US2898508A - Charged-particle accelerator - Google Patents

Description

Aug 4 1959 G. E. MALLlNcKRoD-r CHARGED-PARTICLE ACCELERATOR At, l r @i .1. Il I IIV lll (T ,n/

Filed June 13, 1957 A United States PatentfOflee Patented Aug. 4, 1959 2,898,568 l Y Y CHARGED-muriera ACCELERATOR George E. Mallinckrfodt, St. I'ious, Mo. Application June 13, 1957, Serial No. `665,527 6 claims. (ci. srs-5.42)

This invention relates to charged-partiele accelerators, and with regard to certain more lspecific features, to such accelerators in which charged particles are accelerated by means of the build-up and collapse of'magnetic fields.

Among the several objects of the invention may be noted the provision of a changed-particle accelerator which enables large electric accelerating forces to be applied to the charged particles so as to gain in a relatively short distance of particle movement a relatively large velocity of said particles and a correspondingly high charged-particle energy level; and the provision of' an accelerator of the class described the construction of which is simple and compact. Other objects and features will bein part apparent and in part pointed out hereinafter. Y

The invention accordingly comprises the constructions hereinafter described, the scope of the invention being indicated in the following claims.

In the accompanying drawings, in which several of various possible embodiments of theinvention are illustrated, v

Fig. 1 is a schematic diagram of the invention;

Fig. 2 is a cross section taken on lines 2 2 of Fig. 1; and,

Fig. 3 is a schematic diagram of a second embodiment of' the present invention.

Corresponding reference vcharacters indicate corresponding parts throughout the several views of the drawings. J

The present invention relates to a simplified form of linear accelerator. Referring now more particularly to Figs. l and 2, there is shown at numeral 1 a well evacuated tube or envelope of relatively nonconducting material such as glass, at one end of ,which is a conventional hot cathode 3 for generating charged particles to be ac# celerated, these particles in the present example being electrons. Although it is` not necessary to the operation of the invention to beam the electrons from the cathode, it is preferred that the' electrons emitted by cathode 3 be controlled, accelerated and focused into a beam by control grid 4 and focusing anodes 5, which are connected to power and potential sources in the -usual manner, well-known to those skilled in the art.

This electron source or beam of relatively low velocity l and energy level is directed more'or less along a central axis C-C of tube 1, the opposite end of which tube is closed by a Window of thin metallic foil such as indicated at 7. A number of coils 9 are positioned in spaced-apart relationship around tube 1. Each of these coils is made up of a number of turns or IC-shaped uniplanar (i.e. fiat) loops of conductive material such as copper tubing or wire arranged to define a'torus having its axis substantially coincident with the central axis of the tube 1. The loops 15 are connected electrically in parallel across two parallel ring-shaped electrical buses 11 and 13 by interconnection of the opposing ends of these loops respectively to these buses. These buses 11 and 13 are in turn connected in parallel across two power supplying leads 17 and 19. It will be noted that the planes of the loops 15 are normal to those of the bfuses 11 and 13.

A source of electrical energy for the yaccelerator apparatus is constituted by a condenser 21, which is connectable across leads 17 and 19 :by the closure of contacts 23 of a double-pole double-throw switch 25. A second set of contacts 27 of this switch is provided to complete an electrical charging circuit including a rectifier 29 series-connected with a secondary winding 31 of a transformer 33. A transformer primary winding 35 is connected to any conventional source of A.C.

