When conducting experiments at a synchrotron radiation facility, it is necessary to scan the position of the sample or the beam energy within a certain range. The scanning modes are categorized as step scanning and on-the-fly. In the step-scanning mode, there is a significant amount of dead time in the motion mechanism, which leads to long data acquisition times and low experimental efficiency. By contrast, the on-the-fly mode allows for continuous motion while triggering the detectors and sensors, avoiding the dead time of the motion mechanism and greatly improving the efficiency of the experiments.

This study aims to propose and implement a hardware-triggered on-the-fly system to achieve rapid and continuous scanning during experimental processes for Hefei light source (HLS).

The proposed on-the-fly system mainly consisted of a synchronous signal acquisition module, a synchronous motion control module, and a software control module. The design of the hardware synchronous trigger module in the synchronous signal acquisition module was based on the field-programmable gate array (FPGA) development board Zynq7020. The encoder signals were decoded into position signals and used to trigger other devices based on position or time. This made it the central component for the on-the-fly mode. The design of the synchronous motion control module was based on a highly synchronous EtherCAT bus. The motion controller supported multi-axis coordination and programmable trajectory motion to meet the requirements of different experiments. The software control module utilized the experimental physics and industrial control system (EPICS) architecture for device control, and experiment flow control and data acquisition were implemented using Bluesky platform. Finally, the proposed on-the-fly system has been deployed and tested at the Soft X-ray Magnetic Circular Dichroism (XMCD) experimental station of HLS.

The experimental results demonstrate that the on-the-fly mode system not only meets the spectral performance requirements, but also reduces the single acquisition time from tens of minutes in the step-scanning mode to approximately 1 min.

Therefore, the on-the-fly system designed and implemented in this study significantly improves the experimental efficiency and user experience.