US2871407A

US2871407A - Electron discharge device

Info

Publication number: US2871407A
Application number: US655731A
Authority: US
Inventors: Ernest C Okress; Ralph J Green
Original assignee: Westinghouse Electric Corp
Current assignee: CBS Corp
Priority date: 1957-04-29
Filing date: 1957-04-29
Publication date: 1959-01-27
Anticipated expiration: 1976-01-27

Description

Jan. 27, 1959 E. c. OKRESS ET AL 2,871,407

ELECTRON DISCHARGE DEVICE Filed A ril 29, 1957 2 Sheets-Sheet 1 ENTORS v M Erne .Okress and k Refocfory Metal Ralph ATTOR NEY E. c. OKRESS ET AL 2,871,407

ELECTRON DISCHARGE DEVICE Jan. 27, 1959 2 Sheets-Sheet 2 Filed April 29, 1957 Fig. 6.

Refoctory Metal Coating Refoctory Metal Coating Fig.9.

Fig.7.

Fig.ll.

Fig. I3,

Fig. IO.

United States Patent ELECTRON DISCHARGE DEVICE Ernest C. Okress, Eimira, N. Y., and Ralph JMGreen,

Newark, N. 1., a'ssignorsto'westiughouse Electric Corporation, 'E'astliittsbnrgh, 11%., a corporation of Penn- :sylvania Application April 29, 1957,Serial No. 655,731

9 :Claims. .(Cl. BIS-69.69)

This invention relates to electron discharge devices, and more particular-1y -to electric spark and arc erosionresistant structures used in electron discharge devices, particularly of the magnetron type.

In oscillators of the standard magnetron type, ap'lurality of cavity resonators, generally of substantially the same natural frequency, is arranged in a circular manner surrounding a cathode. As a result of their-position with respect 'to each other, the cavity resonators are electrically coupled together and are put-into a-stateof-oscillation because of their reaction with 'an electron stream when the magnetron is operated with an axial magnetic field. It has been found in-the operation of magnetrous, particularly when used for high power purposes, that electric arcs may "be created'between various elements of the magnetron. Thesearcs tend to erode these elements, and therefore, tend to 'limit'th'e life of the magnetron.

Accordingly, it is an obj'ect'of' this invention'toprovide an improved spark and are erosion-resistant electron discharge device. 7

It is another object to provide an improved-arc erosionresistant magnetron.

It is another object to provide an improved anode suitable for use in a magnetron.

These and other objects of our invention will be apparent from the following description taken in accordance with the accompanying drawings throughout which like reference characters indicate like parts, which drawings form a part of this application, and in which:

Figure l is a top view of theelectrodestructure of a magnetron according to one embodiment of our invention;

Fig. 2 is a side sectional view along line IIII of Fig. 1;

.Fig. 3 is a perspective viewof 'aportionof a magnetronsimilar to that shown in"F-i'gs. 1 and'2 according to one=embodi1nent of our invention;

Fig. =4 is a side sectional view of an 'anode segment of the magnetron-similar to thatshown-in'Figs. l, '2 and 3 according to one embodiment of oursinvention;

-Fig. 5 is a sidesectional view of-a portion ofan'anode segment i of the magnetron a'ccording *to another embodiment of our invention;

Fig. 6 is --a side Niew of "an anode :segment .of -.the magnetron in accordance with another embodiment of our invention;

Patented Jan. 27, .1959

2 magnetron shown :in :Fig. 10 along the lines according to one embodiment of ourinvention;

*Fig. 112 isa :side view of an anode segment of the magnetron shown in Fig. 10 taken along line XII'XII according "to another embodiment of our invention; and

-Fig."1-3 is aside-viewof the anode segment of "a magnetron similar to that shown in Fig. 10 taken along lines XILJQI according to still another embodiment of our invention.

In Figs. 'l 'and l, there "is shown an electrode structure of-amagnetroniincluding:an anode block 11 having a number of cavity resonators 13 therein. The cavity resonators 13 are separated from .each other :by anode segment members 15 which delineate'an axial cavity-37. 'A cathode 1-7 is positioned in the *center of the axial cavity 37 and includes -a cathode sleeve member 23 wliih=may be directly heated as in Fig. 2 or indirectly heated by an internal heater. In this particularembodi-- ment, a cathode sleeve lead member 21 connects thecathode s'leeve member '23 to an outside voltage source, and a cathode '-1eadmember 22 connects a cathode-conductive -mem=ber 33 to theoutside voltage source. For the sake-of simplicity, the external connections to the heater lead members and the energy input and output: connections are not-shownin this particular embodiment. Cathode hats 19 .are positioned at each end of thecathode sleeve 'memb-er 2-3 to prevent electron leakage from the iuteraction 'space oft-heaxial cavity These cathode hats 19 must not be. self-emitting. End plates 25 are positioned at the top and bottom of the mag-- "netron, and a recess -3'lis located in the segment end. portions 47.

