US1701356A - Electrical discharge device - Google Patents

Description

w. .BRUCKEL EI' AL.

ELECTRICAL DISCHARGE DEVICE Feb. 5; 1929.

Filed June 5, 192A 2 Sheets-Sheet Inventors WuLdemclr Br-UckeL Franz Lausfer.

Their Attorney.

Feb. 5, 1929.

W. BRU CKEL ET AL ELECTRICAL DISCHARGE DEVICE Filed June 5, 1924 2 Sheets-Sheet 2 Invento r-s WaLdernar- Bn'jckel.

Franz Laust'er The-LrAttorney Patented Fa. 5,1929.

PATENT OFFICE.

wammm .BB'UCKEII, 013mm,

GERMANY, ASBIGNOBS TO GENERAL YORK- AND FRANZ LAUSTER, OI IBAUISCHULENWEG, ELECTRIC COMPANY, A COBPOBLTIOII 01' m DISCHARGE DEVICE;

LPP LIUOII 1110 Inc I, 1984, Serial H0. 717,943, and in Germany June 9, 1928.

The present invention relates to improvements in electron emittin electrodes intended for use in devices of t e space current be neutralized or compensated so that they will exert no deviating influence upon the space current originating from such cathode.

It is another object of the invention to provide a cathode which .shall be capable of 29 withstanding prolonged operation with heavy currents.

The current used for heating the cathode of an electron discharge device attains considerable magnitude as the output of the tube increases. Unfortunately, as the heating current increases the magnetic field generated thereby and which surrounds the cathode also increases and this field impedes the flow of electron or space current inasmuch as 30 the electrons will be deviated from their path and hindered from 00-0 crating with the other elements of the device, unless the voltage is impressed beyond a certain critical value. For example, when the cathode of an electron discharge device consists of a tungsten wire of appreciable thickness, say 5 mm. and which is heated to 2500 C. the impressed voltage must exceed a critical value of 10,000 in order to overcome the impeding 49 effect of the magnetic field surrounding such wire and to insure an electron discharge from the cathode to the anode. Again, as-

. suming the anode to have a diameter of 10 mm. where the diameter of the cathode is as about 10 min. a critical voltage of about 100,000 would be required. Although this magnetic field may serve a useful purpose in guiding the space cur rent in certain devices, for example the Hull 50 magnetron which is described in the J ournal of the American Institute of Electrical Engineers, October, 1923, it is undesirable in other cases where precise electrostatic control is required.

. In accordance with the object of the invention the cathode is so constructed that'the disturbin and impeding influence of the magnetic elds engendered by the heating cur.-

rent is eliminated. With this object in view the cathode structure which embraces a radical departure from the filamentary form is so designed that when the heating current is passed therethroughin a certain manner the magnetic fields produced compensate or neutralize each other to such an extent that the flow of space current between the co-operatin electrodes is not interfered with.

he novel features which characterize the invention are pointed out in detail in the appended claims. The invention itself, however, will be better understood by reference to the followingdescription taken in connection with the accompanyin 7 drawing in which Fig. 1 shows a longitu 'nal cross-section of one form of the electrode structure.

Fig. 2 shows a cross-sectional view of a modification thereof.

Fig. 3 illustrates one method in which the heating current may be passed through the structural elements of the cathode so as to insure compensation! of the magnetic fields produced.

Fig t serves the double purpose of illustrating first, one of the variations in'external confi ration which the retaining member 2 may e made to assume as further set forth below, and second, of indicating the course taken by the current in its path through the elements of the cathode after the same have become heated.

Fig. 5 illustrates diagrammatically a conventional arrangement of the electrode of the invention in a space current device.

Fig. 6 shows one arrangement of the heating circuits; Fig. 7 shows an arrangement of switching means for connecting parts of the cathode together. 7

Referring in detail to the structures dcpicted in the drawing, the cathode shown in Fig. 1 comprises a core 1 of a refractory metal, such as tungsten, platinum or the like which is made either hollow or solid and which is disposed, within a shell or retaining member 2. This retaining member is made of metal,

preferably the same metal of which the core is constituted and it may comprise either a seamed or seamless tube, or else a substantially closed but unseamed cylinder or other figure of revolution.

