US3048727A - Anode structure - Google Patents

Description

Aug. 7, 1962 H. E. KREFFT 3,

ANODE STRUCTURE Filed Sept. 17, 1959 3 Sheets-Sheet 1 INVENTOR. H. E KEEFF' T Aug. 7, 1962 H. E. KREFFT 3,048,727

ANODE STRUCTURE Filed Sept. 1' 1959 5 Sheets-Sheet 2 INVENTOR. M E. KEEFFT F76. 4 I WW)- A TTOENEY H. E. KREFFT ANODE STRUCTURE Aug. 7, 1962 Filed Sept. 17, 1959 5 Sheets-Sheet 3 32 3 i I 2TH 35 f V g INVENTOR. F/G 6 H. E. KEEFl-"T BY z z A Tro mvsv United States Patent 3,048,727 ANODE STRUCTURE Hermann E. Krelft, East Orange, N.J., assignmto Kuthe Laboratories, Incorporated Filed Sept. 17, 1959, Ser. No. 840,772 9 Claims. (Cl. 313-39) The invention relates to an anode structure for electrical discharge tubes, such as rectifier or switch tubes. More particularly, it relates to hydrogen filled thyratron tubes which are provided with a ceramic envelope, and in which the anode forms part of the envelope wall.

In hydrogen thyratrons, which are switch tubes operated with current pulses of extremely high magnitude and short duration, the anode is, under certain conditions, for instance, low operating pressure or high pulse repetition rates, heated to a very high temperature which may lead to the destruction of the tube. In order to avoid such overheating, the anode is made from a material having high thermal conductivity, like copper, where feasible, and it is directly exposed to the atmosphere by making it a part of the tube envelope. However, those parts of the anode which are struck by the discharge have to be made from a more refractory material like molybdenum or tungsten which are poor conductors of heat. In order to provide good thermal contact, these materials have to be connected to the copper components of the structure by brazing which is difflcult to carry out, as molybdenum or tungsten have low thermal expansion, while that of copper is three to four times as high. Brazing of such different materials naturally results in a considerable deformation of the brazed assembly which is highly undesirable for mechanical and electrical reasons.

In view of these imperfections, it is one object of the invention to provide an anode structure which is not deformed in a harmful manner; another object is to provide an anode structure which will not overheat under a high load; still another object is to provide a structure which permits exhausting the tube through the anode.

These objects are attained by providing an anode plate with a massive support structure consisting of a slotted ring behind those portions of the plate receiving the electrical discharge and forming paths for conducting heat rapidly away from the plate.

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 anode structure;

FIG. 2 is a bottom view of the structure with the anode plate partly removed;

FIG. 3 is a. partly sectional side view of the same structure;

FIG. 4 is an enlarged sectional view illustrating the brazed connections within the anode structure;

FIG. 5 shows the anode structure as a part of a ceramic thyratron tube; and

FIG. 6 illustrate a modification of the anode structure provided with an exhaust tubulation.

As shown in FIGURES 1, 2 and 3 which illustrate a preferred embodiment of the invention, the novel anode structure consists of a round flat plate 1, a compact cylindrical support structure 2 which will be called the anode block, and a thin walled flanged cup 3 to which the anode block is firmly connected. The plate 1 is made from a highly refractory metal as, for example, molybdenum or tungsten, which metals possess a relatively low thermal expansion. It is this part of the anode structure which is exposed to the major portion of the discharge resulting in large amounts of heat being generated in this region during operation of the tube. This thermal energy must be removed quickly from the plate which otherwise would become incandescent and the tube inoperable. Heat from the plate is efliciently carried away by the anode block 2 which is made from pure high conductivity copper and has a relatively large mass. Connection between these two parts is made by brazing. The anode block 2 is positioned within the flanged cup 3, which is preferably made from high conductivity coper, and is brazed to the inside of the cup, as shown in FIG. 3. This structure is sealed to one end of a ceramic tube envelope so that a fraction of the heat absorbed by the cup will be conducted to the ceramic envelope by means of a flange 4, which forms part of the cup 3. In this position the upper side 5 of the anode block is exposed to the atmosphere and forms part of the tube wall. Electrical connection to the anode is made by means of a tapped hole 6 situated in a thickened portion of the' upper side 5 of the anode block.

