US2187184A - Electron multiplier - Google Patents

Description

Jan. 16, 1940. K. SIEBERTZ ELECTRON MULTIPLIER Filed Nov. 17, 1937 INVENTOR. KARL S/EBERTZ ATTORNEY.

I Patented Jan. 16, 1940 UNITED STATES PATIENT OFFICE,

ELECTRON MULTIPLIER Application November 17, 1937, Serial No. 174,917 In Germany November 30, 1936 M 4 Claims.

7 The invention relates to an improvement in an electric discharge device serving for the increase of electric currents by utilizing the principle of electron multiplication through secondary electron emission. It is immaterial whether the currents to be amplified are supplied from a -photo-sensitive cathode or from a thermionic cathode and modulated by a control grid.- Electron multipliers of the secondary electron emissionItype have a rowof electrodes which are maintained at difi'erent potentials and which are formed only as plates, or are provided with shields by means of which an electron optical efiect is secured directing in as concentrated form as possible the secondary electrons released at the electrode having the lower potential to the electrode having the next higher potential. In electron multipliers in which the electrodes are formed as platesit has been proposed to avoid mutual disturbance of the individual electrodes by interposed screens which are held at a con- 1 stant' potential.

In accordance with the invention the individual electrodes, which may be simple plate electrodes or electrodes especially designed to obtain a well defined electron optical effect, are arranged concentrically about each other in the form of rings which are of increased diameter in the direction in which the potential increases. In thisway there is obtained on the one hand a favorable shielding of the inner electrodes against outside influences, and on the other hand, the surface load of the individual electrodes. can in this 'way be rendered uniform.

Some illustrative embodiments of the invention' are shown diagrammatically in the accompanying drawing in which Figure 1 is a crosssection and Figure 2 a plan view of the electrode assembly of one form of multiplier having a photoelectric cathode, and Figure 3 is a longi-, tudinal section of a modified form having a thermionic cathode with a control grid. Figures 1 and 2 show, as an example, an electrode assembly in which the individual electrodes are in the form of plates. In this form of device the current to be amplified is supplied from a photo-cathode I on which light may impinge'in the direction of the arrow 2. Flat annular secondary electron emitters or elec- 65 Other fl t 8 1. 1 3? emitters I, 8, 9, and I!) are trodes3, 4, and 5, of different diameters, increasmounted concentric with the cathode l in a plane parallel to the plane of the first set of emitters so as to be opposite the spaces between them. All of the electrodes have impressed on them in the conventional way. potentials which increase from the cathode to. the output. electrode. Between the individual electrodes the cylindrical shielding rings II are arranged. These shielding rings may be maintained at constant potential, for instance, at ground potential, or at a potential which increases in the direction towards the 7 output electrode. The electrons released at the cathode or electrode I, flowing in the direction indicated 'by' the arrows, impinge first on the emitter electrode I, where they cause secondary emission and are multiplied, then on the emitter or electrode 3, this multiplying action being repeated in the direction of the arrows until the multiplied current reaches the output electrode 6, where it can be put to use. If the potential of the electrode or cathode I is zero, and the potential on the 'electrodelis :1:, it will be advisable to impress on the electrodes 8, 9 and I0 the potentials 3x, 5x, and Ix, and on the electrodes 3, 4, 5, and '6 the potentials 2:17, 40:, 6:0, and 8x, respectively. t

Currents influenced by a control grid may be amplified by disposing the control grid opposite the electrode I, with an electron source arranged on the other side of this control grid.

