US1655925A - Electron device adapted for high potential - Google Patents

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ELEGTRN Dmvcm' ADAPTED FOR HIGH P'GWENTML Filed 'mmf-.2a 192.2

llilntnntetll lllll, ltli .ltpplicaticnldled lll'eveinber 5th, .ltll. berlal llo. tOi-litt,

rllhis invention relates to electron or ltray devices and more particularly to such devices so constructed that a reduction ot the electrical stresses in the wallsot the envelopes thereot is ellected.

Mdln object oit my invention is 'to se coni struct electron-devices, tor enample, liaay tubes, that severe electrical stresses, tending,`

' to j ,auncture the Walls ont such devices, when lil-l high voltage is applied during operation,

vvill not develop.

another object ol my invention is the cone struction ot envelopes lor electron devices, "with a conductive lilm or coating,1 on the outside ot the cathode end thereol and connected to the cathode, vvhereby a ditlerence in potential between the inner and outer surlaces oit the envelope is prevented 'troni building up to a dangerous entent.

.lli further object ot" niy invention is the prevention ot the accumulation ot negative electric charges on the interior oit the envelope et the electron device, to such an en tent as to cause rupture oit the material coinu 25 prising the envelope.

l il. still further object is the provision ot envelopes tor electronr devices, so constructed that punctures are avoided when a high poi tential is impressed thereon.,

@ther objects and advantages oit the invention vvill be apparent upon reading the lolloiving detailed description..

llt isA Well lvnown that the envelopes oit high voltage electron devices, such as Illfray tubes, are subject to puncture when in opera-- tion. ltlunctures trom electrical discharge usually occur in the cathode or negative end et the tube. The possible enplanation ot this phenomenon is that the inside surtace ot the envelope becomes negatively charged by electrons coming1 directly trom the cathode or by the secondary or reflected electrons 'trom the anode or target oi the device.

'lhe influence oi the electrodes is such as to cause a denser charge in the cathode end than in the anode end ot the tube. tlucli a negative charge on the inside ot the tube will Htl tltl

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cause the outside surtace thercot to becomel positively charged by electrostatic induction i especially since the surrounding air is 1oniaed ley lrays. 'llhe charges accumulate on the opposite surfaces ot `the glass until the saine islorolren by the electrostatic stress developed therein.

The above explanation is :tor the simple case of a high vacuum, high voltage llray tube with a hot cathode and operated trom. a source ot direct current. fl. tube operated on alternatingcurrent Will stand a higher crest voltage than it Will when operated on direct current, because the time interval bctvveen pulses is sufficient to allow the elcctri cal stress to be relieved by leakage.

According to my invention li prevent elec t-rical stress ot such intensity as to cause puncture in lli-ray tubes or other electron devices by either neutralizing` the ell'ect et the negative charge on the interior ot the tube, preventing1 the accumulation ot such negative charge or making; the Walls of the tube vvhere such vnegative charge occurs of sullicient thickness to sately resist the saine.,

lli/ly invention will be better understood by referring to the accompanying drawingv in which,

ledig. l represents a high voltage ll-i-ay tube constructed according to my invention; and

Figs. E?, and tl represent tubes constructed according to modilication ot' my inventive ideao 'llhe evacuated tube d (litio. ll, may be termed otglass or other transparent instr lating material and, as shown, may comprise a niain substantially spherical 'compartment l, a relatively short substantially' cylindrical extension il and a relatively long substanm tially cylindrical extension 9 extendingn in the opposite direction trom the eatension lin electron emitting),n cathode ll is preterably sealed into the short extension il and a targetor anode 12 may be sealed into the extension 9, itorrningn a complete liiaay tube..

rl'he short cylindrical entension 8 and the cathode portion oi the main compartment l may be coated with a conductive lilm 13, as shown, Which is inelectrical contact with the cathode ll.` 'lhe iilni i3 may be extended to cover' a hall or more ot the main compartment and may be applied in any desired manner, for example, the tube may be painted with metallic paint, such as aluminum enamel., or may b e coated With tintoil or other metallic or conducting loll. v'lihe conducting coatingdl obviously shortens the etl'ective length oi the tube ior insulating' purposes and tor this reason the anode en tension tl is made unusually long" so that the 'lll lt ti effective length of the tube, that is, from the termination of the conductive film on the main compartment 7 to the portion of the Y to accumulate onthe inner surface of the walls at the cathode end of the'tube.

