US1938374A - Electron discharge device - Google Patents

Description

Dec. 5, 1933. E, E CHARLTQN 1,938,374

ELECTRON DISCHARGE DEVICE Filed Nov. 11 1922 JHEA'TERJ Inventor: Ernest E.Ch arlton,

2%2 His Attorney Patented Dec. 5, 1933 ELECTRON DISCHARGE DEVICE Ernest E. Charlton, Schenectady, N. Y., assignor to General Electric Company, a corporation of New York;

Application November 11, 1922 Serial No. 600,207

1 Claim.

The present invention comprises an improved electric discharge device of the non-self-sustainingtype, such as photo-electric devices.

Most photo-electric devices now in use contain a filling of fixed gas, such as argon or nitrogen. The current thus conducted varies with conditions such as applied voltage, intensity of illumination and so forth, but is never greater than a few hundred microamperes.

I have discovered that when an alkali vapor is used in discharge devices in place of other gases, that currents of a higher order of magnitude may be transmitted. Particularly favorable results can be obtained by transmitting current through caesium vapor at an appreciable vapor pressure.

The accompanying drawing illustrates three embodiments of my invention. Figs. 1 and 2 show photo-electric devices containing a heater, the device of Fig. 1 having three electrodes, and therefore suitable as an amplifier and the device of Fig. 2 having two electrodes; Fig. 3 shows still another modification with an external heating means.

The device shown in Fig. 1 comprises an envelope, or container 1, consisting of suitable refractory glass into which are sealed several conductors. The conductor 2 leads to an electrode 3 capable of emitting electrons when illuminated, preferably consisting of caesium, rubidium, although other alkali metal can be used. The conductors 4, 5, are connected to a heater 6, consisting of a fine wire of tungsten, or other suitable resistance material, and a conductor 7 leads to a control electrode 8, one end of which is sealed into the glass stem 9 which is constituted by the flattened portion of the glass envelope. In this modification the anode consists of a wire 10 which is sealed through the stem 9 and is surrounded by a sleeve 11 of glass within the envelope except for an exposed tip which projects beyond the glass sleeve. It is also possible to utilize the heater 6 as an anode when the heater operates at so low a temperature that no electrons are emitted by it, thereby dispensing with a separate anode 10.

Fig. 2 shows a slightly modified device in which the cathode consists of a cup 15 consisting of nickel-iron alloy, preferably copper coated, which is sealed into the container at 16, and is provided with a layer 17 of caesium, rubidium, or other suitable alkali metal. The anode is constituted by a wire 18 consisting of tungsten or other suitable material sealed into a stem 19 projecting through the side arm 20. A heater 21 is connected to leading-in conductors 22, 23.

In the modification shown in Fig. 3, the cathode is constituted, by a metal disc 24 consisting of molybdenum, copper or nickel on which a layer of alkali metal is deposited. The anode 25 is constituted by a wire sealedinto the side arm 26. An external heating means is diagrammatically 69 indicated by the enclosure 27.

In the preparation of my improved photo-electrio device the glass envelope or container is evacuated and baked out at about 450 C. according to the most improved methods of electron tube 55 exhaust. When the interior has been thoroughly freed from water vapor and deprived of gas an alkali metal, preferably caesium, is introduced from an external chamber communicating with g the container 1. The drawing shows a sealing off tube 12, which remains when the external chamber is removed, by heating the communicating tube to the softening point in the usual manner. This external chamber (which is not shown) may contain a mixture of caesium chloride and calcium by the interaction of which at an elevated temperature metallic caesium is formed which distills over into the container 1 in a very pure state, both the main container and the reaction chamber being evacuated. When sufll- 99 cient caesium has been introduced the external chamber is removed without admitting foreign gas, and the tube 1 sealed off from the pump as indicated at the tube 13.

Even at room temperature a greater photoelectric current is obtained in devices prepared in accordance with my invention containing caesium and rubidium when suitable potential is impressed between the electrodes 2 and 10, and

the cathode is suitably illuminated. At elevated temperatures the device will conduct currents of higher order of magnitude than heretofore conducted in photo-electric devices. For example, when the device is heated up to about 100 0. either by means of an internal heater, 9 as shown in the device in Figs. 1 and 2, or by externally applying heat, as indicated in Fig. 3, a photo-electric current of about five to fifty milliamperes is obtained depending on conditions with an impressed electromotive force of 300 about 250 volts, when illuminating the cathode by a lamp of about 750 candle power. While with operating bulb temperatures from room temperature upward a substantial improvement in current with a given light source is obtained in the presence of pure alkali metal vapor, preferably the operating temperature should be somewhere within the range of about 100 to 125 C.

The volt-ampere characteristics of my new device is positive, that is, as the voltage across the tube increases the current also increases.

The method of maintaining the temperature by means of a heater above the caesium electrode, as shown in Figs. 1 and 2, is recommended instead of an external heating space about the device, as thereby the neighborhood of the cathode is maintained slightly cooler than the rest of the tube, and the alkali metal is caused to condense upon the cathode.

Cesium at a temperature of about 100 C. has a vapor pressure of about one micron. I find it is highly sensitive to the range of wave lengths found in ordinary light. When using rubidium as a photo-sensitive material a somewhat higher operating temperature is advisable, say, from 120 to 150 C. For a given pressure, a temperature of about 10 C. higher is required for rubidium than for casium. V

A device such as shown in Fig. 1 containing current controlling electrode 8 can be usedas an amplifier or radio detector by impressing upon the electrode 8 variable electric voltages or charges in the well understood manner. I have obtained by this means good tones in a telephone circuitwhen using such a device in the reproduction of speech and music. For example, in Fig. l, I have shown an input circuit 28, 29 containing the secondary of an input transformer 30 the primary of which is supplied with the current to be amplified. The circuit 31, 32 connected to the main electrodes 3 and 10 contains a source of current, represented by a. battery 33 and an electro-responsive device represented by a telephone 34. During operation the cathode is illuminated by light of steady intensity either from an external source or derived from the internal resistor when operated at incandescence.

Where in the appended claims I have specifically included cesium vapor as the current carrying'medium, I wish also to include as equivalents the vapor of other alkali metals used in the absence of appreciable amounts of other or foreign gases in the discharge space of devices operating with a non-self-sustaining discharge. The metals caesium and rubidium are preferred because of their relatively high vapor pressure enabling them to be used more readily without attack of the container material which conveniently consists of glass.

What I claim as new and desire to secure by Letters Patent of the United States, is:-

A photo-electric tube comprising a container, electrodes therein including a cathode, an anode and a control member, said cathode consisting of photo-sensitive material adapted'to be vaporized when heated, means in said tube for heating said material, said means including a heater element positioned nearer the control member than the cathode whereby the cathode is maintained at a lower temperature than the control member and the vaporized material is caused to condense at a position remote from the control member.

I ERNEST E. CHARLTON.

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