GB1588766A - Transit time tubes - Google Patents

Description

(54) IMPROVEMENTS IN OR RELATING TO TRANSIT TIME TUBES (71) We, SEMENS AS:TXNG SELL- SCHAFT, a German Company of Berlin and Munich, German Federal Republic, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement : The invention relates to transit time tubes having an electron beam collector in the form of a hollow central metal core thermally and mechanically coupled to, but electrically insulated from, a conductive metal outer sleeve by an intermediate sleeve of electrically insulating material. Such constructions are described for example, in the United States Patent Specification No.

3,471,739 or 3,666,980.

In many cases, for example in travelling wave tubes using a "depressed collector" with a collector potential which is lower than the line potential, the collector must satisfy two contradictory requirements.

Firstly the collector component which is bombarded by electrons has to be able to dissipate heat rapidly, but at the same time it must be reliably electrically insulated from the environment.

If, as provided in the above-mentioned patents, a ceramic sleeve is soldered to a copper core, then because of the differing heat expansion - characteristics of the two soldered members, the danger exists that the solder connection will break open during operation, and consequently the initially good insulation and heat conductivity will be impaired in an unforseeable fashion.

Therefore, the aforementioned US Patent No. 3,666,980 has proposed that the central hollow body be provided with lonigtudinal cuts which are directed towards the body axis and render the hollow body compressible. However, if the production but lay is to be kept within limits, this type of ribbing arrangement does not produce really reliable joints.

For this reason, recently the practice has been increasingly to dispense with voltage loaded metal-ceramic joints, and to support the intermediate insulating sleeve on elastic sheet metal plates (US Patent Specification No. 3,717,787), or to transform the inter mediate insulating sleeve into a structure composed of ceramic rings with interposed sheet metal lugs which are alternately fixed to the hollow body and the outer body (US Patent Specification No. 3,824,425), or even to split the sleeve into individual spacing elements which are impressed between the electrically conductive bodies which generally consist of ductile copper (US Patent Specification No. 3,679,929).With all these concepts, the requisite short-circuiting reliability is attained at the cost of a loss of mechanical stability, and in part a relatively complicated construction, and always a reduced heat conductivity.

One object of the present invention is to provide a transit time tube with an in ternally insulated collector having a high sparkover resistance and good heat dis.

sipating properties, which can be produced in a relatively simple fashion and has a mechanically robust construction.

The invention consists in a transit time tube having an electron beam collector in the form of a hollow central metal core on the electron beam path, thermally coupled to, but electrically insulated from, a coaxial conductive metal outer sleeve by an intermediate sleeve of electrically insulating material, said metal core being cast with said intermediate insulating sleeve, and containing a heat expansion deceleration means in the form of an auxiliary intermediate annular layer which extends axially within the core material for a length substantially equal to the axial length of the contact surface between said core and said intermediate insulating sleeve, and which consists of a metal whose thermal expansion coefficient is lower than that of the metal of said core.

Preferably, said outer sleeve consists of a good heat conducting metal to provide conduction cooling and is also cast with the intermediate insulating sleeve, with its own auxiliary intermediate annular layer which extends axially within said outer sleeve material for a length substantially equal to the axial length of the contact surface between said intermediate insulating sleeve and said outer sleeve, and which consists of a metal whose thermal expansion coefficient is lower than that of the metal of said outer sleeve. Tensions produced by heat are particularly low if a copper core is provided with a molybdenum auxiliary intermediate layer and the insulating sleeve is composed of ceramic.

Intimate metal-ceramic contact is not impaired by any separating phenomena, and so produces ideal heat transfer between the individual components. As the casting joint is also free from solder of any type, the assembled collecter of a tube constructed in accordance with the invention can be exposed to exceptionally high heating and operating temperature without any disintegration of the vacuum such as might be due, for example, to vaporising solder or to leakage formations due to solder diffusion. To this can be added the fact that virtually no premanufactured components are required, the intermediate insulating sleeve can be a blank having no tolerance conditions, and the casting material can consist of various semi-products. These facilities lead to a considerable production simplification and a substantial reduction in costs.

