US2651727A - X-ray tube - Google Patents

Description

Sept 8, 1953 w. EHRENBERG ET AL 2,651,727

X-RAY TUBE 2 Sheets-Sheet l File'd April 7, 1950 A A .QN m n N www n@ n mw E n, NN @w .w20 m0 mw NN Sept 8 1953 W. EHRENBERG ETAL 2,651,727

X-RAY TUBE 2 Sheets-Sheecl 2 Filed April 7, 1950 cathode.

from cathode to anti-cathode, extending at least Patented Sept. 8, 1953 esta? X-.RAY TUBE Werner;Ehrenberg,jHayes, and 1 alter Eric, 5119er:

London, England .Apvlieatifm April?, 1959,'*Seria h1 Great Britain Match@ 6 laiins. l

This invention relates to X-ray tubes and has for its object to provide improved andsimpliied X-ray tubes in which the electrons from a thermionic cathode are concentrated in a nefocus on the anti-cathode.

For many purposes, notably for crystallographic work and micro-radiographic Work gen-v erally, it is required to ,provide an X-ray tube in which the electrons from a thermionic cathode are focussed to a very small areaon theanti- Hitherto great diihculties have .been experienced in satisfying this requirernent vwithout excessive complexity in structure or inconvenience operation Vand known X- ray vtube arrangementscapable of giving a fine electron beam focus on the anti-cathode have involved the use of magnetic focussing, or of complexelectrode systems, or of an inconveniently large nurnber of dierent, high, operating potentials applied to dierent electrodes. The present invention avoidsthese defects and provides improved X-ray tubes which will give a focus of less than one-tenth of a millimeter in diameter on the anti-cathode purely electrostatically i. c. without using magnetic focussing, without requiring a considerable number of high operating potentials .and by means of an electrode system of unusual mechanical simplicity. Indeed, as will be seen later, in the preferred embodiments o f the invention, the only electrode vof the tube which is not at cathode potential, or in the region of cathode potential, is the anti-cathode itself.

According to this invention an X-ray tube comprises a cathode, an anti-cathode, and v an electrostatic lens electrode systemproviding an equi-potential surface in the region of cathode potential said equi-potential surface substantially vsurrounding the electron discharge path over the Whole length of said pathandbeingof a diameter Which is relatively small at the cathode end o f said path and relatively large at the antifcathode end thereof.

The electrostatic lens .electrode system may be such as to produce an equipotential .surface in the region of cathode potentialand whichincreases gradually in diameterfrom the cathode end to the anti-cathode end of the electron discharge path. It is, however, preferred to in- News@ l95o .L shapeftheagis of Weigh .isindicaea by a@ @han crease the diameter of said surfaceinasingle large step.

`In a preferred X-ray tube in accordati@ zlll/.ith theinvention the'electrostatic lens electrodesystem comprises a rst cylindrical electrode offrelafer adiueti tudinal ,pesitienf the.,catb0ele ,in .thetube- 11b of the -theushit i. sions slrOxIInareonly by wayof example. The

`Vtively...smell AV.dimet,erlea2 it1-ly vsurrounding the eethede and .haring an epertured diaphragm .eubetentlallyin theielene ,gf .the effective emis- ,Sive .aree of .Seisiathede an V.extensiymfl cylindrical. electrode. of relativelymall diameter co-axial with anden .the .antl-.eathode sideet ,seid ret `.eyr.ltiltieel eleetrodeendathird .cylindrical e'leeeharge .l path :from cathode .te entifeathede The llrst .and .extensien .eyliudri'eal eettredet .may be andpreierably are mechanically uitetl ,Sa-that the, latter. ifs also mechanically et ,exten- Sien .of :the former'- Meariseiterriel cf thetute, may ,be .provided lOntheaiis of thel tube the longi- ,stead ef. eras welles. thus,previcinmeeheniea adjustment; the third cylindrical electrode may .be provided .ier-eleetritaLMustment nurtesew Y`with an ,internal er :transverse partition wleh is peeitienedin enieneadieeent the Plne .aetifeethede :endet ,the extension ,ei/1in- .Il he..1nre1.1ti91 .illuetratedsin and further explained in leenneetien ,with ,the ,eeeemperlyirle drawings; in .which Figure .1Q is @elevation partly in. centerline se ion of a preferred. embodiment sary to an understanding of the inventionbroken Qmittedtemplify the drawing; Fig. .2 L@iste ,eenventienel ...mmf .equi-p .lteferrigs te Fie-.1 .thexfrey tube therein hewnlsef theeustemery eleneeted eylindrieel .ereeietie ofthe aetel .dimens/iene @fthe tute Aef 1Fie- .1 .ef timetlies .iS included,

