US3329848A - Particle accelerating tubes - Google Patents

Description

y 4, 1967 TAKESHI ADACHI ETAL 3,329,848

PARTICLE ACCELERATING TUBES 4 Sheets-Sheet 1 Filed Sept. 2, 1964 F l G. F

PRIOR ART FIG/2 PRIOR AR T v Maw am W311i KWW INVENTORj y 1967 TAKESHI ADACHI ETAL 3,329,848

PARTICLE ACCELERATiNG TUBES v Filed Sept. 2, 1964 4'Sheets-Sheet 2 INVENTORJ BY W y 1967 TAKES'HI ADACHI ETAL 3,329,848

PARTICLE ACCELERATING TUBES Filed Sept. 2, 1964 4 sheets-sheet 5 7376 7123 23 U 7 "r an n J A m LE 29.

INVENTORJ July 4, 1967 TAKESHI ADACHI ETAL 3,329,848

PARTICLE ACCELERATING TUBES Filed Sept. 2, 1964 4 Sheets-Sheet I r F I G. 9 5 5%, M

INVENTOR.

BY Q

United States Patent 3,329,848 PARTICLE ACCELERATING TUBES Takeshi Adachi, Kawasaki-ski, and Hiroshi Kamogawa,

Setagaya-ku, Tokyo, Japan, assignors to Tokyo Shibaura Electric (30., Mei, Kawasaki-ski, Japan, a corporation of Japan Filed Sept. 2, 1964, Ser. No. 393,980 Claims priority, application Japan, Sept. 5, 1963, 38/46,620; Sept. 27, 1963, 38/50,857; Sept. 30, 1963, 38/51,756; Oct. 15, 1963, 38/77,378

6 Claims. (Cl. 313-63) This invention relates to particle accelerating tubes and more particularly to particle accelerating tubes adapted to accelerate such particles as deuterium, electrons, etc., to generate neutrons, X-rays and the like.

Such particle accelerating tubes have been used in many fields in combination with a Cockcroft type, Van de Graaff type or resonance transformer type high voltage generating apparatus but still involve many problems to be solved.

Accordingly, it is the principal object of this invention to solve such problems.

A more specific object of this invention is to provide a novel particle accelerating tube having simplified construction so that it can be fabricated easily and at a low cost.

Another object of this invention is to provide a novel particle accelerating tube which is mechanically and thermally rigid.

Still another object of this invention is to provide a novel particle accelerating tube which is free from danger of electric shock.

Yet another object of this invention is to provide a particle accelerating tube having shorter length than the prior accelerating tube.

Further object of this invention is to provide a particle accelerating tube wherein an assembly of acceleration electrodes does not limit the evacuation path thereby enabling the attainment and maintenance of a high vacuum.

Still further object of this invention is to provide a novel accelerating tube including a plurality of assemblies of acceleration electrodes whereby enabling to operate continuously over a long period of time or accelerate different kinds of particles to generate neutrons, X-rays and the like.

Briefly stated, according to this invention a particle accelerating tube is provided comprising an insulator cylinder adapted to define therein an air-tight chamber, an assembly of acceleration electrodes eccentrically disposed in said air tight chamber in parallel to the axis of said insulator cylinder, a source of particles such as deuterons or electrons to be accelerated which is disposed outside of said air tight chamber but inside of said insulator cylinder, a target mounted outside of said air tight chamber on the side opposite to said source of particles, said electrode assembly, source of particles and said target being axially aligned, means to energize said source of particles and said acceleration electrodes, and means connected to said air tight chamber to evacuate said air tight chamber.

The electrode assembly constructed in accordance with this invention is a unitary cylindrical structure comprising a plurality of spaced electrodes each in the form of a circular disc having an opening at its center to pass said particles, a plurality of insulator sections interposed between adjacent electrodes, a plurality of voltage divider resistor sections interposed between adjacent electrodes, an end plate mounted on one end of the cylindrical structure, a focussing electrode disposed in said cylindrical structure adjacent to said end plate and a source of particles mounted on said end plate.

With this construction as the high potential electrode assembly is housed in an air tight vacuum chamber there is no high potential portion thereof exposed to the atmosphere so that not only the length of the accelerating tube can be decreased but also the construction of the electrode assembly can be greatly simplified. In addition, since the electrode assembly is not required to act as the evacuation duct, it is easy to attain and maintain the interior of the air tight chamber at a high vacuum.

