US2144524A - X-ray apparatus - Google Patents

Description

Jan; 117 19390 E E. CHARLTON El AL X-RAY APPARATUS 5 Sheets-Sheet 2 Filed Dec. 2, 1936 \/\/i| [em F. Westendorp,

The n Attorn ey.

m m ST m 0 +U E v& me n T E Jan. 1 1939. E. E. CHARLTON ET AL X-RAY APPARATUS Filed Dec. 2, 1936 3 Sheets-Sheet l km 1% Q Q G 5 IfivefitoTs Ernesi: BChavlton, l lem F Westedor by WM Thew Attorney Jan. 17, 19399 E. E. CHARLTON ET AL X-RAY APPARATUS Filed Dec. 2, 1936 3 Sheets-Sheet 3 Inventor wljlirneg\%.cnardlton, i em est n orp,

Their Atconney.

Patented .lan. 17, 1939 2,144,524

' UNITED STATES PATENT OFFICE X-RAY APPARATUS Ernest E. Charlton and' Willem F. Westendorp,

Schenectady, N. Y., asslgnors to General Electric Company, a corporation of New York Application December 2, 1936, Serial No. 113,862

14 Claims. (Cl. 250-87) The present invention relates to electrical diswhich may lead to an expansion tank and at its charge apparatus such as high oltage X-ray lowest point with a drainage valve l3. Since it equipment is contemplated that the apparatus as a whole It is an Obje t o the ihvemiieh to Provide a may be rotatable about one or more axes and shock-proo semieportable y equipment to a certain extent portable, the casing may be 5 which is adapted both for medical and industrial provided with suitable mounting means consistapplications and. which may be safely operated at ing in part of a trunnion support indicated in potentials at least as great as 500,000 volts. Par- Fig. 2 by the numeral l4 and preferably located ticular features of the invention which mm on a line passing through the center of gravity tribute to this result are an improved arrangeof the apparatus. 10 ment of the X-ray tube with respect to its ener- With th i th 1 provided l si in e nove means for preventing eleeing means comprising a transformer which intrical breakdown between the various parts of l d l i t core 5 set into cooperating the equ pm n nd special provisions for safely recesses formed in the tank walls. A primary l5 regulating the cathode temperature and the outindi suitably consisting of a single helical p of the tuben a Preferred embodiment. layer of copper ribbon I8, is wound on one leg of the equipment as a whole comprises an -fi l the transformer core, and an insulating sleeve ca ing en l n a i h voltage transformer and I9 consisting for example, of paper impregnated the cathode end of an X-ray tube, e anode end With shellac, is interposed between this winding of the tube be n arranged to project ex erna y and the laminations of the core. Connections to of the casing wall. an external source of power may be made by The novel features which are considered to be means of insulated conducting straps 22 and 23 characteristic of the invention are pointed out to whose ends there may be connected leadnn with particula ty n t e pp Claims. The conductors sealed through the wall of the casing.

25 invention itself, together with further objects In the arrangement illustrated, the trans- 25 and advanta s thereof y best be understood former secondary comprises an elongated coil 26 by reference to the following description taken having one n adjacent t and partiany upin connection With the drawings in which Fig. 1 ported by the lower casing wall 2! to which it is a sectional view of a complete apparatus suitmay also be electrically connected. Such a con- 30 ably embodying the invention; Fig. 2 i a p rtial nection is preferably made indirectly through a plan view of the structure of Fig. 1 showing ceru t; m t r, for l by means of a tain of the upp r lem r m v Fi 3 is a ductor 28 brought out through the wall of the fragmentary view showing in detail the construccasing, tion of the X-ray tube cathode indicated more The upper end of the secondary coil 26 is apgenerally in Fig. 1; igs. 4, 5 and 6 illustrate the preciably spaced from the casing and is adapt- 35 details of the X-ray tube anode and the tube ed to be maintained at a high potential with remounting; Fig. 7 is a compos te ec o taken spect to the casing and the various metal parts along line 'll of Fig. 2 and showing the conconnected therewith. In the use contemplated struction and a ra em of e energizing the potential developed across the secondary coil 40 means, and Fig. 8 illustrates schematically pre- 26 maybe in excess of 500,000 volts so that conferred circuit connections for the apparatus. siderable electrostatic stress will exist between Referring particularly to Fig. 1 there is shown the upper turns of the coil and the apparatus an X-ray apparatus enclosed in a. casing or tank parts which are at casing potential. In order to In which is preferably of fabricated construction reducethis stress and to increase the uniformity and is so assembled as to be essentially vacuumof the electrostatic field existing in the casing, 45 tight. The form of the tank illustrated is such there is provided in connection with the upper as to permit the minimum volume consistent with end of the coil an electrostatic shield in the form the requirement of maintaining adequate spacof a hollow conducting body 30 having a relativeing between the various enclosed high potential ly large radius of curvature. This body may elements. suitably comprise separable upper and lower The casing is filled during operation with a dimetal parts and is adapted to enclose various electric medium, for example, insulating oil or an operative parts of the apparatus within its coninsulating gas. To permit the ready introducfines; tion and removal of such a medium, the casing is Thestructure so far described constitutes provided at its highest point with a conduit l2 means for energizing an Xray tube or a simi- 55 lar electrical discharge device. We have illustrated a particular device as comprising an elongated envelope consisting at least in part of vitreous insulating material and provided at its opposite ends with terminals connecting with encloseddischarge electrodes. More specifically, the tube envelope consists of spaced insulating sections 35, for example, of glass, and. interposed metal sections 36 sealed thereto. At the end of the envelope which projects toward the interior of the casing Hi, there is provided a cathode including a separately heated filament 31 and a focusing cup 38, these members to be described more fully hereinafter. Arranged at the other end oi the tube, there is an anode consisting of an elongated metal cylinder 40, while between these main discharge electrodes, there are arranged a plurality of evenly spaced intermediate electrodes I. These latter electrodes preferably comprise longitudinally extending tubular conducting members. They are supported by and connected to conductive envelope portions 36 which thus constitute exposedterminals for the enclosed electrodes.