to be understood l that the dimenu envelope of the tubehasnietal Aparts i and 2 ..111etllarli.tally,jeiriedend insulated from one ew other byafsuitableglass part 3. The metal part I has .e ,Side .elttrereh pipe ...t .which leads te e vx r ac uum p urr'ip (not (shown) which is kept running whenthetubeis inuse. It is to be under stoodhowever, that theinvention isequally apof the continuously pumped type. Mounted from one end of the envelope is a cathode shown as of the hairpin filament type. The filament, which is indicated at is carried in any convenient way from a cylindrical mounting member 6 which houses the filament supports (not shown) and through which the lament heating leads (not shown) pass. In use the mounting member is in the region of cathode potential. Also carried from the mounting member is a electrode 'I of relatively small diameter which is also in the region of cathode potential and concentrically surrounds the cathode 5. By the expression in the region of cathode potential as employed in this specication is meant at cathode potential or different from cathode potential by an amount which is small in relation to the difference of potential between cathode and anticathode. Thus, to quote practical gures, in a tube in which the difference of potential between cathode and anti-cathode may be of the order of from kv. to 50 kv. the cylindrical electrode 1 may be at earth potential and the cathode 5 itself may be given a positive bias up to, say, a couple of hundred volts or so. The electrode 1 has a diaphragm 8 with a central aperture 9 and is substantially co-planar with the cathode tip i. e. the effective emissive point thereof. The electrode 1 is extended to provide an extension cylindrical electrode I0 of the same diameter and also in the region of potential, this extension electrode terminating in an anti-corona ring II as well known per se. The electrode I need not be mechanically united with the electrode 1 though it is preferred to make it so. The electrode 1 is shown broken away to permit the hairpin filament 5 to beseen but the details of the filament leads and supports, being of any form well known per se, are not shown so as to simplify the iigure.

To allow of longitudinal adjustment of the cathode the cathode structure is provided with a rearwardly extending axial stem I2 which passes through a bellows I3 and screws into a member I4 having a screwed stem I5 which extends through the rear end of the envelope. The stem I5 is engaged by an internallythreaded gland member I6 which can be rotated by a knurled or winged member I1. The structure here is only diagrammatically shown but it will be obvious that by'rotating the member I1 the cathode can be adjusted longitudinally back or forth along the axis.

Carried in the other metal end member 2 of the envelope is a tubular anti-cathode I8 which is illustrated as of the water cooled type having inlet and outlet pipes I9 for the cooling liquid. The anti-cathode is fixed in place by a tapered plug fixture of normal type. Reference character 2I designates the normal X-ray tube window (shown dotted) and 22 designates the conventional guard and anti-coronarings.

In use, the electrodes 1 and I0 are maintained in the region of cathode potential as also is the metal part I of the envelope. The parts 1, I0 and I together constitute the preferably earthed members of an electrostatic lens system, the envelope part I also serving as an electrode which extends over and well beyond the whole electron discharge path from cathode to anti-cathode. The last mentioned electrode is, of course, maintained at a suitable positive potential with respect to the other electrodes I, 1 and I0 vwhich may be permanently connected together if desired by being structurally united as in the illusrst cylindrical v4 trated tube of Fig. 1. If desired, however, separate leads may be provided to the electrodes I, 1 and I0 to enable the potentials applied thereto to be adjusted. In practice, however, these electrodes, if not all at exactly cathode potential, are as already explained, in the region of cathode potential and co-operate to provide an equi-potential surface, in the region of cathode potential, which surrounds the electron discharge and is of small diameter near the cathode, enlarging to a much bigger diameter beyond the anticathode end of the extension electrode I0. In general the potential of the parts 1, III and I will be earthed and the anti-cathode potential will be positive to earth but obviously, it is only relative potentials which matter and the anti-cathode might be earthed and the other electrodes held negative to earth.