Brazing of the anode plate 1 to the block 2 presents a serious problem which stems from the considerable difference in thermal expansion existing between molybdenum or tungsten, and copper, which has a thermal expansion of 10- as compared to 55 10-' and 44x10- respectively, for the other two metals. When brazed together, these metals form a bimetallic system which tends to bow or deform in some uncontrolled way when cooling. This results in a warped anode which would make alignment and spacing within the tube, and sealing to the ceramic envelope, very difficult if not impossible. This difiiculty is overcome in accordance with the invention, by slotting the thick-walled cylindrical part of the anode block which, in this way, is divided into numerous equal segments 7 by a plurality of radial slots 8, as shown in FIGURES 2 and 3 in more detail. These segments as a whole provide more flexibility than a solid cylinder as each may more easily yield to radial or tangential forces present during the cooling period after brazing, or during any subsequent change in temperature. Radial flexibility is further increased by an undercut 9 in each segment. Thermal conductivity and removal of heat from the anode plate is not appreciably affected by slotting of the block, as the slots can be made very narrow, for instance, of an inch. An anode structure utilizing a slotted block still suffers a small deformation after brazing at about 1000 C. and subsequent cooling to room temperature; but the deformation now consists of a slight bow which will be entirely symmetrical. A molybdenum anode plate of 2 /2 inches diameter and A of an inch thickness, for example, has a uniform bow corresponding to ten one thousandth of an inch deviation at the center from a plane passing through the periphery.

The brazed connections between the three component parts constituting the anode structure are shown in more detail in FIG. 4. A particularly safe method for producing a brazed connection of great mechanical strength between anode plate 1 and anode block 2 is provided by setting the segments 7 of the anode block in a flat groove about 6 of an inch deep machined into the surface of the anode plate. The bra-zed connection is made between the plane faces of the segments 7 and the bottom and side Walls of the groove. As brazing material, an alloy composed of 82% gold and 18% nickel is used, which, as a washer 36, is placed in the groove 10' of anode plate 1 between the two parts when the structure is being assembled. After brazing, the faces are firmly connected to each other and fillets 11 are formed on both sides and between the segments which provide additional strength. At the same time as this operation is carried out, the anode block 2 is brazed to the inside of the flanged cup 3, as illustrated by FIG. 4. In order to position the anode block within the cup correctly, so that a small clearance 35 of about A.; of an inch is maintained between the plate and the plane end of the cup 3, a step 12 is provided in the inner cup wall which supports the flat bottom part 13 of the anode block. Brazing material is provided by a gold-copper alloy brazing ring 37 which is placed on the ring shaped end 14 of the anode block in close contact with the cup wall when the anode structure is assembled for brazing. As a result of the brazing, the bottom part 13 is joined over its whole circumference to the inner wall of the cup, and a fillet 15 of brazing material is formed.

The anode structure, as described, is sealed to the ceramic envelope of a thyratron tube in a manner illustrated in FIG. 5. The seal is made between the metallized faces of ceramic body ring 16 and ceramic end ring 17, and the flange 4 of the anode cup. Silver-copper alloy is used as brazing material. In tubes of this kind, the small clearance 18 between the anode cup and the inner wall of the envelope is very critical and must be kept within a few thousandths of an inch in order to avoid uncontrolled electrical breakdown between the anode and the grid 19 or the cathode 20. An anode structure which is not distorted and which permits good alignment with the envelope wall is, therefore, indispensable. The entire tube envelope is formed by this section containing the anode, a second body ring 21, and a cup shaped base 22 which is sealed, by means of a flange 23, to the end of body ring 21 in the same manner as the anode to body ring 16. In a similar way, a flange 24 which forms part of a grid structure 19, is sealed between the other faces of body rings 16 and 21. The base is provided with insulated lead-in terminals 25, 26 through which a heating current is supplied to the indirectly heated cathode 20, and it further has an exhaust tabulation 27, shown as it appears after tipping oif the tube.