It-has been fou-nddesirable for the efiicient operation of many magnetrons to connect the alternate anodeseg-- ments of the magnetron to each other, and these con neat-ions are known in =the magnetron art as straps.

' In Figs. ,1 and 2, there is shown a double-strapped magnetron in which .:an inner -strap Z7 is placed in an inner strap groove 39 of the recess 31 and is connected to alternate anode segments. An outer strap '29 is placed over an outer strap groove 41 and is connected to the remaining alternate anode segments. Segment tips 35 are positioned between the inner strap and the cathode in this particular embodiment for reducing the zero mode field in "the interaction space 37 and 'for the protection of the strap members. Usually, the anode block 11 is made-of a material known as O-FHC (oxygen-free high conductivity) copper. While copper has the desirable electrical and thermal conductivity, it has some in'herent disadvantages as will'be shown.

The magnetronsho-wn in Figs. 1 and 2 is known as a symmetrical magnetron because the cavity resonatorslS are of the same shape. With strapped symmetrical magnetrons, it has been found that the-electric gradient between thecathode hats 19 and the anode block 11 is highest 'at the segment tips 35 of the anode segments :15. Also, most-cathode hats l9 and anode segments 15 are contaminated with emission material from thecathode.

I'n addition, the cathode hats 19 of refractory type cathodes "operating at relatively high temperature 1500- 1 600 C. B.) generally operate at about -l000 C. by v-irtue ofintercepted thermal radiation from thecathode andby direct'thermal conductiontherefrom. When these magnetronsareoperating at a high power level,-spurious primary emission, as well as secondary emission from theacathode hats =19, causes'sparks to originate from the cathode-hats 19 which terminate on the segment tips '35. When "the segment tips are made of copper, the terminationof the spark on the tip 35 may quickly reach temperatures at whichthe copper begins to melt and evaporate. "The acopper .icns so formed become the source of an electric are between the cathode hat 19 and the segment tip 35. This electric arc causes erosion of the segment tip and leads to shortened life power limitation and eventual total failure of the magnetron.

Also, in high power magnetrons, the electrons from the cathode 17 may impinge on the inner strap 27, and portions of the sides of the segment tips 35, causing secondary electron emission which, in turn, may lead to sparking and arcing between the inner strap 27 and the segment tip 35 with the attendant melting and erosion of these members. The are between the cathode hat 19 and the segment tip 35 is an essentially direct current are and that between the segment tip 35 and the inner strap 27 is exclusively an alternating current (microwave) arc.

In order to fulfill the requirements for high power operation in magnetrons, it is necessary to eliminate existing limitations resulting in arcing of the magnetrons, particularly during long pulses. Therefore, besides reducing the emissive constituent in the cathode to a minimum consistent with maintenance of space charge emission, we propose to replace portions of the magnetron electrodes with refractory materials which have are erosion-resistant properties.

These refractory materials should have a high thermal diffusivity (between that of copper or silver and tungsten), a low vapor pressure and evaporation rate as a function of temperature (comparable to that of molybdenum or preferably tungsten, which have vapor pressures at 2000 K. of 7189x10 mm. Hg and 6.45 l" mm. Hg respectively and evaporation rates at 2000" K. of l.00 l0- gm./cm. /sec. and l.l14 10 gm./cm. /sec. respectively), low secondary emission properties (between those of tungsten and carbon-between 1 and 1.5 maximum regardless of the sticking potentials or incidence angle) and a melting point of 2340 C. or above. It should be noted that the melting point of copper is only 1084 C., while tungsten melts at 3387 C. Also, while copper has a vapor pressure of about l0 micron Hg at 1035 C., tungsten has a vapor pressure of about 10* micron I-Ig at the high temperature of 2554 C.

Consideration of the melting points, vapor pressure and rates of evaporation, thermal diffusivity and sec ondary emissive properties mark tungsten (Wolfram) as a very suitable refractory material. Other suitable refractory materials include molybdenum, tantalum, ruthenium, osmium and iridium and their alloys.

If portions of the electrode, such as the segment tips 35, the inner straps 27 and other portions of the anode segments 15, as will be discussed below, are made of these refractory materials, the erosion of the surfaces due to arcing is markedly reduced or eliminated. Because these surfaces are not so easily vaporized, the tendency from a spark to develop into a metallic arc is reduced.

