High precision real-time beam position measurement system

A system for real-time measurement of beam position is being constructed for the ALADDIN electron storage ring. High-precision measurements with a bandwidth large enough to allow their use in closed-orbit feedback are required. The hardware at each station consists of a pair of position-sensing electrodes connected through a p-i-n diode switch to a narrowband receiver tuned to the second harmonic of the storage ring RF frequency. The receiver input is switched between the electrodes at a 12.5-kHz rate. The output of the receiver is synchronously demodulated to obtain a signal proportional to the difference between the electrode signals. The difference signal is normalized to beam intensity with an automatic gain control (AGC) loop controlling the average output of the receiver. The AGC loop has a useful dynamic range of 80 dB, and is capable of reducing beam signal fluctuations at frequencies up to 200 Hz