In accordance with the invention, the X-ray tube is arranged so that its major axis is'transverse to andpreferably perpendicular to the axis of the transformer coil 28, the cathode end of the tube being adjacent the upper end of the coil while the anode end of the tube projects through and is supported by the casing wall 42. In order to insure uniform distribution of potential along the length of the X-ray tube envelope connections are made between the spaced electrodes ll and correspondingly spaced points along the length of the transformer coil 26. The angular relationship existing between the tube and the axis of the coil permits these connections to be made in a manner which creates no danger of electrical breakdown regardless of any difference in length which may exist between individual tube and coil sections. Additional safety in this respect may be obtained by forming theconnecting members as conducting tubes or rods of relatively largedlameter as indicated. It may. further be desirable to incorporate high resist-.

ance sections 46 in the members 45, such sections being useful in limiting the current which is able to flow in caseof a disruptive breakdown with the X-ray tube.

Inasmuch as in operation the successive intermediate electrodes are energized at progressively higher potentials with respect to. the casing, strong radial fields exist between these electrodes and the casing walls. Due to the relatively small radius of curvature of the electrodes and the disparity between the dielectric constant of the vacuum within the envelope and the oil or other dielectric medium outside, extremely high potential gradients may be established adjacent the electrode surfaces. With operating potentials of the magnitude contemplated, these gradients may, in

the absence of protective measures, be sufiicientto produce cold cathode discharges in a radial direction and to cause puncturing of the envelope walls.

In'order to prevent such occurrences, our inpotential electrodes. As illustrated, each of these members is formed so as to present no sharp edges and is positioned between its corresponding intermediate electrode and the wall of the casing. As a result of the favorable shape of the members 41 and their disposition in the dielectric medium outside the discharge envelope, high local gradients are avoided and the danger of disruptive discharges precluded.

The various shielding members are mechanically supportedby means of an insulating cylinder 48 consisting, for example, of paper impregnated with shellac. This cylinder is positioned between the envelope and the shielding members and may be secured at least against rotary motion by means of a keying connection (not shown) with the hollow conducting body 30. Connections between the shielding members and the electrode terminals 36 may be effected by means of spring-pressed slidable contacts whose nature and'function will be more fully explained hereinafter.

The details of the tube construction and particularly of the anode construction will be more readily apparent upon reference to Fig. 4. In this figure, the anode is shown as comprising an elongated metal tube 40 terminating at its lefthand extremity in a relatively heavy metal plate 49 inclined to the main axis of the tube. This plate is provided centrally with a target surface 50 comprising an insert of metal, for example, tungsten. During operation the stream of electrons proceeding from the cathode may be focused to converge on the target by means of a magnetic coil 52 arranged so that its axis coincides with that of the tube and excited in any desired manner. The plate 49 is maintained at a temperature below the melting point of the target surface by circulating water or an equivalent cooling fluid in contact with its outer face. A