It has long been known in the art to limit the thermal expansion of highly conductive collector electrode structures by means of clamping rings having a relatively low thermal expansion coefficient (US Patent Specification No. 3,586,100), and also it is known to fill the space between two sleeveshaped collector components formed of a sealing alloy with melted copper solder (German Patent Specification No.

1,098,620). However, apart from the differences of a purely constructive type, these two known arrangements do not constitute internally insulated collectors.

The invention will now be described with reference to the drawings, in which: Figure 1 schematically illustrates a collector of one exemplary embodiment of a tube constructed in accordance with the invention; and Figure 2 schematically illustrates a collector of a further exemplary embodiment of a tube constructed in accordance with the invention, utilising liquid cooling.

Figure 1 shows a longitudinal sectional view of the collector of a travelling wave tube. It consists of a central hollow core 1 composed of copper, an intermediate sleeve 2 consisting of BeO-ceramic, and a solid outer sleeve 3 of copper. All three components are rotationally symmetrical, and are assembled coaxially in one another.

Respective molybdenum auxiliary intermediate sleeve 4 and 5 are arranged within the material of the core and outer sleeve, concentric to the collector axis.

The hollow core 1 contains - a cavity 6 in which the electrons of the incident electron beam are collected. This cavity is connected via a channel 7, passing through the end of the hollow core to an area at the rear of the core. In the direction of the longitudinal axis, an outer sleeving 3 is provided at both ends with a multi-component connecting flange 8 and 9 respectively, and in the present case the flanges each consist of Vacon matching rings 10 and 11, together with associated plates 12 and 13 of Vacon placed against these Vacon rings. The Vacon plate 13 is provided with a ceramic duct 14 in order to allow the core to be brought to a specific potential.

The described exemplary embodiment can be produced as follows: In a mould consisting of graphite, an already metallised ceramic intermediate sleeve, pre-annealed molybdenum tubes, and the matching components of the connecing flanges are inserted in the correct position relative to one another. Then the required quantity of copper is inserted into the melting component of the mould and is melted in a vacuum furnace. After the melting process, the graphite mould is removed, connecting flanges are completed, and an electrical connection for the core is established.

As a result of the melting, the whole of the material is degassed, and a connection which is free of shrink holes is formed between all the individual components, thus both between the copper and the ceramic, and also between the copper and the molybdenum.

The proposed tube can employ a collector cooled other than by conduction, Figure 2 shows a tube collector which features liquid cooling. This design fundamentally differs from the first only in that its outer member does not consist of a single copper sleeve 14, but is a hollow structure provided with baffle plates. This structure contains the copper sleeve 14 which bears against the outer surface of the intermediate sleeve, a baffle plate 15 and an outer wall 16 which latter is provided with a liquid inlet 17 and an outlet connecting piece 18 for a pump (not shown). Copper layer 14, baffle plate 15 and outer wall 16 are arranged coaxially, and the copper layer is fused to the intermediate ceramic sleeve, during the same process as the core fitting. In the present case the flange which adjoins the collector base consists not of one part, but a terminal 19 composed f V2A-steel and a Vacon plate 20, whilst the ceramic sleeve 2 is connected to the terminal 19, so as to be impervious to liquid.

The invention is not limited to the illustrated exemplary embodiments. Thus, in particular the case of liquid-cooled collectors, it is not always necessary for the intermediate insulating sleeve to be mechanically enclosed by a body to which it is cast. A copper layer having good adhesive properties could also be applied by electrolytic deposition. However, electrolytic copper does not possess such good properties as the vacuum copper which is automatically formed during the melting process.