In some cases the retaining member may be formed of a sheet metal strip Wound in helical fashion so that the closely compacted convolutions impart a cylindrical configuraficient degree.

by first passing the current through the me-- tion to the completed casing. The casing or retaining member may also assume a foraminous or sieve-like structure, as is illustrated for example in Fig. 4.

These structural variations enable one to proportion the extent of the emission surface in accordance with the size of the electrode desired but it is to be understood that the variations indicated are merely illustrative and that other forms of retaining members may be devised.

The path of the current is clearly shown in the drawing. where, in Fig. 1, it will be observed that the current entering at a passes along the core 1 and traverses the outer casing thus constituting a heating circuit Whose external magnetic fields are neutralized or compensated, and the structure may therefore be considered a magnetically con'ipensated cathode.

Although the general structure of the electrode coming-within the purview of the invention may comprise merely the core and retaining member disposed as shown in Fig. 1, itis nevertheless preferable for structural reasons that the space between the core 1 and the shell 2 be filled with a mass 3 of a mineral material, preferably a conductor of the second class. Although the exact composition of this mass does not relate to the essence of the invention, it may be remarked that various refractory metallic oxides and other compounds constitute suitable materials and that these may be employed in powdered, granular, briquetted or otherwise agglomerated form. The mass of course must be capable of withstanding high temperatures without decomposition. If such a mass 3 is used in connection with the structure of Fig. l and if the same constitutes a conductor of the second class, it will of course become a conductor of the electric current when heated to a suf- Heating is suitably effected tallic structural elements of the electrode for a short time until the mass within the retaining member has absorbed suflicient heat to become a conductor itself after which the current will follow the path indicated by the arrows at 0 (Fig. 1) passing through the oxide mass. I-Iere also, the magnetic fields surrounding the electrode will be compensated or neutralized.

In view of the fact that in the structure shown in Fig. 1 the cathode extremity farthest removed from the leading-in conductor menace will remain relatively cooler than the more adjacent portions when current is deflected through the oxide thus tending todecrease the emissive efiiciency of the cathode as well as subjecting the structure to temperature stresses, it may be more advantageous to use permits complete neutralization or compensation of the magnetic fields. Here the metallic parts of the cathode are first connected by means of a suitable external switch (not shown) so as to form a starting or primary heating circuit and when the oxide mass has become sufliciently heated and hence conducting, said switch is opened so that the heating current enters at a and a and leaves at b and b passing then through the oxide mass and maintaining the same at an elevated temperature. Automatic means for effecting this purpose are well known, e. g. in the Nernst glow lamp art and need not be discussed here.- v

The electrode may be operated by means of a transformer as shown in Fig. 3. Here the elements of the cathode are associated in non-metallic conducting relation with the terminals of the. secondary windings of two transformers or of one and the same transformer. When an alternating current is applied to the primary 4, Fig. 3, secondary currents of equal magnitude and opposite direction will be induced in the windings 5, 6, and will heatthe cathode members. lVhen the oxide has become sufiiciently heated and hence a conductor, the current changes its course and flows 'in the direction indicated by the arrows in Fig. 4. In both cases the magnetic fields produced by the heating current will be substantially neutralized or compensated and thus prevented from impeding the flow of space current from the electrode.

Other suitable transformer connections may be conceived to effect the same purpose, e. g. the main current circuit may be branched 0a in the middle of one of the secondary windings in order to obviate temperature unbalance and voltage displacement incident to superposition of the discharge current with respect to the heating current. Such an arrangement is shown in Figs. 6 and 7. In the latter figure switches 11 and'12 are shown in the starting position. When the oxide has.

become conducting. the switches are thrown to the positions indicated by the dotted lines.

