Development of a Prototype Capacitive Bpm for the University of Maryland Electron Ring

Work has been performed at the University of Maryland by the electron beam physics group to design and develop a prototype capacitive Beam-Position-Monitor (BPM) for an electron ring project. Extensive theoretical work and PSPICE simulation of the equivalent circuit of the BPM have been conducted to fully understand the behaviour of the capacitive BPM. This BPM has 4 pieces of electrostatic pickups around a beam pipe of 2-inch diameter. The capacitance between the electrode and the beam pipe is approximately 0.55nF, which results in a time constant long enough to reproduce the current waveform faithfully. A bench test of this prototype BPM has been completed. The test shows that the capacitive BPM has a very fast response to the beam current with high sensitivity. Also, the BPM can measure the beam centroid displacement with adequate accuracy. In addition, this BPM can measure the total beam current by appropriate calibration.