US2362816A - Electrical discharge device - Google Patents

Description

Nov. 14,194 D. HARKER ELECTRICAL DISCHARGE DEVICE Filed April 15, 1943 Inventor David Harker,

His Attorney.

Patented Nov. 14, 1944 Ilavifl rker, Alpla man ement a come; fiiqn N wxctk Application April 15, 1943, SerialiNo. 483,157; (01. 25,1 1,442

. fi aims- Thepresent invention relates to electrical" dis charge devices operating by-virtue of; the ioniza- Qn' i a h s lve tenua eda n inp s ar Pro de an impr Xdar dev c t is n of th 'ebies b mr nvention t r vide an X ray' tube a tubulareirtension of v Smell he e el stone-fourth inch am te satani e ih fill i bumpers intore tr c ss cbas t e na meat o th ad n e n e ev shqu uman restricted to the medical field nor infacttp the weld.

st; tn; st s e -teen kenat 2T2 i b rfimmt the a ami e-- era es-M19 at ewritin wind amqdiflta ,nm i d vide th fellm 'g. nterpretin s ed rs or h ts.- iii e W996 .Y smaller diam ter. omprise m M l wbularr enve ope: c a cam.-

5- lqre tec a d meet trative purposes. Other known forms of oath-- I by a disk M into which is sealed a thin metal the' glass cylinder d n tb cori sid das necessarily V smalltube oranode housing-Shave spaced metal Q l a ei fsh i. own bmke to conserve space); (11) a c athode housing 5; (also: shown broken for; the same IQQSQI M2 5 (c) an; anode h usin 5- 'l h -lmusinsstandt consist; ofmetal tubes andareconnectedto ground. An anodeor tar e In? Musing. 5. t e. latter; extending. o war ly trom thehm in land bein ali ned normal to the surfas fi. 0f1- aicathode l, as shown. in Fig; 1. when the, deyice. is intended: to. emit. cathode rityssrnoseparate target isrequired, as shown in Fig; 3 12116 beam of electrons or' cathode rays th n penetrate the end 'wall- 2 which may be madethin. The cathode seaihousing 3. contains an-insul atingzone the remote end. of this housing being at cathode potential.

'gheacathode I, which. isof the non-thermionic or fc ld cathodemtype, is; supported on a ubular cathode stem .8; into. which projects a conduitfi. Theppenzendiisjoinedzby a vacuumtight solder joint to. disk. [42. ConduitQsupplies coolin fluid as; for example, oil or water.

he cpolin m diumzleaves the conduit a (as-indicated by the. arrows), comes: into contactzwith the closed end; of the: tube ;8, and returns :through thetubefl from whence it is discharged by the conduit; I'll. Tubes 9 and I0 pass through a plate 25130 which; they are joined bya watertight solder joint. Theplate-25 is held ii place by, the thneadedring 2w and'the washer 26. v A cathode plate I l', whiohmay'consist ofaluminum or; beryllium, is held in close--- thermal contact with the tube 1} by a threaded ring l2: This particular: form of cathode is shown for illusil 1 Qcatedr tstheiremoterend of the tubucylinder l5 which is in turn sealed into a glass cylinder 16'. A second thin metal cylinder I1 is sealed into the opposite (right-hand) end of H3; Lhis metal cylinder I! isjoine dto'a'heavy ring [8 l hese cathode seal partsare mounted on a metal, tube l91constituting an extension of' the anode supporting tube. A ring 20 is fastened by a vacuum-tight solder joint to the anode'supporting tube. A gas-tight seal is provided by pressing a suitable washer. 22- against the interstice between rings 20 and H3 by means of the ring '2! and the heavy threaded ring 23. The'opposite end of the oathodechamber isrendered gas-tight by a solder joint. between cathode stem 8 and plate l4. A guard ring 21 protects thecathocle seal from damage by the discharge, the spacings between the 'adjacent partsbeing so close that a discharge does not ocour betweenparts charged to unlike potentials. I

The cathode housing 4 and the communicating walls 29" and 30 which are arranged to be'cooled by: the circulation of a coolingfluid supplied by N the=inletconduit 31. (Fig. 2), the fluid being discharged by the; conduit 32'.

The course of the cooling fluid isconfined byran appropriate longitudinal partition',.as:indicated at: 34, which constrainsthe cooling fluid to fiow the full length of; the tubular extension 5' through the space between the-wallsziil, 30.; on onecside of the par.- titicn, the space between the anode and the end of thetubeand? returning through thespace between the-two Wallson=theopposite side of the. partition.

The space within the hollow structure may be exhausted;andfcharged' with a suitable gas, as

. for examplevain. at: an; appropriate pressure by the conduiti33t The anode 6 may comprise a target 3.5; which is: backed. by a heat-absorbing plate" 35;. X-rays may leave the tubular chamber 5.1 by passing. through a thin-walled window 31 which may consist of beryllium or other'suitable" material, or; the; electronbeam may be utilizedin other-desired manner.

