US3025428A - Cathode structure - Google Patents

Description

March 13, 1962 H. E. KREFFT CATHODE STRUCTURE 3 SheecsSheet 1 Filed Oct. 15, 1959 INVENTOR. H. E. KEEP/'7' BY WM}- A TTORNE Y March 13, 1962 H. E- KREFFT CATI-IODE STRUCTURE 3 Sheets-Sheet 2 Filed Oct. 15, 1959 F/G. Z

INVENTOR. h. 5. KEEFFT March 13, 1962 Filed Oct. 15, 1959 H. E. KREFFT CATHODE STRUCTURE 3 Sheets-Sheet 3 INVENTOR. HE. K'PEFFT MW A- A T TORNE Y i it 3,025,428 Patented Mar. 13, 1962 3,025,428 CATHUDE STRUCTURE Hermann 1E. Kreift, East Orange, N.J., assignor to Kathe Laboratories, Incorporated Filed Get. 15, 1959, Ser. No. 846,715 3 Claims. (Cl. 313244) This invention relates to a cathode structure for gas discharge tubes of the type which employs an indirectly heated oxide coated cathode operated at incandescent temperatures in a gas or vapour of low pressure. More particularly, it is related to hydrogen filled thyratron tubes in which a pulsed discharge of several hundred to several thousand amperes peak value is supplied by the cathode.

In such tubes the cathode is exposed to very severe requirements. It must heat up quickly, as little time is allowed for warm-up of the tube prior to operation of the discharge. The entire emitting surface must be heated up in a manner as to supply current to the discharge uniformly. If a uniform discharge is not obtained then stripping of the cathode or the formation of arcs occurs Which may destroy the cathode Within a short time and make the tube inoperable. Furthermore, the electrical connections to the cathode must be made in a manner such that the cathode surface will emit uniformly so that emission spots will be prevented.

In the design of such cathodes it is very essential that sputtering or evaporation of the activating material is decreased to a minimum. Other design considerations which are of a mechanical nature and relate to the entire structure must be carefully considered since thyratron tubes are often exposed to severe shocks and vibrations. It is also very important to reduce the effect of the periodically variable magnetic field of the heater coils through which the cathode is heated, and which produces undesirable time jitter in the electron discharge pulses.

An object of the invention is to provide an improved novel cathode assembly.

Another object of this invention is to provide a cathode having a uniform temperature distribution throughout its structure and which is sturdy, reliable and readily manufactured.

A further object of the invention is to minimize localzed heating or hot spotting of the cathode.

Still another object is to provide an improved cathode of high heating efiiciency and capable of handling very high currents.

According to the invention, these requirements are met, and the disadvantages of customary cathodes are over come, in a cathode structure of the indirectly heated, activated type which comprise as a feature of this invention, a circular vane system, a substantially fiat heater positioned close to said vane system, a supporting structure for said vane system and for said heater, current leads connected to said heater, and a cup-shaped container surrounding said vane system, heater, supporting structure and leads. The circular vane system consists of a plurality of concentric ring shaped vanes of different diameters, said vanes having a cylindrical portion and a plane portion, said plane portions overlapping each other and forming a substantially flat bottom portion of said vane system, wherein said cylindrical portions form between each other and said plane portions annular spaces having a considerable surface area, and wherein said vanes are coated with an electron emitting material.

The above-mentioned and other features and objects of this invention will become apparent by reference to the following description taken in conjunction with the accompanying drawings, in which:

FIG. 1 is an exploded view of the cathode structure showing its principal components;

FIG. 2 is a front view of the same structure with its container partly removed;

FIG. 3 is a top view showing part of the vane system and one heater coil; and

FIG. 4 shows a hydrogen thyratron tube provided with the novel cathode structure.

Referring to FIGS. 1, 2 and 3, a cathode structure according to the invention consists of a system of circular vanes 1, a supporting structure comprising a bracket 2 which is firmly connected to the vane system and provides electrical connection to it, a pair of heater coils 3 positioned close to the flat bottom portion of the vane system, and a cup-shaped container 4.

The vane system which constitutes the cathode, is composed of a plurality of concentric circular vanes 8, 9, 10, 11, 12 and a central cup 13 which provides the innermost vane. The shape of a vane ring is shown in FIGS. 1 and 2. It consists of a cylindrical vane portion 14 and a flat bottom portion 15. A set of such rings, differing in diameter by, for example, one-quarter inch between adjacent vanes forms a nest in which the overlapping bottom portions are spot-welded together so that a cathode having a substantially fiat bottom part is formed as shown in FIG. 2. The vane rings are drawn or spun from a thin nickel sheet of high chemical purity.

A cathode composed in this way has the advantage that heat from a source positioned near the flat bottom portion is quickly transferred to the circular vanes. Also, the thermal capacity of the system is small as very small quantities of nickel are required to build it up. The temperature drop from the bottom to the ends of the vanes is kept to a minimum.