Fig. 2 is an enlarged diagram showing the form of equi-potential line distribution obtained with this electrostatic lens system. Fig. 2 is a'diagrammatica section showing the essential electrodes on one sideonly of the axis of symmetry X-X. The references used in Figs. 1 and 2 refer to the same parts. Equipotential surfaces are indicated by thin curved lines marked with relative potentials in arbitrary units and the spacing between the filament (not shown in Fig. 2) and the anti-cathode is also subdivided into arbitrary units of division.

The following ranges of relative dimensions for the arrangement of Fig. 1 are given as a guide to construction: If the diameter of the electrode 1 and of the extension I is taken as unity, the axial length of the said extension I0, measured from the diaphragm 8 should be 0.75i025.; the axial spacing between the diaphragm B and the fiat face of the anti-cathode should be 1135x025; the internal diameter of the envelope electrode I should be not less than 1.5 and preferably about 2; and the diameter of the tubular anti-cathode should be about 0.8.

Fig. 3 shows a detail modification differing from Fig. 1 in that"the envelope electrode I is provided with a transverse partition electrode member 3 in a plane parallel to and adjacentV the plane which passes through the far end of the extension electrode IQ, said partition member having an axial aperture of about the same diameter as that of the electrode I6. Also, as illustrated in Fig. 3, an anti-corona ring IIa on the inner edge of the member 23 replaces the ring II of Fig. l. The advantage of the arrangement of Fig. 3 is that it provides electrical adjustment of the lens to correct focus. This adjustment, which is obtained'by varying the potential between the electrodes 1, I6 on the one hand and I, 23 on the other is, from the point of view of sim'- plication of structure, obviously advantageous as compared to providing for mechanical movement of the cathode as in Fig. 2, though both types of adjustment may be provided if desired. In Fig. 3 provision of electrical adjustment is indicated by showing separate leads 24, 25 taken to different points, one (or both) variable, on a potentiometer 26 which is connected across a source of potential (not shown), Of course, in any construction in accordance with this invention, the applied potentials must 'be selected, in accordance with known electron-optical principles, to suit the tube dimensions and produce the desired iine focus on the face of the anticathode but the provision of electrical adjustment as in Fig. V3, in conjunction with or instead ofthe mechanical'adjustment providedby axial movement of the cathode, gives great vpractical convenience without material added. complications.

We claim:

l. A fine focus X-ray tube comprising ancenvelope, a cathode, an anti-cathode, an electrostatic focussing lens system, said lens system including a first cylindrical electrode of relatively small diameter co-axially surrounding said cathode and having an apertured diaphragm substantially in the plane of the ebective emissive area of said cathode, an extension cylindrical electrode of relatively small diameter cob-axial with and conductively connected withsaid rst cylindrical electrode on the anti-cathode side thereof, and

a third cylindrical electrode of relatiyelv vlarge diameter co-axial with the two other cylindrical electrodes and extending at least over the whole length of the discharge path from cathode to anti-cathode means, operable externally of said envelope for adjusting the position of said cathode and said electrostatic lens system as a unit longitudinally along the axis of said envelope, and means for applying a potential of the order of kilovolts between the cathode and anti-cathode and a potential not exceeding the order of tens of volts between the cathode and the electrostatic lens system.

2. A iine focus X-ray tube comprising an envelope, a cathode, an anti-cathode, an electrostatic focussing lens system, said lens system including a rst cylindrical electrode of relatively small diameter co-axially surrounding said cathode and having an apertured diaphragm substantially in the plane of the effective emissive area of said cathode, an extension cylindrical electrode of relatively small diameter co-axial with and conductively connected with said first cylindrical electrode on the anti-cathode side thereof, and a third cylindrical electrode of relatively large diameter co-axial with the two other cylindrical electrodes and extending at least over the whole length of the discharge path from cathode to anti-cathode, said third cylindrical electrode forming part of said envelope means, operable externally of said envelope for adjusting the position of said cathode and said electrostatic lens system as a unit longitudinally along the axis of said envelope, and means for applying a potential of the order of kilovolts between the cathode and anti-cathode and a potential not exceeding the order of tens of volts between the cathode and the electrostatic lens system.

