US2238607A - Electron multiplier - Google Patents

Description

April 5, 1941. H. SCHNITGER 2,238,607

ELECTR ON MULTIPLIER Filed Jan. 24, 1959 ATTORNEY Patented Apr. '15, i941 UNITED STATES: PATENT OFFICE Herbert Schnitger, Berlin-Spandau, Germany, assignor to Fides Gesellschaft fiir die Verwaltun: und Verwertung von gewerblichen Schutzrechten mit beschrankter Haftung Berlin, Germany, acorporation of Germany Application January 24, 1939, Serial No. 252,553

In Germany June 8, 1938 1 Claim. (01. 250-175) The invention relates to amplifying tubes and especially the type of tube known as an electron multiplier.

An object of the invention is to increase the efficiency of the type of tube known as electron I Fig. 1 is a cross-section through a tube having a preferred embodiment of the invention.

Fig. 2 is an enlarged detailed view of a portion of'Fig. 1.

Fig. 3 is an enlarged detailed view of a modification of electrode structures of Fig. 2.

Fig. 4 is a cross-section through a modification of the electrode arrangement disclosed in the other figures.

In amplifier tubes, and especially those operated for electron multiplication through secondary emission, a succession of grid-shaped electrodes in series is utilized. These grids are connected to potentials which increase as the anode is approached. The amplifying action is brought about by the fact that the secondary electrons liberated by the impact of electrons against an electrode come partly by their own velocity under the influence of the field of the following electrode which field reaches through the grid mesh and these electrons are accelerated and finally strike against the following electrode. Only a relatively small part of the emitted secondary electrons are under the influence of the next following electrode and can attain the next higher voltage. Accordingly, the efficiency of such a tube is small and a relatively high number of steps must be used and also a high voltage applied in order to obtain the desired degrees of amplification.

The invention contemplates utilizing a magnetic field to increase the production of secondaryelectrons in a secondary emission multiplier with screen or grid-shaped electrodes. This magnetic field lies about perpendicular to the discharge path preferably in the direction of the grid laterals which are so adjusted and dimensioned that under their influence the electrons for the most part strike a part of the surface of each individual electrode which is facing the following electrode. Provision can also be made that the mean electron orbit is practically tangent to the plane of the electrode surface and the electrons in most part strike against the side surface of the laterals of the grid or screen electrode and thus produce secondary electrons which upon emissionare under the influence of the electro-static field of the next following electrode of high voltage. Moreover, a large part of the electrons hit the electrode part at glancing angles, so that for this reason a relatively high yield of secondary electrons is produced.

By suitable choice of electrode spacing, mesh, strength of magnetic and electric fields, a slope of the final end or tail ofthe electron orbit can be produced directing practically the total crosssection of the electron bundle towards one wire of the next electrode and preventing any portion of the electron bundle from passing by this electrode and striking other electrodes which have no accelerating effect on them. In view of the considerable curvature of the orbit of the electrons, produced by the magnetic field, it is desirable that the individual electrodes be arranged opposite one. another in direction of the deflection of the electrodes in order to avoid losing a part of the electrons.

A preferred embodiment of the invention is disclosed in Fig. 1 in which the primary electrode l is preferably a photo-cathode. A hot cathode with control grid can also be utilized. A plurality of grid-shaped intermediate electrodes 2, 3, 4, 5, and B are inserted between the cathode l and the anode I. These electrodes are preferably grid laterals formed of wires perpendicular to the plane of the drawing. All electrodes are enclosed in a highly evacuated container 8. The magnetic field arranged according to the invention, penetrates the electrode system perpendicular to the plane of the drawing.

This magnetic field can be produced, for example, by the coil 9 illustrated in Fig. 1. As an alternate, the container can also be placed between the pole pieces of a, permanent magnet or of an electro-magnet.

In Fig. 2 a portion of the discharge system is illustrated in a magnified scale. The electron orbits are indicated by dotted lines. It is noticed that the electron travelling, for example, from grid wire 2, strikes the succeeding electrode 3 in a curved path so that when the secondary electrons are emitted from 3 they are on the side of the electrode 3 which is facing the electrode 4 and accordingly, are immediately under the influence of the field produced by the higher voltage of the electrode 4.

Instead of circular grid laterals, fiat laterals can also be used. These fiat laterals might be strips which are bent preferably at an acute angle towards the axis of the system and are so arranged that the surface parts hit by the electrons face the following electrode of higher voltage. Such an example of this type is shown schematically in Fig. 3. The axis of the system is indicated by the arrow ID. The electrodes consist of a number of strips which can be'formed like the so-called meshed grid in amplifier tubes. Their position to the electron orbits is apparent from the illustration in Fig. 3, namely, at an angle to the direction of the axis and also the plane of the strips forming the same electrode are at an acute angle to the direction of the system axis.

Instead of arranging the individual parts of the grid or screen electrode in planes that can be placed in curved surfaces, Fig. 4 illustrates an example in which concentric electrode structure is utilized. The photo-cathode illustrated in I is preferably replaced by a hot cathode indicated by II and a control grid I2 surrounding it. The grid electrodes 2, 3, 4, 5, and 6 are placed radially intermediate the hot cathode ll, control grid I 2 and the anode I. The magnetic field provided according to the invention is perpendicular to the plane of the drawing and can be produced similar to the magnetic field of Fig. l. The electrode systems themselves are formed of Wires or strips which are arranged along a concentric cylindrical surface. Through suitable choice of electrode space, voltage, and strength of magnetic field, the electron orbits are substantially tangent to the electrode surfaces so that the electrons for the most part strike surface parts and produce secondary electrons which are directed and facing the next electrode of higher voltage. One of such electron orbits is indicated by dotted lines in Fig. 4.

An improvement in efficiency is obtained by the grid laterals being arranged diagonally to the magnetic field. In the use of screens with crossed wires, the parts of the electrode diagonal to the magnetic field contribute to the amplification. It is not essential that the electrode wires or laterals lie in one entirely fixed direction to the magnetic field, but it is sufficient if they lie in a surface which does not cut or only slightly cuts the magnetic field. It is also not essential for the object of the invention that the electrons liberated at one grid lateral strike the neighboring lateral of the following electrode. It is sufficient, if any lateral of this electrode is impinged u-pon. It is apparent, that many modifications may be made in the number, form and arrangement of the various parts illustrated in the preferred embodiments.

I claim:

An electron multiplier comprising a cathode and an anode spaced therefrom, a plurality of grid electrodes therebetween, said grid electrodes having flat laterals inclined to the axis from the cathode to the anode and having one side facing towards the cathode and the other side facing towards the anode, and means for curving the path of electrons to strike the facesof said grid electrodes facing towards the anode.

HERBERT SCI-INITGER.

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