GB1326677A - Electron gun devices - Google Patents

Abstract

1326677 Electron guns HITACHI Ltd 19 April 1971 [1 April 1970] 25525/71 Heading H1D An electron gun device as in an electron microscope for example, includes a field emission type cathode having a tip 1 of needle shape, means for heating the tip, an anode 2, and means for applying electric voltage between the tip and anode to produce a field for electron emission, shield electrode 12 surrojnding the anode and means for applying the same voltage to the shield electrode as to the cathode e.g. via spring 13 whereby the shield electrode shields the anode from the earthed portions of the device. Second anode 3 on insulator 11 may be included, while the shield electrode 12, includes portion 16 which shields the two anode from one another, as well as the earthed parts, discharge readily occuring between contact portions 17, 18, or 19, 20. Second shield 14 may surround the end portion of insulator 6 in which the cathode tip is mounted, and hair-pin W filament 8 adjoins terminal electrodes 8, 9. -30 kv may be applied to tip 1, -27 kv to anode 2 through contact spring 10, and second anode 3 earthed. The field on tip 1 may reach 10<SP>7</SP> to 10<SP>8</SP> v/cm and electrons are caused to emit from the tip when an electric current flows through filament 8 to heat it. The tip may be a W wire of 0À1 to 0À2 mm diameter with a 500 Š curvature at the end. Insulator 15 may withstand at least 5 kv. Portion 16 is modified in Fig. 2 (not shown) to portions 12<SP>1</SP> of different geometry.