RU2285310C2 - High-power helical traveling-wave tube - Google Patents

Abstract

FIELD: microwave device design and technology.

SUBSTANCE: proposed traveling-wave tube is characterized in high specific heat load on helical slow-wave structure and in that its vacuum envelope is combined with magnetic circuit of periodic magnetic focusing structure. Insulating supports are joined with slow-wave structure helix by means of insulator solder whose melting point is over 1050 °C and with case assembled of magnetic-system pole shoes copper-soldered together, as well as with their separating bushings by means of metal solder whose melting point is 780 to 1000 °C. Nonmagnetic bushings separating pole shoes of periodic magnetic focusing structure are made of vacuum ceramics whose coefficient of linear thermal expansion is lower than that of pole-shoe and insulating-support materials. Expression for choosing thickness of nonmagnetic bushing is given in invention specification.

EFFECT: enhanced output power, mechanical strength, and reliability of traveling-wave tube.

15 cl, 4 dwg

Description

The invention relates to the design and technology of microwave devices, namely to powerful traveling-wave spiral tubes (TWTs) and to miniature low-voltage TWTs with a high specific heat load on the coil using magnetic periodic focusing.

The requirements for creating new promising radio equipment in the centimeter wavelength range dictate the need to develop reliable and compact spiral TWTs for high-power (more than 1 kW) output stages of ground transmitters and, on the other hand, miniature low-voltage TWTs with increased power (hundreds of W) for on-board equipment . A key problem in the development of both classes of TWT is the insufficient heat removal from the TWT spiral. The temperature of the spiral of powerful TWT is allowed up to 300 ° C when it is made of copper and about 500 ° C in the case of molybdenum. Typically, a spiral in powerful TWT is made of molybdenum. Particularly promising designs for these classes of TWTs are those in which the vacuum shell in the region of the retarding system is combined with the magnetic core of the magnetic periodic focusing system (MPFS). An ideal thermal contact would be ensured by soldering all the heat-removing elements between themselves with metal solders. But, with an increase in operating frequencies to a 3-cm range and above, when the diameter of the spiral and the pitch of its winding are already fractions of a millimeter, this method of fixing the spiral becomes problematic, because reliable electrical isolation between adjacent turns of the spiral is required. The use of soldering to connect the dielectric supports of the spiral with the casing is difficult due to the large length of the seam, which requires perfect matching of dissimilar parts of the junction according to the coefficient of thermal linear expansion.

There are known designs of spiral TWTs in which, to improve heat dissipation from the spiral (to reduce the thermal resistance between the spiral and the cooled surface of the TWT case), tight mechanical contact between the spiral and the dielectric supports fixing it in the case, as well as between the supports and the case itself, is provided by precision machining and various technological methods, the most common of which is the "thermal compression" of the spiral-support-housing system [1, 2]. Moreover, a thin metal tube is usually used as a housing (vacuum shell), onto which the pole tips of the MPFS magnetic circuit are subsequently attached.

The disadvantages of these designs are the following: significant thermal resistance in the areas of mechanical contact of the parts to be joined, instability of this resistance (tendency to increase) during operation during repeated heating and cooling, as well as the presence of additional thermal resistance at the contact points of the tube and disk pole tips of MPFS, from which heat is removed by blowing them with air or using liquid cooling.

The prototype of this technical solution is a broadband spiral TWT [3] with a spiral surrounded by heat-removing ceramic supports made of beryllium oxide (BeO), containing a metal body that is part of a vacuum shell and combined with the magnetic core of a magnetic periodic focusing system in which the pole pieces are made in the form of disks soft magnetic material and separated by metal bushings of non-magnetic material. In this design, the spiral supports contact directly with the inner surface of the tips of the magnetic circuit and the bushings separating them of non-magnetic material (monel alloy), connected by vacuum-tight seams and forming a vacuum sheath of the TWT in the region of the retardation system. The undoubted advantages of this design is the lack of an inner tube, usually used for crimping the spiral-support system. This allows you to eliminate additional thermal resistance between the tube and the magnetic circuit, increase the magnitude of the magnetic field on the axis of the device and the alignment of this magnetic field with the axis of the device.