Figure 3 shows an example of construction according to the invention, in which, through appropriate design of the electrodes, the electronoptical conditions are rendered more favorable than in the arrangement shown in Figure 1, al--' though the arrangement of'Figure 1 has the advantage over Figure 3 in that the entire electrode arrangement is more open so that it will be easier to produce layers of high emission property. In the construction of Figure 3 the initial electrode, which may be a photoelectric cathode or a secondary electron emitter and which is designated by I2, has arranged concentrically to it" the annular emitter electrodes I3, I4, I5, and I6, and the final or output electrode I'I. Each of the electrodes I3, I4, I5, and I 6 consists of two profiled rings, produced for instance by pressing, and the electrodes are maintained by braces distributed along their circumference in position to provide an annular channel which is zigzag along a radial section. The annular emitters are spaced to leave between them annular gaps I8, which permit of the development of electrical fields acting as electron lenses to concentrate the electron streams on the electrodes. If the initial electrode I2 is a photoelectric electrode, it will be impinged upon by a light beam in the direction of the arrow Hi. If desired, a thermionic cathode 20 and a control grid 2| may be placed opposite the electrode I2, which, in this case, has applied to it a potential which is positive with reference to the cathode 20, so that there passes to the initial electrode an electron current controlled by the control grid 21. The space surrounding the cathode should be shielded in a suitable manner against the action of the emitter electrode l3.

Tubes made in accordance with the invention have a very low internal resistance, and are well suited for amplifiers for amplifying very high frequencies, where the difficulty arises that in View of tube capacities, the load resistance cannot be chosen high enough to fairly match the internal resistance of tubes of ordinary type. In such an amplifier the natural capacity of the tube does not play such an important part as in the case of tubes of usual construction owing to the low internal resistance.

In the electrode assembly according to Figure 1, as well in the discharge device of Figure 3, the electrodes may be fastened to one or several common supports of insulating material. It is advisable to support the electrodes by several braces of insulating material extending radially of the assembly so that the material for activating the secondary electron emitting surfaces can readily penetrate into the interior of the electrode system.

In an electron multiplier of cylindrical form and constructed in accordance with the invention the secondary electron emitting surfaces increase in area greatly with each stage of the multiplication, so that the density of discharge per unit area of emission and consequent heating of the emitter is Well within safe limits even at the last emitter, where the current is many fold the current at the first emitter. By making the emitters annular and concentric with the initial electrode, the maximum increase in emitter area with each stage of multiplication is obtained.

I claim:

1. An electron multiplier comprising a source of electrons, an annular output electrode surrounding and concentric with said source, two sets of annular electrodes of different diameters mounted concentric with said source and spaced to provide from said source to said output electrode a channel limited by said annular electrodes for directing the discharge from said source radially of said annular electrodes to said output electrode, and annular shields projecting between adjacent electrodes of each set into the channel between said sets to direct the electron flow from an electrode of the first set to an electrode of the second set and back to the next electrode of the first set.

2. An electron multiplier having an annular electrode system comprising an annular output electrode, a'set of spaced annular secondary electron emitting electrodes inside and concentric with said output electrode and of progressively decreasing size toward the center of the system, a second set of similar annular electrodes spaced from said first set, concentric annular shields between. and concentric with said emitting electrodes and extending above the surface of said emitting electrodes toward the median plane of the system, and a source of electrons at the center of said system adapted to emit electrons radially to said output electrode and into the space between said sets of electrodes.

3. An electron multiplier having an annular electrode system comprising a source of electrons at the center of said system, an annular output electrode, and two sets of spaced annular secondary electron emitters inside and concentric with said output electrode and of progressively decreasing diameter toward the center of the system, said sets of emitters being spaced from each other to form a channel extending from said source radially of the system and having annular portions projecting toward and at an angle to the median plane of the system to prevent a direct flow of electrons from said source to said output electrode.

4. An electron multiplier having an annular electrode system comprising an annular output electrode, a source of electrons concentric with said output electrode, and two sets of spaced annular secondary electron emitters of dilifering diameters mounted concentrically with said output electrode between said source and said output electrode and spaced to provide between said sets a channel extending from said source to said output electrode, each set of emitters having annular shields projecting toward and at an angle to the median plane of the system with the edges of opposing shields spaced to leavenarrow annular gaps to produce between adjacent shields of difierent potentials an electron lens effect.

KARL SIEBERTZ.

Images