GB1223873A - Vacuum gap devices - Google Patents

Abstract

1,223,873. Cold-cathode tubes. GENERAL ELECTRIC CO. 25 April, 1968 [19 May, 1967] No. 19712/68. Heading HID. A vacuum-arc discharge device includes two electrode arrays extending from two baseplates respectively and arranged in an interdigitated fashion with respcet to one another, such that the vector product of current density and of magnetic field in the arc discharge is substantially zero in the spaces between the electrodes, whereby the formation of anode spots due to the constriction of current flow by the magnetic field is avoided. The two sets of electrodes 16 and 18 are mounted on end plates 15 and 17 respectively of the metal envelope, and are insulated from one another by the seal 14, which is protected from the deposition of vaporized metal particles by a pair of bafflese.g. 26. Each electrode consists of a central rod 19 or 22 joined at one end to the end plate, and at the other end-which is spaced from the opposite end plate-to a coaxial cylinder 20 or 23, whereby oppositely directed current flow occurs in the cylinder and rod of each electrode, with cancellation of the external magnetic field. The device is evacuated to 10-<SP>5</SP> torr or less, the arc being initiated by the injection of plasma from a trigger assembly 27 which includes a trigger electrode 28 formed of a metallized ceramic cylinder having a scored gap, the metal on opposite sides of which is connected to the portion 29 of the base-plate 17, and to the lead 32, respectively. Alternatively, the arc may be triggered by an electrode which normally contacts the end disc 21 of one or more of the electrodes, and which is capable of being withdrawn out of contact from outside the tube envelope (Fig. 2, not shown); and the sidewall 13 of the envelope may be glass, alumina, or ceramic, protected by a cylindrical conductive shield. In another arrangement (Figs. 4 to 7, not shown), of simpler structure but providing less complete cancellation of the magnetic field, the electrodes projecting from the end plates are solid, the field of a given electrode being partially cancelled by the fields of the neighbouring electrodes. In a further arrangement (Figs. 8 and 9, not shown) the electrodes are in the form of radially extending plate-like vanes, the avoidance of the constriction of current flow arising from the fact that the resultant magnetic field between the vanes is substantially parallel to the direction of the arc current. In modifications of this arrangement, the vanes are in the form of solid segments (Fig. 10, not shown), or are V-shaped (Fig. 11, not shown) in order to provide inter-electrode regions of uniform width.