WHAT WE CLAIM IS:- 1. A transit time tube having an electron beam collector in the form of a hollow central metal core on the electron beam path, thermally coupled to, but electrically insulated from, a co-axial conductive metal outer sleeve by an intermediate sleeve of electrically insulating material, said metal core being cast with said intermediate insulating sleeve, and containing a heat expansion deceleration means in the form of an auxiliary intermediate annular layer which extends axially within the core material for a length substantially equal to the axial length of the contact surface between said core and said intermediate insulating sleeve, and which consists of a metal whose thermal expansion coefficient is lower than that of the metal of said core.

2. A tube as claimed in Claim 1, in which said outer sleeve consists of a thermally highly conductive metal also cast with said intermediate insulating sleeve with its own auxiliary intermediate annular layer which extends axially within said outer sleeve material for a length substantially equal to the axial length of the contact surface between said intermediate insulating sleeve and said outer sleeve, and which consists of a metal whose thermal expansion coefficient is lower than that of the metal of said outer sleeve.

3. A tube as claimed in Claim 1 or Claim 2, in which said core and said outer sleeve consist of copper, each having a respective auxiliary intermediate layer of molybdenum within, said intermediate insulating sleeve consists of ceramic.

4. A transit time tube having a collector electrode assembly substantially as shown in Figure 1 or Figure 2.

5. A method of manufacturing a transit time tube as claimed in any one of Claims 1 to 4, in which said intermediate insulating sleeve and the or each auxiliary intermediate layer are introduced into a mould and supported therein in position relative to one another, and that the material to be melted is then inserted into the melting component of the mould and thereafter fused in a vacuum.

6. A method as claimed in Claim 5, in which said mould consists of graphite, said intermediate insulating sleeve is a ceramic which is metallised on both sides, and that the or each auxiliary intermediate layer is a pre-annealed molybdenum tube.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims (6)

**WARNING** start of CLMS field may overlap end of DESC **. The invention is not limited to the illustrated exemplary embodiments. Thus, in particular the case of liquid-cooled collectors, it is not always necessary for the intermediate insulating sleeve to be mechanically enclosed by a body to which it is cast. A copper layer having good adhesive properties could also be applied by electrolytic deposition. However, electrolytic copper does not possess such good properties as the vacuum copper which is automatically formed during the melting process. WHAT WE CLAIM IS:-

1. A transit time tube having an electron beam collector in the form of a hollow central metal core on the electron beam path, thermally coupled to, but electrically insulated from, a co-axial conductive metal outer sleeve by an intermediate sleeve of electrically insulating material, said metal core being cast with said intermediate insulating sleeve, and containing a heat expansion deceleration means in the form of an auxiliary intermediate annular layer which extends axially within the core material for a length substantially equal to the axial length of the contact surface between said core and said intermediate insulating sleeve, and which consists of a metal whose thermal expansion coefficient is lower than that of the metal of said core.

2. A tube as claimed in Claim 1, in which said outer sleeve consists of a thermally highly conductive metal also cast with said intermediate insulating sleeve with its own auxiliary intermediate annular layer which extends axially within said outer sleeve material for a length substantially equal to the axial length of the contact surface between said intermediate insulating sleeve and said outer sleeve, and which consists of a metal whose thermal expansion coefficient is lower than that of the metal of said outer sleeve.

3. A tube as claimed in Claim 1 or Claim 2, in which said core and said outer sleeve consist of copper, each having a respective auxiliary intermediate layer of molybdenum within, said intermediate insulating sleeve consists of ceramic.

4. A transit time tube having a collector electrode assembly substantially as shown in Figure 1 or Figure 2.

5. A method of manufacturing a transit time tube as claimed in any one of Claims 1 to 4, in which said intermediate insulating sleeve and the or each auxiliary intermediate layer are introduced into a mould and supported therein in position relative to one another, and that the material to be melted is then inserted into the melting component of the mould and thereafter fused in a vacuum.

6. A method as claimed in Claim 5, in which said mould consists of graphite, said intermediate insulating sleeve is a ceramic which is metallised on both sides, and that the or each auxiliary intermediate layer is a pre-annealed molybdenum tube.