US2538597A - Magnetron - Google Patents

Description

Jan. 16,Y 1951 H. STEELE, JR

MAGNETRON Filed June 18, 1946' M Wy. u a w ws. m L E W ik AXA v. Mv n 0% "Vm/ 3 i 1 l Z a n m i 3 a N 1 Z I J ,y g. r rl 1 VLl .H 1MMAI g I 3Q 4 1 E n .5. u. j Z ITI 4 4 Patented Jan. 16, 1951 y l- 1 f assiste 7 'MAGNETRON v award "L, israele, sa, loomnela, IN. J., assigner to lWe'stinghouse Electric ,Corp'oratiom East Pittsburgh, Ta., a corporation of Pennsylvania Application J unels, 1946,"Seia1No.-67'1,464

- invention relates :to magnetrons, and f more particularly to introduction and 'utilization of electrons 'within a `hollow anode.

vThe lusual magnetron" provides an annui-"e` sur-i rounding a v'cathode coaxial therewith, the anode having cavity resonatorsiradiating therefrom and 'the cavities constitntingv salti resonators, as ywell as the central hollow orcavity 'for the cathode 'all opening into end spaces at each end :for 'the anode. AFor 'reasons `not believed necessary 'to vdiscuss "here, `many electrons emitted :by fthe 4"cathode 'return thereto'f-'after excursion in and 'absorptionof energy from the region between 'the cathode 'and anode. The excess energy of the returning electrons 'is `converted into 'heat fin the cathode, and 'tends to yovcrlneat and iresti-oy rthe cathode. Y .A

An `object-'l'5`.tl'1'e .present invention 'is to provide-a magnetron the Lcathode of which is -removed *fromthe reg-ion where `affected by electron bombardment. Y y

Another l'object ofthe invention is `lto provide a Acathode which isoutside the anode region but which will 'introducev electrons "to that region.

A Afurther object of the -'invention to obtain :electron 'functioning within the anode #as if produced therenupon electrons producediexternally 'of the anode.

Yet k'another object @of the yinvention lis to maintain the usualano'de and Yeewitydimensions 1fanti arrangement inclusive 'of a core corresponding to 'dimensions Yand position of the cathode of 'the prior art.

Still y'further objects include 'the "provision of electron beaming structnrefwit'hin 1an-end space; "to prevent 'any 'substantial return ilow of Select'ron's; to l.provide 'for `fcopious electron emission fand control 'thereof @and 'to obtain simplicity 'of construction yand increased -efiiciency .or roperv-aticn.

`'ther objects 'of the invention Twill appear to those skilled lin 'the art tto lwhich it1lappertailns Figure 5 isa vertical diametrc sectional view, on the plane lincluding the lead-in wire, of the focusing collar.

The prsent magnetron, as in the prior art, .provides `a magnetron body 10 Aof vgenerally .cylindrical 'conliguration and provided therein with end spaces i l, l2 sealed vacuum tight :by end or cover plates i3. One 4of .these eind spaces, as H, 'is `deeper:ijhanthe otherto accommodate mechanisms described hereinafter and since in the drawing vthe deeper end `space is `the :one nearest the top ofFigure 1, it will be arbitrarily referred to ,for brevity as the upper .end space Without being-restrictive vas to position in use.

-as the description proceeds, 'both "Shy/direct rreci ita'tion thereof and by implication from 'thelc'ontext.

Referring 'to the accompanying drawing 'in which like numerals yof reference'indioate simi lar parts 'throughoutjthe Iseveralviews",

Figurev 1 iis 'a vertical diamettic section of a magnetron embodying' -lnoy invention; l

Figure zis ahorizontal section beneath the top closure, as online II'-II of zFigure "li: l

'Figuref is a fragmentary section'b thecathoole as shown in VvFigure l but on enlarged scale;

Figure@ isa plan of-the grid; 'and 1Vlithn (the magnetron the body provides Aan 'anode 'lil of ,generally cylindrical shape and shorter thanthe outsideof the body so as to pro- A'V'i'ce'tl'ie 'Said end spaces 11,7112 at opposite ends ofthe anode. Within the "anode and in direct communication witha'nd between the end spaces, 'is' 'an'axial cavity lrom which 'radiate suitable cavities i6, functioning as cavity resonators, which are open-,ended Vinto the said end spaces "H, T2. Between theradiating resonator cavities T6 the anode is accordingly 4'formed with radiating segments nl 1 thereby forming what may be termed a v multi-segment anode. .Following usual practice, alternate segments .are .preferably electrically connected at their ends and next the axial cavity by `split rings, known in the art as g. .straps Vl1'.