The disadvantage of this technical solution is the presence of purely mechanical contacts between the contacting surfaces of the parts (spiral - supports and supports - body) that remove heat from the spiral. Such tight mechanical contacts have significant thermal resistance and, moreover, the stability and reliability of this resistance decreases over time, after repeated heating and cooling cycles during operation.

The aim of the proposed technical solution is to increase the output power of spiral TWT through the use of soldered joints to improve heat dissipation from the spiral to the TWT case without compromising the reliability and mechanical strength of the connection.

The goal is achieved by the fact that in the proposed design:

The bushings separating the pole pieces of MPFS are made of vacuum ceramics with a coefficient of thermal linear expansion less than the coefficient of thermal linear expansion of the material of the pole pieces and the coefficient of thermal linear expansion of the material of the supports, the supports are connected to the spiral by a layer of dielectric solder with a melting point above 1000-1050 ° C, and with the case - a layer of metal solder with a melting point from 780 ° C to 900-1000 ° C, and the thickness of the sleeve l _in selected from the ratio:

l _in = l (α _n -α _o ) / (α _n -α _in ) = (0.56 ÷ 0.76) l,

where l is the total thickness of the pole piece and the sleeve along the axis of the housing [m],

α _n - coefficient of thermal linear expansion of the material of the pole pieces [K ^-1 ],

α _o - coefficient of thermal linear expansion of the material of the supports [K ^-1 ],

α _in - coefficient of thermal linear expansion of the material of the bushings [K ^-1 ].

Powerful spiral traveling-wave lamp, characterized in that aluminosilicate material is used as a dielectric solder.

Powerful spiral traveling-wave lamp, characterized in that SK-27 glass cement is used as a dielectric solder.

Powerful spiral traveling-wave lamp, characterized in that a PSr70M copper-silver alloy is used as a metal solder.

A powerful spiral lamp of a traveling wave, characterized in that a PZl80M copper-gold alloy is used as a metal solder.

A powerful spiral traveling-wave lamp, characterized in that a PZl90Sr gold-silver alloy is used as a metal solder.

Powerful spiral traveling-wave lamp, characterized in that PM88G copper-germanium alloy is used as a metal solder.

Powerful spiral lamp of a traveling wave, characterized in that the metal solder is applied galvanically to the inner surface of the body.

Powerful spiral lamp of a traveling wave, characterized in that the metal solder is applied to each support in a galvanic manner in the form of a longitudinal strip on the outer sides of the supports.

Powerful spiral traveling-wave lamp, characterized in that a layer of additional metallization is placed between the metal solder and the sleeve with good adhesion to the material of the sleeve.

Powerful spiral traveling-wave lamp, characterized in that an additional metallization layer is placed between the metal solder and the support with good adhesion to the support material.

Powerful spiral traveling-wave lamp, characterized in that molybdenum or molybdenum-manganese metallization paste of grades P-1 or PM-1 is used as the material for metallizing the bushings.

A powerful spiral traveling-wave lamp, characterized in that molybdenum or molybdenum-manganese metallization paste PST-1 or PSTM-1 is used as the material for metallizing the supports.

A powerful spiral traveling-wave lamp, characterized in that a buffer layer of a nickel coating is placed between the metallization layer and the metal solder.

A powerful spiral lamp of a traveling wave, characterized in that cooling channels parallel to its axis are made in the housing.

Powerful spiral traveling-wave lamp, characterized in that the bushings are made of a package of double-sided metallized ceramic layers using multilayer ceramic circuit board technology.

