GB1334767A - Electron beam apparatus - Google Patents

Abstract

1334767 Automatic stabilization of electron beams PHILIPS ELECTRONIC & ASSOCIATED INDUSTRIES Ltd 25 Aug 1971 [28 Aug 1970] 39879/71 Heading G3R [Also in Division H1] A beam stabilizing arrangement, particularly for an electron microscope, includes a doublefocusing magnetic bending device providing a field perpendicular to the beam. The beam emerging from the bending device is sampled to produce a control signal for application to a beam accelerator. In the system shown, a Van de Graaff generator belt 4 supplies electrons at a high-voltage electrode 5 to an electron gun 7. A beam 8 of electrons is accelerated in a tube by ring electrodes 11 and passes through a diaphragm 17 to a bending magnet 16 including inclined pole plates and magnetic windings, Fig.3 (not shown). The magnet 16 forms an image at its exit end close to a foil or pair of foils 18 which peripherally intercept a small fraction of the beam and scatter it to a detector 19 comprising a diode in which conduction is dependent on electron bombardment. The remainder of the beam passes to an image-forming device 20, Fig.1 (not shown) The detector output is amplified 51 and corrected for beam current and diameter variations before passing to an opto-electronic converter 53 which supplies a photo-amplifier tube 54 controlling a variable voltage source 55 connected between the high voltage electrode 5 and the first electrode 56 of the accelerator tube. The electron gun 7 is connected to the electrode 56 through a constant voltage source 57 and has a current control 58. Stabilization of beam position and velocity is achieved.