Long-term phase stability is a significant issue for Low-level RF systems. Crosstalk and temperature effect on the RF field detectors would significantly limit the performance of phase detecting and phase locking. A novel microwave switch-based LLRF system has been developed in Tsinghua Accelerator Lab. Microwave switches are applied in the chopper circuit to turn continuous waves into pulse waves in the time domain to avoid mutual interference of signals. In this paper, the LLRF sys-tem based on microwave switches is presented. The result of preliminary long-term experiments shows the phase stability can achieve about 50fs RMS slow drift. The peak-to-peak value of the slow drift was ~100fs (~2 °C p-p) in 4 days.
The phase drift of the RF signal in the low-level radio frequency (LLRF) system is observed in the long-term operation, which limits the performance and stability of the LLRF system. The long-term drift was reproduced in the lab. Its effect and sources of error were explored in the simple LLRF46 board and the simplest LLRF system. It is founded that the temperature will significantly lead to the phase distortion of the two signal channels, although with the same electron device. The distortion will finally cause the long-term drift with temperature floating. A fixed phase calibration signal (CAL signal) is applied to deal with the signal channels difference. The preliminary tests were conducted and the results were analysed.
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