Beam reference orbit compensation for the HLS-II storage ring

Abstract The stability of the beam orbit is essential for a storage ring based light source. An orbit feedback system is usually adopted to help maintain the beam circulating on a reference orbit. The movement and deformation of the Beam Position Monitor (BPM) chambers due to thermal effect can affect the BPM readings. The BPM misreading leads to shift of the reference orbit for the orbit feedback system. The feedback system then corrects the beam to a different closed orbit, resulting in a change in the real beam orbit. Online experiments are carried out to measure the BPM readings dependency on the temperature of BPM chambers in the Hefei Light Source II (HLS-II) storage ring. To improve the beam orbit stability, a compensation system is developed to mitigate the reference orbit shift accordingly. With this compensation system, the stability of the reference orbit is improved to be better than 10 μm in the horizontal plane and 5 μm in the vertical plane. This paper reports our work on the measurement of BPM readings dependency and the development of the reference orbit compensation system for the HLS-II storage ring. The online compensation results are also presented.