US2605442A - Electron discharge device - Google Patents

Description

July 29, 1952 G. D. O'NEILI.

ELECTRON DISCHARGE DEVICE Filed March 19, 1948 ma Y .d 3. u W. n a

Patented July 29, 1952 ENT f f- .LECTRON DISCHARGE DEVICE yGeorge D. oNeiu,

Port Washington, N.

Signor to Sylvania Electric Products Inc., a. cor?` "l i poration' of Massachusetts L ".ppication March 19, 194s, serial No. '15,933 i :I

i l. This invention relates to electron discharge de,- vices and more particularly to electron discharge devices of the 4velocity modulation type employy 5 claims. (c1. 315-5) ing hollow*rescunnatorsin*whichy a streamof` e1ec= trons from a cathode ispassed through a gap'in said resonators andy reflectedfbackjthrough the gap by a reflecting electrode; Suchdevices are commonly known as reflex klystron tubes. It has been observed that in the` operationA of such de- Vices as generators of high frequency oscillations, a lcondition is frequently encountered'wherein the reflector voltage for oscillation may.' change during operation of the oscillation and after operating conditions have apparently been stabi' lized,l The required readjustxnentof the potential of the reector to maintain oscillation maybe of'such magnitude that oscillation will not again commence at the new value of reflectorcvoltage if the tube is turned off and. allowedy to cool for a period which may vary from seconds tov hours. This effect may be called fmode jumping. The tube-may operate in oneor more distinct and mutually exclusive modes in' which the number ofthe mode 'is designated N. such thatlN=fT Where f is the resonant frequency. and T is the time an electron spends in the drift space-the space between resonator grid and reflector. Also, N= 1LY1A1 where .11. isan.integer greater than zero. The time rl'depends upon the field in the drift space. If all other charged bodies'v are far removed, TV dependsv upon the reflector voltage. Specifically,

elf-e,- where :r is'the grid-reflector spacingyV is the electron velocity at the grid, eb is the grid voltage andl er is thereecto'r voltage.' Often the change in potential of the 'bulb lisi'such that the; tube does not stop oscillating, but shifts or jumps from one mode to another. Now', since the direct potential ofthe reflecting electrode is different from that ofthe grid electrodes or apertures associated with thev hollow resonator, insulation must be provided in the tube between these elements. Such insulating means may constitute a part of the envelope ofthe tube. It appears that the mode jumping referred to above may ber caused by a change in surface potential of the insulating walls of the tube between the reflector electrode and the resonator' electrodes. This change in potentialafects the field distribution in the retarding region between the resonator and the reflector electrode and `therefore requires Va compensating change inthev l:reflector potential. If the tube is then turned off; the surface charge may leak off. Whenithe'tube is again turned on the potential on thereflector electrode must be returned to its original value.) 1 I An object, therefore, of sthe .present invention is to provide a means for stabilizing the rretardingreld between thel grid associated with the resonator and the reflector.v l

Another object of the presentzinvention vis the provision of means forstabilizing the mode of operation of a reflex electron beam oscillator.

Still another object of the present invention is the improvement of the stabilityof operation of a reflex klystron. y 1

.Experiments which have been made seem to indicate that the change in potentialof the envelope between the reflector electrodelafnd the resonator electrodesyis a'result of its being struck by charged particles. Since the change 'required in the reector voltage after oscillation starts is usually in the negative direction, itlappearsthat the glass surface'has become positivelyl charged due, presumablyjto the emission of` secondary electrons caused'by its having been bombarded by primaryl electrons originating at the cathode of the tube andzpassing throughthe' resonator grids b-ut are not returned 'to the grid by there'- flectorV electrode. lIn the absence of 'special means to prevent the bombardment of theenvelope' by the primaryelectrons, it is impossible toV maintain steady oscillation or to predictfthe'reector voltage required for oscillation ina given mode,'since the surface charge on the glass is' not constant. When the present invention is employed in the operation of the electron discharge tube, it is found that operation is constantand the voltage' conditions for the variousmodes of operationvare constant. Thisis substantially-'true with regard to any individual tube of the'same design', or to `a given tube substantially regardless'fof time or temperature variations."

