Advanced Light Source (ALS) beam position monitor

The requirements, design, and performance of the ALS BPM (beam position monitor) system are discussed. Considerable effort has gone into the storage-ring BPM system design because very fast and accurate measurements are needed. The speed and accuracy requirements in the electronics are met with parallel processing and error-correction techniques. A tuned receiver is provided for every beam position pickup, and for every array of four pickups there is a microprocessor controlling the measurement and recording data. To be useful during storage-ring commissioning, injection studies, and at other times when instant response is required, the BPM system must respond to a single turn of beam and also be able to store data from many turns. This is especially important with a low injection rate. The required bandwidth in this case is about 2 MHz. Accuracy and resolution of 0.5 mm are adequate for these high-speed measurements