Патент USA US2112746код для вставки
March 29, 1938. Y A. WOLFEL Y ' 2,112,746 X-RAY TUBE Filed April 16, 1935 mg. I. > ' Inventor‘: Albrecht‘ Wdlfel by ttorney. Patented Mar. 29, 1938 2,112,746 UNITED STATES PATENT OFFICE 2,112,746 X-RAY TUBE Albrecht Wolfe], Rudolstadt, Germany, assignor to General Electric Company, a corporation of New York Application April 16, 1935, Serial No. 16,673 In Germany May 15, 1934 1 Claim. In order to adapt an X-ray tube to more than one purpose, for example, therapeutic and radio graphic, which necessitate different load condi tions, i. e. different sizes of focal spots, etc., one may provide the tube with two or more ?la mentary cathodes of di?erent electron-emitting capacities. Obviously, the cathodes require dif ferent amounts of heat. Consequently, when (01. 250-35) these objects, my invention contemplates in brief, the use of a resistance or inductance in series with the smaller ?lament, i. e. the cathode of lower heating capacity, and mounting the resist ance or inductance within the con?nes of the envelope so as to be surrounded by an evacuated space in case the envelope is highly evacuated. that it is desired to- energize the smaller cathode The invention will be clearly understood when reference is made to the following description and the accompanying drawing in which Fig. 1 represents a view, partly in section, of an X-ray tube containing a cathode construction improved in accordance with the present invention; Fig. 2 from the same source of electromotive force as is an end view of the focusing member and as changing the operation of the tube from one use 10 to the other, as for example, when substituting the cathode of smaller electron-emitting or heat ing capacity for the larger cathode, and assuming r‘ the larger cathode, it is desirable to reduce the heating voltage impressed across the smaller cathode. In order automatically to reduce the energy supply to the smaller ?lament under these con~ ditions, it has' been proposed to insert a resist ance in the heating current circuit of the oath ode and in case the cathode is energized by an alternating current source, a choke coil or a trans former may be used. The choke coil, transform er or resistance is usually connected in the ?la ment circuit external to the tube and in order to make the structure of a unitary design, it has been proposed to enclose the coil or resistance in the base cap of the tube. However, when the voltage-reducing device is enclosed within the base cap, certain di?iculties arise. In the ?rst place, the cap on the cathode side of the tube must be enlarged to accommodate the extra ele ment which may present some difficulty in ?tting the tube and its cap into existing apparatus and protective housings. In addition, more especially when using a resistance, but also in the case of a choke coil or transformer in lesser degree, there is the further disadvantage in that the voltage-changing device may give off considerable heat and deleteriously affect the material of the cap. An object of the present invention is to provide an improved all-purpose X-ray tube containing sociated cathodes; while Fig. 3 is an enlarged diagrammatic view of the cathode structure per se including the voltage-reducing element. Referring more particularly to Fig. l, numeral l designates the envelope of an electrical dis charge device containing an anode 2, which in the case of an X-ray tube may have an inclined face and be provided with a target. The anode is supported Within the envelope in any suitable manner, for example, by means of a rigid rod 3 secured to a reentrant stem 4 which terminates one end of the envelope. The other end of the envelope is also provided with a reentrant stem 5 in which are fused several rigid rods serving as combined leading-in conductors and supports for the improved cathode structure. This struc ture includes ?laments 6, 1, one of the ?laments,‘ e. g. ?lament 6, being of greater heating capacity and therefore of greater electron-emitting ca pacity than the other ?lament. There may also be provided a hemispherical focusing member 8, supported within the envelope by means of a rod 9 which is secured to one of the conductors passing through the stem 5. The conductor 9 may be connected to one or both of the ?lamena tary cathodes or as is more usually the case, may be taken out through the envelope as a separate lead to which any desired potential may be ap plied. two or more ?lamentary cathodes of different The cathodes are preferably constituted of the same material, for example, tungsten wire of the electron-emitting or heating capacities, and in same gage, and since one cathode is intended to which one cathode may be substituted for the emit greater amounts of electrons than the other cathode, it follows that the lengths of the respec other cathode when desired, and is adapted to be energized from a common source of electro 50 motive force. A more speci?c object is to em. ploy in a tube of this character, an improved form of voltage-reducing device or element in connection with the cathode of smaller electron emitting or heating