US2108573A - X-ray tube - Google Patents

X-ray tube Download PDF

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Publication number
US2108573A
US2108573A US745335A US74533534A US2108573A US 2108573 A US2108573 A US 2108573A US 745335 A US745335 A US 745335A US 74533534 A US74533534 A US 74533534A US 2108573 A US2108573 A US 2108573A
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United States
Prior art keywords
target
cathode
focal spot
anode
filament
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Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Expired - Lifetime
Application number
US745335A
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English (en)
Inventor
Alfter Josef
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Koninklijke Philips NV
Original Assignee
Philips Gloeilampenfabrieken NV
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Application filed by Philips Gloeilampenfabrieken NV filed Critical Philips Gloeilampenfabrieken NV
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Publication of US2108573A publication Critical patent/US2108573A/en
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    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01J—ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
    • H01J35/00—X-ray tubes
    • H01J35/24—Tubes wherein the point of impact of the cathode ray on the anode or anticathode is movable relative to the surface thereof
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01J—ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
    • H01J35/00—X-ray tubes
    • H01J35/02—Details
    • H01J35/04—Electrodes ; Mutual position thereof; Constructional adaptations therefor
    • H01J35/06—Cathodes
    • H01J35/064—Details of the emitter, e.g. material or structure
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01J—ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
    • H01J35/00—X-ray tubes
    • H01J35/02—Details
    • H01J35/04—Electrodes ; Mutual position thereof; Constructional adaptations therefor
    • H01J35/06—Cathodes
    • H01J35/066—Details of electron optical components, e.g. cathode cups

