Characterization of a Nonlinear Beam Position Monitor
for Hall C Compton Scattering Experiment
Student: Paul S. Kennedy
School: Virginia Polytechnic Institute and State University
Mentored By: John Musson
In particle accelerators, beam position monitors (BPMs) provide valuable information on the location of the beam within the enclosure. The unique form factor constraints of the Hall C Compton Scattering experiment require a nonlinear BPM consisting of four button electrodes and a new position algorithm. This study investigates several methods of characterizing this nonlinear BPM's response to beam position. Initially, a field map of the electrodes' response to beam position was produced. Analytical solutions, neural networks, look-up tables, and fitting a POISSON model to the measured signals were explored as possible methods for determining position. Here we found that the POISSON model accurately approximates the field map of the electrodes' response to beam position with a root mean square (RMS) error of 1.5 mV. The analytical model and the neural network solution proved to be accurate but impractical to implement. While a look-up table based on the field map is a reliable model of the tested BPM, the POISSON model provides greater flexibility. Thus, the data suggest the button electrode BPM for Hall C's Compton Scattering Experiment will accurately determine position.