Development And Applications Of The Tune Measurement System For The HLS-Ⅱ Storage Ring

Through half a century’s development of the particle accelerator science, syn-chrotron based on strong focusing principle has been a standard concept for the high energy particles acceleration. Compared with synchrotrons, storage rings focus not on-ly on the achievable maximum of the particle energy but also on the equality of the particle beam. Of special interest is to use electron storage rings as synchrotron radia-tion light sources which provide the users with brilliant photons.The new storage ring is the main part of the upgrade Hefei Light Source (HLS-Ⅱ) which determines the performance of the light source. For storage rings, tune is a key parameter. Tune is defined as the betatron oscillation number of a particle travelling once around the circular accelerators, which reveals the overall focusing "sensed"by the particle in the ring. The precise measurement for the tune not only helps avoid the beam loss due to resonance but also provides researchers rich information about the extra effects on the beam focusing.A Swept-Frequency Excitation (SFE) based tune measurement system has been developed for the HLS-Ⅱ storage ring during the upgrade project of HLS-Ⅱ in 2011-2014. This dissertation introduces the development details and applications of the SFE based tune measurement system of the HLS-Ⅱ storage ring.It is clear from the analysis of the beam transverse spectrum that tune can be ob-tained from the beam position signal. However, the radiation damping effect has an impact on the tune observation. Thus a RF dipole kicker needs to be added on the beam to excite significant betatron oscillation.The development of the SFE based tune measurement system consists three part-s:hardware construction, software structure and the system commissioning. Spectrum analyzer is the heart of the system which determines the system performance. With corresponding signal exciting circuit and signal processing circuit, tune can be extract-ed from the strip-line BPM. The task of the control system development is to control the spectrum analyzer under the EPICS frame work. The system has a measurement resolution better than 0.00007 with a refresh rate of 1 Hz, which meets the physical needs.The SFE based tune measurement system has been widely used during the com-missioning of the HLS-Ⅱ storage ring. Based on the tune shift principle, the betatron function, natural chromaticity, corrected chromaticity are measured during the commis-sioning. The betatron function is measured using quadrupole modulation. The natural chromaticity and the corrected chromaticity are measured using the dipole modulation and RF modulation respectively. The measurements play important rules in the commis-sioning work of the HLS-II storage ring. As a direct measure of the ring circumference, the central RF frequency is also measured using sextupole modulation. The obtained central RF frequency demonstrates that the the circumference deviation from the design value is less than 1 mm.This work is supported by National Natural Science Foundation of China (11105141, 11175173) and the upgrade project of Hefei Light Source.