This cathode is heated to a uniform temperature by a pair of flat heater coils 3 made from tungsten wire and which are fiat shaped to conform to the bottom portion of the vanes. In this way, a large part of the coil body can be positioned very close to the bottom of the cathode. The heater coils have bifilar winding by means of which the magnetic field produced by the alternating heater current is minimized and time jitter during operation of the tube is considerably reduced. The heater coils are supported by the same brackets 2 which also carry the cathode. One end, 16 (FIG. 1), is directly connected to bracket 2 while the other end, 17, is led through an insulating bead 18 and connected to a lead 19 through which current is supplied to the coil. The middle portion of the coils 20 is supported by a pin 21, and insulated by a head 22 which in turn is secured to the other bracket. In order to prevent sagging of the heater coil and improve shock resistance, an insulating head 23 which supports the coil body near the center is mounted on the flat part 24 which interconnects brackets 2. The vane system is firmly connected by spot-welding of its flat bottom part to the flanged ends 25 of the brackets 2.

The brackets 2 thus serve three purposes, to support the cathode mechanically and to supply to it the very high current forming a pulse, and to carry the heater coils.

The circular vanes which together with the flat portions of the vane rings form the cathode of this structure are coated with an electron emissive material as, for example, the oxides of barium, calcium, or strontium, or mixtures of these materials. Coating is preferably done by spraying. Thus both sides of each vane and the flat parts between the vanes are coated and annular spaces or pockets are formed which have a considerable total surface area and within which the electron emissive layer is well protected against ion bombardment.

The assembly of the vane system and the supporting structure is mounted within the cup-shaped container 4, the bottom part of which is provided with four slots 26 accommodating the legs 27 of brackets 2. Thus, the

cathode and the heater coils are effectively shielded against heat losses. Lead wires 28 through which current is supplied to the coils are led through holes 29 provided in the bottom of the cup.

This cathode structure is mounted within a hydrogen filled thyratron tube, as illustrated by FIG. 4. The tube shown here by way of example has a ceramic envelope which is composed of high alumina rings 36 and 31 and it is provided with an anode 32-, a grid 33, and a base 34. The flanges '35 of these components are sealed in a known manner, by brazing to the faces of the rings. The cathode structure is mounted, by means of the four legs 27, on a plate 36 which in turn is connected by means of brackets 37, to the base 34. Thus, a short path having high conductivity and low inductance is formed through which high current pulses are passed from the base to the cathode during operation of the tube. Insulated terminal pins 38 provide lead through connections to lead wires ZS and to the heater coils.

The cathode structure as described above which has very favorable operating characteristics will now be explained by reference to a practical example. In this example, the diameter of the cathode is two inches and it consists of six vanes .219 inch high with a uniform spacing of .125 inch between adjacent vanes. The heater power is 100 watts. The cathode structure constructed in a manner as described above, warmed up sufficiently for operating the tube-within three minutes and had a life exceeding 1000 hourswhen operated, in a ceramic hydrogen thyratron, at a power level of 12 megawatts. It complied with all the requirements set forth, that is, during operation of the tube the discharge was uniformly distributed over the entire surface of the cathode, the formation of hot spots and stripping were entirely avoided, and time jitter of the discharge pulses was prevented.

While I have described above the principles of my invention in connection with specific apparatus, it is to be clearly understood that this description is made only by way of example and not as'a' limitation to-the scope of my invention as set forth in the objects thereof and in the accompanying claims.

What is claimed is:

-1. An electron discharge device comprising an envelope, an anode within said envelope, an emissive coated cathode assembly, means for uniformly heating said emissive coated cathode assembly, means for supporting said emissive coated cathode assembly and 'said heating means within said'envelope, said emissive coated cathode assembly comprising a plurality of concentric shaped vanes for producing a uniform electron discharge in a direction toward said anode, wherein said concentric shaped vanes are spaced from each other a distance such that ionic bombardment between adjacent vanes will be prevented, and each of said concentric shaped vanes has a flange which overlaps the flange of an adjacent vane so as to form a substantially fiat continuous bottom portion.

2. An electron'di'scharge device comprising an envelope, an anode within said envelope, an emissive coated cathode assembly, means for uniformly heating said emissive coated cathode assembly, means for supporting said emissive coated cathode assembly and said heating means within said envelope, said emissive coated cathode assembly comprising a' plurality of concentric shaped vanes for producing 'a-uniform electron discharge in a direction toward said anode,wherein said heating means comprise a plurality of bifilar windings in the form of fiat helices so shaped as to conform to the bottom portion of said emissive coated cathode, and said windings being woundso as to minimize jitter of the electron discharge when the heating means are energized by a pulsating current.

3. An electron discharge device comprising an'envelope, an anode within said envelope, an emissive coated cathode assembly, means for uniformly heating said emissive coated cathode assembly, means for supporting said emissive coated cathode-assembly and said heating means within said envelope, saidemissive coated'cathode assembly comprising a plurality of-concentric shaped vanes for producing a-uniform electron discharge in a direction toward said anode, wherein said supporting means comprise a cup-shaped container, a bracket having two side members, means for mounting said cathode assembly directly upon the tops of said side members 'With the contact therebetween being over a small proportion of the total area 'of the bottom of said cathode assembly, means for mounting said bi-filar'windings between-and suspended from said side members, means for energizing said bi-filar windings, means for mounting said bracket member in said container, a mounting base, and means for mounting said supporting means on said mounting 'base.

References Cited in the file of this patent UNITED STATES PATENTS 1,651,398 Lorenz Dec. 6, "1927 2,006,081 Anderson June 25, 1935 2,014,539 Stansbury Sept. 17, 1935 2,279,872 Llewellyn Apr. 14, 1942 2,624,024 Jansen Dec. 30, 1952 2,786,957 Huber Mar. 26, 1957

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