US2053792A - X-ray generator - Google Patents

Description

H. K. HUPPERT ET AL X-RAY GENERATOR Sept} 8, 1936. 2,053,792

Filed July 19, 1933 2 Sheets-Sheet 1 In III/0170 INVENTORS,

HENRY K. HUPPERT.

THOMAS H. FORDE.

ATTORNEY 4o RECTIFIER. L

16 s 4 so @vg $52 f;j"s c .32 M 49 Q50. III NI I p 1936- H. K. HUPPERT ET AL 2,053,792

X-RAY GENERATOR Filed July 19 1933 2 Sheets-Sheet 2 .llym

RECTIFIER. g RECTIFIER.

I INVENTORS, HENRY K. HUPPER T.

THOMAS H. F ORDE.

50 ATTORNEY Patented Sept. 8, 1936 earns-r OFFICE X-RAY GENERATOR Henry K. H'uppert and Thomas H. Forde,

. San Francisco, Calif.

Application July 19, 1933, Serial No. 681,104

3 Claims.

Our invention relates to X-ray generators having a-hot cathode; and more particularly to such tubes having a control element" therein whereby the direction and amount of the cathode ray stream between anode and cathode may be changed at will independently of the cathode or anode'supply. ljhe invention further relates to methods of generating X -rays having peculiar characteristics, this application being a continu- 0 ation in part of our prior application, Serial No.

580,836, filed December 14, 1931.

Among the objects of our invention are: To provide an X-ray' tube wherein the electron Stream can be controlled independently of the ano'de'and cathode supply; to provide an' X-ray tube in which a space charge is present during a substantial part of the time that X-rays are being generated; to provide an X-ray tube which may be made self-oscillating at high frequencies;

' to provide" an X-ray tube in which the size of the focal spot may be changed electrically; to provide an X-ray tube in which the position of the focal spot may be changed electrically; to

provide an X-ray tube in which the envelope is '25 effectively protected from secondary electron bombardment; to provide an X-ray tube in which stray X-rad'iation outside the main beam is reduced. to a minimum; to provide an X-ray tube or increased efficiency; to provide an X-ray tube of simple construction and in which the elements are in concentric relation; to provide an X-ray tube having a minimum band of X-ray wavelengths" in the active beam; and to provide a greatly improved X-ray generator and novel 35 methods of operation.

Other objects of our invention will be apparent or will be specifically pointed out in the description forming a, part of this specification, but we do not limit ourselves to the embodiment 0 of our invention herein described, as various forms may be adopted within the scope of the claims.

Referring to the drawings, which illustrate sev eral' embodiments of our invention:

Figure 1 is a view in elevation of the elements of a right angle X-ray tube embodying our invention, the envelope being cut away and shown in section.

50 Figure 2 is an enlarged plan view of the cathode and control electrode, the cover of the control electrode being removed.

Figure 3 is an enlarged view partly in section and partly in elevation showing the relations of anode, cathode and. control electrode,

Figure 4' is a sectional view of another embodiment of our invention.

Figure 5 is a schematic diagram of? a circuit in which the tube may be used.

Figure 6 is a schematic diagram of another 5 embodiment of our invention as used to control the position of the focal spot.

Figure 7 is a schematicdiagram of the tube of our invention as used in an oscillating circuit.

Our invention, broadly considered from the 19 point of view of apparatus, comprises an X-ray tube containing an annular cathode, and-an anode, preferably of conical shape positioned in the axis of the circle described by the cathode, the apex of the anode cone being usually placed in substantially the center of the circle. The cathode is enclosed by a control electrode having preferably a concentric annular aperture between the cathode and anode. The control electrode is adapted to be separately energized to give con- 20 trol of the electron how tothe anode. It may also be desirable to make use of the control thus afforded to cause the X-ray tube to be selfoscillatory at high frequencies by the use of proper exterior circuits, thus giving rise to an X ray beam pulsating at high frequencies.

Considered broadly as to methods involved, we are able to-control the cathode ray current and consequently the intensity of the X-ray beam by changing the thickness of the cathode ray stream. We also utilize the method of changing the thickness of a discoidal cathode ray stream to change the size of the focal or impact spot, and we also change the direction of the discoidal stream to change the position of the 3 focal spot. We may desire to make the X-ray beam pulsate at high frequencies by making the cathoderay current self-oscillatory, thereby producing an X-ray having peculiar results of unexpected character.