Vln they prior art it is usual to provide a cathode .coaxally Within vthe axial cavity l5, but in the Ypresent invention I .provide thereat a core 18, which may berrcferred to as a dummy cathode in y .that Yit Vis 'the size and shapeof the usual cathode and occupies the position 4normally occupied .by a cathode, --but -is :not intended primarily for ernissive purpose. The desired characteristic of this core -I'8 is its ability to resist erosion or .deterioration'hy .heat andfby its location to .maintain usual electro-magnetic modes `of vthe energy propagation within .the axial cavity, These desidera'tums may .be accomplished by utilization of a ceramic-material for said core, but inasmuch as I desire to apply a potential to said core, it is ,preferably made of an appropriate .metaL of which tungsten, .molybdenumand the like are examples. While thesemetals, and infact, all metals, are more or'less eniis's'ive oi electrons, the one selected is 'preferably a poor emitter but capable of withstanding high temperatures. The 'lower end oisaid core'may conveniently kcarry a hat i8 of appro'xirnately the diameter of the v cathode cavity. y

Y into the axial cavity I5. The structure therefore provides a--cathodey'which is entirely loutside of the axialcavity'cii:` the anode,re`mot 'e from that cavity, but profusely emissive of electrons which enter the said cavity and function with respect to the anode and its cavity resonators comparable mechanically supporting and'A electrically ,isolating said core, the upper end thereofis shown at 4 y It may be here stated that all of the above described lead-in structures 2|, 29, 32, 35 and 38, may be alike, and consequently the sectional showing in Fig. 1 of structure 32 is exemplary of all others as well. Each includes a radio frequency choke' 39 and a glass seal 40.

energypickgup oroutputiloop 4l is provided infone ofthe cavity resoators preferably one most remote from the aforementioned lead-in awires, said loop making connection with the usulalycoaxial line output structure 42 which includes, to electrons of the prior art emitted from a co as will be understood, an appropriate seal so the evacuated -,condition of the interior of the magnetron body lshall not;- be lost.

tached to a lead-in Wire whichextends upf wardly and then radially therefrom'in end space humped shell 26 of incomplete circular shape xed onthe upper face ofi said ring 22. Said shell is welded or otherwise made integral atits peripheral rims to the peripheral rimsof" said By virtue of thev several electrodes (in which term is included core or dummy cathode i8) each having a lead-in wire thereto, the device may y bevariously connected and used. As one example ring, thereby constituting an. enclosurefor in-A 'sulative material 21.thereinfand withinjwhich y 'the heater wre'24 is embedded. The end of the ithcrle thusv formed .aridlto which; thelieat'ei wire is attached is arri'ed'fby a lead-inw V.28 -'which projectsr'adially therefrom through .the

Vendgspac'e' l IV and through the side vofthemagne'- tron body free ofcontact th'erromand; carried rigidly by a usual lead-in insulating and sealing structure 29. The other end of theheater. Wire 24 is-made fast, asby spot welding, toa'bracke't 39 which in turn is securedlupon'another lead-in wire 3! which likewise projects radially through plyau thejemirsrson, but-With direct Current, the

the end space I! and through the side 'of lthe magnetron body free Vof contactV therefromland carried rigidlyby a usual lead-in insulating'ja'nd sealing structure 32, A

Below the cathode and interposed between lsaid cathode and end of the anode, isa focusing collar 33 the purpose of which is to directelectr'ons as a beam from the cathodeinto the laxial cavity ofthe anode.

said collar 3,3 and cathode IS 'as well as coreor vdummy cathode le are all coaxial and-that the inside -diameter of said v collar is slightly lessthan Y the diameter of the axial cavity I5 of the-anode.

said focusing collar* is out ,of cntactfrom 'the cathode and anode,'and is shown rigidly supported by a lead-in wire 34 projecting V-Vradi'ally therefrom through the end space l l and'through the magnetron body free of contact therefrom and carried by a usual lead-in insulating and v` shown, and for electrically connecting and lrigidly mounting the same is secured at onepart of its periphery to a lead-in wire '31 which projects radially. through the side of the. magnetron body free of contact therefrom'and carriedhby a usual lead-in insulating and sealing structure 38.

The construction shown," there-V fore,` provides that the v anode and its axial cavity,

of use, the focusing collar 33 is connected to have a .potential near.. to.: that of.. the-.high negative potential ofethe cathode, the anode f. .course being at ground or. positive potential, in this-case grid 36.woul`d probably haveA to contributet'o'a positiveield in. order to .get suicientemission Finto the` axial vcavity as. the penetration .of-"the re1atiye1y. .p osinye.edem from'the a'rodeV will "be reduced' due .to presence' of. the potential bri-,th focusing collar. Varying the potentiallof-'the collarunder these conditionsgives it a grid action of-its own by Virtue of Vits effect on the:penetration of the field from Ythe anode The usual'fmagnetic field employed withiVmagnetrons obtains spirallingvfof the electrons in the said axial cavity andA the electrons accordingly function, in .Y said axial cavity substantially as iff-emitted from the core or dummy cathode'. Thefoc'us'ing `at hig-lrnegative potential..prevents-.substantial return travel of the electronsbakclfto thev cathode. Thev adyantageisthus gained: that the-,cathode is not subjected to excessive; heating by back- .bombardment, whichis especially important for direct current and continuous Wave operation. The cathodej-inftheabsence,of secondary emission from the core, I nust'bel large enough to sup- POWer that. can be dissipated by the anode will be a limitation of the current at which-themagneuen-should operate. However, seme secondary emission fromvthen core:` l8- isT-permissible to augment; 'chef-primary ;emission'.irom ,the cathode, and .with thencore of 'a highV melting point material, cooling thereof need not be included. With continuous wave 'operation the core attains a much higher-temperature 'than with pulsed operation -and in thatevent inclusion of 'good heat conductiontherefromor even forced coolingmay be-"provided, VThe copiousfemission from the cathod'e .makesitunnecessary for the core to be a good secondary emitter, and by preference, especially whengused for amplitudefmodulatipn, the core is preferably va poor 4secondary emitter.

