US2342789A

US2342789A - Supervoltage X-ray tube

Info

Publication number: US2342789A
Application number: US389351A
Authority: US
Inventors: Cassen Benedict
Original assignee: Westinghouse Electric and Manufacturing Co
Current assignee: CBS Corp
Priority date: 1941-04-19
Filing date: 1941-04-19
Publication date: 1944-02-29
Anticipated expiration: 1961-02-28

Description

Feb. 29, 1944. B. cAssEN 2,342,789

SUPER VOLTAGE X-RAY TUBE Filed April 19. 1941 q) A W d .Z4 y t\ I Ig ned/f 605.560 @u i W f m m "A BY WITNESSES: INVENTOR ATTORNEY Patented Feb. 29, 1944 UNITED STATES PATENT OFFICE Westinghouse Electric & Manuf Colnpany, East Pittsburgh, Pa., a corporation of Pennsylvania Application Api-u 1a, 1941, serial No. 389,351

(ci. 25o-1oz) 11 Claims.

My invention relates to electric discharge apparatus and has particular relation to high voltage discharge tubes, such as generators of hard X-rays.

In producing X-rays having a wave length less than .25 angstroms, a potential greater than 50,000 volts is impressed between the cathode and the anode. If the potential is impressed directly from an alternating current source or from a battery of accumulatore, the usual high voltage problems arise. Either the cathode or the anode is at a high potential relative to ground and elaborate insulation is required to prevent arcing between the parts of the system in electrical contact with or adjacent to either of the two electrodes. The cooling coils, which are essential for such high power apparatus. present a particularly serious problem in this respect. Protective equipment of elaborate design is also required to assure that operators, people who are being treated with the apparatus and others in the vicinity of the apparatus are not injured by the high potentials.

It is, accordingly, an object of my invention to provide a generator of hard X-rays having a wave length less than .25 angstroms which shall incorporate no high voltage insulating and protective equipment.

A more general object of my invention is to provide a high voltage electric discharge device which shall incorporate no insulating and protective equipment for high voltages.

Another general object of my invention is to provide an eilicient high voltage electric discharge device.

A more specific object of my invention is to provide apparatus for radiating X-rays in precisely timed discrete pulses.

An ancillary object of my invention is to provide a circuit for coupling an oscillation generator to a hollow body resonator in such manner that the generator locks into stable oscillation with the resonator.

Another ancillary object of my invention is to provide an emcient hollow body resonator.

More concisely stated, it is an object of my invention to provide an efficient high voltage X-ray system that shall not incorporate the insulating equipment ordinarily required for the high voltage involved.

My invention arises from the realization that the high voltage necessary to produce hard X- rays may be impressed as the electric component of a high frequency electromagnetic field entirely within a hollow body resonator. Externally such lli -of a completely closed hollow cylinder.

a resonator is throughout at ground potential, and, therefore, neither the cooling system nor the other parts of the apparatus need be elaborately insulated in spite of the high potential impressed within the resonator.

In accordance with my invention, I provide a discharge device comprising a hollow body resonator within which an electron emitter is disposed. The resonator is coupled to a suitable oscillation generator which produces an electromagnetic iield within the resonator and under the action of the iield electrons ow from the source through the resonator. An X-ray target is disposed in the path of the electrons, andas the electrons impinge thereon, X-rays or the desired wave length are produced.

In accordance with the broader aspects of my invention, the resonator may be an ordinary hollow tank, the internal surface of which is conductive. When such a. tank is excited to oscillate,

a standing electromagnetic wave or fraction of a' wave is produced along a dimension of the tank corresponding to the mode of oscillation and the electrons from the emitters iiow through the tank along. a path determined by the electric component of the field of the wave. The wave has a potential nodes at conductive walls of the tank which are transverse to the dimension of oscillator and voltage loops intermediate the nodes. Hereinafter, I shall refer to the potential produced by the electromagnetic eld as the electromagnetic potential to distinguish it from the usual direct or low frequency alternating potentials which may be used in the apparatus. The electron iiow is produced by a field which arises from the dlerence of electromagnetic potential between the emitter and the points in the resonator which are at any instant at a higher electromagnetic potential than the emitter. The emitter should be so disposed in the tank that the electrons in passing through the tank are subject to the potential of the field for an interval of time that is short compared to a period of the field. If the electron path is so long that the electrons are aiected by the field during an interval of time of the order of a period of the field, the electrons are both accelerated and decelerated while traversing their path and do not have the necessary energy when they impinge on the target.