During operation, pulsed gas discharge currents having high peak values pass from the cathode to the anode plate 1. This discharge is made to operate through a tortuous passageway imposed by the grid structure 19 which, in the case illustrated by FIG. 5, consists of sixteen short radial slots 28 near the periphery and a baffle 29 which has one central aperture only. Additional baffling is provided by a disc 30 and a shield 31 which are interposed between the cathode and the grid structure. Thus, the discharge, after leaving the grid on its way to the anode, is composed of sixteen narrow beams which strike the anode plate in sixteen well defined spots. As heat is generated on the plate at these spots only it is obvious that heat conductive backing of the anode block is necessary in these areas, and that the other areas may be left without such backing. In the example described in this specification, the position of the segments which form part of the anode block is adapted to the pattern of the discharge beams. For other beam patterns, a different arrangement of the segments is desirable and even necessary, since, as a general rule, the segments should always be adjacent the points where the discharge hits the anode plate, so that heat has to travel a mini- 4 mum distance through the plate and is quickly passed to the block 2 In a modification of the anode structure described, the anode block has a central bore 32 to which is connected an exhaust tabulation 33, as shown in FIGURE 6. Exhaust of the tube through the anode is desirable for a number of reasons. However, an exhaust channel cannot be used in conventional anodes, as so-called long path conditions for the discharge are produced which cause electrical breakdown between the anode and other electrodes. These conditions do not exist in an anode structure constructed according to the invention, as the aperture 34 of the exhaust channel is not directly exposed to the discharge. Connection from this channel to the inside of the tube is made through the narrow slots 8 in the anode block, and through the small clearance 35 of approximately of an inch which is provided between the cup 3 and anode plate 1. High exhaust speed is obtained in these passageways owing to the large number of slots and the large circumference of the plate-tocup clearance. This narrow gap does not interfere with the discharge.

While I have described above the principle 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, a cathode, and an anode plate, means for mounting said cathode and said anode plate in spaced relation, and heat conducting means in contact with said anode plate for conducting heat away from said plate, said heat conducting means comprising a plurality of symmetrically spaced blocks on the opposite side of said plate from said cathode for preventing deformation due to thermal distortion of said heat conducting means.

2. An electron discharge device comprising an envelope, a cathode, a conductive gas within said envelope, an anode plate, mean for mounting said cathode and said anode plate in spaced relation, means for directing discharge from said cathode to symmetrically spaced portions of said plate, and heat conducting means in contact with said anode plate for conducting heat away from said plate, said heat conducting means comprising a plurality of blocks on the opposite side of said plate from said cathode and spaced in alignment with the portions of said plate receiving the discharge for preventing deformation due to thermal distortion of said heat conducting means.

3. An electron discharge device, as defined in claim 2, further comprising energy conducting means at one end of the heat conducting means and extending away from the anode plate forming an energy conducting path.

4. An electron discharge device comprising an envelope, a cathode, a conductive gas within said envelope, an anode plate, heat-conducting means in contact with said plate for conducting heat away from said plate comprising a plurality of paced, solid blocks, and energyconducting means at one end of the heat-conducting means and extending away from the anode plate and forming an energy-conducting path, said heat-conducting means comprising a support member with the solid blocks mounted on one side of said member and the energyconducting means mounted on the other side of said member, a hollow cup member having a flange extending from its edge, the outer edge of said flange being sealed to said envelope, said cup being rigidly connected to said support member and forming a hollow shield fitting over said solid blocks, said anode plate being rigidly connected to said blocks, and energy-conducting means extending through said hollow cup member, whereby an energy-conducting path is formed.

said energy conducting means further include tubulation 10 2,680,209

means extending therethrough.

6 9. An electron discharge device, as in claim 4, wherein said anode plate is brazed to said blocks, said hollow cup member is brazed to said support member, and the material of said braze is an alloy composed of 82 percent gold and 18 percent nickel.

References Cited in the file of this patent UNITED STATES PATENTS 2,621,303 Law Dec. 9, 1952 Veronda June 1, 1954 2,955,225 Sterzer Oct. 4, 1960

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