Development Of BPM Chamber Displacement Monitor In HLS

Significant drifts in the horizontal beam orbit in the storage ring of HLS (Hefei Light Source) have been seen. The main reason is the horizontal drift of Beam Position Monitor (BPM) chambers due to thermal expansion caused by the synchrotron light and ambient temperature, which will definitely influence the beam position readout. Accordingly the slow orbit feedback (SOFB) system will make a wrong correction based on the false readout continuously. The mistake results in the instability of the beam.To monitor the BPM chamber motion for all BPMs, a BPM Chamber Motion Measurement System is built in real-time. With the help of the sysytem, the displacement of the BPM chamber motion will be measured and fed back to SOFB so that the beam orbit could be corrected rightly.The BPM Chamber Motion Measurement System in HLS is mainly composed of 24 raster gauges and an IPC, which connect with each other through RS485 bus. The IPC is responsible for the collection of the data from raster gauges, processes and sends them to the HLS control system.The drifts in the horizontal beam orbit will be restrained by the BPM Chamber Motion Measurement System, which will stabilize the beam orbit as a compensation strategy.This work was supported by the Natural Science Foundation of China (10275062 & 10675118).