The interior: ofithe device is kept at a low ga pressure by any: suitable well known means, as for-instance a pumpand leak valve. Depend ing. on: the geometry ofthe tube, various pressures within; a range of; about 1 to lOOmicrons may be used. Theinterion geometry ofithe tube is-such-that the resultant electrostatic-field constrains; electrons leaving the tubular enclosure totravel at right anglesto its surface under the influence of the impressed x ray producing potential: When the electrode- 'l'functions as anode".

millimeters before again impinging upon a conducting member; while electrons leaving the electrode 1 when functioning as cathode can travel several centimeters before reaching an opposing electrode. At a low gas pressure prevailing within the tube, for example microns of mercury pressure, an electron has a mean free path of several centimeters so that electrons leaving the,

tubular electrode when it is negatively charged almost never collide with gas molecules. On the other hand, electrons leaving'the electrode 1 when it is functioning as cathode will usually collide with and ionize gas molecules. Consequently, a self-perpetuating glow discharge can be set up in the region in front of the cathode 1 when it is negative with respect to the enclosing electrode. As no glow discharge can occur in the reverse direction, the device is rectifying, that is, transmits only half waves of an impressed alternating current.

During the glow discharge period positive ions bombard the cathode plate H, thereby heating it and increasing its electron emission. These electrons travel perpendicularly outward from the cathode plate ll, ionizing the gas molecules with which they collide and forming a cloud of positive ions in the discharge space, the positive field of which constrains the discharge to pass down the center of the tubular housing 5. In other words, this cloud of ions focuses or constricts the electron stream into a .fine beam which is coaxial with the anode housing, the discharge traversing the tubular extension 5 and impinging on the target 35. As a consequence the tubular extension 5 may be made of smaller diameter than in X-ray tubes heretofore provided forsimilar purposes.

Although one important field of usefulness of an X-ray device embodying my invention is the field of medicine and surgery, it is advantageous in other fields, for example in X-ray diffraction apparatus, as it permits bringing material to be examined close to the source of X-rays where the intensity of X-ray radiation is maximum.

What I claim as new and desire to secure by Letters Patent of the United States is:

1. An electron discharge device comprising an the electrons do not travel farther than about 5 charged, the field of the positive ions resulting from said discharge through said gas causing enclosed within said tubular electrode remote envelope adapted to function as an anode, a

non-thermionic cathode enclosed thereby, means for insulating said electrodes from one another, a charge of gas at a pressure in the range of about 1 to 100 microns contained in said envelope and filling the space between said electrodes, the

geometry and spacing of said electrodes being favorable to the operation of a self-perpetuating unidirectional gas ionization discharge therebetween which is constricted into a fine beam, and a tubular extension for said envelope so aligned that said beam discharge will traverse said extension.

2. An X-ray device comprising a metallic housing which functions also as anelectrode, a second electrode enclosed by said housing, an outwardly projecting tubular extension for said housing having a diameter less than the diameter of said housing, an X-ray target located near the outer extremity of said extension, means for sealing and insulating said housing and a charge of gas at a pressure within the limits of 1 to 100 microns in said housing, the spacing and alignment of the electrodes being favorable to the conduction therebetween of a gas ionization discharge only when the enclosing electrode is positively from said target, sealing and insulating means between said electrodes, and a charge of gas at a pressure of between 1 and 100 microns in the discharge space between said electrodes, said tubular anode having a configuration and spacing which constrains an electronic discharge between said electrodes to pass in a direction substantially perpendicular to the face of said cathode. through said gas and positive ions generated in said gas will causesuch electronic discharge between said electrodes to assume the form of a constricted beam passing axially through said tubular electrode.

. 4. An X-ray device comprising a tubular electrode, a second electrode enclosed by said tubular electrode and located remote from one end thereof, means for hermetically sealing said tubular electrode, means for insulating said electrodes from one another, an attenuated gas in said tubular electrode at a pressure of about ten microns, the geometry of said electrodes and the pressure of said gas being so correlated that by ionization of said gas a self-sustaining discharge can occur therebetween which traverses longitudinally said tubular electrode, such discharge being constricted by the field of the positive ion column created in said gas by said, discharge, the pressure Of the gas contained in said tubular electrode being too low to permit of an ionization discharge in the space between'juxtaposed parts of said electrodes and an X-ray target located at the extremity of said tubular electrode in position to have said constricted discharge impinge thereon.

5. An X-ray device comprising a tubular metal container which also functions as an electrode, a charge of gas therein at a pressure of about 10 microns, a non-thermionic cathode mounted therein, means for insulating and sealing said cathode from said container, the distance between said container and said cathode being shorter than the mean free path of an electron discharge therebetween a metal tube of lesser diameter extending longitudinally from said container, an X-ray target at the extremity of said container, and an X-ray transmitting window sealed into the wall of said tube adjacent said window.

6. An electron discharge device comprising a main tubular sealed metal envelope which functions as an electrode, a non-thermionic electrode within said tubular container, means for insulating;.said electrodes from one another, a gas at a pressure of about ten microns of mercury contained in said envelope, and a tubular extension of lesser diameter than said envelope aligned normal to said interior electrode and projecting outwardly from said envelope, said electrodes being constructed and spaced so closely as to permit passage of a gas ionization discharge through said gas only when said enclosed electrode is functioning as cathode,'the field of the positive ions generated in said gas by such discharge focusing the discharge into a fine beam which traverses said tube.

. DAVID HARKER.

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