If thorium or other suitable oxide has been added to the metal of the shell during its manufacture there may exist a tendency towards the formation of an electron-emitting film upon the exterior of the retaining shell or casing as is known to the prior art, e. g. in the United States Patent No. 1,244,216 to Langmuir. Such a film materially increases the emissive efficiency of the electrode. If a foraminous structure is used for the retaining casing it may be desirable that the oxide mass the structure shown in Fig. 2. This likewise menses therein contained also possess considerable electron emissivity.

Although it would appear from structural considerations that'the foraminous type of casing used in conjunction with an electronemitting oxide mass may conduce towards greater electron emissivity, it seems that the solid surface type of retaining member is preferable in that its relative immunity to temperature stresses lessens the danger of damage to such surface film.

It is of course essential that the various elements composing the cathode be made of materials which are readily freed from gas during the evacuation process so'that no undue difiiculties may be introduced into the manufacture of such electron discharge devices.

The circuits and structures depicted in the drawing are of course merely illustrative. It will be further appreciated that electrodes falling within the purview of the invention may be disposed as shown in Fig. 5 within a vitreous bulb 7, a metallic receptacle or other enshrouding envelope. Such an electrode may be mounted as shown at 8 in conducting relation to suitable terminals and supports and in electron responsive relation to other electrodes represented for example by 9 and 10 in Fig. 5 in accordance with the prevailing practice of the art. In some cases it may be desirable to use a plurality of such electrodes in one device.

1. A cathode fora space current device,

comprising a plurality of conducting membars capable of being heated by an electric current, said members being spaced from one another b a refractory material and so disposed wit respect to each other that the magnetic flowin throu b said members, are caused to neutr ize eac other to prevent magnetic deviation of space current flow. I I

2. An electrode for a space current device,

fields, produced by the heating current com rising an electron emitting member, a con uctor of the second class retained by said memberand a. metallic conductor retained by said conductor ofthe second class, said parts being so arranged in relation to one another that the magnetic fields of a heating current traversing said electrode and conductor are compensated.

3.' A cathode for a space current device comprising a shell, arefractory mass disposed within said shell, a conducting member embedded in said refractory mass, said shell and member being connected to permit heating current to be passed therethrough in opposite directions to neutralize the magnetic fields thereof.

42. In combination, a cathode comprising a tubular member and a conducting member extending through said tubular member, means for supplying alternating current to said members, said members being so connected and arranged that the magnetic fields produced by the currents flowing in the members will substantially neutralize each other.

In Witness whereof, We have hereunto set our hands this third day of May, 192%.

WALDEMAR BnuoKnL. DR. FRANZ 'LAUSTER.

QERTIFICATE or CORRECTION.

l atent No. 1,701,356. I GrantedFebruary 5, 1929, to

' WALDEMAR BRUCKEL ET AL,

It is ,hereby certified that error appears in the printed specification of the above numbered patent. requiring correction as follows: Page 3. after line 70,

insert the following as claim 5:

5-. A cathode comprising a cylindrical conducting member, a central core member, a filling ofrefractory material between sa-idmembers, and'connections from a source of ene gy to said members whereby the magnetic fields produced by current flowing through the members are completely neutralized.-

.and that the said Letters Patent should be read with this correction therein that the same may conform to the record of the case in the Patent Office. Signed and sealed this 26th day of March, A. D. 1929.

p M. J. Moore, (Seal) 7 Acting Commissioner of Patents.

CERTIFICATE OF GORREQTION.

Patent No. 1,701,356. Granted February 5, 1929, to

WALDEMAR BRUGKEL ET AL.

It is hereby certified that error appears in the printed specification of the above numbered patent requiring correction as follows: Page 3, after line 70, insert the following as claim 5:

5. A cathode comprising a cylindrical conducting member, a central core member, a filling of refractory material between said members, and connections from a source of energy to said members whereby the magnetic fields produced by current flowing through the members are completely neutralized.-

- and that the said Letters Patent should be read with this correction therein that the same may conform to the record of the case in the Patent Office.

Signed and sealed this 26th day of March, A. D. 1929.

M. J. Moore, (Seal) Acting Commissioner of Patents.

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