Conveniently my invention may be practiced in its broad aspects with a resonator in the form In the principal mode of oscillation of such a cylinder the resonant electric eld is in an axial direction and has a wave length approximately equal to twice the diameter. Conducting leads carrying an electron emissive filament are sealed through one base of the cylinder and a target is supported from the opposite base. The height of the cylinder or the length of the filament leads should be such that the path over which the electrons are accelerated by the field is short compared to a quarter wave length of the resonant field. When the cylindrical resonator is excited to oscillate the potential wave has a node at the circumference of the cylinder and a loop on the axis; the potential difference within the cylinder is axial. The maximum potential difference at any instant is impressed between the bases along the axis. Current flows between the emitter and the target under the action of the axial potential difference. The return path of the current is along the wall of the cylinder, along the base through which the emitter is sealed and along the emitter leads.

The resonator is excited to oscillate from a suitable oscillation generator coupled to the resonator. In the practice of my invention I have found that the cylindrical resonator is bulky if it is designed to have a resonance wave length at which sufilcient power for X-ray purposes is available.

This situation may be remedied by providing in lieu of the cylindrical resonator, a resonator made up of a cylindrical shell with a reentrant cylindrical protuberance through which the emitter projects. The length of the protuberance is such that its inner terminal is disposed adjacent to the opposite base of the resonator. The emitter extends just through the end of the protuberance adjacent the resonator base and the target is mounted within the base. Such a resonator has a principal resonant wave length approximately equal to four times the height of the shell. The lines of force of the electric field produced when the resonator is excited to oscillate extend radially between points on the protuberance and corresponding points on the shell. The distance between the protuberance and the opposite base of the resonator is such that the time during which the electrons are subject to the field between the emitter and the base is short compared to a quarter period of the resonance frequency. When the resonator is excited to oscillate, a wave having a potential node in the region Where the protuberance joins the shell and a loop near the opposite base of the shell is produced. In this case the return path for the current which flows between the emitter and the target is along the internal surface of the outer cylinder, along the surface joining the outer cylinder and the protuberance, and along the internal surface of the protuberance. In addition to the discharge current there is a large high frequency resonant current which is greatest along the joining surface and tends to concentrate at the junction of the protuberance and the surface.

To minimize power loss, it is desirable that the area bounded by the curve which is dened by the junction (the diameter of a circle if the protuberance is a circular cylinder as is usual) be as large as is practicable. This desideration cannot be achieved simply by providing a protuberance having bases of large area because as small an area as is practicable is desirable at the internal end of the protuberance. The magnitude of the electromagnetic voltage produced is dependent on the'characteristic impedance of the resonator in the region of the voltage loop. The latter impedance is the greater, the greater the ratio of the area of the base of the outer shell to that of the protuberance in the region of the loop. Where the shell and the protuberance are of circular cross section the characteristic impedance is proportional to the logarithm of the ratio of the diameter of the outer shell to the diameter of the protuberance in the region of the loop. For a given shell diameter, the ratio and, therefore, the electromagnetic voltage, is a maximum if the protuberance diameter at the internal end is a minimum.

The conditions for minimum power loss and maximum electromagnetic voltage may both be satisfied by providing a resonator having a reentrant conical protuberance. The protuberance is preferably of circular cross section and tapers from a large diameter base at one base of the shell substantially to a point near the other base of the shell. The junction c urve between the protuberance and the formerbase of the outer shell is a circle of large diameter, and the losses at the junction are minimized. The ratio of the diameter of the shell near its other base to the diameter of a point is high and therefore the electromagnetic voltage is large for the dimensions involved.