If it were not for the conducting film 13 on the outer surfaceof said cathode end,

said electrons forming a negative charge on said inner surface, would induce a corresponding positive char e on the :outer surface of said tube, thereby p acing the glass therebetween under electric stress, depending on the intensity of the accumulated charges.

Coating the exterior of the tube at the cathode end, not only prevents a large potential differenee from developing between the inner and outer surfaces of the glass by providing a negative charge corres onding to the negative charge developed on he interior of the glass, but tends to prevent any negative charge from forming on said inner sur- 'face of the glass because ofi'the well` known vtransparent "to X-rays I num, o erung toward the anode and closed in repelling action of like charges. That is, by reason of said negatively charged conductive coating on the exterior of the cathode end of the tube, thev harmful effect of a possible negative charge on the interior surface of ,the tube is not only prevented, but said 'charged outer coating exerts a directingin` iluence on the stream of electrons from the cathode because of its repelli'ngeffect and therefore has the effectr of causing a greater proportion of electrons' to be thrown on the anode or target of .the device.

Thedevice shown in Fig. 2 comprises an envelope 14, which may be of conventional form and contain a cathode 15 and an anode 16 'as'shown The cathode in this case is provided with a directive conducting shield 17 as shown, formed of material substantially `for example, alumiother 'irections whereby the electrons emit- -ted from the cathode are intercepted by said shield, fexcept those which travel in the general direction of the target 16. .'Ih'e shield preferably. extends to partly surround the anode as shownyso as to intercept electrons reflected from the anode. In this way, an electron or negative' charge its prevented from The device shown in Fig. 3 may comprise a tube 18 of conventional forni containing a V,cathode 19 andan anode 21 of any usual type. The wall 22 of the mainportion 23 of the tube adjacent the cathode end' and part of the cathode extension is thickened considerably, as shown, whereby it is adapted to resist a considerably greater electric stress than ordinarily.

The coating 13 in Fig. 1, if extended into the path of the X-rays', the shield 17 in Fig. 2 and the thickened glass wall 22 in Fig. 3 will naturally exert a filtering actionI on X-rays passing therethrough and will absorb theV softer rays, to some.l extent, even though made of material substantially transparent to X-rays. This result is not undesirable, as

filters are used for such purpose with X-ray tubes operated on high voltage.

Although I have disclosed what I now consider to be the preferred embodiments of lmy invention, it is to be understood that the same are merely illustrative, that 1n invention is adapted for application to ot er electron devices besides X-ray tubes and is only limited bythe spirit and scope of the appended claims. i What is claimed is:

1. An X-ray tube of the high voltage typev comprising an envelope having cathode and anode arms extending outwardly therefrom, an electron-emitting cathode supported by one arm and an anode supported by the other arm, and an electrically conductive..

material covering the cathode arm and a portion of the envelope, said material being intimately united to said cathode, whereby said material becomes negatively charged during the operation of saidtube and thereby prevents any 'accumulation of electrons on the interior surface of the envelopeand exerts a'directive influence on the streamV of electrons owing between said cathode and anode. y

' 2. An X-ray tube of the high voltage type comprising an envelope having cathode and anode arms extendin outwardly therefrom, an electron-emitting cathode supported by one of said arms and an anode supported by the other of said arms, one of ros said arms being materially longer than the f 3. An X-ray tube of the high voltage type comprising 'an envelope having cathode and anode arms extendingoutwardly there` from, an electron-emitting cathode supported by one arm and an anode supported by the other arm, and a coatingcovering,` the cathode arm and a portion 'of 'the envelope,

msaid material being intimately united to said Cathode, whereby said material becomes negatively charged during the operation 4of said tube lation of electrons on the interior surface of the envelope and exerts a directive influence ont-he stream of electrons flowing between said cathode and anode.

4. An X-ray tubeof the high voltage type comprising an envelope having cathode and anode arms extending' outwardly thereed by one and thereby prevents any aeouniu# the envelope and exerts from,y 4n electron-emitting cathode support of said arms and' an anode sup ported by the other of said arms one of said arms being materially longer than the other arm, and a coating1 covering the cath ode armand a portion of the envelope, said material being intimately united to sai( cathode, whereby said material becomes negatively charged during the operation of said tube and thereby prevents any accumulation of electrons on the interior surface of a directive influence on the Stream of electrons flowing between said cathode and anode.

In testimony whereof, l have hereunto subscribed my name this 27 th day of November, 1922.

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