3. A fine focus X-ray tube comprising an envelope, a cathode, an anti-cathode, an electrostatic focussing lens system, said lens system including a rst cylindrical electrode of relatively small diameter co-axially surrounding said cathode and having an apertured diaphragm substantially in the plane of the eiective emissive area of said cathode, an extension cylindrical electrode of relatively small diameter co-axial with and on the anti-cathode side of said first cylindrical electrode, and mechanically united therewith and forming a continuous electrically conductive surface, and a third cylindrical electrode of relatively large diameter co-axial with the two other cylindrical electrodes and extending at least over the whole length of the discharge path from cathode to anti-cathode means operable externally of said envelope for adjusting the position of said cathode longitudinally along the axis of said envelope, and means for applying a potential of the order of kilovolts between the cathode and anti-cathode and a potential not exceeding lope,' a cathode, an anti-cathode, an electrostatic 'focussing ylens system, said lens' system including af first cylindrical electrode of relatively. small diameter co-axially surrounding said cathode and 'having Y an `apertureddiaphragm 'substantially in the plane of the effective emissive area of said cathode, an extension cylindrical electrode of irelativelysmall diameterpco-axial with and .condu'ctively connected with said first cylindrical "electrode `on` 'the anti-cathode side thereof, and 'a third-cylindrical electrode of relatively large -diameter co-axial with the two other cylindrical "electrodes, andextending at least over the` whole length of the discharge pathirom cathodeto anti-cathodeineans operable externally of said envelope for adjusting-the position of said cathode longitudinally along the axis of said envelope, and means for applying a potential of the order of kilovolts between the cathode and anticathode and a potential not exceeding the order of tens of volts between the cathode and the electrostatic lens system.

5. A ne focus X-ray tube comprising an envelope, a cathode, an anti-cathode, an electrostatic focussing lens system, said lens system including a rst cylindrical electrode of relatively small diameter co-axially surrounding said cathode and having an apertured diaphragm substantially in the yplane of the eifective emissive area of said cathode, an extensive cylindrical electrode of relatively small diameter co-axial with and conductively connected with said rst cylindrical electrode on the anti-cathode side thereof and mechanically united therewith and forming a continuous electrically conductive surface, and a third cylindrical electrode of relatively large diameter co-axial with the two other cylindrical electrodes and extending at least over the whole length of the discharge path from cathode to anti-cathode, said third cylindrical electrode being provided with an internal annular transverse partition which is positioned in a plane adjacent the plane of the anti-cathode end of the extension cylindrical electrode and has an aperture the diameter of which is approximately equal to the diameter of the anti-cathode end of the eX- tension cylindrical electrode means operable externally of said envelope for adjusting the position of said cathode longitudinally along the axis of said envelope, and means for applying a potential of the order of kilovolts between the cathode and anti-cathode and a potential not exceeding the order of tens of volts between the cathode and the electrostatic lens system.

6. A fine focus X-ray tube comprising an envelope, a cathode, an anti-cathode, an electrostatic focussing lens system, said lens system including a rst cylindrical electrode of relatively small diameter co-axially surrounding said cathode and having an apertured diaphragm substantially in the plane of the effective emissive area of said cathode, an extension cylindrical electrode of relatively small diameter co-axial with and on the anti-cathode side of said rst cylindrical electrode and mechanically united therewith and forming a continuous electrically conductive surface, and a third cylindrical electrode of relatively large diameter co-axial with the two other cylindrical electrodes and extending at least over the whole length of the discharge path from cathode to anti-cathode, said third cylindrical electrode forming part of said envelope and being partition which is positioned in a planey adjacent the plane of the anti-cathode end of therextension cylindrical electrode and has an aperture the diameter of which is approximately equal to the diameter of the anti-cathode end of the extension cylindrical electrode, and a corona ring carried by said partition on the side opposite the last mentioned end of said extension cylindrical electrode means operable externally of said enve- -lope for adjusting the position of said cathode longitudinally along the axis of said envelope, and means for applying a potential of the order Vof kilovolts between the cathode and anti-cathode and a potential not exceeding the order of tens of volts between the cathode and the electrostatic lens system.

' WERNER EHRENBERG.

WALTER ERIC SPEAR.

l8 References Cited in the iile of this patent UNITED STATES PATENTS Number A Name Date Holst et al Apr. 26, 1927 Holst et al. June 14, 1927 Ulrey et al. May 28, 1929 Coolidge July 4, 1933 Bouwers Feb. 27, 1934 Olshevsky Aug. 24, 1937 Mutscheller May 9, 1939 Hirsch Jan. 9, 1940 Cassen Aug. 4, 1942 Stephen Feb. 8, 1944 Webster Feb. 27, 1951

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