The essence of the invention lies in the fact that in the proposed design compared to the prototype due to the use of soldered seams between the spiral and the supports and between the supports and the housing, the heat sink from the spiral is significantly increased, since the thermal resistance of the contacts between the heterogeneous materials of the spiral, supports and the housing decreases Thus, it is possible to operate such a spiral at high levels of TWT output power. But in the TWT constructions used in practice [3], such metal junctions cannot be realized due to high mechanical stresses arising in the joints of dissimilar materials. This is especially true for the extended joints of the joints of the supports with the body. In addition, metal solders for brazing the helix to the supports should be applied locally so as not to electrically short-circuit the coils of the helix. This extremely complicates the assembly and soldering technology and provokes electrical breakdowns between the turns of the spiral at high powers. The use in the proposed design of step-wise spiral brazing with dielectric high-temperature solder to the supports and, then, this assembly into the case with a lower-temperature metal solder with the mandatory use of vacuum ceramic bushings separating the MPFS magnetic circuit disks and forming a soldered vacuum-tight shell of the device with them, solves this problem. To ensure the first stage of step soldering, i.e. For brazing the spiral assemblies - supports and bodies formed from the pole pieces of the magnetic system and bushings separating them from non-magnetic material (ceramics), glass cement with a melting point above 1050 ° C and pure copper with a soldering temperature of 1083 ° C were selected, respectively, as dielectric solder . The soldering of the spiral node - supports in the housing is the second stage of the process, carried out using metal solder with a melting temperature in the range from 780 ° C to 1000 ° C. Due to the lower supports (ceramics made of beryllium oxide) and the soft magnetic material of the pole pieces (pure iron and its alloys), the coefficient of thermal linear expansion of the bushings in the proposed design, it is possible to create a reliable solder joint in which local stresses do not reach destructive values. With the appropriate choice of the thickness of the sleeve and the thickness of the pole piece in the joint sleeve – pole tip, the absolute values of the absolute values of the elongations of the body and supports along the MPPS half-life (sleeve – pole tip) can be equal with high accuracy, i.e. mechanical stresses in the joint do not accumulate in retarding systems with extended seams. When using the material of the pole lugs of the currently existing soft magnetic alloys of iron and pure iron with coefficients of linear thermal expansion from 110 × 10 ^-7 (KF-48 alloy) to 145 × 10 ^{-7, the} ratio of the thickness of the sleeve to the total thickness of the sleeve and tip is ranging from 0.56 to 0.76. These limits are close to optimal for existing materials suitable for use as elements of a combined vacuum shell of powerful TWTs with magnetic periodic focusing. Due to the proximity of the coefficient of thermal linear expansion of molybdenum and many dielectric materials used for the manufacture of supports, as well as to the small extent of junctions, destructive stresses do not occur in junctions of molybdenum spirals with supports. Even in junctions of materials such as vacuum ceramics and iron or its soft magnetic alloys, dangerous stresses do not arise with real transverse dimensions of the TWT cases of the centimeter range. The junction shape also contributes to this - ceramics on both sides are covered by pole pieces with a large coefficient of thermal linear expansion.

The invention is illustrated by drawings, where:

figure 1 shows a cross section of a powerful spiral TWT, passing through one of the bushings;

figure 2 shows an enlarged fragment C of a cross section of a powerful spiral TWT (figure 1);

figure 3 shows a longitudinal section of a powerful spiral TWT along the line BB of figure 1;

figure 4 shows a longitudinal section along the line BB of figure 1 of an embodiment of a powerful spiral TWT.

The proposed powerful spiral lamp of a traveling wave includes a housing made up of pole tips 1 MPPS in the form of disks and bushings 2 of non-magnetic material separating them. In the space between the pole pieces 1, ring magnets 3 are installed. Inside the case, along its axis there is a retardation system including a spiral 4 and dielectric supports 5. The supports 5 are connected to the spiral 4 by a brazed seam using dielectric solder 6, and to the case by a brazed seam behind account of the layer of metal solder 7, galvanically deposited on the inner surface of the pole pieces 1, as well as on the metallized 8 by high-temperature incineration of the metallization paste and coated with nickel 9 the surface of the bushings 2. Naru The screen in this design of the retarding system is formed by the inner surfaces of the pole pieces 1 and metallized (layers 7, 8, 9) bushings 2. The outer face of the rectangular supports in cross section (to increase the contact area) of the supports 5 is also metallized (layer 10) and coated with nickel 11 . In the thickness of the ceramic-metal case, cooling channels 12 can be made to increase the heat sink. For the same purpose, the bushes can be made of multilayer metallized ceramics 13 layers using multilayer circuit technology, which is still more it increases the heat sink from the spiral to the outer surface of the housing, or to the cooling channels 12. The dimensions of the TWT structural elements, namely the thickness of the bushings l _in and the total thickness of the bushings and pole pieces l, are shown in Fig.3.

