US3274502A

US3274502A - Particle accelerator

Info

Publication number: US3274502A
Application number: US246449A
Authority: US
Inventors: Pinel Jacques; Mourier Georges
Original assignee: CSF Compagnie Generale de Telegraphie sans Fil SA
Current assignee: Thales SA
Priority date: 1962-01-10
Filing date: 1962-12-21
Publication date: 1966-09-20
Anticipated expiration: 1983-09-20
Also published as: GB976677A; FR81627E; DE1197995B; FR1318737A

Description

Sept. 20, 1966 J. PINEL ETAL 3,274,502

PARTIGLE ACCELERATOR Filed Dec. 21, 1962 2 Sheets-Sheet 1 C I a w.

, FIGZ I NV ENTORS G-MDUR/ER 21 J PINEL ATTORNEY Sept. 20, 1966 J. PINEL ETAL 3,274,502

PARTICLE ACCELERATOR Filed Dec. 21, 1962 2 Sheets-Sheet 2 1O FIG.4 9 6 INVENTORS G-HOl/RIER d J- PINEL ATTORNEY United States Patent 3,274,502 PARTICLE ACCELERATOR Jacques Pinel and Georges Mourier, Paris, France, as-

signors to CSF Compagnie Generale de Telegraphic Sans Fil, Paris, France Filed Dec. 21, 1962, Ser. No. 246,449 Claims priority, application France, Jan. 10, 1962, 884,375, Patent 1,318,737; May 3, 1962, 896,281 8 Claims. (Cl. 328234) The present invention relates to accelerator devices for charged particles, such as protons, etc., and more particularly relates to accelerators of the cyclotron type.

In the cyclotrons, the particles describe spirally-shaped paths or trajectories on the inside of an accelerating chamber composed of two semicylindrical throughs usually called Ds or Dees, separated by a slight interval, the form of the trajectories as paths being due to the action (1) of a direct-current or constant magnetic field which imparts to the particles a circular movement with a radius proportional to the speed thereof, and (2) of a high-frequency electric field, established between the'two Us in such a manner as to accelerate the particles while they pass from one D to the other.

With such classical arrangement, the accelerating action of the high frequency extends therefore only over a minute portion of an entire cycle of the trajectory, that is of the period during which a particle describes 'a complete angle of 21r.

The present invention has for its object an improved cyclotron, characterized by a new arrangement in which the charged particles are subjected to the action of a highfrequency electric field during the entire duration of the trajectories or paths thereof, or at least during the major portion of these trajectories.

Consequently, a cyclotron according to the present invention, which comprises an accelerating chamber placed within the air gap of an electromagnet, a source of charged particles on the inside of the accelerating chamber, and means for accelerating the particles with the aid of a high-frequency electric field perpendicular to the magnetic field produced by the electromagnet, is characterized by an arrangement enabling the said electric field to exert its effect throughout the entire space comprising the trajectories of the particles or at least within the major portion of this space.

In the novel arrangement according to the present invention the accelerating chamber is no longer divided into separate Us or Dees.

According to a preferred mode of construction of the present invention, the high-frequency electric field is produced on the inside of the accelerating chamber with the aid of a delay structure coupled in any suitable manner to a high-frequency generator.

A cyclotron thus modified in accordance with the teachings of the present invention presents a certain number of advantages and particularly an improved output and a current of utilizable particles of increased density due to the fact, in contrast to the classical constructions of cyclotrons, that the novel arrangement according to the present invention assures to the flux or flow of particles an important and significant phase focusing action.

Accordingly, it is an object of the present invention to provide a particle accelerator, particularly of the cyclo tron type, which assures an improved output as compared to that realizable with the known prior art constructions.

It is another object of the present invention to provide a cyclotron .particle accelerator in which the particles are subjected along most if not all the trajectories or paths thereof to a high-frequency electric field thereby improving the performance of the device.

Still another object of the present invention resides in the provision of a cyclotron-type particle accelerator which is simple in construction, obviates the need for separated Dees and permits a significant phase focusing within the particle flux.

