Abstract:
The beam current dependence (BCD) is an important problem for the beam position measurement system. Normally, the beam position measurement result should be independent of beam current. However, it is found that there are some correlations between the beam position measurement result and the beam current in actual operation of BPM system. This paper focused on how to find and analyze the causes of the BCD, and then to solve the BCD problem in BPM system. First, the digital BPM system was briefly introduced. It included the BPM system framework, the basic measurement principle as well the calculation method. Secondly, the possible causes of BCD were analyzed. It was about the RF signal channel nonlinearity and the offset of ADC output. Finally, simulations for the nonlinearity of the BPM RF signal channel, the offset of the ADC output, and the inconsistency of the gain of the BPM signal channel were carried out by using the Matlab. According to the simulation results, the RF signal processing circuit and signal processing algorithm of the home-made BPM electronics were optimized. The laboratory test and BEPCⅡ on line test results show that the BCD of the homemade BPM electronics is basically solved.
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