, a new storage ring with some new physical parameters makes us develop a new transverse digital feedback system. Because of the space limitation, we use only one transverse stripline kicker to accomplish both of the horizontal and vertical feedback. The top-off injection has been realized in the HLS II storage ring, and the horizontal feedback system can damp the residual oscillation caused by the bump injection efficiently to reduce the perturbation of the users’ experiments. In addition, the transverse digital bunch-by-bunch feedback system can measure the betatron Tune without affecting the users’ experimental activities.We have no enough time to do more experiments and just obtain some preliminary experimental results because the HLS II storage ring is still on commissioning. A lot of work must to be done to deepen the research of the digital bunch-by-bunch feedback systems in the future.This work is supported by the Natural Science Foundation of China (11175173,11005105) and the HLS major maintenance and reconstruction project.