US1645304A

US1645304A - X-ray tube

Info

Publication number: US1645304A
Application number: US548636A
Authority: US
Inventors: Slepian Joseph
Original assignee: Westinghouse Electric and Manufacturing Co
Current assignee: CBS Corp
Priority date: 1922-04-01
Filing date: 1922-04-01
Publication date: 1927-10-11
Anticipated expiration: 1944-10-11
Also published as: DE477498C; GB195594A; NL13446C; FR562660A

Description

Oct. 11, 1927. 1,645,304

J.- SLEPIAN X-RAY TUBE Filed April 1, 1922 2 Sheets-Sheet 2 INVENTOR Joseph Slap/m.

7 ATTORNEY Patented a. 11, 1927.

UNITED STATES PATENT OFFICE JOSEPH SLEPIAN, OF SWISSVALE, PENNSYLVANIA, 4mm "1'0 WESTINGHOUSE ELECTBQIG a MANUFACTURING COMPANY, A CORPORATION 01' PENNSYLVANIA.

x-BAY TUBE.

Application filed April 1,

My invention relates to electron-tube devices and articularly to such devices as A are adapted to generate X-rays.

An object of my inventlon is to prov de I an electron tube having an electron-emitting element and a co-operating element or target, wherein the electrons, em1tted from said source are caused to attain a velocit greater .than that which is given by the in uence of any electrostatic, potentials impressed upon said elements.

Another object of my invention 1s to provide an X'-ray tube which is capable of producing useful X-rays with relatlvely low 18 voltages,-in comparison to the voltages heretofore considered necessary.

A further object of my invention is to provide an X-ray tube which is slmple 1n design and in construction and which has 20 highly desirable operating characteristics.

Heretofore, in order to produce X-rays having suflicient penetration or hardness to be useful, it has beennece'ssary to employ relatively high voltages, as from 20,000

28 volts to 100,000 volts, or more. Such X-ray tubes comprise an electron-emitting cathode and a target upon which electrons emitted from the cathode are caused to impinge with extremely high velocity. The maxi- 3o mum velocity with which the electrons strike the target has heretofore been determined solely by the difierence in potential between the cathode and the target. Tubes employing potential differences of 100,000v0lts or more are now in common use, and the tendency of the art is toward a constantly increasing voltage.

It is obvious that the use of such voltages constitutes a great element of risk, especially when it is necessary to work in confined quarters or to bring the tube close to the body of a patient under treatment.

According to my invention, I cause the electrons which produce the X-rays to attain an extremely high velocity without depending upon the usual direct electrostatic action between the cathode and the target, which, as stated, requires the use of extremely high potentials.

The desired result is obtained by subjecting the electrons to the inductive effects of a varying magnetic field. It is well known that a varying magnetic field has associated therewith an electric field, the

.mode of operation, the circuit arr 1922. Serial No. 545,030.

field, and it is this electric field which I utilize to impart velocity to the electrons, all as will be explained more fully hereinafter.

With these and other objects in view, my invention further consists in the nature, the ment and the constructional details hereinafter more fully-set forth andclaimed.

In the drawing, Fighre 1 is .a diagrammatic re resentation'of circuits and apparatus em .ody' g my invention, shown partially in section;

Flg. 2 is a top plan view of the evacuated container of Fig. 1, illustrating the path taken' by the electrons when under the infiuence of an electrostaticforce between the cathode and the target and when under the influence of an additional transverse magnetic field;

Fig. 3 is a view similar tothat of Fig. 2, showing the efi'ect upon the electron path of a varying magnetic field;

Fig. 4 is a horizontal sectional view of a structure embodying the preferred formof my device, the section-plane being indicated by the line IV-IV in Fig. 5;

Fig. 5 is a longitudinal section on the hne V-V of Fig. 4. I

In Fig. 1 is shown a. disk-sha e electron tube 1 having opposite parallel aces 2 and 2 An electron-emitting element 4, which 1s energlzed from a source 5 of direct-current energy, is centrally disposed within the tube 1. An anode or target 6 is disposed adjacent the outer periphery of the tube 1.

A conductor 7 serves to connect the ano de 6 and 'the cathode 4 and may include a direct-current source of energy 8, the effect Of"Wl1lCh 1s to draw the electrons from the .surface of the cathode 4, and thereby give the initial electron loop aslarge a radius as possible; The advantage of this condit1on willr'be explained hereinafter.

