US3275866A

US3275866A - Magnetron cathode structures

Info

Publication number: US3275866A
Application number: US126370A
Authority: US
Inventors: Zwobada Rene; Piatti Enrico; Beal Jacques; Juillerat Remi
Original assignee: Lignes Telegraphiques et Telephoniques LTT SA
Current assignee: Lignes Telegraphiques et Telephoniques LTT SA
Priority date: 1960-06-14
Filing date: 1961-05-25
Publication date: 1966-09-27
Anticipated expiration: 1983-09-27
Also published as: DE1294561B; FR1334312A; GB937449A

Description

Sept. 27, 1966 zwo ET AL MAGNETRON CTHODE STRUCTURES 5 Sheets-Sheet 1 Filed May 25. 1961 l/VVE/WOS REN ZWOBADA ENRICO PI'ATTI JACQUES BEAL' REMI JUILLERAT Sept. 27,196 R. ZWOBADA ETAL 3,275,366

' MAGNETRON CATHODE STRUCTURES Filed May 25, 1961 5 SheetsSheet 2 F:3 /NVENOS REN ZWOBADA ENRICO PIATTI JACQUES BEAL REMI JUILLERT Sept. 27, 1966 R.ZWOBADA ETAL MAGNETRON CATHODE STRUCTURES Filed May 25, 1961 5 Sheets-Sheet 5 INVEA/7OS REN ZWOBADA ENRICO PIATTI JACQUES BEAL REMI JUILLERT United States Patent 3,275,866 MAGNEIRON CAIHDE STRUCTURES Ren Zwobada, Enrico Piatfi, Jacques Beal, and Rerm Juillerat, all of Paris, France, assignors to Societe Lignes'Telegraphiques et Telephoniques, Paris, France, a joint-stock company of France Filed May 25, 1961, Ser. No. 126,370 Claims priority, application France, June 14, 1960,

829,880; Oct.3l, 1960, 842,663; Apr. 27, 1961,

6 Claims. (Cl. 313-37 The invention relates to improvernents in high frequency, high power magnetrons and bears especially on the tube structure. As mentioned in French Patent No. 1,104,932 of May 19, 1954, the main problem in magnetrou manufacture is precise positioning of the cathode with respect to the anode block. In the above mentioned patent is described a magnetron structure designed in order to make cathode centering casier during tube manufacture and to reduce misalignnment which might occur during the tube lite. According -to the above mentioned invention, cathode centering with respect to the anode block is visually controlled during tube assembly. An especially designed supporting part is provided to allow setting of the pole piece without requiring any further high temperature heating which may affect cathode center- It has been described in French Patent No. 1,200,355 bf April 23, 1958, the particular problems to be 301ved in manufacturing a high power, very high frequency magnetrou. One of the main difliculties lies in eliminating a large quantity of heat through the cathode structure, combined with the necessary heating of the cathode by an external source in order to bring the cathode coating at thC right temperature for initiating oscillation. The cathode structure which is described in the last mentioned patent is a cylindrical unit which supports at one end the heater and, at the other end, the cooling device, the emissive coating being located inbetween on the cylinder. Such a structure has proved to be very reliable and to provide a long lifetime. As shown in the dfawing appended to this patent, the cathode structure is only snpported at one end, the heater end is not connected to any solid part of the tube envelope. This design Will not provide for suflicient mechanical stability when the tube is submitted to high vibration or acceleration since conditions may happen when the cathode structure will vibrate thereby disturbing normal tube operation.

In order to improve the tube ruggedness, it has been proposed to fix the cathode cylinder at both ends. Such a design is vrydifiicult to manufacture. Indeed, during the tube lite, the cathode assembly is submitted to numer, ous thermal cycles which cause alternate expansions and contractions and it is therefore very difiicult to fix the cathode structure at both ends 10 parts sufficiently solid to provide for mechanical rigidity without excessive stresses being developed in the cathode structure. On the other hand, the unitary cathode structure is metallic and the end to be housed will be set at very high potential during operation. The design of the engaging part is therefore ditficult.

The object of the present invention consists in a magnatron structure with a mechanical stability improved over the structure described in Patent 1,200,355 but still presenting the same advantagesas such structure especially with respect to evacuation of heat from the cathode structure when the magnetron is operated at high power level.

