US2159529A - Electron multiplier - Google Patents

Description

May 23, 1939. 2,159,529

HANS-WOLFGANG LANGENWALTER ET AL ELECTRON MULTIPLIER Filed Aug. 19, 1937- Patented May 23, 1939 UNITED STATES PATENT OFFICE ELECTRON MULTIPLIER Application August 19,

1937, Serial No. 159,992

In Germany September 1, 1936 I 3 Claims.

This invention relates to electron tubes in which use is made of secondary electrons for amplification. Such tubes are for instance used in television to amplify the emission obtained from photocathodes. They are of especial importance forpicture-analyzing tubes in which a part of an electron image is permitted to pass through a stationary scanning aperture.

It is the object of the invention to design the electron multiplier in such a manner that the electrons which enter the multiplier in the shape of a beam of small cross section first impact one or several solid secondary emitting surfaces, from which they liberate secondaries before they arrive in that part of the amplifier which consists of a series of electron-permeable electrodes. Thereby it may seem advisable to decelerate the arriving high velocity electrons before impacting the first electrode to such an extent that they posses the velocity which is most favorable for secondary emission. The electrons liberated from the first surface canbe guided to the side so that the arrangement of electrodes must not lie in the direction of the arriving ray but may be arranged oblique or transverse to the analyzer tube. The solid surfaces first impacted by the arriving electrons are given such dimensions that by suitable choice of their potentials the most favorable form and path of the electron ray impacting the first permeable electrode is obtained. This arrangement is also preferable in an amplifier connected with a cathode ray tube in which a highly concentrated beam is deflected over an edge, whereby a part of the beam in the amplifier is used to produce secondary electrons.

The figures illustrate several embodiments of the invention.

Fig. 1 shows a cross section through the target end of an analyzer tube with a. built-in amplifier, and Figs. 2 and 3 diagrammatically illustrate other arrangements of emitting electrodes.

The analyzing tube I contains an anode 2 in the form of a wall-coating and a cylindrical electrode 3 which carries an opening I8 on the side facing the cathode. In back of this opening lies an electrode 4', which also has the shape of a cylinder. The electrode 4 carries an aperture l9, which may for instance be of square shape, immediately in back of the aperture I8, which permits an elementary area of the electron image to enter. The electron image is oscillated across the scanning aperture in the known manner. The aperture I9 has the dimensions and shape required by the definition and is thus smaller than the aperture l8. It may, however, be pre-- ferred to use the opening l8 as the scanning aperture and to make the opening l9 correspondingly larger. In back of the opening I9 is disposed an oblique plate 5 which faces the gridshaped electrodes 9 to l4 of the amplifier. In back of this follows an end plate 15. The leads to the electrodes are brought out through the projections 6 and l. The lead 8 to the signal electrode, i. e., to the anode of the amplifier as well as the lead to the cylindrical electrode 3 are brought out through the projection 6, and all other leads are brought out through the projection I. The voltages for the individual electrodes are taken from a voltage divider l6 (diagrammatically shown). The voltages are chosen in such a manner that the electrons are highly accelerated by the high potential, for instance 2,000 volts, at which the cylindrical electrode 3 is held in respect to the cathode. After passing the opening l8 the electrons are decelerated, because the electrode 4 is held at a considerably lower potential, for instance 1200 volts. The electrode 5 is positive in respect to the cathode by an amount which conveys to the electrode a velocity favorable for liberation of secondary electrons. The electrodes 9 to l2 are held at increasing positive potentials. The electrodes l4 and I5 act as decelerating electrodes. Some of the secondary electrons from the electrode 5 impact the inner wall of the cylinder 4 and liberate further electrons, whereas others fly directly to the grid 9. In order to spread the electrons liberated at the plate 5 and make it possible that they can all strike the inner wall of the cylinder, the distance between the electrode 5 and the first grid, is made larger than the distance between the individual grids. The signal electrode I3 is either directly connected to the grid of the first amplifier tube 20, as shown in Fig. l, or may also be connected capacitively by means of a condenser. In the first case the cylindrical electrode 3 preferably carries the highest positive potential, whereas in the second case 3 is preferably connected with the anode 2 of the tube and carries the same potential as 2.

Fig. 2 shows an arrangement in which the electrons passing through the opening IS in the electrode 4 impact a small plate H where they liberate secondaries. These impact the inside of the electrode 4 and the electrons emitted from 4 are guided towards the grid 2|. The inside and outside of the electrode 4 may be also insulated from each other and carry difierent potentials whereby it is preferable to hold the inside at a higher potential than the outside. The other electrodes correspond to the electrodes III to Hi.

Fig. 3 shows an arrangement in which a series of liberations of secondaries takes place from the solid surfaces 22, 23, 24, 25. The electrodes 23, 24- and 25 have the shape of hollow truncated cones. All emitting electrodes, solid as well as electron permeable, are coated with a secondary emitting layer in the known manner.

We claim:

1. An electron multiplier comprising an evacuated envelope having therein an accelerating electrode having an aperture therein, a decelerating cylinder disposed withinrsaid accelerating electrode opposite said aperture and having a smaller aperture in alinement with said accelerating electrode aperture, a secondarily emissive plate positioned in alinement with said apertures and obliquely thereto, a plurality of accelerating electron-permeable grids in alignment with said secondarily emissive plate, an electron-permeable signal grid, a decelerating grid, and a collecting plate disposed sequentially beyond said accelerating grids, said signal grid, declerating grid, a collecting plate disposed within said first mentioned accelerating electrode, and individual leads from'said electrodes sealed through said envelope.

2. In combination with a tube, an electron multiplier device comprising an accelerating anode formed on the wall of said tube, a second accelerating electrode disposed transversely to the longitudinal axis of said tube, an aperture formed in said second accelerating electrode and facing in a direction parallel to said longitudinal axis, a cylindrical electrode disposed within said second accelerating electrode and having a smaller aperture formed therein in alinement with said accelerating electrode aperture, a secondarily emissive electrode disposed within said cylinder in alinement with said apertures but obliquely thereto, a plurality of accelerating grids disposed in axial alinement with said decelerating cylinder, said grids being electron permeable and adapted to be held at successively higher potentials, a signal collecting grid, a decelerating grid, and a collecting plate disposed sequentially beyond said accelerating grids, separate leads sealed through said tube from each of said electrodes, leads from said second accelerating electrode and said signal collecting grid being sealed through said tube on theside thereof opposite to that through which the remaining leads are sealed. v

3. An electron multiplier as claimed in claim 1 wherein the secondarily emissive electrodes include a plurality of truncated cones having sequentially arranged surfaces, said surfaces being coated with secondarily emissive material.

HANS-WOLFGANG LANGEN'W'ALTER. ERNST RUSKA.

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