A Simple Beam Position Monitor System for CEBAF

CEBAF is a recirculating linac where the beam passes several times through the linac structures. As a result, up to five beams of different energies may be present in the same linac vacuum chambers simultaneously. One method of distinguishing between the beams involves modulating the current for a time interval of less than one revolution period. In this paper, a very simple low cost beam position monitor system based on the detection of this modulation is presented. Initial results indicated that 1mm displacements for beam currents of 1 micro-amp can be measured. With the incorporation of several improvements to the present monitor design, the sensitivity is expected to be increased to 1 mm for a 100 nA beam