Operation is as follows:

Energization of the cathode, grid and focusing anodes supplies electrons to the inner portion of the left-hand coil 9. Assuming that switch 25 is .in the position shown in Fig. 1 and that condenser 21 is fully charged, actuation of switch 25 will disconnect the condenser from its charging circuit and interconnect it to conductors 17 ,and 19, thus energizing coils 9 as the condenser is discharged. The discharge current flowing through the loops 15 of each of the coils 9 constitutes a first toroidal electric field which rapidly generates or builds up an annular or ring-shaped magnetic flux field around an axis substantially coaxial with that of the torus or coil 9, and that of the tube 1. This ring-shaped flux field is the resultant of the combined magnetic fields of each of the loops 15 as current fiows therethrough in the direction illustrated by the arrows in Fig. 1. The intensity of this annular magnetic field increases rapidly, resulting in a more or less tublular magnetic field being rapidly generated along the length of tube 1 between the cathode 3 and the window 7. By properly choosing the polarities of leads 11 and 13 as shown, this tubular magnetic field generates an electric field which is associated therewith. This electric field exerts an accelerating force on the electrons directed toward the center of the left-hand coil 9. Another way of viewing `this is that the tubular magnetic eld will Igenerate a second toroidal electric field interlinking it. The inner core of this electric field establishes a potential along the axis of the magnetic field, this potential providing the accelerating force above referred to.

This action guides and accelerates the electrons along axis C-C toward the window 7. In effect, the annular fields thus built up at each of coils 9 by the sudden discharge of condenser 21 therethrough can be considered as the fields induced by the primaries of a series of transformers, the stream of electrons along tube 1 acting as a single-turn secondary of each of these transformers It will be noted that the expansion of these ring-shaped magnetic fields is immediately followed by a sudden collapse of these fields, with oppositely polarized annular flux fields resulting. This action would cause an accelerating effect in the opposite direction along the axis C-C of tube 1 and away from window 7. Thus, it is preferred to pulse the electron source in any conventional way, such as by periodically decreasing the negative bias on grid 4 in synchronism with the actuation of switch 25, and thereby supply electrons only during the build-up of the ring-shaped fields (which compositely form the generally tubular magnetic field), and intermittently energizing coils 9 with a sufcient period of time therebetween to permit the recharging of condenser 2l..

By having a'suciently large condenser 21 charged to a sufficiently high potential and a sufficiently large number of tori 9, the accelerating force can be made very large, thus accelerating charged particles to a very high energy level as they are beamed from window 7. This beam can be directed against a target of heavy metal to form X-rays, or can be used directly to irradiate various materials. For example, if it is desired to produce a beam of a one m.e.v. energy level, forty tori 9 should be provided and condenser 21 should `be charged to about a 25 kv. potential level.

The acceleratorembodiment illustratedin Fig. 1 has the loops electricallyconnected in parallel to form each torus or coil 9. The reactanceparameters'of such coils 9 are quite low so .that the timerequired for discharge therethrough is short. Insome instances itmay be desirable to increase the time period for building vup the ring-shaped fields. One way this can be accomplished is to connect individual loops 15 of coils 9 in series as shown in Fig. 3 aroundagurative circle as indicated by the darts 32, thus forming a helix. In this embodiment, the opposite ends of the series-connected loops l5 of each toroid coil 9 are connected by leads 11A and 13A to a capacitor 21 via a set of contacts 23A. A single rectifier 29 and transformer 33, as in the previous embodiment, provide (via contacts 27A and wires 17A and 19A) the high potential D.C. to charge condensers 21', which are shunt-connected thereacross during the charging cycles.

Another set of contacts 28 is mechanically linked to contacts 27A. Contacts 28 are electrically connected across a portion of a voltage divider R, which in turn is energized from a bias supply with the polarity indicated. A slider of this resistor is connected to the grid 4 and normally supplies a negative biasing potential to grid 4 so as to cut off the flow of electrons to the focusing anodes. The contacts 28, 27A, and each of the sets of contacts 23A are actuated as diagrammatically illustrated by a switching unit S and an electric control D. For example, in View of the short electron transit time between adjacent coils 9 or 9', it is preferred that such electronic switches as vacuum tubes, or thyratrons, etc., be triggered individually or sequentially by electrical signals, as is well understood by those skilled in the art.