According to a modification of this invention the length of the insulator cylinder is increased to house also an auxiliary electric source for the electrode assembly which may be provided with an electromagnetic shield. With this modification end plates mounted on the opposite ends of the insulator cylinder can be grounded so that control knobs, deuterium bomb, blower to circulate cooling air through the auxiliary source and the like can be conven iently mounted on one of said grounded end plates.

If desired, a plurality of electrode assemblies may be disposed in parallel within the insulator cylinder so as to operate continuously over a long period or to generate different kind of radiations such as neutrons and X-rays.

The above and other features of the invention which are believed to be new are set forth with particularity in the appended claims. The invention itself, however, together with further objects and advantages thereof may best be understood by reference to the following description when taken in conjunction with the accompanying drawings, in which:

FIG. 1 shows a diagrammatic side view of a prior art neutron generator;

FIG. 2 is a longitudinal sectional view of a prior particle accelerating tube;

FIG. 3 shows a side elevation, partly in section, of a neutron generator utilizing a particle accelerating tube constructed in accordance with this invention;

FIG. 4 shows an enlarged sectional view of the electrode assembly;

FIG. 5 shows a cross sectional view of the electrode assembly taken along a line VV in FIG. 4;

FIG. 6 shows another cross sectional view of the electrode assembly taken along a line VIVI in FIG. 5;

FIG. 7 shows a schematic view, partly in section, of a modified embodiment of this invention;

FIG. 8 shows a schematic cross sectional view of another embodiment of this invention taken along a line VIII-VIII in FIG. 9;

FIG. 9 is a schematic sectional view of another embodiment of the embodiment shown in FIG. 8; and

FIG. 10 is a schematic sectional view of a further modification of this invention.

Referring first to FIG. 1 of the accompanying drawings, there is shown a prior art neutron generating apparatus comprising a main body 1, a source of high potential 2 and a control device and the like not shown in the drawing. An acceleration tube 3 of the main body 1 is provided with an ion source 4 at one end thereof to produce deuterons and a tritium target 6 on the extension at the opposite end. The acceleration tube system is maintained at a high vacuum by means of a vacuum pump 7. In order to operate the ion source of electric supply, 5 is provided including a source of deuterium, a high frequency power source for ionizing deuterium, an electric power source for extracting ions and an electric power source for focussing ions. To support the acceleration tube in horizontal position there are provided a support 8 and an insulating bushing 10 which also serves to support the auxiliary source 5. As shown the source of high voltage 2 is connected to the auxiliary source 5 through a high voltage cable 5a, it being understood that these sources 2 and 5 are arranged to be controlled by a suitable control device not shown.

Referring now to FIG. 2 there is shown a longitudinal cross sectional view of a prior art acceleration tube of a neutron generating apparatus comprising a cylindrical insulating bushing 11 having a corrugated outer surface, a plurality of aluminum electrode plates 12 of frustoconical shape, metal flanges 13 and 14 provided at the base and top, respectively, an intermediate flange 15, an intermediate electrode 16 connected thereto and a potentiometer resistor 17 including a plurality of sections connected between adjacent electrode plates 12. The insulating bushing 11 includes a plurality of sections which are hermetically bonded together by a cementing material to form a unitary structure with each electrode plate sandwiched between adjacent insulator sections.

Generally the component elements of an acceleration tube can be classified into the following three categories depending upon their functions, viz. (a) a high voltage insulation, (b) a vacuum vessel and (c) a high voltage distribution electrode. More particularly, as is well known in the art the base flange 13 is maintained at the ground potential whereas a high voltage is impressed upon the top flange 14 so that the cylindrical insulating bushing 11 serves to insulate this high voltage. The hermetical acceleration tube is formed with a cylindrical inner surface which acts as a vacuum duct to exhaust the deuterium gas emitted from the ion source 4 mounted upon the top flange 14. Electrodes 12 and 16 and the potentiometer resistor 17 cooperate to form an electron lens system to focus and accelerate the deuterons emitted from the ion source.