Definitions

  • the present invention relates to novel means to increase the power output of an X-ray tube Without increasing the dimensions ofthe tube or reducing the sharpness of theV X-ray picture. More particularly my invention relates to X-'ray tubes in which the cathode-ray beamy successively strikes changing portions of the anode target.
  • the anode may be given other than rotary movement, or the-anode and other members of the tube including the envelope, may be moved with regard to a stationary cathode, or again, both the anode andthe cathode may be both rotating and the cathode-ray beam itself is moved electrically or magnetically relatively to the electrodes to successively strike different portions of the target.
  • the discharge current passing through the X-ray tube i. e., the load of the tube, is usually limited by the maximum permissible temperature of the target, i. e., the temperature which the target material can withstand without injury.
  • the maximum permissible temperature of the target i. e., the temperature which the target material can withstand without injury.
  • I provide a cathoderay beam of uneven density and of such character that, when a given target portion enters the cathode-ray beam (the region of the focal spot) or in other Words When such a target portion assumes a position in which it begins to form part of the focal spot, the density of the cathode-ray beam is higher than when this target portion leaves this region, and linearly or otherwise decreases Within this region.
  • I shall refer to that side of the cathode at which a given target portion enters into the cathoderay beam
  • exit side of the cathode I shall refer to that side of the cathode at which a given target portion leaves the cathode-ray beam.
  • entrance and exit edge of a target portion or of the focal spot as used hereafter such terms broadly applying also to such tubes which are not of the movable anode type, but fall within the above defined scope of the invention.
  • the specific load of a target portion is a maximum at its entrance, and a minimum at its exit, and thus the current density over the focal spot is nonuniform, and decreases towards the exit side, for instance in the case of rotating anode tubes in the direction of the rotation of the anode.
  • the higher density of the cathode-ray beam, or higher electron concentration, in the initial load period of a given target portion results in an increase of the total load of the tube and in a correspondingly greater discharge current; at the same time the total load and the discharge current remain constant during the whole exposure.
  • My invention makes it possible to increase initially the specic load at the entrance edge of the focal spot to twice or more the value of the specific load at the exit edge of the focal spot, the latter specic load being determined by the maximum permissible temperature of the target.
  • the result is that the total load or output of the tube can be considerably increased for instance by about 30% and more, over that of tubes having the same dimensions but having a uniform specific load over the whole focal area, without any danger of injury to the target.
  • the specific load which can be applied to the entering edge of a target portion could be made infinite, but practical considerations limit it to a value which, however, as stated, can still be several times as large as the specific load at the exit edge of this portion, whereas the latter specific load corresponds to the maximum secic load permissible in present-day tubes.
  • the cathode filament may be given a higher temperature on the entrance side than on the exit side, or the reflecting properties of the focusing device may be made greater at the entrance than at the exit side.
  • the area of the electron-emitting surface of the cathode may be made greater cn the entrance side than on the exit side or an asymmetrical meshed screen, acting as a grid-which may be given an auxiliary potential, and which is placed between the cathode and the anode-may cause a greater density cathode-ray beam to strike the target at the entrance edge than at the exit edge.
  • Figure 1 is a schematic view of a rotating anode X-ray tube to which my invention can be applied.
  • Fig. 2 is a cross-section of the electrodes of the X-ray tube of Fig. 1 taken along the lines II-II,
  • Fig. 3 is a cross-section of the electrodes, showing schematically an embodiment in which unequal temperature distribution of the cathode is obtained, by making the lament thinner at the entrance side than. at the exit side.
  • Figs. 4 and 5 are top Views of cathode filament constructions giving higher cathode temperatures at the entrance side than at the exit side.
  • Fig. 6 is a cross-section view of the electrodes, showing schematically an embodiment of my invention in Which a meshed grid is used to decrease the density of the cathode-ray beam at the exit side.
  • Fig. 7 is a schematic top view of a cathode lament having a greater emitting surface at the entrance side than at the exit side.
  • Fig. 8 is a top view of a fllamentary cathode formed of two helices of different diameter and providing a larger electron-emitting surface on the entrance side than on the exit side.
  • Fig. 9 is a cross section of the electrodes when ipivsin a cathode lament structure as shown in Fig. 10 is a cross section through the electrodes showing two coiled filament wires one of which serves primarily to heat the entrance side of the other.
  • Fig. 11 is a diagram illustrating graphically the advantages obtained with my invention.
  • FIG. 1 there is shown schematically a rotating anode X-ray tube on hand of which my invention will be explained.
  • a rotating anode X-ray tube on hand of which my invention will be explained.
  • the tube comprises a sealed envelope 20 in which is rotatably mounted an anode 2l driven, for instance electromagnetically by a magnetic stator 22 provided outside of the tube envelope.
  • the cathode 23 comprises a focusing device 3 and a lament 2 which is disposed eccentrically with respect to the anode to oppose one side of the target surface.
  • I represents a portion of the usually ground target surface of the anode 2l and is made as a rule of a refractory metal such as tungsten.
  • the anode in this, as Well as in all of the other figures, is assumed to move toward the right as indicated by the arrow.
