Source of beams for producing a high intensity charge carrier beam

854,277. Electron beam apparatus. ZEISSSTIFTUNG, C., [trading as ZEISS, C. [Firm of]]. Aug. 27, 1959 [Sept. 6, 1958], No. 29387/59. Class 39(1). In a beam generating system for producing a high intensity beam of charged particles comprising a hairpin cathode 1, Fig. 1, a control electrode 2, and an anode 3, a cylindrical magnetic lens 5, 6, adjustable both with respect to field strength and to azimuthal positioning of its major axis is attached to the anode 3 for correcting the astigmatism of the beam generating system. The cylindrical lens consists of two permanent magnets 5, 6 radially arranged on a rotatable disc 4 in threaded engagement with the anode. The magnets are positioned on mounting members 10, 11 which slide in radial slots in the disc 4 and are biased outwardly by springs 7, 8. A ring 9 forces the magnets towards each other when moved upwardly. In another embodiment two pairs of magnets are mounted on separate discs which can be rotated separately or together. In a further embodiment suitable in an apparatus for working e.g. drilling, milling or welding material with a high intensity beam of charged particles, the lens comprises 8 radial electromagnets 22, Fig. 5, which may be separately adjusted electrically and which are carried by a rotatable disc 21 in threaded engagement with the anode 20. The coils and pole pieces are potted in resin. A second cylindrical lens may be provided to correct astigmatism in a second direction, or the cathode may be of wire having a semi-cylindrical profile so that an approximately spherical point may be formed at the end of the hairpin. A mounting guide may be provided for fixing the azimuth of the cathode. The control. electrode bias may be pulsed to produce a pulsed beam.