The ratio which governs the characteristic impedance is a maximum if the shell is cylindrical. However, a conical shell with a conical protuberance is less cumbersome and Weighs less than a cylindrical shell with a conical protuberance. Since for resonators most frequently encountered in practice, the characteristic impedance ratios are not appreciably different for the two structures, I prefer to use a conical resonator with a reentrant conical protuberance in the practice of my invention. My invention is not, of course, limited to this preferred practice.

' In accordance with the broader aspects of my invention, the resonator may have any desired dimensions. However, from a practical standpoint I have found' that certain dimensions are to be preferred.

The resonant wave length of a conical (or cylindrical) resonator having a reentrant protuberance is roughly four times the distance between the bases of the outer shell. Since X-rays are produced in a high vacuum the resonator is highly evacuated and to minimize vacuum problems, it is desirable that the resonator be small. Aside from physical limitations, the exiguity of the dimensions of the resonator is limited by the practical consideration that oscillators for exciting a resonator sufficiently to produce X-rays are not available at small wavelengths. I have found that an oscillator capable of supplying more than 200 watts steady power and 10 to 50 kilowatts in discrete pulses is necessary for X-ray purposes. Such an oscillator is conveniently available only at wave lengths greater than two meters. To avoid vacuum difliculties, the resonance wave length of the resonator should not be greater than l2 meters. In accordance with a specic aspect of my invention, the resonant wave length of the resonator should lie between 2 and 12 meters and should preferably be, of the order of 4 meters.

The oscillator which is used in the practice of my invention to excite the resonator comprises electric discharge valve means, the output circuit of which is connected through a coupling loop to the resonator. The resonator is a massive structure. and its dimensions cannot conveniently be varied for tuning purposes. A problem, therefore, arises in adjusting the oscillator to lock into stable oscillation with the resonator. In accordance with a still further aspect of my invention, the impedance between the loop and the output electrodes of the discharge valve means is varied until the oscillator and the resonator lock into stable oscillation. I have found that stability is attainable over a substantial range of .the impedance and precise adjustment to a critical point is not essential.

It is desirable that the flow of electrons from the emitter to the target be limited to the time 1ntervals during which the electromagnetic potential tending to draw electrons from the emitter is high. If electrons ow from the emitter during the intervals when the potential is relatively low, they, to a large extent, fail to reach the target and circulate in the resonator causing excessive loss. To limit the ilow of electrons in the high potential intervals, the emitter is shielded by a screen conductively connected to the resonator and a biasing potential of several hundred volts is interposed between the emitter and the resonator. The potential prevents the electrons from penetrating the screen into electromagnetic field and the target, unless the potential produced by the fleld is of large magnitude.

The novel features that I consider character istie of my invention are set forth with particularity in the appended claims. My invention itself, however, both as to its organization and its method of operation, together with additional objects and advantages thereof, will best be understood from the following description of specic embodiments when read in connection with the accompanying drawing, in which:

Figure 1 is a diagrammatic view showing an embodiment of my invention; and

Fig. 2 is a graph illustrating the operation of my invention.

The apparatus shown in Fig. l comprises a hollow body resonator 3 made up of an external conical shell 5 and a reentrant conical protuberance 1. The protuberance 1 tapers in the same direction as the shell 5 and is preferably coaxial with the shell. In accordance with the broader aspects of my invention, the protuberance and the shell need not be coaxial, but their axes should preferably be parallel. The distance between the small diameter base 9 of the protuberance 1 and the small diameter base Il `of the shell 5 is short compared to the height of the shell. The ratio between the shell height and the distance between the small diameter bases should be of the order of 5:1 to 10:1. Cooling coils I3 are pro" vided about the surface I5 joining the large diameter ends of the protuberance and lthe shell.

The shell 5, the protuberance 1 and their joining surface I5 of the embodiment shown in Fig. l are composed of an electrically conductive material such as copper. In accordance with the broader aspects of my invention, the resonator need not be composed of conductive material but it is essential that the inner surface of the resonator` be conductive.