  • the focusing device 3, is provided with a recess 25 into which is placed the coiled filament 2.
  • the focal spot is formed on that portion of the target surface I which, at any given instant, opposes, the cathode and is subjected to the cathode-ray beam indicated by dotted lines 50.
  • the recess 25 of the focusing device is made asymmetrical with regard to the filament 2.
  • a larger amount of electrons, or a higher density cathode-ray beam is directed toward the entrance edge of the focal spot than towards its exit edge.
  • This effect can be increased by providing the wall ofthe recess at the entrance side with a highly thermally reflecting surface of metal ⁇ as shown at 4, whereas at the exit side the surface of the recess wall is not provided with .
  • Such difference in the reflecting capacity of the entrance and exit side of the recess 25 may altogether suflice to obtain the desired changing characteristic of the specific load along the width of the focal spot, even with a symmetrical recess as shown in the drawings by dotted line' 5l.
  • the cavityV of the focusing device 6 is symmetrical, and the desired asymmetry is ob- Y tained, by reducing at the entrance side, the cross section of the elliptically wound filament 5, this being .-achieved, for instance, by progressively etchingthe filament towards the entrance side.
  • 'Ihevtapered' thickness of the filament 5 toward the entrance side results in a higher temperature and greater electron emission at the entrance side, and a gradual decrease of same towards the exit side.
  • FIG. 4 Forinstance in Fig. 4 there is shown an electron-,emitting cathode constructed as a harp, the cords 21, 28, 29 and 30 ⁇ of which decrease in diameter from left toward the right.
  • the ⁇ two ends of the individual cords are clamped by ccnductive members l and 8 respectively, which members are connected to the current leads 3
  • the cords 21 to 30 are in parallel connection, as long as they are of identical material, the density of the current passing through the individual cords is the same for all of the cords. However, as the heavier cords have a? smaller heat-radiating surface per unit of volume than have the smaller cords, they assume a higher temperature. Thus the electron emission of the individual cords will decrease from the left toward the right.
  • Fig. 5 an arrangement somewhat similar to that of Fig. 4 is used. However, instead of connecting the cords in parallel, they are connected in series, ⁇ or a single wire having a thickness which increases in steps from the left to the right is used.
  • the clamps 9 and I0 are in thiscase of insulating material and the conductors 33 and V34 are connected to the two ends of the series combination. As a common current passes through the series combination, the current density of the thin portions will be larger than that of the thick portions, withV the result that a higher electron emission will take place on the left of the cathode than on itsright side.
  • both the incandescent filament II and the focusing device 35 surrounding same are symmetrically arranged with regard to the focal spot the asymmetry being obtained by providing between the cathode I I and the target surface I a grid I2, shown schematically and consisting, for instance, of meshed wire having decreasing openings toward the exit side.
  • the grid. I2 may be connected to the cathode or may be insulated therefrom, in the latter case preferably having a small negative potential with respect to the cathode to increase its blocking action.
  • the specific load at any point of the focal spot will have the value represented by OA.
  • the temperature of the focal spot increases ,v towards its exit edge according Vto the curve t1 from a low entrance Value-assumed for the sake of simplicity as being zero--to the exit value CE (orVOD), the latter value being equal or slightly below the maximum permissible target temperature.
  • Vthe temperature of a target portion upon entering the focal spot region could be increased instantaneously substantially to the maximum permissible target temperature and maintained at this temperature throughout, its passage through the focal spot region, thus following the line t2 of Fig. il, a load indicated by the line bz would result. l
  • a very large increase of the total load of the target and thus of the tube could be obtained.
  • the cathode shown in Fig. 7 comprises a flat filament being looped back and forth and having largeprimary loopsi and small secondary loops i3, the secondary yloops I3 being provided only at the left side of the filament (assuming again the anode to move toward the right).
  • the filament may consist of two or more helically-Wound wires, with one or more helices of smaller diameter located eccentrically with regard to the main helix of larger diameter.
  • the filament consists f two helices I4 and I5 having the same pitch and a common tangent I6 on the left side of the filament.
  • the helix I4 has turns of smaller diameter and is preferably of thinner wire than is the helix I5, and its axis falls within helix I5.
  • the individual turns of the two helices are alternately interposed without their touching each other.
  • the electron emission is greater than on the right and the decrease of electron emission toward the right is gradual, and has a substantial linear character.
  • Fig. 9 shows in cross section the anode and cathode with a cathode filament of the type shown in Fig. 8.
  • the recess 4I! of the focusing device IEI besides containing the cathode filament Ill, also contains a heater filament I9 placed to the left and slightly below the cathode filament I3.
  • the filament I9 may serve only to increase the temperature of the filament I8 on its left side and thereby increase its electron emission on this side, or if desired the filament I9 may also contribute to the electron emission of the cathode.
  • the filament is screened from the anode at 43, so that only such cathode beams may pass from the filament I9, which fall within the cathode ray beam of filament I8, thus a widening of the focal spot is prevented.
  • an anode structure having a target portion adapted to be rotated during the operation of the tube, a cathode structure having an electron-emitting filament extending substantially normally to the direction of movement of said target portion, said filament having a higher electron emission at one side than at the other side as taken in the direction of movement of the target portion, and means to continuously rotate said target portion in the direction in which the temperature of the iilament decreases.
