US1565873A - Vacuum tube and method of operating the same - Google Patents

Description

Dee. 15,1925- H. J. VAN DER BlJL.

VACUUM TUBE AND METHOD OF OPERATING THE SAME Filed Aug. 10. 1920 Patented Dec. 15, 1925.

HENDRIX J. VAN DER BIJL, OF NEW YORK, H. Y., ABSIGNOB TO WESTERN ELECTRIC COMPAN Y, INCORPORATED, OF YORK, N. Y., A CORPORATION 01? NEW YORK.

Application filed August 10, 1820. Serial No. 402,527.

To all whom it may concern:

Be it known that I, HENDRIK J. VAN DER BIJ'L, a subject of the King of Great Britain, residin at New York, in the county of New York, @tate of New York, have invented certain new and useful Improvements in Vacuum Tubes and Methods of Operating the Same, of which the following is a full, clear, concise, and exact description.

This invention relates to vacuum tubes and the method of operating the same. More particularly it relates to means and methods for indicating electrical characteristics of alternating currents. I

For convenience this invention will be described in connection with the type of vacuum tube known in the art as the Braun tube which is used primarily for'the measurement or the indication of electrical power, the wave form of alternating currents or potentials, or similar conditions in electric circuits.

The Braun tube embodying this invention preferably has as a source of cathode rays an electron emitting electrode which may be a filament heated by a battery or other suitable source. A pencil of cathode rays is obtained by having a small aperture in the anode of the tube so that only a narrow beam of the rays passes beyond the anode to a suitable receiving screen which may comprise, for example, a coating of calcium tungstate or other fluorescent material deposited directly on the end of the glass tube. As is well known-in the art, this beam of cathode rays may be deflected electromagnetically or electro-statically in accord ance with the wave forms to be studied.

Heretofore it has been considered advantageous to have the vacuum tube of the Braun type, in which a hot cathode is employed, evacuated to such a high degree that a pure electron discharge is obtained and the tube operates with substantially no gas ionization. Such-would be true for example, if the evacuation were of the order of. .001 micron of mercury.

It has been found, however, that the absence of positive ions from gas ionization tends to produce a diffusion of the cathode ray beam due to the mutual repulsion of the electrons, an effect which is objectionable when accurate results are desired because the beam strikes a much larger area of the receiving screen. There is also a tendelfipy for the receiving screen and the walls of the vessel to become negatively charged, there-' Although any gas may be employed which will not attack the hot filament and cause its rapid deterioration, it has been found preferable to employmercury at a pressure from one to two microns.

As stated above, diffusion of the cathode ray beam takes place when there is substantlally no gas in the tube, but it must also be borne in mind that if the tube contains a large amount of gas, giving a pressure of 100 microns for example, diffusion will also take place. For every gas there is an optimum pressure at which suflicient ionizatlon takes place to substantially prevent the diffusion of the cathode ray beam, but difiusion will take place if the ressure is increased or decreased appreciab y from the optimum pressure. In general it may be sald that or heavy gases, such as mercu vapor, this optimum pressure is of the or or of one or two microns, while for lighter gases, such as nitrogen, the optimum ressure will be considerably greater of t e order often microns for examp e. It is preferable, however, to determine by experiment the optimum pressure for any gas which it is desired to employ.

This invention will be better understood by reference to the following detailed description taken in connection with the accompanying drawing, in which Fig. 1 re resents. an oscillograph tube embodying thls invention Fig. 2 is an enlarged view of the electrode structure of the tube; Fig. 3 illustrates the electrical connections preferably employed in connection with the tube of Fig. 1, and Fig. 4 is a detailed view of the type of grid employed in producing anelectrostatic deflection of the cathode ray beam.

Referring to Fig. 1, the cathode ray tube or Braun tube illustrated therein comprises ,1

an elongated evacuated vessel 6 containing a thermionic cathode 7, a perforated late electrode 8 and a tubular anode 9. well known in the art, when the cathode 7 is heated to incandescence it gives ofl electrons and a narrow beam of cathode ra s will pass through the anode 9 when a su cient source of voltageis connected between the hot cathode and the anode. The beam of cathode rays passing through the tubular anode 9 produces a luminous spot on the coating 10 on the opposite end of the vessel, which coating may be of any fluorescent material, such as calcium'tungstate, de osited directly on the glass and held in p ace by sodium silicate.

The electrostatic deflection of the cathode ray beam in accordance with the wave form to be studied may be produced by impressing the potentials to be studied on the gridshaped structures 11 and 12, for which extrnal connections 13 and 14 are provided. If-it is desired to deflect the cathode ray beam electromagnetically, this may be done by a plurality of coils carrying the current to be studied, such as coils 15 and 16, which are preferably located adjacent a constricted portion of the tube. It is to be understood, of course, that any desired number of deflecting grids or coils may be employed.