An0ther object of the invention consists in a cathode structure which allows for high precision centering of the cathode in the anode block without requiring a specially Patented Sept. 27, 1966 designed part to allow for the setting of the second polep1ece.

It is an object of the invention to provide for a magnetron structure in which both the cathode hat diameters may be larger than the anode cavity diameter.

It is an object of the present invention to provide means for eliminating any stress which may occur due to thermal expansion of the cathode structure during tube operation.

It is another object of the invention to provide for means to adjust the cathode position with respect -to the anode block after the tube is assembled.

It is an object of the invention to allow for the reductien et the number of dielectric to metal seals in the tube envelope.

The present invention will be readily understood by referenCe to the following description and the appended V drawings which represent four embodiments of magnovention with a welded cathode structure.

part 1 and an upper part 1".

FIGURE 4 shows a complete tube structure incorporating means for adjusting cathode Centering atter tube assembly.

The cylindrical cathode structure 1 consists of a lower Emissive coating 2 is deposited near the upper end of 1 which is terminated at one end by a centering finger 3 and connected at the other end to the cooling device 4 of the type described in abovementioned French Patent No. 1,200,355. Such device is designed for liquid cooling. Any other type of cooling device such as a set of blades for air cooling may be used. The anode bloc-k is shown at 5. It is brazed or welded t0

pole pieces

6 and 6 as is well known. The lower part 1 of the cathode structure is fixed to the lower pole piece 6 by means of the dielectric ring 7 which is sealed or brazed to pole piece 6 and t0 1 by metallic sealing rings 7' and 7. Cathode part 1 houses the heater 14 and is terminated at its lower end by a centering fiange 109 (cf. FIGURE 2B). It is positioned with respect to upper pole piece 6" by the dielectric ring 13 sealed or brazed by means of

metal sealing rings

13 and 13". Part 1" consists mainly of fiange 9.10, cylinder 11 and tube 12. It can be centered with precision with respect to anode block 5 under visual control from the lower part of the structure. It is then assembled by sealing ring 13

t0

13 and 13" and brazing 13" to the upper pole piece 6" and ring 13' to tube 12 through L profiled ring 12'. Filament 14 is connected at its lower end 15 to fiange 10 and at the upper end 16 to the annular output 17 through stem 17. Filament connection is electrically insulated from the cathode by the dielectric ring 18. The tube envelope is completed by sealing on the insulating glass cup 19 which is the exhaust connection. Heater current flows from 17 to stem 17 which is in conductive relationship with the upper end of filament 14. The second filament connection may be taken at 12 or at the lower end of the cathode structure. It is also the cathode D.C. connection. Cylinder 11 acts as a thermal screen between filament 14 and the tube envelope (13"13, etc.).

When part 1" is positioned, centering finger 3 of the lower cathode part is engaged in the fiange 10 the internal face in which has been high precision machined. In order to make assembly easier,the lower part of internal face of fiange 10 is round and centering finger 3 is slightly conical. Finger 3 is free to slide in flange to take over the thermal expansion of the cathode structure. In order to reduce friction of finger 3 against flange 10, longitudinal grooves are machined in finger 3 so as to reduce the bearing surface between 3 and 10. Such grooves could also be machined in flange 10 instead of finger 3. -Cathode unit 1 is made of molybdenum and 50 is fiange 10. Cathode bats are treated 50 as to rednce emissivity as is well known.

FIGURE 2A shows details of the engagng terminations of parts l'and 1' of an embodimentslighfly different from FIGURE 1. Lower part 1 is a hollow cylinder bearing

cathode bats

8 and 9 which may be either. solid with the cylinder or fastenell brazng. Emissive coating.2 is dep rted between the hats. Part '1' is terminated by centering finger 3. The lowerend of upper part 1'. consists of centering flange 10 supported by cylinder 11 which acts as a thermal screen between filament 14 and the tube envelope.

FIGURE 2B shows details of the engagement between parts l':and 1" of the cathode corresponding to the embodiment in FIGURE 1. Flange 10 acts "as the second cathode hat while performing also its centering function. In this embodiment, flange 10 is made of amon-emissive material such for example as molybdenum carbide, tungsten carbide, tantalum carbide, or othi nitallc carbides which as is well known are non-emissive ,at the tempetaturcs encountered in the operation of tubes of this type. Centering finger 3 is preferab lymade of the same matenal as flange 10. It is thercfore nolonger unitary with the cathode part 1. Finger 3 is tightened to cathode structurel according.to any method known per se brazing, Welding, etc

FIGURE 2C shows the cathode structure as seen in a plane perpendicular to axis of the structure, the trace of which appears as X X on FIGURE 2B. The upper cathode part 1 engages in finger 3, the external face of which is grooved as seen at 3"in order to reduce the bearing surface between finger 3 and centeringflange 10 acting also as one of the cathodehats 9..