As a further example of use of 'the device, the `f cicusing collar33 may be held at or near ground potential, operating below cutoff so far as the ordinary` anode-cathode region is concerned. This lends'itself to-amplitude modulation, as the emitting cathode;isinpositionlwhere its emission can be controlledpyfgrid 36.., Again vthe collar 33 can itselfhave a. grid like effect as a ;chang ing posltiye-potential would iniluenceqemission but would collect only those electrons emitted from the outer edges o fcathode by yirtue of the 4factthat the magneticreld cuts olfthe vemission from near thecenter. In the ordinary magnetron vwith coaxial`cylindr'ical"cathode, grid contrbl'is not feasible, or at least difficult at best, because the crossed magnetic field soon spirals the electrons and any configuration of grid structure for any practical purposes will iind electrons approaching it vfrom all directions. In the present showing, however, the location of the grid closely in advance of a cathode perpendicular to the magnetic flux obtains a control of electrons before spiralling alters the common general direction of the electrons, and grid control therefore is effective and feasible. In this grid controlled use of the device with amplitude modulation, it is preferable to operate at a spot on the performance diagram at which the frequency deviation will be minimum and where the radio frequency or power output lines are cut substantially at right angles to produce the change in amplitude with change of grid voltage.

Finally it may be said that by using a grid of washer shape, with the outside diameter thereof and of the cathode as large as or larger than the axial cavity of the anode, and the focusing collar at least as large thereas, the emission may be partly collinated by the magnetic eld through the grid into the cavity resonator openings at the axial cavity, or what amounts to the same thing, into the cylindrical straps on the anode. rlhis would give a grid tuning control whereas the emission through the washer-like hole of the grid would be maintained constant.

I claim:

1. A magnetron comprising an evacuated body providing an anode therein, said anode hai/'ing an axial cavity and cavity resonators radiating therefrom, a cathode opposite an end of said axial cavity, and a substantially non-emissive core axially within the evacuated body and within and extending the full length of said axial cavity, said core being constructed of material completely resistive to deterioration from any heat developed in operation of the magnetron.

2. A magnetron comprising an evacuated body providing an anode therein, said anode having an axial cavity and cavity resonators radiating therefrom, a cathode opposite an end of said axial .fg

cavity, and a substantially non-emissive ceramic core axially in said axial cavity.

3. A magnetron comprising an evacuated body providing an anode therein, said anode having an axial cavity and cavity resonators radiating therefrom, a cathode opposite an end of said axial cavity, a substantially non-emissive conductive core selected from the group of metals of molybdenum, tungsten and the like axially in said axial cavity, and means at one end of said core both supporting the same and providing an external electrical connection therefor.

4. A magnetron comprising an evacuated body providing an anode therein, said anode having an axial cavity and cavity resonators radiating therefrom, a cathode opposite an end of said axial cavity and having an emitting surface in a plane transverse to the axis of said cavity, a focusing collar interposed between said cathode and anode on a common axis therewith, and a core coaxial with both said axial cavity and said focusing co1- lar and coextensive with the combined lengths thereof.

5. A magnetron comprising an evacuated body providing an anode therein, said anode having an axial cavity and cavity resonators radiating therefrom, a cathode opposite an end of said axial cavity and having an emitting surface directed toward said cavity, a focusing collar interposed between said cathode and anode on a common axis therewith, a conductive core coaxial with both said axial cavity and said focusing collar and coextensive with the combined lengths thereof, and separate lead-in connections for each of said cathode, focusing collar and conductive core, each of said lead-in connections being insulated from the anode.

6. A magnetron comprising an evacuated body providing an anode therein, said anode having an axial cavity and cavity resonators radiating therefrom, a cathode opposite an end of said axial cavity and having an emitting surface directed toward said cavity, a focusing collar interposed between said cathode and anode on a common axis therewith, a planar grid interposed between said cathode and focusing collar, and a core extending substantially from the plane of said grid coaxial with both said axial cavity and said focusing collar and coextensive with the combined lengths thereof. HOWARD L. STEELE, JR.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,247,077 Blewett et al June 24, 1941 2,270,777 Von Baeyer Jan. 20, 1942 2,305,781 Helbig Dec. 22, 1942 2,400,770 Mouromtseif et al. May 21, 1946 2,409,038 Hansell Oct. 8, 1946 2,409,222 Morton Oct. 15, 1946 2,412,824 McArthur Dec. 17, 1946 Y2,450,763 McNall Oct. 5, 1948 2,493,423 Spooner et al Jan. 3, 1950 FOREIGN PATENTS Number Country Date 215,600 Switzerland Oct. 16, 1941

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