Patent GB-1417643-A (GB)
Title: Electron multipliers
IPC: H01J43/24
Filed: 1973-01-19
Abstract: 1417643 Electron multipliers MULLARD Ltd 6 Nov 1973 [19 Jan 1973] 2842/73 Heading H1D [Also in Division B3] A channel plate multiplier has channels with an L/Di ratio #3, and an Ai/Ae ratio #5, each channel having at least the major part of its emissive surfaces at acute angles 0 such as to provide a flared channel form of reducing cross-section from input to output faces. L is the axial length, Di the input diameter or width (e.g. the side for square cross-section), Ai/Ae being the input to output aperture area ratio. In another aspect, each channel has a principal emissive surface at angle # to the normal to plate faces, and other surfaces of larger combined area normal to the faces such as to provide a flared channel form reducing towards the exit aperture. Equipotential surfaces (Fig. 2, not shown) are preferably at 50 to 75 degrees to the secondary emissive surfaces, and may be controlled by the angle #, the photo-cathode in a proximity type (Fig. 1) or conical anode type (Fig. 12, not shown) image intensifier and/or by a grid preferably in contact and with one or more grid conductors across each aperture, the grid may be bowed. Alternatively, an electron permeable conductive film may be used across the apertures which prevents ion feedback and is as in patent Specification 1,175,599. Fig. 2 illustrates field lines for a matrix with resistive surfaces, variations for bulk conduction being also discussed. Materials may be glass (e.g. lead glass) or conductive ceramics. Al may be coated in the channels and on one or both ends provided with an insulator and a resistive secondary emitting layer coated in the channels, e.g. a two part layer of s/c Si layer (500) and alumina (60). Fig. 3 (not shown) illustrates conical channels; Fig. 4 (not shown), square pyramids; Fig. 5 (not shown), irregular pyramids with slit aperture (As), Figs. 6, 7 (not shown), a " ridge " geometry, Fig. 7, having only one multiplier surface per channel; Fig. 8 (not shown), differing inclination angles which may be applied to Figs. 3 to 7, as may curved profiles as in Fig. 9 (not shown). Orthogonal surfaces not intended to multiply may become partially coated and may provide small gains. The section may be convex (Fig. 10, not shown), without a grid, and stepped. Exit edges may not be sharp due to electrode penetration, Fig. 14a (not shown), moulding or pressing fabrication, and may be followed by a diverging extension with conductive walls or resistive walls which provide additional acceleration, Figs. 14b, 14c (not shown). Electrons do not land on surface R2 as it is widely flared. Fig. 14c may be two bonded sheets, and electrode (E2) may intervene (Fig. 14d, not shown). Exit sections may also be parallel with resistiveemissive walls. Fig. 15a (not shown), which may also be inverted, includes substrate electrode (E2m) and insulator (Mi). Electrode (E2) and substrate (E2m) may be separate components. Fig. 15b (not shown) includes metal substrate (Mc) (e.g. Al) with insulator (Mi) (e.g. anodized Al). Multiplying surfaces should be smooth as produced by a machined master for pressing or moulding, Figs. 16, 17 (not shown), respectively. Fig. 16b includes rubber pad 4 and protrusions 3A (Fig. 16c) removed by machine. Fig. 17a (not shown) includes liquid or softened glass 13, irregularities removed by etching. Surface reduction produces resistive surfaces. Indentations may also be stamped or spark eroded. Input and output electrodes are usually continuous, but may be parallel stripes. Applications include c.r.t. and camera tubes and non-scanning image intensifler tubes for medical X-ray use. Fig. 13 (not shown) is an index type colour TV display tube with tricolour striped screen and scanned channel plate I, Figs. 5 to 7, type producing an elongated spot. Phosphor screens may be on a glass window or support W, or the curved face plate with curved plate I. Plate dimensions are given. Reference is made to other Specifications.