Diameter of the cathode bats 8 and 9 (or 10 according to the embodiment) may be chosen as large as suitable to optimize the operating conditions of the magnetron. Indeed,it is no longer limited by the internal diameter of the anode cavity since assembly does not require passing the cathode bats through the anode cavity.

Cylinder 11 operates as a thermal screen between filament l4 and the tube envelope. It is heated at a rather high temperature and is preferahly made of a material which will absor-b the gas which may be liberated during tube operation due to electton bombardment or desorption 'by the anode or envelope walls. simplify the drawing the R.F. chokes which should be provided along cylinder 11 have been omitted. They are necessary in order -to prevent -any. loss of high frequency energy along the cathode structure which should be restricted to the volume of the cvities between the cathode and the anode block 5.

The thickness of cylinder 11 is chosen in order to allow a sufiicient elasticity of this cylindrical part so as to allow it to be distorted under the -ctlntrol of centering adjustment device not represented in FIGURE 1 which is operated as will be explained in relationship in.FIG- URE 4 in order to provide final adjustment of the cathode position With respect to the anode block.

FIGURE 3 represents the same tube structure in which free thermal expansion of the cathode is allowed by means external to the cathode structure and located on the tube envelope, that is at a point which is kept cool even during tube operation. The parts common to the structures descrihed on FIGURESI and 3 bear the same reference numbers.

During tube assembly, centering finger 3 cf part 1' is rigidly fixed in art 1" by brazing or welding to flange 10.. The upper end of cylinder 11 is connected to a pair Iby welding 011 In order, to

4 of fianges 21; and 22. These flanges are made of a metal lie, sheet suficientlythin to allow resilient deformation of the two flanges which constitute a mobile parallel ogram allowing free translation of the whole cathode structure along a direction parallel to its axis. The parallelogram defined by the radial flanges 2122 prevents any radial displacement of cylinder 11 therefore preserving cathode concentricty.

Flanges

10, 21, 22, cylinder 11 and the centering finger 3 are machined on the same tool fiXture so as to allow for the best concentricity which may be obtained. Tube assembly is made as follows: fianges 10," 21 and 22 are welded t0 the upper part 1 subassembly which consiste, of flahge 10, cylinder- Il, filament connection seal18 and the exhaustconnection 19 (shown sealed in the figure).- The subassenflhly is then machined another time to obtain a :high precison inside face for flange 10. It is sealed at 13' andl3 to the anode sub-assembly which comprises 5613"13 13 and 7'-77". The lower part 1 of the cathode structure is mounted.and finger- 3 is engagedin fiange 10. Welding is performed between 3 and 10 and then the envelope is completed by seah'ng 7" -to 1'.

FIGURE 4 shows au embodiment of the invention in which cathode positioning with respect to the anode block may :be adjusted after. assembly of the tube. As shown in the previous figures, the cathodestructure comprises. a lower part 1 associated with the;oolirrg device. 4 and terminated at its upper end by centering finger 3.

The upper part 1' of the cathode structure}houses the.

heater 14 and consistsmainly of cylinderll which acts as a thermal screen, for the heater, andas a support for centering flange 10 in which centering finger.3 is fixed by screwing or any other method known per se. Cylinder 11 is terxhinated by a dielectric wafer 40 which providesfor the electric insulatioh of cylinder 11 with respect to the upper part'of the tube envelope. It is therefore possible; to use the upper end of the cathode structure consisting of metallic tube 12 as one heater output without need of insulafing seal 18 instead of outputl7 of FIGURES 1 and 3. Free expansion of the cathode structure along its axis'is allowed by the elasticity of one Z- shaped thin metallic flange 22 welded to the cathode structure at one end and to the anode =bloek at the other by meansof the tubeenvelope (12"131313"6").