  • an anode structure having a target portion adapted to be rotated during the operation of the tube, means to rotate said target portion, a line focus cathode structure having an electron-emitting filament extending substantially normally to the direction of movement of said target portion and comprising a plurality of members arranged side by side as taken in the direction of movement of said target portion in the vicinity of the filament, each successive member as taken from side to side of the filament having a lower resistance than the preceding member.
  • An X-ray tube comprising an envelope, an anode structure having a target portion adapted tol be rotated during the operation of the tube, a line focus cathode structure having an electron-emitting iilament extending substantially normally to the direction of rotation of said target portion and comprising a plurality of members of the same material arranged side by side, each successive member as taken from side to side of the filament having a smaller cross-sectional area than the preceding member, and means to continuously rotate said target portion in a direction corresponding to the decrease in temperature of the lament.
  • An X-ray tube comprising an envelope, an anode structure having a target portion adapted to be rotated during the operation of the tube, a line focus cathode structure having an electron-emitting element extending substantially normally to the direction of movement of Said target portion and comprising a plurality of series-connected members of the same material arranged side by side, each successive member as taken from side to side of the filament having a smaller cross-sectional area than the preceding member, and means to continuously rotate said target portion in a direction corresponding to the increase in cross-section of the members.
  • An X-ray tube comprising an envelope, an anode structure having a target portion adapted to be rotated during the operation of the tube, means to continuously rotate said target portion, a line focus cathode structure having means including an electron-emitting element to direct a cathode-ray beam towards said target portion, and means including a grid member interposed between said element and said target portion for causing the number of electrons moving toward the target portion to decrease in the direction of the movement of the target portion.
  • An X-ray tube having an envelope, an anode structure having a target portion adapted to be moved during the operation of the tube, a cathode structure comprising means including an electron-emitting element to direct the cathoderay beam toward said target portion, and means cooperating with said target portion to continuously move same, the electron-emitting area of said element decreasing in the direction of movement of the target.
  • An X-ray tube comprising an envelope, an anode structure having a target portion adapted to be moved during the operation of the tube, a cathode structure having an electron-emitting, looped filament and means cooperating therei ing disposed at one side of the electron-emitting lament to produceV a cathode-ray beam Whose density decreases from one side to the oppositeV side, and means to continuously rotate said target portion in such a direction that the target portion passes through the cathode-ray beam in the direction of decreasing density, each ele- ⁇ l1nent of the target during its passage through the beam being at substantially the maximum permissible temperature of the target material.
  • An X-ray tube comprising an envelope, an anode structure having a target portion adapted to be rotated during the operation of the tube, a line focus cathode structure comprising an electron-emitting member and means cooperating therewith to direct a cathode ray beam toward said target portion, said member comprising an outer wire helix and an inner Wire helix having a smaller diameter than that of the outer helix, said inner helix being eccentrically disposed Within said outer helix, and means cooperating with said target portion to continuously rotate same in such a direction that the target ⁇ portion approaches the electron-emitting member from the side to which the inner helix is eccentrically disposed.
  • an anode structure having a target, means including anelectron-emitting member for producing and for projecting upon said target a cathode-ray beam
  • Means including anelectron-emitting member for producing and for projecting upon said target a cathode-ray beam
  • an anode structure having a target, means including an electron-emitting member for producing on said target a focal spot Whose specic load decreases from side to side, and means for continuously changing the relative positions of the target and focal spot, the relative movement, With respect to the focal spot, of the target portion at the focal spot being substantially in the direction of decreasing specific load.
  • an anode structure having a target, means including an electron-emitting member for producing upon said target a focal spot Whose specific load at one edge is more than double the specific load at the opposite edge, and means for continuously changing the relative positions of the target and the focal spot, the relative movement, with respect to the focal spot, of the target portion at the focal spot being from the highly loaded edge toward the opposite edge.
  • an X-ray tube a cathode structure having an electron-emitting element, an .anode structure having a target spaced Vfrom said element to expose a surface area of theA target to the electron emission of said element, and means to continually change the relative positions of said target and element, the electron-emissivity of said element ⁇ decreasing in a direction corresponding to the relative motion, with respect to said element, of the exposed portion of the target.
  • a cathode structure having an electron-emitting element
  • an anode structure having a target spaced from said element to expose a surface area of the target to the electron emission of said element
  • means Vto continuallyV change the relative positions of said target and element, the temperature of said element during operation decreasing in a direction corresponding to the relative motion, with respect to said element, of the exposed portion of the target.