An example of the practical implementation of the invention is the design of a powerful spiral TWT, in which the spiral is made of molybdenum, the supports are ceramic, made of beryllium oxide, grade OB-1, the pole pieces are made of pure iron (steel grade 10864), and the bushings are made of aluminum oxide ceramic of the brand 22XC. Used in soldered joints: pure copper grade MB (1083 ° C) in junctions of pole pieces and bushings, glass cement grade SK-27 (1200 ° C) as dielectric solder in a joint of spirals and supports and galvanic copper-silver solder grade PSr70M (780 -800 ° C) in the junction of the supports with the body. Such a selection of solders provides step-by-step soldering of the case and significantly simplifies the technology of its manufacture. As solders for the second soldering stage, other galvanic solders with a melting temperature from 780 ° С to 1000 ° С can be used, for example, solders of the ПЗл80М, ПЗл90Ср, ПМ88Г grades. For high-temperature metallization of ceramic bearings and bushings, molybdenum-manganese paste of the PSTM-1 and PM-1 grades were used, respectively, and the metallization layer was galvanically coated with a nickel buffer layer from above. A layer of PSr70M solder is deposited on the inner surface of the body galvanically. The galvanic solder layer must be of sufficient thickness so that, during the final machining of the inner surface of the casing, to ensure the minimum guaranteed clearance between it and the external metallized faces of the supports of the soldered spiral-support assembly. When soldering supports with a spiral, the layer of dielectric solder from glass cement should be minimal so that when soldering, it moistens only the outer part of the spiral, without flowing onto its inner side, facing the electron flow in the working TWT. In addition, the technology of brazing a spiral with supports should provide pressure between the turns of the spiral and the supports so that the turns of the spiral, pushing softened glass cement, come into close mechanical contact with the ceramic. In such a node, the thermal resistance between the spiral and the supports will be lower than with the known methods of mechanical or thermal "compression" of the node. During TWT operation, when the spiral is heated to significant temperatures (~ 500 ° С) and even when cooling after soldering (1200 ° С) in the spiral-support assembly, dangerous stresses do not arise in the joint, since The CTLRs of molybdenum, SK-27 glass cement and beryllium oxide ceramics are close (50 × 10 ^-7 , 60 × 10 ^-7 and 87 × 10 ^-7, respectively), and the length of the junctions is small - equal to the width of the supports. At the contact point of the supports with the ceramic-metal case, materials dissimilar in CTLR are soldered with metal solder, but there is no accumulation of stresses in the joint, because the expansion of the junction of the junction, the pole tip, which is most expanded during heating, is compensated by the relatively small expansion of the vacuum ceramics of the bushings, and the total expansion of this pair of housing materials is selected equal to the expansion of ceramic supports of the same length from beryllium oxide. In addition, even for such a heterogeneous KTLR pair, such as vacuum ceramics and magnetically soft iron pole pieces, with maximum junction sizes in the transverse axis of the device, a direction of 10-15 mm and a temperature difference of 800 ° C, the stresses in the joint do not reach destructive stresses. This is favored by the fact that the pole pieces with a large CTRL cover ceramic bushings on both sides, compensating for the bending stresses in the junctions.

For a selected triple of materials, ceramic supports made of beryllium oxide (α _о × 10 ⁷ = 87), the poles of the magnetic core made of iron (α _n × 10 ⁷ = 145) and bushings made of alumina ceramics 22XC (α _in × 10 ⁷ = 69) are optimal from the point In terms of CTRL matching, the ratio of the thickness of ceramic bushings and pole tips was 3: 1, which is close to the typical ratio of the thickness of magnets (3, Fig. 2) and pole tips of MPFS in powerful TWTs of the centimeter range. In addition, this ratio may not be exactly the same as the ratio of the thicknesses of ceramics and metal in the joint of the ceramic-metal shell within reasonable limits (avoiding the small thickness of the magnetic circuit leading to its saturation) due to the different thicknesses of the disks of the magnetic circuit in the joint and behind the shell, in the region of magnets . Varying this ratio is also possible due to the use of other soft magnetic materials (alloys) for pole pieces with other CTLRs. The choice of these materials is wide enough.

