ELECTROMAGNETIC MODELING OF BEAM POSITION MONITORS FOR SNS LINAC

Electromagnetic modeling of the beam position monitors (BPMs) for the Spallation Neutron Source (SNS) linac has been performed with MAFIA. The signal amplitudes and phases on the BPM electrodes are computed as functions of the beam transverse position using time-domain 3-D simulations with an ultrarelativistic beam. An analytical model is then applied to extrapolate the results to lower beam velocities. Based on the analysis results, an optimal BPM design with 4 oneend-shorted 60-degree electrodes has been chosen. It provides a very good linearity and sufficient signal power for both position and phase measurements, while satisfying the linac geometrical constrains and mechanical requirements.