US3441780A - Indirectly heated dispenser cathode for electronic discharge devices - Google Patents

Description

A ril 29; 1,969

v A. HINKELDEY INDIRECTLY HEATED DISPENSER vCATI-IODE FOR ELECTRONIC DISCHARGE DEVICES Filed March 22. 1967 fzzyezzfoz 221720 zi z'zzz zaz United States Patent INDIRECTLY HEATED DISPENSER CATHODE FOR ELECTRONIC DISCHARGE DEVICES Arno Hinkeldey, Munich, Germany, assignor to Siemens Aktiengesellschaft, Berlin, Germany, a corporation of Germany Filed Mar. 22, 1967, Ser. No. 629,858

Claims priority, application Germany, Mar. 29, 1966,

Int. Cl. H01j 1/20, 19/14 US. Cl. 313-346 6 Claims ABSTRACT OF THE DISCLOSURE An indirectly heated cathode structure in which the primary cathode is provided with a bore in which an auxiliary cathode, constructed in the form of a cartridge containing a supply of emission substance, is disposed, such auxiliary cathode being inserted in the bore of the primary cathode body from the rear thereof, which insertion may follow mounting of the cathode body and heating means therefor in the associated electrode system.

The invention relates to an indirectly heated cathode for electronic discharge vessels in which, during operation, emission substances from a supply migrate through fine openings of a disk of refractory metal such as, for example tungsten, sintered in a porous manner which directly covers such supply and subsequently through another such disk disposed at a distance in front of it to the cathode surface of the outer disk forming the actual emission surface and there spread out through dilfusion.

It is of special importance for HF high power tubes, in particular for such tubes with as large as possible an emitting surface, such as, for example, traveling wave tubes of high power.

In cathodes of this type, it is a known procedure to control the emission substance supply, for example the barium supply, for the actual emitting disk of the emission carrier by the feature that the cover overlying the supply consists of at least two consecutively arranged individual elements, sintered in porous manner, out of refractory metal, in particular tungsten, through the pores of which the emission substance migrates to the cathode surface. For this purpose the emission substance first of all must pass through an individual element the porosity of which is regulated to be so difiicult to penetrate that it determines the quantity of the emerging substance in an essentially limiting manner, while the individual element then to be penetrated, forming the actual cathode surface, possesses a larger porosity rendering possible a most uniform covering of the emission surface.

This prior customary type of cathode has some disadvantages insofar as both porous disks, of approximately the same diameter, must have respective tight connections with the supply container itself which technically is difficult, in particular with respect to disks of larger diameter. In addition thereto, during production completely different powder metallurgical conditions, and above all also different compositions of the initial powder, must be selected for the respective porous disks.

The invention is based upon the finding that in the case of a normally constructed and normally operating metal capillary cathode, the quantity of evaporated emission promoting substance emerging at the emission surface of the emission substance disk during operation, i.e., the so-called evaporation rate of, for example, barium, is completely sufficient to not only activate a further, even considerably larger porous emission material carrier disk disposed at a distance in front thereof to a sufficient extent for emission, but to also maintain it capable of emission during operation in which case it is, in contrast to heretofore existing opinion, not even necessary that the pores of the emission material carrier disk form the largest openings for the cathode body formed therewith.

The objective upon which the application is based resides in the selection of a constructional arrangement formation of an MK cathode with two porous disks disposed one after another in such a manner that on the one hand a unform emission from a relatively large emission substance carrier disk is rendered possible and that in addition thereto the insertion of the moisture sensitive supply can be undertaken in a manner as simple as possible, employing techniques which do not require a process connected with a heat treatment, particularly following the mounting of the respective electrode system.

In an indirectly heated cathode for electronic discharge vessels such as initially described, this is accomplished, according to the invention, by the feature that both porous disks have practically the same normal porosity and the innermost porous disk, directly covering the supply, together with the supply container rigidly and tightly connected therewith, an MK cathode complete in itself, preferably cylindrical, which cathode is received into the actual cathode body as an insertion part.

The cathode body, which is provided with a heater, does not have to be tightly connected with the outer carrier disk, and may be mounted in the cooperable electrode system prior to the insertion of the auxiliary MK cathode. The latter may be inserted into the cathode body from the rear of the body in the manner of a cartridge, without specific anchorage means, and likewise does not require an exceedingly tight connection.

The outermost emission material carrier disk connection also can be inserted in or attached to the cathode body especially advantageously without requiring any specific mechanical connection which must be produced only by means of considerably heating.

The porous disk forming the emission surface can have a diameter which is up to six times greater than that of the inner porous dial directly covering the supply container and advantageously can be spaced therefrom an appropriately large distance, at least amounting to ten times its thickness, sufficient for a uniform covering of its rear inner side with active substance, from the inner disk.