A magnetic field, which is t-ransverse to the plane of the tube 1, is obtained by dis-- posingthe disk-shaped pole pieces 9 and 11 of a substantiall U-shape magnet 12 adja'ce'nt opposite aces of the tube 1. The magnet 12 may be excited by means of a magnetizing winding 13, which is wound around a curved ortion 14 of the magnet 12 and energized om a source 15 of directcurrent energy. An input or exciting C011 16 is disposed in the plane of the tube 1 immediately adjacent-the periphery thereof and may be excited from a source 17 o alternating current or condenser discharge.

When neither of the magnetizing windin s 13 and 16 is excited and a potential di erence is established between the electron-emitting element 4- and the anode 6, the electrons emitted from the element 4 are caused to follow the electrostatic lines of force existing between the two elements just mentioned as indicated by dotted lmes a in Fig. 2. I-lere, it will be noted that the velocity of the electrons im inging upon the target 6 is determined sole y by the potential difference existin between the cathode 4 and the target 6. s hereinbefore stated, it has been found necessary to resort to potentials of the order of 100,000 volts or more to produce X-rays having useful penetration values.

When the direct-current exciting windin 13 is energized by the ener source 15, a unidirectional magnetic fiel is roduced, which is transverse to the plane 0 the electron path, and it is found that the current to the anode ceases and that the electrons are caused to move about the cathode 4 in substantially closed paths or loops, as indicated by curved lines 6 of Fig. 2. This has been proved mathematically and is an effect which is well known in the art.

When the alternating-current exciting winding 16 is energized and a varying electric field is produced which lies substantially in the plane of the. container 1, the kinetic energy or velocity of the electrons is greatly increased foreach complete traversal of its path 6. The action is not unlike that observed in the ordinary transformer, the exciting winding 16 corresponding to the primary winding of the transformer and the path represented by one complete revolution of an electron as a secondary coil. In the transformer, the potential of the secondary winding increases with the number of turns and the time rate of change of the flux threading the same. Similarly, in my device, the potential energy dr velocity of an electron increases with each complete traversal of its path and also with increases in the diameter of its path.

At first hand, it would appear that an electron would continue to revolve in its orbit indefinitely and that the velocity thereof would tend to become infinite in value. However, it may be demonstrated mathematically that the action of the centrifugal forces operating upon the electron are such that it tends to traverse a spiral path of ever increasing radius until it impinges upon the target, as illustrated by the spiral curve c of Fig. 3, The exact nature of the spiral produced by the winding 13 an path will be de endent upon the initial veocity of the eectrons, which are emitted from the cathode4, as well as upon the relative valuesof t e constant ma etic field the alternating magnetic field produced by the windin 16.

en the electrons finally impinge upon the target 6, their kinetic energy has attained such value that X-rays are produced of a penetrating value equivalent to that of X-rays which could be produced heretofore only by the application of very much higher external potentials between the cathode 4 and the anode 6 when utilizing the influence of the direct electrostatic action alone. 7 V The device of Fig. 1, however, has a serious limitation by reason of the fact that the maximum practically attainable initial radius of the electron loop 6 is relatively small and, hence, alternating currents of extremely large values and of high frequencies must be applied to the exciting coil 16 to produce the desired results hereinbefore stated- In the referred form, as shown in Figs. 4 and v5, t e cathode 4 and the target 6 are so disposed that the path of the electrons,

upon the electrons comin under the influence of the electrostatic eld, which is associated with the varying magnetic field, has an initial path of such' radius as to obviate the difliculties hereinbefore mentioned.

The structure there shown comprises a highly evacuated toroidal tube 17 having the electron-emitting element 4 dis osed immediately adjacent the inner perip ery thereof and the target 6 disposed diametrically opposite, and adjacent to, the outer peripherythereof. "A lamiriated iron core member 18, similar to that employed in "transformers of the well known shell type, is built around the envelope 17 in such manner that the same is linked by two -

magnetic circuits

19 and 21 having a portion 22 in common, as indicated by the arrows of Fig. 5. The common portion 22 of the two

magnetic circuits

19 and 21 is encircled by a magnetizing winding 23 which may be associated with a source 24 of alternating current or condenser discharge by

conductors

25 and 26.