A central opening I1 is provided inthe base Ii of the shell 5. Over the opening a closed cylindrical tube I9 having a flat cover 2| at an angle of approximately 45 to the axis of the tube is secured. The tube I9 is preferably composed of Monel metal. and the cover 2i has a thickness of the order of one tenth of an inch. The innersurface of the top is faced with lead 23 or any other high-atomic-weight material. Thetube is provided with ears 25 and is held tightly against a gasket 21 disposed over the opening I1 in the shell 5 by bolts 29 which pass through the ears I tuberance 1 and the shell 5 adjacent the supportand engage the small base Il of the shell. A suitable water-coolingjacket ll is provided about the itube I9 and its top 2 I.

The small diameter base 9 of the protuberance 1 is rounded 0H so that it, in eiect, constitutes a point rather than a surface of extensive area. It is provided with an opening 32 through which an electronic emitter assembly 33 extends. The assembly comprises a ring shaped filament 35 of tungsten or any other suitably emissive material 31. A pair of rigid conducting leads 39 are welded to the illament 35. The leads and the l filament are enclosed within a narrow electrically conductive cylinder 4I open at the end remote from the nlament 31. The open end is sealed vacuum-tight by an insulating plug 43 preferably composed of glass and the leads 39 are sealed vacum-tight through the plug 43. The leads are of such length that the filament is adjacent the unsealed end of the tube 4l. The end 45 of the tube 4I near the lament is closed but has a centrai opening 41 of small diameter. Insulating spacers 49 are provided within the tube 4I to prevent the leads 39 from contacting the tube. The tube extends a short distance through the small diameter base 9 of the protuberance 1 and is hard-soldered vacuum-tight to the protuberance by a solder ring 5I melted at the junction between the protuberance and the tube.

The tube 4| is thus conductively connected to the resonator 3 but the filament 31 is insulated `from the resonator. The perforated end 45 of the tube 4I, in effect, constitutes a screen about the lament 31 and the ilow of electrons from the filament may be controlled by controlling the potential between the end 45 (i. e., the resonator) and the filament.

The resonator 3 is supported from hollow tubu lar arms 53 and 55 extending from diametral openings near the large diameter end of the outer shell 5 in a direction perpendicular to the axis of the shell. The arms are soldered vacuum-tight to the outer shell. A sleeve 51 is secured to each of the arms and the sleeves are rotatably supported on ball-bearing wreaths 59 which are suspended from a iixed supporting bracket 6i. The resonator 3 may thus be rotated about an axis determined by the arms 53 and 55.

One of the arms 53 communicates with a pump system 63 through a Sylphon 65. The system comprises a tubular oil-diffusion pump 61, the suction tube 69 of which is secured vacuum-tight to the Sylphon 65 and a mechanical pump 1I having its suction tube 13 connected to absorb gas from the tubular diffusion pump. Sleeves 15 are secured about the wall of the diffusion pump near its oil reservoir 11 and near its suction opening. The sleeves 15 are rotatably supported on bali bearing wreaths 19 suspended from a rigid bracket 8i. The diiusion plunp 51 may' thus rotate with the resonator 3. The tube 83 from the suction opening 13 of the mechanical pump 1I is sufficiently long and flexible to permit free rotation of the diffusion cylinder 61 and the resonator 3, and the Sylphon 65 takes up any difference in displacement between the diffusion pump and the resonator arising from the rotation.

The remaining tubular supporting arm 55 is sealed vacuum-tight by a plug 85 of insulating material, such as glass. A coupling loop 81 extending from terminals 89 sealed through the plug projects into the space between the DKG- ing arm 53. The loop 31 should be so positioned as to be threaded by a portion of the iiux of the magnetic component of the eld produced within the resonator 3 when the latter is excited. When I are connected to movable brushes 9| which engage fixed conductive rings 93.