In' accordancewith an aspect of thev present invention, the building upv o f ak'zhar'ge on' theV the glass surface or secondary'emission from the surface of theglass, y y

' The present inventionwfill be 'more fully :unde'rf stood by reference to the following'ldetailed de-v` scription which is accompaniedI vajdrawing yin which Fig. 1 illustrates in partial longitudinal crosssection a tube embodying the principles of the present invention, while Fig. 2 is a longitudinal cross-section of a portion of a modified form of the invention, while Fig. 3 is still a further modification shown in longitudinal cross-section.

As shown in the drawing, reference numeral I indicates the evacuated glass envelope of an electron discharge device having at one end a cathode structure I2. The cathode structure I2 incorporates a. heated electron emissivesurface and focusing means for producing aV beam of Velectrons. Said beam is projected through grid I3 in apertured electrode I4 andthrough grid I 544 in apertured electrode I6. Electrodes I4 and IB are in.' the form of conductive metal discs paSsiIlg. through the wall of the glass envelope II)Y of the tube. Preferably they terminate in cylindrical rims I8 and 20 adapted to make goodY contact with the walls of. an exterior resonating` chamber. TheY resonating .chamber isA not. shown since it may be of various? forms and of Varying dimensions, depending upon the 'desired frequency of operation of the system.- The. stream of electrons from cathode I2,. afterY passing through grids I3 and I5, is reflectedlbackthrough the resonator gap betweenV grids I3'. and I5. by the suitable negative. potential in .reflector electrode 22. of the tube. are so related to. thezdimensions. of the tube. and the associated resonating.. chamber as to cause the reflected electronsto pass. back through the, gap 4between electrodes i3. and I5 in bunches', thusV exciting theassociated resonant cavity into oscillation.V Y

In the, tube, as so. far described,.and without the provision of somespecialmeansof. preventing such action, electronsmaysofar. fail to; be influenced by.` therefiect/Or electrode 2.2 asV to pass.. between the .edges of. the. reflector electrode 22 andthe electrode. I6 and strikethe glass wall of envelope I0. They may strike the envelope with suiiicientY velocityl toA cause the. emission of secondary electrons. Theemssion of such. electrons from the, glassV results in abound positive charge, thereonpwhich` aiects. the` electric. field distribution between.- theVv resonator` and. reflector electrode to such an extent.. that. ther reflector voltage must beY adjusted toy maintain the desired mode of operation.. that the action may startastheresult of averi7 few electronsV strikingthewallfmaybe one. in a billion. When aA single. electronstrikes the wall and ejectsl two or .more secondaries, it

leaves a small, ,positively-chargedspot;which at.- Y

As`V the spot, begins to.

tracts more electrons. grow it may pull more electronsV toit so'that, after a while, it may grow very rapidly. For example, it may take ve mlllltes'toreach aA critical size, then pull so many electronsV to it thatl in a matter of a second or less the whole bulblumps up to a condition of full positive charge allover. Such charge can only, slowlyY be dissipated, due to the high resistance of, the glassl surface.'l In the modification shown in Fig. 1, in order to prevent s uch action, I have provided amaze including a cup-shaped electrodey 2,4, electrically connected to electrode I6 and having an inturned edge 26. Over cup-shaped electrode 24 is a second cup-shaped electrode 28 electrically connected to the reflector electrode 22 and having down-turned edges 30Y overlapping the upper edge of cup-shaped electrode .24. Thus, a tortuous path is provided between the space between The energizingpotentials onthe electrodes It,` should Y be noted.

- tiofieV 22 passes.

electrode 22 and screen I5, through which no electrons may escape to strike the surface of wall I 0. Thus the potential distribution between electrode 22 and electrode I6 is maintained constant, and a constant mode of operation is attained for the electron discharge tube.