In order to more clearly illustrate the portions of the electrodes involved, there is shown in Fig. 3 a perspective view of a portion of a magnetron similar to that shown in Figs. 1 and 2. A portion of the anode block 11 is shown including anode segment members 15 which separate cavity resonators 13 from each other. Also, a portion of the axial cavity 37 in which the cathode 17 is located is shown. The cathode sleeve member 23 is normally coated with a suitable emissive material, if indirectly heated. lf directly heated, the heating current is conducted directly through the emissive material composed of thoria and a refractory metal power such as molybdenum or tungsten. The cathode hat 19, shown in Fig. 2, is not shown in Pig. 3 for the purpose of clarity and simplicity. In the segment end portion 47, there is shown a recess 31 including an inner strap groove 39 in which the inner strap 27 may be placed and an outer strap groove 41 in which an outer strap 29 may be placed. In this particular segment, the outer strap is not connected to the anode segment 15 shown in section, but is connected to the other adjacent alternate anode segments. Also shown is the anode segment inner face 43 and the anode segment tip As can be seen, the segment tip inner 4 face 45 is really an extension of the anode segment inner face 43.

In Fig. 4, there is shown a side view of a portion of an anode segment 15 similar to that shown in Fig. 3, in which the segment tip 35 and a portion of the recess 31 is made of a suitable refractory material. In this particular embodiment, the segment tip 35 is made separately from the anode segment 15. For example, if the segment tip 35 is made of molybdenum, it may be joined to the copper anode segment 15 by a suitable brazing alloy 15, such as a gold-c0pper eutectic alloy which is brazed to the molybdenum which has been nickel-plated and sintered. If tungsten is used as a refractory material, a gold-nickel eutectic brazing material has been found to be particularly suitable because of its higher melting point and because it will join the tungsten directly to the copper without an additional plating operation. It may sometimes be desirable to make only the segment tip 35 (the part to the left of the dotted line in Fig. 4) of refractory material and not include that part of the recess 31 shown in Fig. 4. Also, as shown in Fig. 4, the inner strap 27 may also be made of the refractory material, if desired. In any case, the outer strap 29 is made of (OFHC) copper as it is not usually affected as much by arcing as the other electrodes. These refractory materials have higher melting points than the copper, as pointed out previously, and have a lower vapor pressure than copper, which is also desirable. However, their thermal diffusivity and their electrical conductivity while still good, are lower than copper.

In Fig. 5, there is shown a side view of an anode segment similar to that shown in Fig. 3 in which the inner strap member 27 and the outer strap member 29 are located completely within the recess 31 so that the top surface of the two straps is below thev segment end po tion 47. A cover plate 49, which in this particular embodiment is an integral part of the segment tip 35, has been placed over the top of the recess 31, but does not extend appreciably over the space between the anode segment members 15. In this embodiment, the inner strap 27, the segment tip 35, portions of the bottom of the recess 31 and the cover plate 45 are made of a suitable refractory material. This cover plate 49 has the advantage of increasing the thermal cross section for better heat conduction from the segment tip 35. As seen in both Figs. 4 and 5, the segment tip inner face 45 is made of a refractory material which reduces erosion due to any arcing tendency between the cathode hat 19 and the segment tip 35. The inner strap 27 may also be of a refractory material, if desired.

It may be advantageous, especially if the high thermal diffusivity and electrical conductivity of copper is particularly desirable, to coat the surface of the segment tips 35 and possibly, but not necessarily, the inner strap 27 with a suitable refractory material rather than make the inner strap and the segment tip 35 entirely of the refractory. We have found that a particularly suitable embodiment is that shown in Fig. 6, in which a side view of an anode segment similar to that shown in Fig. 3 is shown. In addition to the anode segment tip 35, certain portions of the bottom recesses 31 and the top, inner and bottom surfaces of the inner strap 27 may be coated with a refractory material. Also, in this particular embodiment, the entire segment inner face 43 has also been coated with a refractory material. Of course, if desired, only the anode segment tip 35 may be coated rather than the entire segment inner face 43.

One method we have found particularly suitable is to plate a very thin (1 l0- inch) layer of gold on the copper base and then plate a layer (0003-0005 inch thick of rhodium on the gold. This plating forms a good bond to the gold-plated copper and has the advantages of having the high melting point and low vapor pressure of the refractory metal rhodium with the excellent thermal plated portions.

difiusivity of the base metal copper. f course other suitable @refractory materials may be plated on-ithe' copper.

A top view of the "plated anode segment .15 .of Fig.