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  • X-Ray Techniques (AREA)
US745335A 1933-09-30 1934-09-24 X-ray tube Expired - Lifetime US2108573A (en)

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Application Number Priority Date Filing Date Title
DE424822X 1933-09-30

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US (1) US2108573A (enExample)
FR (1) FR778963A (enExample)
GB (1) GB424822A (enExample)
NL (1) NL40878C (enExample)

Cited By (9)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2686884A (en) * 1950-05-01 1954-08-17 Dunlec Corp Space charge controlled X-ray tube
US2862107A (en) * 1951-04-06 1958-11-25 Gen Electric Means for and method of controlling the generation of x-rays
US2967245A (en) * 1954-03-08 1961-01-03 Schlumberger Well Surv Corp Neutron source for well logging apparatus
US3138729A (en) * 1961-09-18 1964-06-23 Philips Electronic Pharma Ultra-soft X-ray source
US3296476A (en) * 1961-10-31 1967-01-03 Licentia Gmbh X-ray tube
US4065690A (en) * 1976-01-29 1977-12-27 Tokyo Shibaura Electric Co., Ltd. X-ray tube with a control grid
WO2008044196A3 (en) * 2006-10-13 2008-06-05 Philips Intellectual Property X-ray tube, x-ray system, and method for generating x-rays
DE102016215375A1 (de) * 2016-08-17 2018-02-22 Siemens Healthcare Gmbh Thermionische Emissionsvorrichtung
EP4567856A1 (en) * 2023-12-07 2025-06-11 Koninklijke Philips N.V. Electron beam focal spot

Families Citing this family (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4764947A (en) * 1985-12-04 1988-08-16 The Machlett Laboratories, Incorporated Cathode focusing arrangement

Cited By (13)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2686884A (en) * 1950-05-01 1954-08-17 Dunlec Corp Space charge controlled X-ray tube
US2862107A (en) * 1951-04-06 1958-11-25 Gen Electric Means for and method of controlling the generation of x-rays
US2967245A (en) * 1954-03-08 1961-01-03 Schlumberger Well Surv Corp Neutron source for well logging apparatus
US3138729A (en) * 1961-09-18 1964-06-23 Philips Electronic Pharma Ultra-soft X-ray source
US3296476A (en) * 1961-10-31 1967-01-03 Licentia Gmbh X-ray tube
US4065690A (en) * 1976-01-29 1977-12-27 Tokyo Shibaura Electric Co., Ltd. X-ray tube with a control grid
WO2008044196A3 (en) * 2006-10-13 2008-06-05 Philips Intellectual Property X-ray tube, x-ray system, and method for generating x-rays
US20100008470A1 (en) * 2006-10-13 2010-01-14 Koninklijke Philips Electronics N.V. X-ray tube, x-ray system, and method for generating x-rays
US7835501B2 (en) 2006-10-13 2010-11-16 Koninklijke Philips Electronics N.V. X-ray tube, x-ray system, and method for generating x-rays
DE102016215375A1 (de) * 2016-08-17 2018-02-22 Siemens Healthcare Gmbh Thermionische Emissionsvorrichtung
US10043632B2 (en) 2016-08-17 2018-08-07 Siemens Healthcare Gmbh Thermionic emission device, focus head, x-ray tube and x-ray radiator
DE102016215375B4 (de) 2016-08-17 2023-01-26 Siemens Healthcare Gmbh Thermionische Emissionsvorrichtung
EP4567856A1 (en) * 2023-12-07 2025-06-11 Koninklijke Philips N.V. Electron beam focal spot

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FR778963A (fr) 1935-03-27
GB424822A (en) 1935-02-28
NL40878C (enExample)

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