US2283004A - Electron multiplier - Google Patents

Description

May 12 1942 R. GEBAUER :TAL 2,283,604

ELEOTRON MULTIPLER Filed Aug. so, 1939 Patented May 12, 1942 sNTj OFFICE ELECTRON MULTiPLIEn Rudolf Gebauer and Heinrich Freiherr Rausch von.Traubenberg, Berlin, Germany, assignors to C. Lorenz Aktiengesellschaft, Berlin-',Tenipelhof, Germany, a company g Application August 30, 1939, Serial No. 292,632

In Germany August 30, Y1938 1 claim. (Cl. 2504174) To lamplify small photo-electric currents by means of an emission of secondary electrons is a method that has been practised with success. Also it has been proposed to employ the same principle in connection with electrons produced by a glowing cathode. In this regard, however, disturbing effects arise. In the rst place the products of volatilization emanating from the glowing cathode are diiiicult to keep away from the so-called impact electrodes, that is, electrodes which 'are adapted to emit secondary electrons by the impact of primary electrons. Such volatilization products change the secondary emission of these electrodes and thereby cause the sensitiveness of the amplifying arrangement to vary during operation. The chief problem therefore is to prevent the volatilization products from reaching the impact electrodes and thereby to insure that only the electrons shall arrive at these. In order to perform this the invention provides an arrangement in which the volatilization products emanating from a thermal source of electrons are caught by a suitablyshaped grid, whilst the electrons are by a magnetic field caused to avoid such cathing grid and hence to arrive at the impact electrodes. The volatilization products are not deflected by the magnetic field. Even if electrically charged, their rectilinear path will be affected by a magnetic eld to a very slight extent only as compared with the electrons, because the mass or substance of these is very much smaller than that of the volatiliza-v tion products. A suppressor grid may be arranged to neutralize the secondary electrons arising at the catching grid. The current passing through the catching grid, and which is free from the secondary electrons arising at this grid, arrives at the concentrically arranged impact electrodes and is in well-known manner still further amplified. The number of such impact electrodes is suited to the special conditions of each case.

In the accompanying drawing, Fig. 1 is a diagrammatic cross-sectional view showing one embodiment of the invention, while Fig 2 is a View similar to Fig. l and illustrating a second embodiment thereof.

K denotes a directly or indirectly heated glowing cathode surrounded with a control grid I 2, 3 designate grids which comprise tapes arranged parallel to the cathode K. These grids are of the same positive potential with respect to the cathode and constitute the catching grid which, as stated, is designed to catch the Volatilization products emanating from the cathode in ous, as will be clear.

rectilinear directions. To suchend the tapes forming the grid 3 are arranged to coincidewith the openings of grid 2, that is, with the interspaces between the tapes thereof. grid 23, which in the present special case also acts as a screening grid in a manner similar to the usual amplifying tubes, is concentrically encircled with impact electrodes 4, 5, 6 A. The positive potential increases from electrode to electrode, that is to say, electrode 4 has a higher positive potential than grid 2, 3, while electrode 5 is of a higher positive potential than is electrode 4, and so on. The last electrode, that is, the catching anode A, is thus given the highest positive potential. The electrodes 4, 5, 6 vto A are made of a line-meshed wire gauze, for instance, and are covered with a layer of high secondary-emission material. The collector electrode A may be substantially continucathode K. By controlling the stream of electrons in this way the electrons are caused to traverse the grid 2, 3 and then to pass through the electrodes 4 to A for further amplification Y whilst the volatilization products will be kept away from these electrodes. The electrons passing through the grid 2, 3 strike against the wires of the electrode or grid 4, this being given a positive potential higher than that of the grid 2, 3, and here act to release secondary electrons. These are attracted by the electrode 5, this being of a positive potential higher than that of electrode 4, and when striking against electrode 5 release a still greater number of electrons which in their turn are attracted by electrode B, etc. The electrons, suitably multiplied in this way, are finally received by the catching electrode or anode A and thence pass through a load resistance not shown here.

The catching grid 2, 3 represented in Fig. l may be replaced by the grid 2' illustrated in Fig. 2. Suchgrid is shown here as used in connec tion with a pentode, for example, the anode cur-y rent of which is amplied by secondary electrons arising at concentrically arranged electrodes in the manner before described. The grid 2' is of tubular shape and is composed of tapes which are parallel to the cathode K These tapes, vhow- The catching In order to aid the elec-l field.

ever, have not the tangential position shown in Fig. 1, but are so positioned and are spaced apart by such distances that volatilization products emanating from the cathode K shall be screened or caught by grid 2. This will be attained if the cathode is not Seen when looking at it in radial direction. Also here the grid 2' while catching the volatilization products at the same time acts as a screening grid in a manner similar to the usual amplifying tubes. However, grid 2', and grid 2', 3, Fig. 1, as well, may be used instead for another additional purpose, such as for control effects, for instance. Fig. 2 a magnetic field of suitable direction and intensity aids the electrons when passing through grid 2 whereas the rectilinear path of the volatilization products is not. inuenced by thisV Consequently, the volatilization products.

will be deposited on the grid 2'. As a result, however, the secondary emission of grid 2 is varied during operation. In order to avoid detrimental iniluence of such variation and to prevent the secondary electrons originating at the grid 2 from reaching the electrode 4, this being of a positive potential higher than' that of grid 2', a suppressor grid 3a is located between grid 2 and electrode 4. Grid 3a may be connected to the Alsor in the case ofv Vcontrol grid surrounding said cathode, means for emitting secondary electrons under the impact of electrons arriving from said cathode, means including two electrically connected generally cylindrical parts encircling the cathode, each of said parts having openings which coincide in radial direction with the wall portions of the other part, and means for producing a magnetic field in said multiplier said field for directing the cathode `electrons through the said openings against the means for secondary emission.

RUDOLF GEBAUER.

HEINRICH FREIHERR RAUSCH` voN TRAUBENBERG.

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