Phase and synchronous detector theory as applied to beam position and intensity measurements
A popular signal processing technique for beam position measurements uses the principle of amplitude-modulation-to-phase-modulation (AM/PM) conversion and phase detection. This technique processes position-sensitive beam-image-current probe-signals into output signals that are proportional to the beam's position. These same probe signals may be summed and processed in a different fashion to provide output signals that are proportional to the peak beam current. This paper derives the transfer functions for the AM/PM beam position and peak beam current processors.
Comparison of beam-position-transfer functions using circular beam-position monitors
A cylindrical beam-position monitor (BPM) used in many accelerator facilities has four electrodes on which beam-image currents induce bunched-beam signals. These probe-electrode signals are geometrically configured to provide beam-position information about two orthogonal axes. An electronic processor performs a mathematical transfer function (TF) on these BPM-electrode signals to produce output signals whose time-varying amplitude is proportional to the beam's vertical and horizontal position. This paper compares various beam-position TFs using both pencil beams and further discuss how diffuse beams interact with some of these TFs.
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.<<ETX>>