An alternative formvof the invention is shown in Fig. 2 wherein the glass envelope @Ill is provided with a conductive 'coating on its inner surface extending from the ring electrode I6 upwardly to within a short distance of the seal through which the lead-in wire for reflector elec- The conductive coating should be of a; material which has an inherently 10W coefficient of secondary emission, such as a thin coating of graphite applied as a suspension in alcohol'and'V sprayed onto the glass. The coating vpreferably extends from the disc electrode I6 upwardly to at least a point above the region ylikely to be bombarded by primary electrons.

In the further modicationlshown inl Fig.y 3, instead of utilizing-a ,glassenvelopefinf'the's region between the ring electrode- I6 and' the point Y where the support andv lead-ineleetrode for-electrode 22.v passes, a -metaLslielL 35 Aelectrically` connected. to ring electrode- 'IIillisv provided.V lThe necessary insulation between the lead-in for'electrode. 2'2 andY themetal shell f (Wis provided bya glassv bead seall 38. Itiwill be'apparent that'in the modicationsshown in FigsrlL and 3,- the Wall of the electron tube-between ring-electrode IIy and up beyondapointawhere electrons from they cathode may strike. thel walk is maintained at a constantpotential equal to that ofithe ring electrode. TheI conductive:- coating-'or -conductive wall', as the case maybe, positively prevents1 the formation of abound'cha'rgei on thewallA ofthe envelope eitheru due to secondary-emission or due to theY collection off: electrons from the cathode structure I2. Thus, aconstant-modeiofoperation of the tube isassured'.'

While I have .described particulanembodi-ments of the present.inventionfori-purposesof illustration, it will beunderstood ;that'various modiiications and adaptations-.thereof maywbe made within the` spirit of the inventionfforexample,`

other forms of'` maze..`consi'.ructionfdrprevent,.- ing electrons, emittedfrom' the. vcathode fromY reaching theglass envelope.Y may' be Jused..

Whatisclaimed is: Y Y 1. A high-frequency tube' including'anevacuated envelope containing an electrode for pro..-V

the path of" said. streamfsaidj envelope 1 being.. coated on its interior with aconductivemateriali from the secondY of said'"disc.elg'ec'trodjes.toapointl adjacent saidreflector electrode. L

2. A high-frequency tube includingan evacuated envelope containing an 'electrode ,for .provide ing a stream of electrons and, a'reilector electrodeY towardrwhich saidstreamisto bedirected, apair of aperturedy disc electrodes interposed in the. path of said stream, 'sai'djenvelopegbeing coated, on lts interior'with a` conductive materiali fromv the secondV of said disc electrodestto a pointad.- jacent said reiector, electrode,` said-,coating being connected to'v saidv seondjdisc electrode.

3. A high-frequency` tubelincluding` an evaeue ated envelope containing .an'electrode forprovidinga stream of electrons-fand a reflector-electrode toward which saidstrearn isdirected-f apair; of` apertureddisc electrodes.interposed-in. the; path of saidstream, said envelope, being-coated on its.

interior with a thin layer of graphite from the second of said disc electrodes to a point adjacent said reflector electrode.

4. A high-frequency tube including an evacuated envelope containing an electrode for providing a stream of electrons and a reflector electrode toward which said stream is directed, a pair of aperture-d disc electrodes interposed in the path of said stream, said envelope being coated on its interior with a thin layer of graphite from the second of said disc electrodes to a point adjacent said reflector electrode, said coating being connected to said second disc electrode.

5. A high-frequency tube including an evacuated envelope containing an electrode for providing a stream of electrons and a reiector electrode toward which said stream is 'to be directed, a pair of apertured disc electrodes interposed in the path of said stream, said envelope being coated on its interior with a material inhibiting` the emission of secondary electrons from the second of said disc electrodes to a point adjacent said reector electrode, said coating being connected to said second disc electrode.

GEORGE D. ONEILL.

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

UNITED STATES PATENTS

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