These and other objects, features and advantages of the present invention will become more obvious from the following description when taken in connection with the accompanying drawing which shows, for purposes of illus tration only, several embodiments in accordance with the present invention, and wherein FIGURE 1 is a schematic cross sectional view through a cyclotron according to the present invention, taken along line II of FIGURE 2;

FIGURE 2 is a schematic cross sectional view through the cyclotron illustrated in FIGURE 1, taken along line IIII of FIGURE 1;

FIGURE 3 is a perspective view illustrative of the known prior art sector focusing systems in relativistic cyclotrons;

FIGURE 4 is a schematic cross sectional view through a relativistic cyclotron according to the present invention,

taken along line IVIV of FIGURE 5;

FIGURE 5 is a schematic cross sectional view of the relativistic cyclotron illustrated in FIGURE 4, and taken along line VV of FIGURE 4, and

FIGURE 6 is a cross sectional view of a modified embodiment of a relativistic cyclotron according to the present invention.

Referring now to the drawing wherein like reference numerals are used throughout the various views to designate like par-ts, and more particularly to FIGURE 1 and 2, there is illustrated in these two figures an accelerating chamber 1 of parallellepipedic form, evacuated and placed within the air gap of an electromagnet 2 having

pole pieces

3 and 4 of circular cross section.

To the inside of the accelerating chamber 1 are secured two series of

arrays

5 and 6 of straight, parallel, metallic bars forming a wave guiding or wave delaying structure.

A source of charged particles, for example, protons,

schematically illustrated in the drawing and designated therein by reference numeral 7, is disposed between these two

arrays

5 and 6 within the central region of the chamber 1.

The delay structure which is composed of the two

arrays

5 and 6, is coupled to a conventional high frequency generator (not illustrated) which produces a signal having a wavelength x.

The electromagnet 2 is realized, as in the conventional cyclotrons, in such a manner, as to supply a magnetic field H satisfying the relation w: (e/m)H, which e and m are, respectively, the charge and the mass of the particles, and w=21rF, F being the frequency corresponding to the utilized wavelength )t.

By having recourse to a wellknown technique, the two

arrays

5 and 6 are excited in the fundamental mode, that is the O-mode, and the necessary steps are taken to obtain between the points A and B a stationary wave, preferably with a node at the center and antinodes of voltage at the two extremities.

One realizes thus within the space comprised between the two series of bars 5 and 6 a high frequency electric field, directed alternately from A toward B and from B toward A of which the intensity varies at the frequency F.

The charged particles, designated in the drawing by reference numeral 8, are therefore subjected, on the one hand, to the action of the magnetic field of the electromagnet 2, exactly as in conventional classic cyclotrons, and, on the other, according to the present invention, to the permanent action of a high frequency field of which the lines of force are perpendicular to the magnetic field, the action of the high frequency field being effective throughout the entire space covered by the particles, or at least within the major portion of the space.

Under these conditions, the paths or trajectories of the particles within the accelerating chamber deviate within a certain measure from the regular spiral form of the classic cyclotrons but, in return, both calculations and tests show that there is produced instead a very important phase focusing effect.

It is necessary in that connection to recall that in the classic cyclotrons the particles present within the accelerating chamber do not all have an identical fate. Those among the particles which traverse the interval separating the Dees exactly at the moment at which the high-frequency field manifests itself therein with the maximum intensity and in the proper direction, that is in the same direction as the movement of the particles, are accelerated under the best conditions. On the other hand, those of the particles which arrive slightly ahead or slightly after this optimum moment are accelerated to a lesser degree. The particles which arrive thereat when the high frequency field becomes zero prior to the reversal of its direction do not undergo of course any modifications in speed, and finally those which arrive later in time and encounter a field of direction opposed to the movement thereof are obviously decelerated. It follows from these phase differences of the various particles that only a portion among them normally finds itself regularly accelerated and are able to reach the output of the cyclotron. Hence, one normally obtains an output from the overall installation of the prior art system that is relatively little satisfactory.

