Importance

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Abstract

A charged particle beam focussing device in which a pair of rod like electrodes having a potential difference maintained between them are arranged on either side of the path of a beam to be focussed. The configuration of the electrodes is such that the significant electric field between them is confined to a short section of the path of the particles. A second pair of similar electrodes are arranged parallel to and in a plane substantially parallel to the plane of the first pair and displaced in a direction parallel to the plane in which the first pair lie, a potential difference being maintained between the second pair of electrodes. The arrangement is such that by variation of the potentials between the electrodes a beam of charged particles passing along the beam path between the electrodes can be caused to come to a focal line in a predetermined plane. A further device arranged at right angles to the first beam is provided to bring the beam to a point focus. The electrodes are preferably passed through earth reflector planes arranged on either side of the path of the beam.

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First Claim