In the ,detailed description of the preferred forms of our invention which follows, wherein certain relative dimensions are shown and described, and certain specific circuits are menti'oned, it is to be understood that these dimensions are relative only and may be departed from widely in order to adapt the apparatus to various kinds of radiographic, therapeutic, diagnostic or experimental uses, and that other equivalent circuits may be substituted for the specific ones disclosed, without departing from the spirit of this invention.

It is also to be understood that we do not at this time, desire to ofier any extended explanation or discussion of the theories involved in this continued experimentation, and coordination and assembly of widespread observations. In such a rapidly advancing. field, additional data might V well modify or completely change presently'held theories-without, however, necessitating change or modification of apparatus or method beyond the scope of the appendedclaims;

In the drawings, referring especially to Figures "1, 2, and 3, an envelopell is;provided with an" fanode arm l2 and a shorter cathode armfl3. j

It ispreferred that the armsbe placed at right I y [from an' alternator 50 either directly whereby angles, leaving a radiation "window 'Mffree 1of 7 1 obstructions. V 1

'.brolts 20;. r '3 Thefcontrol electrode assembly comprises a Alcathodesteni l5j'is sealed in the endorsthe cathode arm and supports a controlrelec trode'assembly I6 by means .of control'rods l'l fastened tota band l9'clamped to the. stem' by hollow cup-shaped body which has; acover 2|, acircumferential side wall- 22 anda" face plate 24,,the latterebeing' provided with a cone shaped radiation aperture ,25 positioned to face the ra-- jdiation ::win'dow: l4. Thetcover 2 I,which-may I be removed bytaking out screws 26,- ,and the inneri'surfaceof'the faceplate are preferably dished sufliciently to form an. annular aperture '21isomewhat narrower in width than the inte- ;rior:'chamberiwidth next the side wall.)

cover fl:isprovided with' a .central anode aper-' r r. """Cathode supports'29are sealed to and; thereby positioned parallelto the control rods. H'- by a spacer. ;3n{pref erably formed'fro n quartz; These f leadsiproject' into the control electrode chamber through cathode support apertures 3|; 1 v 'Anannular cathode 32 preferably formed from 'aj tantalum or. tungsten coilis fastened to the leads concentriciwith. the side wall 22v aboutrnidwaybetween thesidewalland the annular apere V *i turegizl:"Quartz-unlike insulators 34, set'around the side wall carry 'hooks 35 bywhich-thecathode is maintained in'its concentric positions Cathode leads 36 and a control. lead 31 are fsealed-throughia pinch 39 of the'cathode stem and connect with the cathode supports and a co-ntriol rodprespectivelyq g In theian'ode'rarm; a long anode'rod 40, pref-1 erably of heavy copper is provided with a welded skirtr ll of a'material which will seal-to the 5 envelope matelial'toform a 'ring ,s eal 42, with a" reentrant tube 44. 1

Thetanode rod continuesjo n in? the central axis of the tube -and terminates in an. anode plugfl45 preferably oftungsten set into and fas- 'The tip of-the t tened to the-endof the rod, and exposing alcon ed targetsurface 46, .1 V

l W rg et co ne projectsthrough the anode aperture, 28 in 1 the control electrode coverbyan amountwhich maybe varied, V as will I be later; described, but in any event, :it is; 'pren erable thatthe tip of; the (cone. be in the axis of the circle described by the annular .-catho-de.

Itis also desirableft'o makeI-the .totalfdiameter o f the anode rod somewhat larger than the cover aperture so that the shoulders of the anode rod 'will shield the anode endi'of the, tube-from stray] X-radiation, primary or secondary electrons from inside. the controLelectrode assembly. .A slightly different embodiment of ourinvention i's'shown in Figure 4; Here the anode arm leakage in the supports,

, the negative potential will l2 and the cathode arm 13 are in line, the radiation opening in the control electrode being directed toward a side wall of the envelope, and the anode rod being provided with a right angle bend 41 to place the coned target surface in the ings showing the anode tip in different degrees of insertion.