The resonator 3 is excited from a high frequency oscillation generator 95. The generator comprises a pair of three-electrode high-vacuum discharge tubes 91 and 99, each having an anode IDI', a cathode |03, and a control electrode |05. The control electrodes are connected together by a short conductor |01. To the center |09 of the conductor or terminal, a biasing network consisting of a resistor I|| and a capacitor ||3 in parallel is connected. The other terminal of the network is connected to a conductor ||5 which connects the cathodes |03.

From each of the anodes I| of the discharge devices 91 and 99 rigid conductor ||1 extends. Each of the conductors engages a ring 93 to which the loop terminals 39 are connected. The anode conductors ||1 are bridged by a conducting bar ||9, the position of which along the conductors may be adjusted.

The bridging bar I9 is connected to a grounded line conductor I2| of an alternating current source (not shown). The other line conductor |23 of the source is connected to the conductor |I5 which connects the cathodes. The oscillator I5'may be enclosed within a shielding container |25 provided with a neck |21 within which the rings 93 connected to the loop 81 are mounted. The resonator 3 is grounded but the loop 81 and its terminals 89 are insulated from the resonator.

The anode conductors H1, the loop terminals 39. the loop 01 and the bridging conductor H9 constitute the output circuit of the oscillator 95. The character of the interaction of the oscillator and the resonator 3 may be determined by adjusting the position of the bridging bar I|9 along the'anode conductors ||1. The bridging bar may be so disposed that the portions of the anode conductors between the bar and the anodes |0| are shorter than that required for stable oscillation of the generator 95 and the resonator 3 as a unit. This situation arises when the anode conductors and the bridging bar have a low impedance compared to the equivalent impedance of the loop 31 and the resonator 3, and in such an event the oscillator operates independently of the resonator. The bridging bar ||9 may be so rositioned that the portion of the anode conductors between the bar and the anodes are too long. The resistance of the anode conductors and the bridging bar is then so high that no oscillations are produced by the generator 95. Intermediate these extreme positions of the bridging bar 9 there is an extended region for which the resonator 3 and the oscillator 95 lock into stable oscillation.

When the resonator is properly excited by the oscillator 95. an electromagnetic ileld the electric component of which is radial is produced within the resonator and a diil'erence of electromagnetic potential exists between points along the protuberance and points along the shell radially displaced from the protuberance points. Between the apex 9 of the protuberance and the oppositev base of the shell the lines of force of the electric component of the electromagnetic ileld extend at gradually decreasing angles to the axis of resonator as the axis is approached and they are along the axis between the center of the apex and the center of the base ll. An electromagnetic potential difference is therefore impressed between a point Just outside of the screen 45 and a central point near the base I l of the shell 5 opposite the lament.

The standing electromagnetic potential wave which is produced along the resonator 3 is illustrated graphically at any instant in Fig. 2. Dlstance is plotted vertically and potential horizontally towards the right. To illustrate how the potential varies along the resonator, the outline of the resonator is shown in broken lines. The full-line quarter-sine Vr represents the electromagnetic potential difference between corresponding radial points along the protuberance 1 and shell 5. For example the potential difference between point Pp on the protuberance and point Ps on the shell is given by the potential coordinate of the point Vp. The potential difference between the screen 45 and the base I| is given by the maximum voltage coordinate of the curve Vr (at the point L) The potential wave has a node N at the large diameter end of the resonator and a loop L near the small diameter base of the shell. A current loop coincides with the potential node N and the current is, therefore, large along the large diameter surface I5 of the resonator. It is for this reason that the surface is provided with cooling coils |3.

The potentials along the resonator 3 represented by the curve Vr is an alternating potential having a high frequency determined by the resonator 3; the corresponding wave length being approximately four times the length of the resonator. Since the anode-cathode potential impressed on the tubes 91 and 99 of the generator which excites the resonator is of the alternating type, the electromagnetic potential within the resonator is modulated at the frequency of the alternating current potential impressed on the tubes. The alternating current potential frequency is small compared to the resonant frequency of the resonator.