As can be easily understood from the foregoing description, the prior acceleration tube is disadvantageous in that: (a) its construction is relatively complicated and requires many manufacturing steps, for example 123 man hours; (b) the tube is weak or brittle, not only thermally but also mecbhanically because it is fabricated from many component elements. More particularly, as the tube is supported in the horizontal position at one end only, as shown in FIG. 1, it will be subjected to strains due to gravity. Moreover, the tube is not thermally sound because it is fabricated by bonding together a number of parts having different thermal expansion coeflicients, and (c) the length of the acceleration tube is too long, for example, about 78 cm. long. While it is desirable to make as short as possible the length of the acceleration tube, actually the length is determined by considering such factors as the spacing between opposing electrodes in vacuum d e, the distance required to prevent creepage discharge in vacuum d s, the spacing between opposing electrodes in the atmosphere d e, the distance required to prevent creepage discharge in the atmosphere d s and the length dg determined by geometrical conditions. As a number of electrodes and insulator sections are involved the overall length of the tube should not be smaller than the maximum value of any one of id e zd s, Ed e, Zd s and Zdg. Thus for example, in order to withstand high voltage of 200 kv. in a high vacuum of 10 mm. Hg and in the atmosphere of high humidity said spacings or distances are selected substantially as follows:

Thus, as the electrodes are exposed to the atmosphere, the overall length of the acceleration tube is necessarily long as governed by the length of d s which is the maximum.

(d) Further disadvantage of the prior acceleration tubes is that the tube itself disturbs evacuation. More particularly, in the particle acceleration apparatus of the type referred to above the acceleration tube constitutes the evacuation passage since the evacuation pump is usually connected to the grounded side of the tube and on the high voltage side thereof is positioned the ion source which is the principal source of gas leakage. From the standpoint of the evacuation passage the conductance C is represented by an equation (where D denotes the diameter of the tube and L the length thereof) so that it is desirable to make as large as possible the diameter and as short as possible the length.

(e) Another disadvantage is that as a number of high potential elements are exposed to the atmosphere as shown in FIG. 2 the characteristic of the tube is affected by the condition of the atmosphere.

(f) Finally, as the electrode plates are exposed to the atmosphere it is necessary to provide hoops as at 18 in FIG. 2 in order to prevent corona discharge in the atmosphere. Moreover, as the inside diameter of the tube is smaller than the electrode spacing the configuration of the electrodes should be such that they can effectively shield the inner surface of the insulator. In the example shown in FIG. 1 the electrode plates are frustoconical shaped.

As mentioned above the principal object of this invention is to eliminate all of these disadvantages encountered in the prior particle acceleration tube.

Turning now to FIG. 3 illustrating a neutron generating apparatus utilizing a novel acceleration tube of this invention there is shown an insulator cylinder 21 having sufl'iciently large internal diameter, for example about 30 cm. The cylinder has a terminal plate 24 mounted upon one end thereof through a flange 23a and a terminal plate 26 mounted upon the opposite end through a flange 230. Between the opposite ends, the cylinder 21 is provided with an inwardly projecting flange 23b adapted to support an intermediate terminal plate 25. Assuming now that the length of a hermetical chamber 20 defined by the cylinder 21 and each of two terminal plates 24 and 25- is equal to 1 then the position of the intermediate flange 23b can be determined by an equation l D s=2d s. On the side of the terminal plate 24 opposite to the mounting flange 23a is secured a base plate 24a. A target 27 is secured to the outer end of a target holder 28 which is hermetically connected to the terminal plate 24 at the inner end. The interior of the cylinder 21 is evacuated by a suitable evacuating device such as a diffusion pump 70 and a rotary pump 7d which are connected to another opening through the terminal plate v24 via a connection pipe 7a and one or more valves 7b. Mounted on the terminal plate 25' is an ion source 4, which as well as the target holder 28 is preferably parallel to the longitudinal axis of the cylinder 21. An electrode assembly 22, the detail thereof being shown in FIG. 4, is interposed in the hermetical chamber 20 between the ion source 4 and the target holder 28 in coaxial relation therewith. An insulated terminal 30 of a lens electrode 29 extends through the intermediate terminal plate 25 for connection to the ion focussing source contained in the auxiliary source 5.