Especially in the event that the supply container in a complete system is in the form of an MK cathode and inserted in the actual cathode body from the rear in the manner of a cartridge, the cathode body is especially advantageously of thick wall construction whereby the socalled MK cartridge has, on its entire length, a good heat conducting connection with such cathode body and therewith also the actual heater disposed at the outer circumference thereof.

Details of the invention will be explained by means of the example of construction, illustrated purely schematically in the figure. Those parts which do not directly contribute to an understanding of the invention have not been marked in this figure or have been omitted.

The reference numeral 1 designates the actual porous emission material carrier disk, which has a relatively large diameter and is attached to the cathode body 2 along its edge, possibly only at spaced points, for example, by means of spot welding, without the production of an absolutely tight connection. At the main part of the outer circumference the cathode body, preferably of molybdenum, is provided with a heater 3 which in customary manner is provided with an insulating coating, cemented on and surrounded by a ray protective shell 4. The cathode body is provided with a centrally disposed cylindrical bore 8, of relatively small diameter, which diverges toward the outer end to form a cup-like recess of conical or tulip-shaped configuration which extends to the larger diameter of the emission material carrier disk 1. Disposed in the narrow bore 5 of the cathode body is the actual supply container 7 containing a supply substance 8 and may also have a plug 9 of tungsten wire, which is inserted in a cartridge-like manner, with the porous disk 11 tightly closing the container, being located approximately at the base of the enlarged portion of the recess in the cathode body. At the end opposite to the porous disk the MK cartridge 7 may be provided with a cap in the form of a disk which bears on the cathode body, forming a stop without producing a special seal.

A particular advantage of the described, indirectly heated cathode resides in the feature that the emission substance donor does not have to be so tightly connected with the cathode body and can therefore be inserted from the rear into the cathode body like a cartridge without necessitating therefor an operation involving a considerable heat treatment. In particular, it thereby becomes possible to effect the complete construction of a tube including the cathode body and following such assembly to insert the supply container, in the form of a cartridge possibly with an especially sensitive supply substance, only shortly before the sealing of the associated discharge vessel without requiring welding operations which require an expenditure of higher heat, for example, such as required for the production of tight connections between molybdenum parts or with tungsten parts.

Changes may be made within the scope and spirit of the appended claims which define what is believed to be v new and desired to have protected by Letters Patent.

I claim:

1. An indirectly heated cathode for electronic discharge vessels in which during operation emission substances from a supply migrate through fine openings of an inner disk directly covering such supply, sintered in porous manner, of refractory metal, such as tungsten, and subsequently through another such disk disposed at a distance in front of the first disk, to the cathode surface of the outer disk forming the emission surface and there spread through diffusion, characterized in that both porous disks have approximately the same normal porosity, a supply container for the emission substance, to which said first porous disk is rigidly and tightly connected and directly covers the supply, said container and cover disk forming a complete MK cathode, complete in itself with the exception of a heater, a main cathode body to which said second disk is connected in a not necessarily absolutely sealed manner, a heater cooperable with said main cathode body for heating the same, said main cathode body having an opening at the rear thereof, of a size to receive said supply container therein in the manner of a cartridge and retain the same therein in a not necessarily absolutely sealed manner.

2. An indirectly heated cathode according to claim 1, wherein the porous disk forming the actual emission surface has a diameter which is up to six times larger than that of the inner porous disk covering the supply container and is spaced a relatively large distance, amounting to at least ten-fold its thickness from the inner disk to enable a uniform covering of the rear side of the outer disk with active substance received from the inner disk.

3. An indirectly heated cathode according to claim 1, wherein the outer emission substance carrier disk is attached to the cathode body by a connection which does not require production by means of considerable heating.

4. An indirectly heated cathode according to claim 1, wherein the cathode, adjacent the heater is of thick walled construction whereby the cartridge representing an MK cathode has, over its entire length, a good heat conductive connection therewith.

5. An indirectly heated cathode according to claim 1, wherein the cathode body has a hollow cylindrical portion in which said cartridge is received, and an enlarged hollow portion extending from adjacent the inner end of said cartridge to said second disk and which at its outer end approaches the size of said second larger second disk forming the actual emission substance carrier.

6. An indirectly heated cathode according to claim 5, wherein said enlarged portion of the cathode body defines a conical, cup-shaped or tulip-shaped chamber extending between the respective porous disks.

References Cited UNITED STATES PATENTS 2,761,993 9/1956 Katz et a1. 313-337 2,786,957 3/1957 Huber 3l3337 X 2,830,218 4/1958 Beggs 3 13346 3,010,046 11/1961 Dailey et a1. 313-346 FOREIGN PATENTS 1,138,870 10/1962 Germany.

JOHN W. HUCKERT, Primary Examiner.

A. J. JAMES, Assistant Examiner.

US. Cl. X.R. 313337, 345

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