'6 is shown in Fig. 7 to more clearly pointou-t the -plated portions. In Figs. 6 and 7, the-innerstrapZT-is notsconnected to the particular anode segment .15 which-isrshown but :is'connected tothe alternate anode segments. ,However, if strapping is used on the bottom-endoftheanode segment 15, the bottom inner strap would be connected to the anode segment shown, and "the bottom outer strap 29 would not beconnected to the anode segment '15-shown. 4 I

'In Fig. 8, there is-shown-a side viewof-.an:anode.seg inentinwhich the inner strap 27 is-c'onnectedto the anode segment 15 .in which the segment inner face 43, all surfaces of the segment tip .351and the inner and upper surfaeesof the inner strap -27 have been .plated with a suitable refractory-material.

In Fig. 9, there is shown atop view-'o'fthe platedanode segment shown in Fig. -8 to more clearly ,point .outLthe Of :course, there are other embodiments which .-may

be used in plating or making the portions :of the .electrodes which are subject-to arcing, of-refractory-metals.

For example, it'may be desirable .not toqplatevtheportions of therinner strap member 27.s hown as plated-in Figs; 6-9, even though other parts are plated .as shown in those figures. In some instances, .the-entire anode segment inner face *43 .may .be .madeor'p'lated .with ;a refractory metal. While in others, only portions of .the

segment inner face 43 are plated, :for -example,.only .the

segmenttip-metal face 45. Also, in some instances, the

-.cover-,p late'49, similar to that shown .in .Fig. 5,.may be separate from the segmentt-ip .315 and, .ifdesircd, .may

be made-of another material or may .bemade of copper.

not of similar size) magnetron, such-as1that knowntas the "rising sun magnetron, straps are not used. vlI-Iov'vever, our invention maybe used in a rising sun magnetron, the anode of which is shown in Fig. 10. As can be seen, the anode block 49 which, as in most magnetrons, is made of OFHC copper, is provided with a number of cavity resonators. However, in contrast to the cavity resonators shown in Figs. 1 and 2, these cavity resonators are made alternately large 53 and small 51. Also, the cavity resonators 51, 53 are separated by anode segment members 57, the inner faces 59 of which delineate an axial cavity 55 in which a cathode is normally positioned. In this particular figure, however, the cathode is not shown for purposes of clarity. Depending on the power used and other factors, it is desirable to make or plate certain portions of the segment members with a refractory metal, such as those discussed above.

In Fig. 11, there is shown a side view of an anode segment member 57 taken along lines XIXI in which the entire anode segment member 57 is made of a suitable refractory material such as tungsten. As can be seen, the side portions 611, the inner face portions 59 and the end portions 65 are all of a refractory material. In this case, as in the cases of Figs. 12 and 13, only one anode segment member 57 is shown, but it is understood that all segment members 57 are the same in any one magnetron.

In Fig. 12, there is shown a side view of an anode segment member 57 taken along lines XIIX[I in which only a small part of the inner portion of the segment member 57 is made of or plated with a refractory metal. However, the entire segment inner face 59 of the segment member 57 is made of or coated with a refractory metal.

In Fig. 13, there is shown a side view of another anode tions 63 .are of.the refractory metal.

segment member 57 also taken along l ines XIL-IXlilin which the-entire segment inner;face.59 .isno'tmade of a refractory metal but ,onlythe segmenttinner face end por- Of course, =anumher-of variations might be made in Figs. 1.0 through 13 depending on'the areas in which the .arcs would tend to form.

Also, it is understood that while our invention using refractory elements has been shown as used with a magnetron, it may be used in other electron discharge devices in whichsarcs tend .to form and thereby erode metal electrodes, for example, ..in klystrons, traveling wave tubes, 'carsinotrons, .stabilitrons, etc.

While-the present inventionhas -.been shown in a few forms only, it will be :obvious to those skiIled in the ar-t thatit is not so limited'butds susceptible of various changes and modifications without distinguishing from the .spirit and scopethereof.

We claim as ourinvention:

1. A magnetron having a plurality of electrodes, two of said electrodes having .a :high potential gradient be- -tween.them, portions-of.the -surface ofrsaid'two electrodes which are subject-to an alternating current electric arc formation between them being composed of a refractory .metallic material.

2. .A .magnetron having a ,pluralityof electrodes, two

of rsaid electrodes having a .high ;p.otential gradient 'between them, port-ionsof the surface of said two electrodes which are subject to analternating current electric arc formation between them being composed of va-refractory -metallic material havingamelting pointabove 2340 C.

.3. A'magnetron :having.a;plurality of electrodes, two

of said electrodes having :a .high .potential gradient 'beiridium, andtheir alloys.