Referring now to FIG. 4 which is an enlarged longitudinal sectional view of the electrode assembly 22, a plurality of aluminum plates 31 are provided each having a thickness of about 2 to 3 mm. and a perforation 32 of about 30 mm. diameter at its center. Electrode plates 31 and rod shaped insulator sections 37 are successively clamped together by means of clamping screws 37a to complete an integral cylinder. Electrode plates 33 and 34 having cylindrical outward projections are connected to the respective ends of the cylinder by means of bolts 37b and each of the potentiometer resistor sections 38 interposed between electrode plates 31 is connected to the electrode plates 33 and 34 through screws 38a and 3811. An electrode plate 25 closest to the ion source 4 is electrically connected to and mechanically supports a cylindrical focussing electrode 29. Instead of fabricating the electrode assembly by alternately laminating insulator section 37 and electrode plates 31, it may be fabricated by molding a suitable resin such as an epoxy resin to secure the electrode plates in parallel at uniform spacings and in coaxial relation.

The acceleration tube of this invention can maintain higher vacuum than prior acceleration tubes. More particularly, as has been pointed out hereinabove, the space 20 defined by the insulator cylinder 21 and metal terminal plates 24 and 25 is maintained at a high vacuum by the evacuating devices 7c and 7d in FIG. 3. With this construction, however, the electrode assembly 22. inserted in the cylinder 21 does not act as an evacuation duct but the whole space 20 acts for that purpose, thus enabling to attain higher vacuum than the conventional acceleration tube even at its ion emitting source.

Moreover, as the connection to the evacuation pumps is located eccentrically with respect to the longitudinal axis of the acceleration tube it is able to locate the target closer to the acceleration electrodes to increase the yield of neutrons.

Further, according to this invention the ion source 4, the electrode assembly 22 and the target holder 28 are aligned, the ion source 4 is operated to emit deuterium ions (deuterons) along the axis of the electrode assembly and the accelerating high voltage impressed upon the terminal plate 25 and the focussing voltage impressed upon the lens electrode 29 for focussing are uniformly distributed among the respective electrodes of the electrode assembly 22 so that deuterons are effectively focussed and accelerated to bombard the target 27 to generate neutrons at a high efiiciency. The high voltage applied to the terminal plate 25 is insulated by the insulator outer cylinder 21. The insulating distance in the atmosphere between the terminal plate 25 and the grounded plate 24 is designed to be larger than that in vacuum.

The functions of high voltage insulation, defining a vacuum vessel and distributing high voltage among various electrodes required in the acceleration tube are shared among various component elements, that is the required high voltage insulation is provided mainly by the insulator cylinder, the vacuum vessel is defined by the insulator cylinder 21 and the electrode assembly acts as high voltage distributing electrodes.

In the acceleration tube constructed in accordance with this invention the construction of the acceleration electrodes can be simplified because it is not required to act as an evacuation duct as has been the practice in the conventional acceleration tube. Further, as the electrode plates are not exposed to the atmosphere it is not necessary to provide corona preventing hoops 18 as shown in FIG. 2. Moreover, the overall length of the electrode assembly 22 can be greatly reduced because it is not necessary to construct the electrode plates to act as the shield for the insulating cylinder and because the spacing between electrodes can be determined by merely taking into consideration the insulation condition in vacuum.

Secondly, as the acceleration tube can be easily maintained at a high vacuum it is able to reduce the capacity of the evacuation pump. Thirdly, as the exhaust port is positioned eccentric with regard to the axis of the acceleration electrode, it is able to mount the target closer to the electrode assembly whereby to increase the yield of neutrons.

Fourthly, as the high voltage portion exposed to the atmosphere is limited to only one, it is not necessary to provide a corona shield such as hoops 1 8 in- FIG. 2.

FIG. 7 shows a longitudinal section of a modification of this invention in which the length of the insulator bushing 21 is made long enough not only to accommodate an electrode assembly 22 but also an auxiliary source. More particularly, to the right of an electrode plate 25 which defines a vacuum chamber is housed an auxiliary source including a source of high voltage 47 and an insulating transformer 48. A bomb 41 containing deuterium supplies deuterium to an ion source 4 via a conduit 42. A cooling fan 45 also mounted on the outside of an end plate 40 which closes the open end of the insulating bushing 21 supplies cooling air to the auxiliary source via a conduit 46. As schematically shown in the drawing the auxiliary source is arranged to be controlled by control knobs 44 mounted on the end plate 40.

With this construction the electrode assembly 22 and the auxiliary source of high voltage therefor are enclosed in the insulating bushing so that no part of high potential is exposed to the atmosphere. As both end plates 24 and 40 can be grounded, the apparatus is free from the danger of electric shock. If required, either the source of high voltage 47 or the insulating transformer 48 may be located outside of the bushing and can be connected to the other component contained in the bushing through a high voltage casble.