Thus, the present invention will provide the ability to create a powerful, economical in production and reliable TWT spiral for several units of kilowatts of average power in the band from tens of percent to octave and, on the other hand, will create a strong, reliable and resistant to mechanical stress structures for low voltage miniature TWT with a fine-structured spiral.

INFORMATION SOURCES:

1. A.S. USSR No. 290346, IPC H 01 J 23/26, priority from 01/06/1968, "Mandrel for the thermal fixation of a retarding system", author V.I. Yudanov.

2. A.S. USSR No. 322805, IPC H 01 J 23/26, priority of 11/26/1969, "Method for attaching a retarding system", V.I. Yudanov, A.F. Murskov.

3. The dissertation for the degree of candidate of technical sciences in the specialty 05.12.07 "Antennas and microwave devices and their technologies" by Gennady Anatolyevich Azov on the theme "Research and development of powerful broadband TWTs of continuous action of the centimeter wavelength range on spiral decelerating systems, OJSC" Pluto ", Moscow, 2002, pp. 94-99, 109-111.

Claims (15)

1. A powerful traveling-wave spiral lamp containing a housing that is part of a vacuum shell and combined with a magnetic core of a magnetic periodic focusing system, in which the pole tips are made in the form of disks and separated by bushings of non-magnetic material, a retarding system with a spiral, fixed along the axis of the housing with dielectric supports made of a material with high thermal conductivity, characterized in that the bushings are made of ceramic with a coefficient of thermal linear expansion less the coefficient of thermal linear expansion of the material of the pole pieces and the coefficient of thermal linear expansion of the material of the supports, the supports are connected to the spiral by a seam of dielectric solder with a melting point above 1050 ° C, and with the body by a seam of metal solder with a melting point from 780 to 1000 ° C, the thickness of ceramic bushings l _in selected from the ratio l _in = l (α _n -α _o ) / (α _n -α _in ) = (0.56-0.76) 1 [m], where l is the total thickness of the pole piece and the sleeve along the axis of the housing [m], α _n - CTLR material of the pole pieces [K ^-1 ], α _about - CTLR material of dielectric supports [K ^-1 ], α _in - CTLR material of ceramic bushings [K ^-1 ]. 2. A powerful spiral traveling-wave lamp according to claim 1, characterized in that glass-cement based on aluminosilicates is used as a dielectric solder. 3. A powerful spiral traveling-wave lamp according to claim 2, characterized in that glass cement of the SK-27 brand is used. 4. The powerful spiral traveling-wave lamp according to claim 1, characterized in that a PSr70M copper-silver alloy is used as the metal solder. 5. A powerful spiral traveling-wave lamp according to claim 1, characterized in that a PZl80M copper-gold alloy is used as the metal solder. 6. The powerful spiral traveling-wave lamp according to claim 1, characterized in that a PZl90Sr grade gold-silver alloy is used as a metal solder. 7. The powerful spiral traveling-wave lamp according to claim 1, characterized in that a PM88G copper-germanium alloy is used as the metal solder. 8. The powerful spiral traveling-wave lamp according to claim 1, characterized in that the metal solder is applied galvanically to the inner surface of the housing. 9. The powerful traveling-wave spiral lamp according to claim 1, characterized in that the metal solder is applied galvanically to each support in the form of a longitudinal strip from the side facing the body. 10. The powerful traveling-wave spiral lamp according to claim 1, characterized in that between the metal solder and the sleeve there is an additional layer of metallization with good adhesion to the ceramic material of the sleeve. 11. The powerful spiral traveling-wave lamp according to claim 1, characterized in that between the metal solder and the support an additional metallization layer is placed with good adhesion to the ceramic material of the support. 12. The powerful spiral traveling-wave lamp according to claim 10, characterized in that the material for metallization is molybdenum or molybdenum-manganese metallization paste of grades P-1 or PM-1. 13. The high-power traveling-wave spiral lamp according to claim 11, characterized in that the molybdenum or molybdenum-manganese metallization paste PST-1 or PSTM-1 is used as the material for metallization. 14. Powerful spiral lamp of a traveling wave according to claim 1, characterized in that cooling channels parallel to its axis are made in the housing. 15. A powerful spiral traveling-wave lamp according to claim 1, characterized in that the ceramic bushings of the housing are made of multilayer metallized ceramic using multilayer ceramic circuit board technology.

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