A potential |28 is interposed between the filament 35 and the resonator 3 maintaining the direct current potential of the resonator negative relative to that of the filament. The potential functions as a negative bias between the perforated cover 45 of the tube 4| which encloses the filament and the leads 39 and controls the ow of electrons from the filament to the small diameter base of the shell.

Electrons flow from the filament 35 under the combined action of the biasing potential |28 and the modulated electromagnetic potential. The electron flow from the iament is blocked by the biasing potential until the electromagnetic potential exceeds a predetermined magnitude. At this point the electrons are drawn from the eld of the screen 45 into the high electromagnetic field between the screen and the small diameter base Il of the shell 5. In the latter region, they are accelerated and pass through the opening |1 in the small diameter base into the tube I9. The space within the tube is eld free and the electrons pass through the tube and impinge on the target 23 producing X-rays. The electromagnetic potential difference to which the electrons are subject is so high that X-rays having a wave length less than .25 angstrom are produced. The radiation is in discrete pulses having a periodicity and amplitude determined by the modulating frequency and amplitude and the biasing potential. i

In a system constructed in accordance with my invention, the length of the resonator 3 is 48 inches. The largest diameter of the outer shell 5 is 32 inches. The smallest diameter` of the outer shell is 14 inches. The distance between the small diameter base Il of the outer shell and the small diameter base 9 of the protuberance 1 is 9 inches. The large diameter of the protuberance is 18 inches. Its small base is a roundedoif-surface originally 4 inches in diameter. 'I'he discharge devices 91 and 99 used in the oscillation generator 95 in an embodiment o my invention are Westinghouse WIr-889 tubes. The anode-cathode potential impressed on each of the devices is an ordinary commercial 60cycle potential having a peak magnitude of 12,000 volts. The resistor IH in the biasing network is 5,000 ohms, and the capacitor in the network is the distributed capacity of the resistor.

Although I have shown and described certain specific embodiments of my invention, I am fully aware that many modications thereof are possible. My invention, therefore, is not to be restricted except insofar as is necessitated by the prior art and by the spirit of the appended claims.

I claim as my invention:

l. Electric discharge apparatus comprising a hollow body resonator, means for impressing on said resonator an electromagnetic iield of a frequency corresponding to the resonant frequency of said resonator, a source of electrical charges disposed to project charges under the action of said eld, and charge collecting means disposed to collect the charges projected from said source, the distance over which said charges are subjected to said iield being short compared to a quarter wave length corresponding to said frequency.

2. Electric discharge apparatus comprising a hollow body resonator, means for impressing on said resonator an electromagnetic eld of a frequency corresponding to the resonant frequency' of said resonator, a source of electrical charges disposed to project charges under the action of said field and charge collecting means disposed to collect the charges projected from said source, the distance over which said charges are subjected to the action of said iield being short compared to a quarter wave length corresponding to Said frequency and said field being of such magnitude that X-rays of substantial intensity are emitted from said collecting means when said charges impinge thereon.

3. Electric discharge apparatus comprising a hollow body resonator, means for impressing on said resonator an electromagnetic eld of a frequency corresponding to the resonant frequency of said resonator, a source of electrical charges disposed to project charges under the action of said field, charge collecting means disposed to collect the charges projected from said source, the distance over which said charges are subject to the action of said field being short compared to a quarter wave length corresponding to said frequency, and said neld being of such magnitude that X-rays of wave length less than .25 angstroms of substantial intensity are emitted from said collecting means when said charges impinge thereon.

4. Electric discharge apparatus comprising a hollow body resonator having a resonance wave pressing on said resonator an electromagnetic eld oi a frequency corresponding to the resonant frequency of said resonator. a source of electrical charges disposed to project charges under the action of. said eld, and charge collecting means disposed to collect the charges from said source, the distance over which said charges are subjected to said field being short compared to a quarter wave length corresponding to said frequency.