particular means for accomplishing such circulation is illustrated as comprising an inlet tube 5| wound helically around the anode throughout its length and terminating in a series of labyrinthine chambers on the outer surface of the plate 49. From these chambers the cooling fluid is permitted to escape through an opening 43 into the annular space between the anode tube I and a surrounding shell 54. From here it may be finally drawn of! through an outlet connection ,In order to permit variation of the direction of the X-ray beam, the tube structure as a whole may be rotatablymounted with respect to the casing iii, an exemplary such mounting being illustrated in Fig. 4. Essentially the structure shown comprises cooperating bearing surfaces 59 having interposed between them suitable oiltig-ht packing means 60. The movable element of this bearing combination is connected to a gear wheel 6i which in turn supports the tube structure as a whole through the intermediationuof a flange 62. The gear wheel 6i may be driven to produce a desired rotation of the tube bymeans of a worm gear 83.

Inorder that rotation of the tube-may not interfere with the electrical connections between "'31 and a focusing cup 38, of metal or other conducting material. Insulated lead-in conductors 68 and 69 are provided for the filament while a similar conductor 10 is attached to an externally exposed portion of the focusing cup. Heating current for the filament is derived from a secondary coil H comprising a few turns of wire wound about the insulating ring 32 and constituting in efiect an extension of the main secondary coil 26 (Figs. 1 and 7).

The cathode end of the X-ray tube is positioned near the high potential end of the secondary coil 26 in such a way that the cathode as well as all its external connections are enclosed within the hollow conducting member 30. Since the enclosure comprises essentially a field-free space it is unnecessary to take any precautions with respect to the form or insulation of the enclosed parts in order to prevent electrical breakdown to the other parts of the apparatus. Also contained within -the hollow conducting member, there are provided means for regulating the filament temperature and the output of the X-ray tube, such means suitably comprising a variable impedance device in circuit with the cathode. One may use, for example, an inductor having an adjustable iron core adapted to vary the effective impedance of the inductor. One desirable arrangement of such an inductor device is indicated in Figs. 2 and '7 in which the inductor is indicated by the numeral 15. An enclosed core (not shown) may be regulated as to position by a mechanism comprising, for example, a pair of bevel gears 18 and a screw drive (also not shown). The regulation of the inductor and, consequently, of the cathode heating current may be accomplished externally of the casing I by means of an insulated shaft 19 operable by a handle 80 connecting with the shaft through the wall of the casing. The inclusion of such an irregularly formed mechanism within the walls of the casing would create considerable danger of electrical breakdown except for the advantageous arrangement indicated whereby all the irregular parts are enclosed within the conducting member 30.

The circuit connections for the entire apparatus are indicated schematically in Fig. 8 in which a simplified tube structure has been illustrated for purposes of clarity. In this figure elements corresponding to parts previously described are in dicated by identical numerals. Adjustment of the operating voltage is accomplished, for example, by the combination of a variable tap autotransformer 8i and a series resistor 82 connected in circuit with the main transformer primary I8. A voltmeter 83 connected across this primary serves to indicate the prevailing conditions of operation. The transformer secondary 26 is connected between the anode and cathode of the X-ray tube through a suitable current meter 84, which meter may be safely disposed externally of the casing since all the parts to which it is connected are ground potential. The intermediate electrodes ll are maintained at desired potentials by connection to spaced points along the transformer secondary 26 as previously indicated.

The focusing cup 38 is maintained at a negative potential with respect to the filament 36 by suitable biasing means connected between them. Such means may comprise, for example, a resistor 86 of relatively high value, say 200,000 ohms, connected in parallel with a condenser 81 having a capacitance on the order of .2 microfarad. Under these conditions, assuming a current flow through the X-ray tube of about 10 milliamperes, a negative bias, which may be about 2,000 volts, will be maintained on the focusing cup due to the relatively high capacity of the condenser 81. This bias will be retained from cycle to cycle since the time constant of the condenser circuit is greater than the duration of a single cycle.

The condenser 81 and the resistance 86 may suuitably be enclosed within the hollow conducting member 30 as is'indicated in Fig. 7. If desired, the resistance may be also made of adjustable value in which case its regulation may be accomplished externally of the apparatus casing by means corresponding to the regulating rlreans described in connection with the inductor As a result of the construction described in the foregoing, there is made available a shock-proof and semiportable X-ra-y apparatus adapted to be operated with a voltage of at least 500,000 volts. The flexibility of the construction is such that 1t may be moved and manipulated to an extent which makes its use in industrial fields entirely practicable. Thus, the apparatus as a whole may be operated on a factory floor so that the anode arm may be projected inside the various cavities of a metal casting which might itself be too massive to allow convenient manipulation.