Mounted above and below the container 17 are a series of segmentally-shaped guiding

magnets

27 and 28. The several magnets are so disposed upon the opposing faces of the tube 17 as to produce transverse fields near the inner and outer walls of the tube in order to produce a strong crowding action upon the electrons within the same; that is to say, an eflect which tends to deflect the electrons from the inner and outer walls and to maintain them in a circular path which is midway between the inner and the outer 3X 10*D. To obtain 7 joining the cathode 4 and the target 6 may or may not include an energy source 8.

hen the filamentA is energized, electrons are driven off, some of the same moving toward the left in Fig. 4. The electrons are deflected from the inner and outer peripheries of the container by the action of the strong magnetic fields which exist there by reason of the resence of the-

magnets

27 and 28. Hence, e ectrons are caused to revolve around the control magnetizable core in a substantially circular path. The effect of the varying flux in the control core, during one half-cycle of the alternating current, is to develop an accelerating potential, by transformer action, causing the electrons to increase in velocity, for reasons hereinbefore mentioned. Asthe electrons increase in velocity, the effect of the increasing centrifugal forces causes them to penetrate farther and farther into the magnetic field adjacent to the outer periphery and, ultimately, to strike the anode 6 and produce X-rays.

For illustrative purposes, I will give a practical example of the solution of certain design problems connected with my invention, although it is to be understood that my invention is not necessarily limited to any particular desi Assuming that the highest vacuum t at can be maintained is 10 mm. of mercury, the mean free path of an electron, which it will travel before striking a molecule, will be approximately 500,000 cm. If an electron velocity corresponding to 100,000 volt potential is desired,

a voltage-gradient of? volts per cm. is necessary for optimum operating conditions. If D is the diameter of the circular path traversed by an electron, and 2B is the cross-sectional area of themagnetizable 'core extending therethrough, the maximum total flux is and, since the length of a turn is 1rD, the

volts per cm. are

% 10- fDB.

Assuming a flux density of B=10,000 and a frequency of f=60, the volts per cm. are

D= cm., approximately. If a freqency of f=600 cycles. per second were employed, the

volts per cm.,

diameter of the meanpath of the electrons would be.D=7 cm., approximately.

While I have shown my inventlon embodied in'two difl'erent constructions, it is apparent that it is not to be limited thereby,-. and that the broad, principle, WhlCh has prior art or indicated by the appended claims.

I claim as my-invention:

1. The method of increasing the energy of an electron which consists in subjecting said electron to the influence of a varying magnetic field of suflicient magnitude to cause said electron to move in a path comprising repetitions approximately like whorls the energy of said electron increasing with each traverse of a repetition.

2. The method of increasing the energy of an electron which consists in subjecting said electron to the influence of an electric field and a varying magnetic field, the rate of change of said magnetic field being suificient to cause said electron to move in a path comprising repetitions approximately like whorls, the plane of said ath coinciding with that of said electric eld, whereby the velocity of said electron will increase with each traverse of one of said repetitions in said path.

3. The method of increasing the velocity of an electron which consists in subjecting it to the influence of an electric field and of a varying magnetic field of sufiicient magnitude and rate of change to cause the electron to traverse a spiral path, the direction of said magnetic field being such that the planeof said ath will coincide with that of said electric eld, whereby the velocity of said electron will increase with increased length of said spiral and will correspond to a potential exceeding that producing said electric field.

4. An electron tube having a source of electrons and an electrode, said source and said electrode constituting the limits of the electron path and means for establishing a varying magnetic field across said path of an average intensity sufficient to prevent the electrons traveling the whole length of said path in a single whorl and of a rate of variation sufficient to increase by a substanelectrons to move in nearly closed paths and means for causing the velocities of said elec trons to increase throughout the lengths of said paths.

'tial amount the magnitude of the impact 6. An electron tube in combination with means for causing the electrons'to move 1n a fiat spiral path of more than one whorl.

7. An electron tube com rising a source of electrons, means for esta lishin ing magnetic field in the vicinity t ereof of sufiicient intensity and suflicient rate of variation to cause said electrons to traverse paths of'increasingly larger diameters embracing a portion of said varylng magnetlc 8. An electron-tube device comprising an evacuated toroidal envelope, a source of electron emission disposed adjacent the inner periphery of said envelope, an anode disposed adjacent the outer peri hery of said envelope and means for estab ishing a varying magnetic field so disposed as to link said envelope.

9. 'An electron-tube device comprising an annular-shape envelope, an electron-emitting element disposed adjacent to the inner periphery thereof, a second element disposed adjacent to the outer periphery thereof, means for etablishing forces in said tube tending to constrain electrons to a closed path extending around the annulas within the envelope and means for developing an accelerating force acting upon said electrons moving in said path. v

10. An X-ray tube having an electronemitting element and a co-operating ele ment, means for producing a field of force between said elements and means acting throughout substantially the Whole travel of the electrons for increasing the kinetic energy of the electrons emitted from said electron-emitting element to values higher than that produced by said field, of force.

