A fast beam position monitor based on arrays of secondary emission monitors

We describe an instrument for a fast determination of the beam position of a rastered high-energy electron beam with an intensity as low as 10 nA. Two arrays of stripes of thin metal foils, one in the horizontal and one in the vertical direction, are inserted into the beam. They work as a position-sensitive Secondary Emission Monitor (SEM) with a resolution of 1 mm. The charges from the stripes are amplified and converted into position signals using electronics providing a low vibration sensitivity and a fast beam position measurement. At a beam intensity of 10 nA a measurement can be carried out with an integration time of only 130 μs.