Fig. 2 is an enlarged view of the electrode structure of the tube 6 of Fig. 1 and shows the cathode 7 in close proximity to the apertured disk 8, the aperture in which is in alignment with the axis of the tubular anode 9. Lead-in wires 18 and 19 are provided for supplying heating current to the cathode,

while lead-in wires 20 and 21 are provided for applying, suitable potentials to the disk 8 and the anode 9.

The preferred circuit connections for tube 6 are shown in Fig. 3, in which a battery 22 is provided for heating the filament 7 battery 23 for maintaining disk 8 at a positive tential with respect to cathode 7 and a igh voltage batter 24 for producing the desired potential di erence between cathode 7 and anode 9. The potentials to be studied may be impressed on the grid 11 and 12 by meansof lead-in wires 25 and 26 if electrostatic deflection is desired, while the currents to be studied may be impressed on the coils v 15 and 16 by lead-in wires 27 and 28 provided electromagnetic deflection of the oathode ray beam is desired. In the operation of tube 6, it has been found preferable to connect one of the grids 12 directly to anode 9 while connecting the other grid to anode 9 through a path containing a high resist.- ance 30.

The deflecting plates 11 and 12 are preferably of grid-like structure as shown-in Fig. 4, in order that the eddy currents produced therein will be negligible.

The particulai circuit arrangement and electrode construction of tube 6 is not a. part of this invention but is described and claimed in a co-pending application of Johnson, Serial No. 426,505, filed November 26, 1920, entitled Vacuum tubes.

As stated above it has been found preferable not to have tube 6 evacuated to such a high degree that the tube operates as a substantially .pure electron discharge device and independently of gas ionization. The tube would operate as a pure electron discharge device for example, if its evacuation were of the order of .001 micron of mercury. The absence of gas ionization tends to produce a diffusion of the cathode ray beam due to the mutual repulsion of the electrons, and there is also a tendency for the various parts of the tube including the receiving screen 10 to become negatively charged, thereby impairing the efficiency of the tube if not entirely destroying its action.

In accordance with this invention it has been found that these disadvantages may be overcome by inserting a gas in the tube at such a pressure that the electron discharge from the cathode produces a sufiicient num ber of positive ions to overcome the diflusion of the cathode ray beam due to the negative space charge. The presence of the positive ions will also neutralize the tendenc of parts of the vessel to become negatively charged. It is preferable that the gas introduced for this purpose should be an inert gas, that is, onewhich will not appreciably attack the hot cathode 7 and cause its rapid deterioration. The presence of gases such as oxygen which Will attack the filament is avoided by thoroughly evacuating the air a vapor pressure of one .to two microns of I mercury which is sufficient to produce the desired number of positive ions. Mercury vapor is also preferable since its positive ions are heavy and consequently slow moving particles so that each positive mercury ion will remain longer incombined with a negative ion or electron than a light positive ion such as that of oxygen or nitrogen. The slow moving positive 1ons of mercury will therefore be more eficient in preventing the difl'usion of the cathode ray beam than would lighter positive ions of some other gas. It

is therefore preferable to employ in tube 6 a gas having reiat-ively heavy positive ions,

' ten microns for example.

although it is possible to cinplo light gases such as hydrogen, argon or he ium.

The use of mercury is also advantageous for the reason that the pressure in tube 6 will always be the same regardless of the length of time tube 6 is worked. It is well known that cathode ra tubes containing a small amount of air liar-den when used, due to the absorption of the gases by the walls of the vessel. Owing to a suflicient amount of liquid mercury in tube 6, the amount of gas in the tube will always be the same at a given temperature.

If it is desired, however, to employ in tube 6 a permanent gas such as nitrogen for example, it will be preferable to employ means for regulating the degree of evacuation of tube 6 in order to keep the pressure within the tube substantially constant. Since pressure regulating means for cathode ray tubes and X-ray tubes are well known in the art, such a regulator has not been shown in the drawing. The regulating means may be of the form shown, for example, in the British Patent No. 8927 of 1915. In case, however, gases such as nitrogen are employed which are lighter than mercury vapor, the optimum pressure would be more than two microns, It is also to be understood that if desired, any mercury amalgam may be substituted for pure mercury for the purpose of preventing difiusion of the cathode ray beam.

It is to be undersood that the amount of gas pressure in tube 6 will depend to someextent upon the temperature of the hot cathode and upon the potential difference applied between the anode and cathode. A pressure of one or two microns of mercury has been found satisfactory when a filament consisting of a platinum wire coated with earth oxides was employed with the heating battery of two volts producing heating current of 1.3 amperes, while the voltage applied between the anode and the cathode varied from 200 to 1,000 volts or even higher.