11. An electron tube comprising an annular shaped envelope having an electronemitting element and a co -Operating element suitably disposed therein and means for establishing a varying magnetic field so disposed as to link said envelope.

12. An electron tube comprising an annular-shape envelope having an electron-emitting element and a co-operating anode suitably disposed therein, means establishing forces in said tube tending to drive electrons circumferentially around said tubes and means for establishing strong magnetic fields adjacent the inner and outer circumferences of said envelope tending to maintain the orbits of said electrons substantially circular.

13. An electron tube comprising an annular-shape envelope having opposite faces, an electron-emitting element and a co-operating element suitably disposed therein, means establishing forces in said tube tending to drive electrons emitted from said element circumferentiallyaround said tube and guiding ma ets so disposed upon the opposite faces 0 said envelope as to establish strong a varyma netic fields adjacent the inner and outer peripheries of said envelope tending to maintain the orbits of said electrons substantially circular.

14. An electron-tube toroidal envelope, an electron-emittin element and a co-op'erating element suitably disposed therein, a maghetizable member adapted to form a magnetic circuit linkin sai envelope, means for energizing sai memberand means for establishing magnetlc fields transverseto the plane of said envelope adjacent the inner and the outer peripheries thereof, said fields bein such that electrons are repulsed when ten ing to enter the same.

15, An electron-tube device comprising a toroidal envelope, an electron-emitting element disposed adjacent the inner periphery thereof, a co-operating; element disposed adjacent to the outer periphery thereof, a magnetizable member adapted to form a magnetic circuit linking .said envelope, means for variablyenergizing said member, and guiding magnets so d1sposed-as to establish a magnetic field transverse to the plane of said envelope adjacent to the inner and the outer peripheries thereof, said fields being such that repulsive forces are exerted upon electrons tending to enter the same.

16. An electron-tube device comprising an evacuated envelope, :1 source of electrons therein spaced from the outer periphery thereof, means for developing forces tending to cause said electrons to traverse closed paths, comprising repetitions approximately like whorls, the energy of said electron increasing with each traverse of a repetition, an anode within said envelope substantiall outside of said paths, and means for pro ucing a varying flux linking said paths and varying in such direction as to impress an acceleratingpotential upon said electrons, whereby said paths ultimately increase in diameter sufliciently for the electrons to impinge upon said anode.

17. An electron-tube device comprising an evacuated envelope, 2. source of electrons therein spaced from the outer periphery thereof, means for developing forces tending to causes said electrons to traverse an initial substantially circular path of predetermined diameter, an' anode within said envelope substantially outside of said path, and means for producing a varying flux linkin said path and varying continuously in suc direction as to impress accelerating potentials upon said electrons, whereby said path ultimately increases in diameter sufiiciently for the electrons to impinge'upon said anode, the continuous unidirectional variation in flux being continued at least for a period commensurate with the mean time required foran electron to travel from cathode to node a device comprising a 18. An electron-tube device comprising a substantially toroidal evacuated envelope, a source of electrons therein spaced from the outer wall thereof, magnetic means operative near the walls thereof for developing forces normally tending to restrict the movement of the electrons to paths near the center of the cross-sectional area of the evacuated space, an anode within said enveloge adjacentthe outer wall thereof and outsi e of the normal electron-paths, and means for producing a varying flux linking said paths and varying in such direction as to impress an accelerating potential upon said electrons, whereby said paths ultimately increase in diameter sufficiently for the electrons to impinge upon said anode.

19. An electron-tube device comprising a substantially toroidal evacuated envelope, a source of electrons therein spaced from the outer wall thereof, magnetic means operative' near the walls thereof for developing forces normally tending to restrict the movement of the electrons to paths near the center of the cross-sectional area of the evacuated space, an anode within said envelope adjacent the outer wall thereof and outside of the normal electron-paths, and means for producing an alternating magnetic flux linking said toroidal container, whereby, during at least one half-cycle of said alternating flux, said electron-paths ultimately increase in diameter sufliciently for the electrons to impinge upon said anode, the half-period for said alternating flux being at least-large enough to be commensurate with the mean time required for an electron to travel from catode to anode.

In testimony whereof, I have hereunto subscribed my name this 29th day of March,

JOSEPH SLEPIAN.