InFigure 5, the cathode 32 is energized by asource. 49, the anode being usually energized the tube becomes self-rectifying, or preferably through a'rectifier, as is well known in the art.

The control electrode is maintained at a potential difierent from that of the cathode by a biasing source 55;: or insome cases by a resistor 52 I which will; then cause the control electrode to become nfigative due .to accumulation of electrons during operation.

7 In some cases it may be desirableto let the control electrode float free without connection, in which case it will charge up to a high negative potential, but will notusually block theanode current at the anode potentials in vogue, as there is always someslight In operation the annular cathode an annular cloud of electrons, some of whichare drawn through the annular aperture to the coned target surface and others are returned to the cathode, a discoidal stream of =electrons being. formed Which is dense near the cathode and thinning out toward the anode. This cloud of electrons constitutes thespacecharge, and its formation is encouragedfby the enclosure of the cathode. Varying potentials placed on the control electrode will control the amount of current reaching" the anode; in general, a negative potential decreasing the. current, and a less negative potential increasing it. l I

Due to the shape of the annular aperture however, placing a potential on the control electrode will also change the dimensions or shape of the stream. The ,equipotentiallines produced when he. control electrode is energized are indicated by the numeral 54 and the generalpath of the stream sectio-nby the dotted line 55. Increasing the negative potential onlthe control electrode will make the stream thinner, and decreasing thicken itQ Th'u s the thickness of the stream can be controlled, the end result being the same .as if the physical annular aperture 21 were to be changed in dimension. We have therefore given the name of electricalaperture to the condition existing in the annular aperture when energized.

Several results apart from: the gross control of current may be accomplished by the use of the electrical aperture. By changing the thickness of the stream a greater or, less amount of target surface may be bombarded,'thus changing the size of .the focal spot, for-various types .of radiography. The shape ,of the spot willbe determined by the position of the coned target surface. If placed so that the apex of the cone passes completely through' thestream, the spot will be a ring which" maybe made narrow or 'wide, If the cone is retracted as in Figure 5,

of varying size allot which adds to the versatility f thedevice.

In case the tip is withdrawn along the axis of the circle away from the center as in Figure 5,

pass out of the electrical aperture, thereafter the anode turning toward the tip. As the electrons are rapidly increasing their velocity, they drive close to the center of the circle before turning to bombard tip. In other positions where the tip is close to the center, practically no dishing occurs. .1

In Figure 6 a circuit is shown, as in Figure except thatthe upper and lower portions of the control-electrode are electrically distinct and a separate biasing source 56 is shown for the upper portion. By adjustment of potentials, both the direction and amount of the stream may be controlled to produce conditions only obtainable in the previously described tube by physically withdrawing or inserting the anode tip into the stream, a construction which is not easily feasible in a single tube.

Figure 7 represents a circuit in which the tube as above described will oscillate. The circuit is l the well known tuned grid tuned plate circuit, a

control resonant circuit 51 being placed in series with the control bias, and an anode resonant circuit 59 in series between the anode and cathode. A blocking condenser 60 is preferably placed between the anode and the resonant circuit and the high voltage parallel fed from the usual transformer 6| through the rectifier.

We have found that the tube as described can be set into self-oscillation at a frequency of 7,500 kilocycles without difficulty and when it is oscillating the high frequency pulsating X-ray beam appears to have a penetration quality somewhat difierent than that to be expected from the actual applied voltage. Such penetration has been experimentally observed and therapeutically used, but we are not at this time ready to express an opinion as to the reason therefor.

However, as the frequency of oscillation is determined by the tuning of the control electrode circuit, the reaction of the anode circuit being inductive, variation of the tuning of the anode resonant circuit will change the relative phase of the anode potential and anode current, without substantially changing the oscillation frequency. This change in phase relation gives rise to internal conditions diifering widly from those in the ordinary X-ray tube, and may well modify ant phase relations produce a pulsating X-ray beam having entirely difierent characteristics than that produced by an ordinary tube having the anode energized by high frequency alternating current.