5. In combination, a hollow body resonator, a source of electric charges disposed to project charges through said resonator, an electrode for collecting said charges after they pass through said resonator, an oscillator for producing electromagnetic oscillations at a resonant wave length of said resonator coupled to said resonator to excite it, means for impressing on said oscillator a periodically pulsating potential for modulating its output and a blocking potential interposed between said source and said collecting electrode for blocking the iiow of charges to said collecting electrode during the portion of the periods of said modulating potential when its magnitude is below a predetermined magnitude.

6. In combination, a hollow body resonator, a source of electric charges disposed to project charges through said resonator, an electrode for collecting `said charges after they have passed through said resonator, an oscillator for producing oscillations at the resonant wave length of said resonator, means for exciting said oscillator to produce oscillations at said resonant wave length modulated at a period having a substantially longer wave length than said resonant wave length, means for coupling said oscillator to said resonator to excite said resonator and a blocking potential interposed between said source and said collecting electrode permitting the flow of charges during each period of the modulating frequency only for an interval of short duration compared to said period.

7. In combination, a hollow body resonator, a source of electric charges disposed to project charges through said resonator, an electrode for collecting said charges after they have passed through said resonator, an oscillator including electric discharge valve means having output circuit means for producing oscillations at the resonant wave length of said resonator, means for impressing in said output circuit means a periodic potential having a frequency substantially lower than that corresponding to said resonant wave length to excite said oscillator to produce oscillations at said resonant wave length modulated at said substantially lower frequency. means ror coupling said oscillator to said resonator to excite said resonator and a blocking potential interposed between said source and said electrode permittlngtne now of charges during each period of the modulating irequency only for an interval or' short duration compared to said period.

8. In combination, 'a hollow body resonator, a source or electric charges disposed to proJect charges through said resonator, an electrode disposed to collect said charges after they have passed through said resonator, an oscillator for producing electromagnetic oscillations at the resonant wave length or said resonator, means for coupling said oscillator to said resonator so that it impresses an electric eld at said resonant frequency on said charges, and means for length between 2 and 12 meters, means for imu blocking the iiow of electric charges between said source and said electrode when said electric field is below a predetermined magnitude.

9. Electric discharge apparatus comprising a hollow body resonator having a reentrant protuberance, means for establishing an electromagnetic iield Within said resonator of a frequency corresponding to the resonant frequency of said resonator, said protuberance having an inner end spaced from the opposite wall of said resonator a distance which is short compared to a quarter wave length corresponding to said frequency, a source of electrical charges disposed to project charges through the space between said protuberance end and said opposite wall, and charge collecting means disposed to collect said charges projected from said source.

10. Electric discharge apparatus comprising a hollow body resonator having a reentrant pro tuberance, means for establishing in said resonator an electromagnetic eld of a frequency corresponding to the resonant frequency of said resonator. said protuberance having an inner end spaced from the opposite wall of said resonator a distance which is short compared to a quarter wave length corresponding to said frequency, a source of electrical charges disposed to project charges under the action of said field from said `protuberance end to said wall. and charge collecting means constituting a portion of said wall disposed to collect said charges projected from said source.

11. Electric discharge apparatus comprising a hollow body resonator including a hollow enclosure having a reentrant conical protuberance with the axis of said protuberance parallel to the axis of said enclosure, the internal surface of said enclosure including the protuberance be' ing electrically conductive, means for establishing an electromagnetic field within said enclosure having a frequency corresponding to the resonant frequency oi.' said resonator, the inner end of said protuberance being spaced from the opposite wail of said enclosure a distance which is short compared to a quarter wave length corresponding to said frequency, a source of electrical charges disposed to project charges under the action of said field from said protuberance end to said opposite wall, and charge collecting means constituting a portion of said opposite wall disposed to collect said charges projected g5 from said source BENEDICT CASSEN.

DISCLAIMER 2,342,789.Benedz'ct Gassen, Pittsburgh, Pa. SUPERVOLTAGE X-RAY TUBE. Patent dated Feb. 29, 1944. Disclaimer led Feb. 16, 1945, by the assignee, Westinghouse Electric cf: lanufactur'i'ng Company. Hereby enters this disclaimer to claims 1 and 9 of said specification.

[Oficial Gazette March 27, 1.945]