That is claimed is:

1. In combination, a gas tight enclosure con taining means including an electron emitting cathode for producing independent of gas ionization a narrow beam of cathode rays, a screen for receiving said rays and an atmosphere of gas incapable of producing rapid deterioration of the cathode in said enclosure at such a pressure as to substantially prevent ditiusion of said beam, said enclosure being substantially free of gas capable of producing rapid deterioration of the cathode.

2. In combination, a thermionic filamentary cathode, means for producing a narrow beam of rays therefrom, a screen for receiving said rays and a gas tight enclosure for containing said cathode, said enclosure containing an ionized gas of a. substance in equilibrium with another state of said substance, said gas being at such a pressure as to substantially revent diifusion of said beam of rays and being suitable for use with a thermlonic filamentary cathode.

3. In combination, a thermionic filamentary cathode, means for roducing a narrow beam of cathode rays tierefrom, a screen for receiving said rays, and a vacuum tube for containing said cathode, said tube containing a gas composed substantially entirely of mercury at a pressure of the order of 1 micron of mercury to substantially prevent diffusion of said beam of cathode'rays.

4. In combination, a thermionic filamentary cathode, means for producing a narrow beam of rays therefrom, a screen for receiving said rays and a gas tight vessel for containing said cathode, said vessel containing a gas, suitable for use with a thermionic filamentary cathode, at a pressure of the order of one to ten microns of mercury, depending upon the atomic weight of said gas, to substantially prevent diflt'usion of said pencil of rays.

5. In combination, a thermionic filamentary cathode, means for producing a narrow beam of rays therefrom, an apertured body in the path of said rays, a gas tight vessel for containin said cathode, a screen for receiving the cam of said rays passing through the aperture in said body, and means within said tube for limiting the area of said screen on which said beam of rays impinges to a size approximating the size of the aperture in said body, said means comprising an atmosphere of gas, incapable of producing rapid deterioration of the cathode, at a pressure not greater than the order of ten microns of mercury nor less than one micron of mercury.

6. In combination, a gas tight vessel containing means including an electron emitting cathode, for producing independent of gas ionization a narrow beam of cathode rays, an apertured body in the path of said rays, a screen for receiving the beam of said rays passing through the aperture, and means within said vessel for limiting the area of said screen on which said beam of rays impinges to a size approximating the size of the aperture in said body, said means comprising a gas composed substantially entirely of mercury at a pressure of the order of one to two microns of mercury.

7. In combination, a gas tight vessel containing means including an electron emitting cathode for producing independent of gas ionization a narrow beam of electrons, a screen for intercepting said beam and an atmosphere of gas, suitable for use with an electron emitting cathode, at a pressure of the order of one to ten microns of mercury dependent upon the atomic weight of the gas, said gas being ionized by collision with said electrons whereby a plurality of positive ions are added to said beam for preventing the diffusion of said beam due to the mutual repulsion of said electrons and for preventing said screen from becoming negatively charged.

8. 'A combination, accordin which said gas is composetf substantially entirely of mercury vapor at a pressure of the order of one to two microns of mercury.

9. In combination, a vacuum tube containing means including an electron emitting cathode and an anode for producing inependent of gas ionization a narrow beam of rays from said cathode, and means for impressing between said anode and cathode a voltage of the order of two hundred to a thousand volts, said tube containing an atto claim 7, in

mosphere of gas, incapable of producing rapid deterioration of the cathode, at such a pressure as to substantially prevent difi'usion of said beam free of gas capable of producing rapid deterioration of the cathode.

10. In combination, a gas tight enclosure containing an electron emitting cathode, means comprising an anode for producing a and being substantially narrow beam of electrons from said cathode, means for impressing between said anode and cathode a voltage of the ,order of two hundred to a thousand volts, and a screen for receiving said beam, said enclosure containing an atmosphere of gas, suitable for use with an electron emitting cathode at a pressure of the order of one to ten microns of mercury to prevent the diffusion of said beam and to prevent said screen from becomin negatively charged.

11. he method of preventing the difi'usionof a beam of cathode rays produced independent of gas ionization from an electron emitting cathode, in a gas tight vessel, which method comprises ionizing a gas incapable of producing rapid deterioration of the cathode introduced into said vessel at a pressure of the order of one to ten microns of mercury so as to add to said beam a plurality of slowly moving positive ions whereby the mutual repulsion of the negative electrons comprising said beam is neutralized.

In witness whereof, I hereunto subscribe my name this 2nd day of August A. D., 1920.

HENDRIX .I. VAN der BUL.

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