capacity and also an im 55 proved position of the device. In carrying out tive cathodes are different. When a tube of this character is operated, it is desirable to be able to switch from one cathode to the other in case the same tube is alternatively serving two Widely different purposes, as for ex ample, when used in therapy and radiography. In case a common source of electromotive force 55 2, 2,112,746 ‘ ' ‘ - '1 is employed to energize both cathodes, obviously In the event that the element I0 is required to the voltage impressed across the cathode of smaller heating or electron-emitting capacity must be less than the voltage applied to the dissipate or consume considerable energy and thereby is rendered su?iciently incandescent to emit electrons, it may be desirable to provide a cathode of larger heating or electron-emitting capacity. The necessary reduction of voltage in case it is desired to substitute the smaller cathode metal shield 13 interposed between the element for the larger cathode, is conveniently obtained order to provide a mechanical barrier for electrons which tend to leave the end of the element Ill near the envelope. The shield may be supported 10 by means of a resistance or choke coil l0 con nected in series with the smaller ?lament 1. As shown, the adjacent ends of the ?laments 6, ‘I are connected together by a common leading-in con ductor and the opposite end of the larger ?lament is connected to another leading-in conductor, while the free end of the element I0 is connected to the remaining leading-in conductor. The ?la m‘ents are conveniently arranged side by side within the opening at the bottom of the spherical focusing member 8 as is shown more clearly in Fig. 2. When the ?laments 6, l are energized from a common source I I of alternating or direct current, and when a switch I2 is provided in the and the anode. This shield may be given any suitable shape, e. g. an angular con?guration in within the envelope in any suitable manner. In addition to the shield I3 and as shown in Fig. 3, there may be provided other angular mem bers I4 positioned respectively between the free ends of the ?laments 6, l and the envelope. All 15 of these shields or screens serve to prevent any electrons from reaching the anode from unde sired parts of either cathode or associated ele ments. While I have described my invention more espe 20 cially in connection with an X-ray tube for the reason that cathodes of different electron-emit circuit for selectively connecting the ?lament 6 ting capacity are frequently employed ‘in. this or ‘I. to the source, the same voltage may now be connection, it will be understood that the present invention is not limited to tubes of this type but is su?iciently broad to embrace all forms of elec trical discharge apparatus, highly evacuated or gas-?lled, in which a plurality of ?lamentary cathodes are employed having different electrical applied, without danger to the smaller ?lament 1, as isapplied to the larger ?lament 6. Obvi ously, the voltage actually impressed across the ?lament 1 represents a reduced voltage obtained by the effect of the resistance or inductance l0 30 which serves to dissipate or consume the energy of the undesired voltage. It is desirable when the element i0 is constituted of resistance, that the latter should be made of the same wire as the ?laments. 6 and ‘I. It is also apparent that 35 the combined resistance of the ?lament 'l and the resistance II] should be substantially equal to the resistance 'of the ?lament 6. By placing the voltage-reducing element I0 within the envelope instead of being positioned external to the en velope and contained within a base cap at the cathode end of the tube, the element is in such a position as not to cause any deleterious heating e?'ects, nor does it necessitate a large cathode cap within which to be accommodated. It will be ‘advantageous to mount theresistance close to the cathode, since in this case the heat generated in it will heat only such internal constructional parts of the tube as are heated by the cathode itself and are therefore designed to withstand the heat 50 produced. Moreover, the improved position of the element I0 o?ers a unitary and compact con struction. characteristics and which are selectively ener 30 gized from a common source of electrom'otive force. > What I claim as new and desire to secure by Letters Patent of the United States, is,— An electrical discharge device comprising an 35 envelope containing an anode, a main cathode and a secondary cathode, said cathodes being ar ranged adjacent to one another, a voltage-reduc ingelement within said envelope and connected to said secondary cathode, the combined resis tance of the secondary cathode and said element being substantially equal to the resistance of said main cathode whereby equal voltages may be ap plied to the main and secondary cathode circuits to produce equal heating currents, and a shield mounted adjacent to said voltage-reducing ele ment for preventing radiation of electrons by said element but permitting radiation by the secondary cathode. _ ALBRECHT ' WOLFEL.