Adjustment of cathode position is manually controlled by means of the device 31 to 36 associated with the lower. This adjustment isob-- part 1' of a cathode structure. tained by deformation of a thin walled resilient cylinder 31 connected at its upper end 10 the cathode structure 1' by means of a solid ring 35 and welded at its lower end to a rigid metallic ring 34of the tube envelope. 34

bears several drilled holes in which are introduced controlscrews such as32 and 33, the end.of which bears against cylinder 36 which belongs to the cathode struc;

ture 1" and surrounds the cooling device 4. As willbe readily understood :by screwing *or unscrewing .screws.

32, 33, etc.,jthe lower end of cylinder 31 is displad with respect to cathode structure 1'. The upper end of cylinder 31 tends also to move thereby carrying along 1'. The whole cathode structure tends.to rotate, the center of rotation being located at the seal lbetween the cathode structure -and flange 22'. This displacement of the whole cathode structure will change the position.of enfissive coating 2 in the anode cavity.

Tube assembly is carried on as follows: 2

threaded and is screwed in flange 10. Solid ring 21 slides along collar l3 during this operaon. the tube envelope is completed by brazing co1lar 13 to ring 21.

We claim:

1. A magnetron comprising in combination: an clongated cathode structure including first and second parts; a filamentary heater housed within said first part; means connected to said second part affording connection of a cooling means thereto; an emissive coating on said structure adjacent said first part; at least one cathode hat integral -With said second part; an apertured anode surrounding at least the emissive portion of said structure, the aperture being of less diameter than the diameter of said bat; pole :pieces connected to said anode; and envelope means connected between said cathode structure and said po1e pieces.

2. The combinafion defined by claim 1 in which two cathode hats are integral with said cathode structure, one positioned on either side of said emissive coating.

3. The combination defined by claim 2 in which said enveIope means includes resilent portions connected 13etween one of said cathode parts and said po1e pieces.

4. A magnetron comprisng in combination: an clongated cathode structure including first and second parts; a filament heater housed within said first part; means aflording connection of a cooling device to said second part; an emissive coating on said second part adjacent said first part; a cathode hat on said second part on one side of said emissive coating; a centering finger on said second part on the other side of said coating and extending longitudinally of said second part; a centering flange terminating said first cathode part adjacent said second cathode part; an apertured anode surrounding said emissive coating, the aperture therein being of less diameter than either said hat or fiange external diameters; po1e pieces connected to said anode; and envelope means connected between both said cathode parts and said pole pieces.

5. A magnetron comprising in combination: an clongated cathode structure including first and second parts; a filament heater housed within said first part; means afiording connection of a cooling device to said second par-t; an emissive coating on said second part adjacent said first part; a pair of cathode bats, one on each side of said emissive coating; an apertured anode surround ing said emissive coating, the aperture theren being of Iess diameter than said cathode bats; pale pieces connected to said apertured anode; envelope means counected between each of said cathode parts, said means including a resilient cylinder connected between said second cathode part and said pole pieces; and adjustment means contacting said second cathode part and said reslient cylinder.

6. The combinafion defined by claim 5 and further including at least one resilient part connected between said first cathode part and said pole pieces.

References Cited by the Examiner UNITED STATES PATENTS 2,574,562 11/1951 Hanse]l 31539.63 X 2,894,171 7/1959 Vaughan et al 31339.51

JAMES W. LAWRENCE, Przmary Examiner.

JOHN W. HUCKERT, GEORGE N. WESTBY,

Examiners. V. LAFRANCHI, Assistant Examiner.

Claims

1. A MAGNETRON COMPRISING IN COMBINATION: AN ELONGATED CATHOD STRUCTURE INCLUDING FIRST AND SECOND PARTS; A FILAMENTARLY HEATER HOUSED WITHIN SAID FIRST PART; MEANS CONNECTED TO SAID SECOND PART AFFORDING CONNECTION OF A COOLING MEANS THERETO; AN EMISSIVE COATING ON SAID STRUCTURE ADJACENT SAID FIRST PART, AT LEST ONE CATHOD HAT INTEGRAL WITH SAID SECOND PART; AN APERTURED ANODE SURROUNDING AT LEAST THE EMISSIVE PORTION OF SAID STRUCTURE, THE APERTURE BEING LESS DIAMETER THAN THE DIAMETER OF SAID HAT; POLE PIECES CONNECTED TO SAID ANODE; AND ENVELOPE MEANS CONNECTED BETWEEN SAID CATHODE STRUCTURE AND SAID POLE PIECES.