Use of Movable Beam Position Monitors for Beam Size Measurements

The use of beam position monitors (BPMs) as non-intercepting emittance monitors has been proposed in 1983 by Miller et al. The emittance measurement relies on the beam size dependency of the BPM signals. It is shown that the original proposal can be improved by using movable BPMs. Changing the BPM position with a stepping motor allows accurately calibrating the beam size measurement. The absolute scale on the beam size measurement is given by the scale of the stepping motor and can be determined in the laboratory and measured in situ. Uncontrolled changes of the beam position can be monitored through the use of a BPM triplet.