While we have illustrated a particular embodiment of the invention, it will be apparent that many modifications may be made by those skilled in the art without departing from the invention. we therefore, aim in the appended claims to cover all such alternative structures as may fall within the true spirit and scope of the foregoing disclosure.

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

1. An electrical discharge apparatus including the combination of a casing enclosing a dielectric medium, a coil immersed in said medium, said coil having one end thereof electrically connected to the casing and its other end appreciably spaced from the casing and adapted to be maintained at a high potential with respect thereto, a hollow conducting member arranged to modify the electrostatic field adjacent the high potential end of the coil and an electrical discharge device at least partially contained within said casing, said discharge device having an anode electrically connected with the casing and a separately heated cathode connecting with the high potential end of said coil within said conducting member, and means also within the conducting member for regulating the heating current to said cathode, said means being adjustable externally of said casing.

2. An electrical discharge apparatus including the combination of a casing enclosing a dielectric medium, a coil immersed in said medium and adapted to develop a high potential difference be tween its ends, a hollow conducting member arranged to modify the electrostatic field adjacent one end of the cell, an electrical discharge device at least partially contained within the casing and having a separately heated cathode connecting with the said one end of said coil within said conducting member, said device also including an anode connecting with the other end of said coil, means including an adjustable impedance device enclosed within the conducting member for regulating the heating current to said cathode and means operable externally of said casing for controlling the adjustment of said impedance.

3. A high voltage apparatus including a metal casing containing a dielectric medium, a discharge device at least partially enclosed by the casing and comprising an evacuated envelope enclosing a plurality of electrodes, at least some of said electrodes being within the confines of the casing and being maintained at high potential with respect thereto during the operation of the device, and one or more electrostatic shielding members connected with a corresponding number of said high potential electrodes, each of said members being outside the envelope and interposed between its corresponding electrode and the wall of the casing so as to decrease the radial electrostatic field acting on such electrode.

4. In combination, a metal casing containing a dielectric medium, a discharge device extending at least partially within the casing and comprising an elongated envelope enclosing oppositely disposed discharge electrodes and a plurality of spaced intermediate electrodes, said intermediate electrodes comprising tubular conducting members extending longitudinally of the envelope, means electrically connecting one of said discharge electrodes to the casing, means for energizing the remainder of said electrodes at progressively higher potentials with respect to the casing, and tubular shielding members connected to at least some of the intermediate electrodes, each of said shielding members being arranged outside the envelope so as to surround its corresponding intermediate electrode and being interposed between such electrode and the wall of the casing.

5. A high voltage X-ray apparatus including a metal casing, an X-ray tube within the casing comprising an elongated envelope enclosing an anode, a cathode and a plurality of spaced intermediate electrodes, said anode projecting externally oi the casing and being electrically connected thereto, means within the casing for energizing the intermediate electrodes and the cathode at progressively higher potentials with respect to the casing, and electrostatic shielding members electrically connected with at least some of the intermediate electrodes, each of said shielding members being arranged outside the envelope and interposed between the casing and its corresponding electrode.

6. In combination, a metal casing enclosing a dielectric medium, a discharge device extending at least partially within the casing, said device comprising an envelope enclosing oppositely disposed discharge electrodes and a plurality of spaced intermediate electrodes, at least certain ones of said intermediate electrodes being within the confines of the casing, means for maintaining one of said discharge electrodes at a relatively low potential and the remainder of said electrodes at .tween its corresponding electrode and the inner wall of the casing.

'7. In combination, a metal casing, a discharge device within the casing comprising an elongated envelope enclosing oppositely disposed discharge electrodes and a plurality of spaced intermediate electrodes, said device being rotatably mounted with respect to the casing, means for energizing the discharge electrodes at a high potential, electrostatic shielding members outside the envelope interposed between each intermediate electrode and said metal casing, terminals for said intermediate electrodes arranged along the length of the envelope wall, means including sliding contacts co-operating with said terminals for maintaining an electrical connection between each shielding member and its corresponding intermediate electrode during rotation of the discharge device, and means including said sliding contacts for energizing successive ones of said electrodes at progressively higher potentials with respect to the casing.

