The calibration of BEPC beam position monitors

The basic requirement for the BEPC beam position monitor is the measurement of the beam orbit with 0.1 mm precision near the collision point. To improve the measurement accuracy, the response of the beam position monitor pickups was mapped in the laboratory before they were installed in the BEPC ring. The microcomputer-controlled test set consists of high frequency coaxial switches to select each pickup electrode, a movable antenna to simulate the beam, a signal source, a spectrum analyzer to measure the pickup signals, and analysis software. The signal source operates well below the -3 dB cutoff frequency of the pickups (buttons). We believe that the low-frequency measurement yields the same information as the real beam. The button signals were clear. This calibration technique is satisfactory for BEPC operation.