The X-radiation of the device however, does have a homogeneity, to which we believe there is a reasonable explanation. It is well known that the X-rays from a tube consist of two main classes; the heterogeneous spectrum of general radiation within a range of quality which depends solely on the speeds of the parent electron streams;-and the homogeneous or monochromatic radiations which are characteristic of the targetmetal. At high voltages the bulk of the radiation is of the latter type, but in tubes using unfiltered alternating clurrent, there is a large component of the softer heterogeneous rays generated as the anode voltage rises to the point where the homogeneous radiations begin, the relative amounts depending on the wave form applied to the anode.

By creating a space charge, and by using a strong negative potential on the control electrode, we are able to prevent anode current from flowing during the low voltageportions of the wave at the beginning and end'of each half cycle, and thus greatly reduce the amount of the socalled general radiation, leaving the bulk of the X-ray beam hard rays of the homogeneous type. The efiectiveness of the tube and the therapeutic efiiciency is thus greatly improved.

It should be observed that high negative potentials may be used on the control electrode without changing the quality or hardness of the X- radiation from the anode. The net potential difference between the anode and cathode is the dominating factor, controlling as it does, the speed of the electrons bombarding the anode. The velocity of the electron stream will be held down by the potential of the control electrode while the electrons are within the limits of its influence, but after they escape through the electrical aperture and pass toward the anode, they are accelerated again at a rate which will land them against the anode with not less than the same velocity as they would have if they had started from the cathode and proceeded to the anode without influence of any control electrode or control potential.

There is also experimental evidence to indicate that the quality or hardness of the final X- ray is such that greater penetration for a given anode-catrode potential difference is obtained from our tube with the cathode emission controlled by the electrical aperture of our invention. While we realize that the quality or hardness is customarily said in textbooks to be entirely determined by the anode potential, we have obtained reliable experimental evidence of greater effective penetration in the rays emitted from the tube as described, although we do not at this time care to ofier an explanation of that discovery.

Several further features of our invention should be pointed out. The cathode and focal spot being enclosed, and the walls of the control electrode being of sufficient thickness to stop casual X-rays, practically no X-radiation passes out except through the radiation aperture. The cover 2| of the control electrode, although it may be somewhat thinner than the rest of the control electrode, prevents X-radiation along the back of the tube, and as the diameter of the anode rod is larger than the aperture in the cover, complete shielding is provided. Furthermore, the enclosed construction prevents stray electrons from striking the glass to form hot spots and eventual puncture. The construction as shown therefore, completely shields the envelope from both the cathode rays, and the X-rays except through the proper path, and no auxiliary internal or external shields are necessary for the protection of the operators from stray radiation.

It is also possible to regulate the anode current to provide a uniform output even though slight chargeor control; such? variatio-n'svin line voltage change the cathode temperature with resultant V fluctuations of milliampera'ge and much: elaborate compensating equipment;

We claim:

;. 1'.- Themethod: of" generating: X-rays which comprises the steps of; forming. anannular'clo'ud of-electrons, 1 directing said electrons inwardly to a common center, intersectingsaid cloud adjapcent 'saidcenter to produce; a streamof X-r'ays directed outwardlyalongi aaline perpendicular to t the plane-of the-"electron:path;andtvaryingthe thickness of' the electron stream to-= vary' the d1- 'ameter of the X-ray stream.

-2.- Themethodof controlling-:the X-rayb'eam emitted'oircumferentially from-a conical anode,

irregularities inlline *v'oltage' maywocc'ur. In ordinary tubes opera-ting at saturation-without space which comprises formingran'annulai cloudofelectrons concentric with the axis'o'f said: anode, di resting"said:elctronsinwardly to bombard the coneof-"said anode; and varying the thickness of the;e1ecl7r0n stream todefine-vthe amount-of anode surface bombardedrby said electrons.

4, Tlie'method of generating X-rays'whjch comprises the steps: of forming an annular cloud of electrons;-, directingsaid electrons inwardlyito a common center; intersecting said cloud: adjacent saidacentertdproduce a stream of; X-rays directed outwardly along a; line perpendicularto the plane of" the electron pathl-zand varying the thickness of the electron stream to control the X-rays, pro-,- duced;

K. HUPPERT. THQMAS H.- FORDE'.

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