8. In combination, a metal casing containing an insulating dielectric, a discharge device extending into said casing and comprising an elongated envelope enclosing oppositely disposed discharge electrodes and a plurality of spaced intermediate electrodes, said device being rotatably mounted with respect to the casing, means for energizing the discharge electrodes at high potential, electrostatic shielding members outside the envelope interposed between at least some of the intermediate electrodes and the metal casing,

means including a nonrotatable insulating shell positioned between the envelope and the shielding members and supporting the latter, means for maintaining an electrical connection between each shielding member and its corresponding intermediate electrode during rotation of the discharge device, and means connecting with the shielding members for maintaining them at high potential with respect to the casing.

9. An electrical discharge apparatus including the combination of a casing, an energizing means therein having a part thereof electrically connected to the casing and another part at high potential with respect to the casing, a discharge device comprising a portion projecting externally of the casing and a portion projecting internally of the casing, an anode enclosed within the externally projecting portion and electrically connected to the casing, said anode having its active surface at a. point relatively remote from the outer wall of the casing, a cathode arranged adjacent to the extremity of the inwardly projecting portion of the discharge device and at a point relatively remote from the inner wall of the easing, means electrically connecting the cathode to the high potential part of said energizing means, a plurality of intermediate electrodes provided in said device between the anode and cathode, all of said intermediate electrodes being within the confines of the casing, and electrical connections for energizing the successive intermediate electrodes at progressively higher potentials with respect to the casing. i a

10. An electrical discharge apparatus including the combination of a casing, a coil within the casing, said coil being electrically-- grounded at one end to the casing and having its other end at high potential with respect thereto, a discharge device comprising a portion projecting inwardly of the casing and a portion projecting externally thereof, said device being rotatably mounted on a wall of the casing, an anode enclosed within the externally projecting portion of the device and electrically connected to the casing, the anode having its active portion at a point relatively remote from the outer wall of the casing, a cathode arranged adjacent the extremity of the inwardly projecting portion at a point relatively remote from the inner wall of the casing, means electrically connecting said cathode to the'high potential end of said coil, a plurality of spaced intermediate electrodes provided in said device between the anode and cathode, all of such electrodes being within the confines of the casing, means providing electrical connection between the intermediate electrodes and correspondingly spaced points along the length of said coil, means accessible externally of the casing for rotating the discharge device, and means for maintaining said electrical connections during rotation of said device.

ll. An electrical discharge apparatus including the combination of a casing, a high voltage coil within the casing, said coil having one end thereof insulatingly spaced from the casing and adapted to be maintained at a high potential with respect thereto, a hollow conducting member arranged to modify the electrostatic field between the said high potential end of thecoil and the wall of the casing, an electrical discharge device at least partially contained within the casing and comprising an anode and a cathode, and energizing connections between the cathode and the said high Potential end of the coil and between the anode and the other end of the coil, the discharge device being so positioned that both the cathode and its energizdng connections lie substantially entirely within the confines of the said hollow conducting member.

12. An electrical discharge apparatus including the combination of a metal casing. an X-ray tube lying partially within the confines of the casing, said x-ray tube including an anode and a cathode, a high voltage coil within the casing for energizing the x-ray tube, said coil having one end a thereofgroundedtothecasingandtheotherend thereoiinmlatinglyspacedfmnthecuingand Mtobemainhinedathiahpotentialwith respect thereto, means providing electrical connections between the said anode and the casing and between the said cathode and the high potential end of the coil, and a hollow conducting member connected to the high potential end of the coil for modifying the electrostatic field between the same and the wall of the casing, the X-ray tube being so positioned that the anode end thereof projects outwardly through a wall of the casing and that the cathode and its energizing connections lie substantially entirely within the confines of the said hollow conducting member.

13. An electrical discharge apparatus including the combination of a casing enclosing a dielectric medium, a coil immersed in said medium, said coil having one end thereof insulatingly spaced from the casing and adapted to be maintained at high potential with respect thereto, a. hollow conducting member arranged to modify the electrostatic field between the said high potential end of the coil and the wall of the casing, an electric discharge device at least partially contained within said casing and comprising cooperating discharge electrodes, said device being energized by connection to the coil, and circuit regulatng means enclosed within the said hollow conducting member for controlling the operation of the discharge device, said means being adjustable externally of said casing.

14. An electrical discharge apparatus including a casing enclosing a dielectric medium, a discharge device immersed in said medium, means connected to the terminals of the discharge device for energizing the same, at least one of the terminals of the device being maintained at high potential with respect to the casing by such means, a hollow conducting member of generally smooth contour surrounding the said one terminal and effective to modify the electrostatic field between such terminal and the wall of the casing, and circuit-regulating means enclosed within the said hollow conducting member for controlling the operation of the discharge device, said means being adjustable externally of the casing.

manner 1:. CHARLTON. wnrm 1''. RP.

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