The operation of the Fig. 3 embodiment, although generally the same as explained above in regard to Figs. l and 2, differs in certain important aspects. For example, instead of discharging condenser 21 simultaneously through all of coils 9, in this instance controller D will actuate switch contacts 28, 27A and 23A in a timed sequence whereby (l) a portion of divider R is shunted by closing contacts 28 to decrease briefly the grid bias of the electron source and direct a pulse of electrons along tube axis C-C; (2) the charging circuit for condensers 21 is broken by the opening of contact-s 27A; and (3) each of the toroid coils 9 is connected across its respective condenser 21', one after the other, thus building up the annular fields as the pulse of electrons is increasingly accelerated along tube 1 toward Window 7. The principle of the build-up and collapse of the accelerating tubular field is the same as that disclosed above.

It will be understood that charged particles other than electrons (e.g., ions) could be utilized, and that energy sources other than a charged condenser, such as a charged inductance, and that means for switching the circuits other than mechanical switches, such as spark gaps or gas discharge tubes or equivalents thereof, may be used. Also, the number and relative positioning of the coils 9 and 9 can be modified to a considerable extent. For example, one, or ten, or more coils could be utilized, either with a common energy source or separate synchronously timed energy sources. The number of coils, the spacing, and the potentials of lthe energy sources are determined by the .circuitry parameters and the energy level of accelerator-charged particles desired. Additionally, the coils 9 and 9 need notbe linearly arrayed ybut could be disposed to form a circular, elliptical or helical acceleration path instead of being aligned on a straight center line C-C, as shown.

In view of the above, it will be seen that the several objects of the invention are achieved and other advantageous results attained.

As various changes could be made in the above constructions without departing from the scope of the invention, it is intended that'all Amatter contained in the above description or shown in the accompanying drawings shall be interpreted as illustrative and not in a limiting sense.

I claim:

l. A charged-particle accelerator comprising a plurality of coils, each coilhaving aplurality of C-shaped uniplanar loops of conductive material and a pair of parallel spaced apart ring-shaped electrical buses of conductive material, the opposing ends of each of said C- shaped loops Ybeing 'respectively electrically connected to said buses thereby defining a torus, the planes of each of said loops being normal to the planes of said parallel buses, means for supplying charged particles to the interior of one of said tori, said coils being positioned rela- 4 tive to .each other to establish a substantially predetermined path of acceleration for said charged particles, a plurality of sources of electrical energy, and means adapted to electrically connect said energy sources respectively to said coils in timed sequence whereby a generally tubular shaped magnetic field is produced which generates an electric field to accelerate the particles along said path.

2. A charged-particle accelerator as set forth in claim 1, wherein said means for supplying charged particles comprises a hot cathode adapted to supply pulses of electrons.

3. A charged-particle accelerator as set forth in claim 1, wherein the sources of electrical energy are charged condensers which supply a series of pulses of electrical energy'to each of said coils.

4. In a charged-particle accelerator having an evacuated envelope and means for supplying charged particles to the interior thereof; a coil comprising a pair of parallel spaced apart substantially ring-shaped bus bars of conductive material surrounding said envelope, said bus bars being connected to the extremities of a plurality of C-shaped uniplanar loops of conductive material, all of said loops being located on the same side of said bus bars with respect to the common axis thereof, the planes of said loops intersecting along said common axis, and a source of electrical energy adapted to be electrically connected to said coil whereby a ring-shaped magnetic field is produced around an axis substantially coaxial withfthat of said common axis and which field generates an electric field to accelerate the particles in a direction substantially parallel to said common axis.

5. In a charged-particle accelerator as set forth in claim 4, said means for supplying particles comprising a hot cathode adapted to supply pulses of electrons.

6. In a charged-particle accelerator as set forth in claim 4, said source of electrical energy comprising charged condensers which supply a series of pulses of electrical energy to said coil.

References Cite'd in the file of this patent UNITED STATES PATENTS 2,299,792 Bouwers Oct. 27, 1942 2,489,082 De Forest Nov. 22, 1949 2,593,845 Casimir i Apr. 22, 1952 FOREIGN PATENTS 855,502 France May 14, 1940

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