A narrow-gap ion chamber for beam motion correction in proton radiography experiments

A small gap, segmented hydrogen ion chamber was constructed for beam position monitoring in dynamic proton radiography imaging experiments at the Los Alamos Neutron Science Center. The radiographs, acquired by a set of individually gated CCD cameras, are normalized ("flattened") using CCD images of the raw beam. However, movement of the beam centroid from pulse to pulse introduces errors in this image normalization process. The ion chamber operates in a burst mode and provides measurements of beam centroid location on a pulse-to-pulse basis. Performance was tested for pulse time separations as low as 358ns. The chamber makes possible flattening of dynamic CCD images on a per pulse basis and substantially reduces normalization errors due to beam movement.