Patent GB-1080211-A (GB)
Title: Improvements in or relating to spark gaps
Inventor: MARTIN JOHN CHRISTOPHER
IPC: H01J21/00
Filed: 1964-01-03
Abstract: 1,080,211. Discharge apparatus. UNITED KINGDOM ATOMIC ENERGY AUTHORITY. Dec. 23, 1964 [Jan. 3, 1964], No. 430/64. Heading H1X. A spark gap includes a trigger assembly paced from a main electrode of the gap, the assembly including a trigger electrode having a sharp edge and separated from a further electrode by a thin layer of dielectric material which extends beyond the sharp edge, such that the application of a trigger pulse between the trigger electrode and the further electrode produces corona discharge at the sharp edge. A trigger assembly for a main spark gap between electrodes 1 and 2 is formed by a narrow copper band 9 mounted around an insulating pillar 6 from which it is separated by a layer of insulant 10, a sheet copper electrode 11 connected to the mid-point of the supply potentiometer of electrodes 1 and 2, a further layer of insulant 12, and a second sheet copper electrode 13, which is connected to electrode 2 by tab 16, to form a capacitor between electrodes 2 and 11. The trigger pulse is applied between electrodes 11 and 9, the intense field at the sharp edge of the latter causing corona discharge, with consequent successive breakdown of the gaps between electrodes 9 and 2, and 2 and 1. In modified apparatus (Fig. 3, not shown) for use at higher voltages, the capacitance between electrodes 9 and 11 is reduced by housing the portion of electrode 11 directly beneath electrode 9 in a groove in pillar 6 (Fig. 4, not shown), the periphery of electrode 9 just overlapping the edge of the recess. Alternatively, sheet 11 may be divided circumferentially into two halves, the inner edge of each just lying under electrode 9. In a further embodiment (Fig. 5, not shown), a plane trigger assembly constituted by electrodes 9 and 11 (Fig. 6 or 7, not shown) is disposed between main electrodes 1 and 2; for minimum trigger voltage and fast working, the two halves of the gap in such an arrangement have neither equal spacing nor voltage; a discussion of the optimum conditions is included. In the trigger assembly of Fig. 9 (not shown), a copper strip 211 is axially disposed with respect to, and held upon, on insulating cylinder 106 by an insulating sheet (not shown) wrapped around the whole, a further, circumferentially displaced copper strip 114 being held upon the sheet by copper wire 209 wrapped helically around the sheet, the trigger voltage being applied between the two copper strips and giving rise to corona discharge from the portions of the copper wire lying above the innermost strip. In the self-triggered gap of Fig. 10 (not shown), a copper strip 114<SP>1</SP> is held by wire 209<SP>1</SP> upon an insulating sheet (not shown) wrapped around a metal cylinder 106<SP>1</SP> which is joined by a metal member 122 to a second parallel metal cylinder 121, the spark gap being defined by the second metal cylinder and the wire wrapped around the first. In a further self-triggered gap (Fig. 12, not shown) a spherical electrode 321 is held at an adjustable height above a plane insulating block 306 having, in a shallow recess disposed beneath the sphere, a disc electrode 311 covered by an insulated, earthed metal sheet 309 having a circular aperture 350, the edge of which just overlaps that of the disc electrode. The potential induced by the sphere between the electrode disc 311 and the sheet electrode 309 produces corona discharge at the edge of the aperture in the latter.