4. A magnetron including. ananodeha-ving .anaxial ;cavity and.a. plu r=ality ofcavity resonators radiating there- ,from, .a cathodelocated within said ax-ial cavity, said caviitytresonators being separated by anode, segmentmembers,

said segment members having aninner face adjacent said axial cavity, said segment members including an end portion having a recess therein, said segment members having a segment tip member between said recess and said axial cavity, said segment tip member having a tip inner face constituting a portion of said segment inner face, and a metallic strap member connected to alternate segment members of said anode, said metallic strap member having an inner surface facing toward said segment tip member, said metallic strap member being positioned within said recess, said tip member face and said inner surface of said metallic strap member being composed of a refractory metallic material having a melting point above 2340 C.

5. A magnetron including an anode having an axial cavity and a plurality of cavity resonators radiating therefrom, a cathode located within said axial cavity, said cavity resonators being separated by anode segment members, said segment members having an inner face adjacent said axial cavity, said segment members including an end portion having a recess therein, said segment members having a segment tip member between said recess and said axial cavity, said segment tip member having a tip inner face constituting a portion of said segment inner face, and a metallic strap member connected to alternate segment members of said anode, said metallic strap member having an inner surface facing toward said segment tip member, said metallic strap member being positioned within said recess, said tip inner face and said inner surface of said metallic strap member being composed of a refractory metallic material selected from the group consisting of tungsten,

7 molydenum, tantalum, ruthenium, osmium, iridium, and their alloys.

6. A magnetron including an anode having an axial cavity and a plurality of cavity resonators radiating therefrom, a cathode located within said axial cavity, said cavity resonators being separated by anode segment members, said segment members having an inner face adjacent said axial cavity, said segment members including an end portion having a recess therein, said segment members having a segment tip member between said recess and said axial cavity, said segment tip member having a tip inner face constituting a portion of said segment inner face, a metallic strap member connected to alternate segment members of said anode, said metallic strap member having an inner surface facing toward said segment tip member, said metallic strap member being positioned Within said recess, and a cover plate covering said recess, said tip inner face and said inner surface of said metallic strap member being composed of a refractory metallic material having a melting point above 2340 C.

7. A magnetron including an anode having an axial cavity and a plurality of cavity resonators radiating therefrom, a cathode located Within said axial cavity, said cavity resonators being separated by anode segment members, said segment members having an inner face adjacent said axial cavity, said segment members ineluding an end portion having a recess therein, said segment members having a segment tip member between said recess and said axial cavity, said segment tip member having a tip inner face constituting a portion of said segment inner face, a metallic strap member connected to alternate segment members of said anode, said metallic strap member having an inner surface facing toward said segment tip member, said metallic strap member being positioned within said recess, and a cover plate covering said recess, said tip inner face and said inner surface of said metallic strap member being composed of a refractory metallic material selected from the group consisting of tungsten, molydenum, tantalum, ruthenium, osmium, iridium, and their alloys.

8. A magnetron including an anode having an axial cavity and a plurality of cavity resonators radiating therefrom, a cathode located Within said axial cavity,

said cavity resonators being separated by anode segment members, said segment members having an inner face adjacent said axial cavity, said segment members including an end portion having a recess therein, said segment members having a segment tip member between said recess and said axial cavity, said segment tip member having a tip inner face constituting a portion of said segment inner face, a metallic strap member connected to alternate segment members of said anode, said metallic strap member having an inner surface facing toward said segment tip member, said metallic strap member being positioned within said recess, and a cover plate covering said recess, said cover plate having a top surface, said tip inner face, said top surface of said cover plate and said inner surface of said metallic strap member being composed of a refractory metallic material having a melting point above 2340 C.

9. A magnetron including an anode having an axial cavity and a plurality of cavity resonators radiating therefrom, a cathode located Within said axial cavity, said cavity resonators being separated by anode segment members, said segment members having an inner face adjacent said axial cavity, said segment members including an end portion having a recess therein, said segment members having a segment tip member between said recess and said axial cavity, said segment tip member having a tip inner face constituting a portion of said segment inner face, a metallic strapmember connected to alternate segment members of said anode, said metallic strap member having an inner surface facing toward said segment tip member, said metallic strap member being positioned within said recess, and a cover plate covering said recess, said cover plate having a top surface, said tip inner face, said top surface of said cover plate and said inner surface of said metallic strap member being composed of a refractory metallic material selected from the group consisting of tungsten, molybdenum, tantalum, ruthenium, osmium, iridium, and their alloys.

References Cited in the file .of this patent UNITED STATES PATENTS Wooten Dec. 26, 1950