FIGS. 8 and 9 show further modification of this invention wherein two electrodes assemblies 50 and 51 identical with that shown in FIG. 3 are arranged in parallel in a vacuum chamber 52 defined by end plates 53, 54 and an insulating cylinder 55 and evacuated by an evacuation pump 56. In this modification, the electrode assemblies 50 and 51 may be used to accelerate particles of different types. For example, the electrode assembly 50 is provided with a source of ions 57 which may be identical with the source 4 while the electrode assembly 51 has an electron gun 58. Auxiliary sources 59 for these particle accelerating devices may be disposed in the insulating cylinder 55 in the same manner as in FIG. 7. Thus, the electrode assemblies 50 and 51 can selectively produce either neutrons or X-r-ays, respectively, by a mere switching operation of the electric sources. If the sources of particles 57 and 58 are both electron guns the area of irradiation can be doubled by concurrent energization of these particle sources. Since fabrication of -a plurality of electrode assemblies can be made relatively easily at low cost, provision of them in a common single insulating cylinder greatly reduces the overall size and cost of the apparatus. Moreover, it is able to continuously operate the apparatus by successively utilizing a plurality of particle accelerators, Without the necessity of renewal of broken filaments.

The combination of particles sources may be of any one of ion-ion, ion-electron and electron-electron combinations. This modification can be embodied in any one of various particle accelerating devices or neutron generators of Cockcroft Walton type, Van deGraaff type and resonance transformer type.

While in the above embodiments the accelerating apparatus have been shown horizontally, it is obvious that they can be disposed vertically. In the latter case it is able to reduce the height of the building which houses the accelerator.

It is thus apparent that this invention provides a novel particle accelerating tube, which is simple and cheap in construction, free from the danger of electric shock, can easily attain and maintain high vacuum and has shorter length than the prior art tube.

While this invention has been shown and described in connection with preferred embodiments thereof it will be obvious that this invention is by no means limited thereto but various alterations and modifications can be made without departing from the true scope and spirit of the invention as defined in the appended claims.

What is claimed is:

1. A particle accelerating tube comprising a cylinder of insulating material forming an air-tight chamber,

a plurality of accelerator electrode assemblies disposed in said air-tight chamber and open to said air-tight chamber,

each of said accelerator electrode assemblies having a plurality of plates having openings therethrough,

fastening means joining said plates into a unitary cylindrical structure,

a target respectively associated with each of said accelerator electrode assemblies,

7 and a source of particles mounted in axial alignment with each of said targets and the openings in said plurality of plates of each of said accelerator electrode assemblies. 2. The particle accelerating tube of claim 1, further characterized by said source of particles including a plurality of separate particle sources, each of said accelerator electrodes assemblies mounted in co-extensive relationship with the other of each of said accelerator electrode assemblies. 3. The particle accelerating tube of claim 2, further characterized by an evacuating pump connected at one end of said air- 'ght chamber, and said accelerator electrode assemblies eccentrically disposed in said air-tight chamber with respect to the axis of said cylinder. 4. The particle accelerating tube of claim 1, further characterized by said source of particles including a plurality of separate ion sources. 5. The particle accelerating tube of claim 1, further characterized by said source of particles including at least one ion source, and at least one electron source. 6. The particle accelerating tube of claim 1, further characterized by said source of particles including a plurality of separate electron sources.

References Cited UNITED STATES PATENTS 2,151,559 3/1939 McEachron 315-59 2,570,158 10/1951 Schissel 31363 2,762,941 9/1956 Turner 313-63 3,022,933 9/1959 Ellis 230-69 DAVID J. GALVIN, Primary Examiner.

Claims (1)

1. A PARTICLE ACCELERATING TUBE COMPRISING A CYLINDER OF INSULATING MATERIAL FORMING AN AIR-TIGHT CHAMBER, A PLURALITY OF ACCELERATOR ELECTRODE ASSEMBLIES DISPOSED IN SAID AIR-TIGHT CHAMBER AND OPEN TO SAID AIR-TIGHT CHAMBER, EACH OF SAID ACCELERATOR ELECTRODE ASSEMBLIES HAVING A PLURALITY OF PLATES HAVING OPENINGS THERETHROUGH, FASTENING MEANS JOINING SAID PLATES INTO A UNITARY CYLINDRICAL STRUCTURE

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