In the improved cyclotron according to the present invention, the electric field is present all along the trajectories of the charged particles on their movement in the acceleration chamber. At each point of the trajectory the electric field may be considered as the geometrical sum of a tangential component, which is tangent to the trajectory, and a centrifugal or radial component which is perpendicular to the tangential component. This radial component of the high frequency electric field increases the tangential speed of the particles delayed with respect to those of optimum phase and diminishes those particles which are ahead. The particles thereby group themselves into chapelets about those among them which have the best phase, and the ratio of the numbers of particles used to nonused particles is considerably increased in comparison with what has been noted in cyclotrons known heretofore.

The described arrangement according to the present invention therefore provides an improved output and permits the realization of particle currents with an increased intensity.

The present invention is applicable to cyclotrons of all energies. Nevertheless, the present invention presents a particular interest in the case of so-called relativistic cyclotrons in which the particles acquire very high energies rendering the relativistic variation of the mass thereof non-negligible.

It is known that in the relativistic cyclotrons the dual difiiculty of focusing the accelerated particles and to maintain the movement thereof in phase With the high frequency accelerating field has been resolved in a satis factory manner by the use of a magnetic field having alternate gradients. A well-known realization of this principle is the so-called sector focusing system which consists of adding to the pole pieces of the magnet or of the electromagnet ferromagnetic sectors, generally curved in spiral shape and separated by intervals of the same shape, whereby the common apex of all the sectors is located at the center of the pole pieces. There are thus produced between the pole pieces, zones with a strong field, so-called hills or crests alternating with zones with a weak field, so-called valleys whereby the air gap is shorter in the former than in the latter.

The focusing is therefore realized in prior art relativistic cyclotrons by a modification of the structure of the pole pieces of the magnet or of the electromagnet of the primitive cyclotron, that is, of the nonrelativistic cyclotron.

Within a cyclotron according to the present invention, it is possible to produce a magnetic field with alternating gradients or zones Without modifying the pole pieces but by arranging the accelerating chamber, and more particularly the delay structure disposed within this chamber in an appropriate manner.

Since the delay structure is composed of bars made of non-ferrous metal, which is a good conductor of electricity, the improvement according to the present invention consists in utilizing hollow bars containing on the inside thereof pieces of ferromagnetic metal in such a manner as to create within the accelerating chamber zones with iron to obtain a relatively strong magnetic field alternating With zones Without iron to obtain a relatively Weak magnetic field.

FIGURE 3 illustrates the known principle of sector focusing by showing in perspective view a .pole piece 11 on which are fixed sectors of ferromagnetic metal 12, separated by intervals 13. Facing the sectors 12 are obtained zones having relatively strong field or hills, and facing the intervals 13 are obtained zones with a relatively weak field or so-called valleys.

FIGURE 4 which is a cross sectional view taken along line IV-IV of FIGURE 5, and FIGURE 5 which is a. cross sectional view along line V--V of FIGURE 4 illustrate in what manner a substantially sector focusing is realized in a cyclotron according to the present invention. In this type of cyclotron, the accelerating chamber 1 encloses a delay structure composed of two superposed arrays of

bars

5 and 6, made of non-ferrous metal, that is a good electrical conductor, such as, for example, cop- The

bars

5 and 6 are hollow, and on the inside thereof are disposed ferromagnetic pieces 9, the length of the various pieces and the position thereof being chosen in such a manner as to fill zones defined by spirally-curved sectors. The common apex or point of intersection of the sectors is located within the axis of the accelerating chamber 1 which is also the axis of the pole pieces of which the surface is indicated by the circle 10 in dash lines.

With such an arrangement, the lines of force of the magnetic field, produced by the pole pieces of the magnet encounter within the accelerating chamber zones alternately with and without iron, which in turn, causes the intensity of the magnetic fiux to have alternately very strong and very weak values that is hills or crests for those spaces with iron and valleys for those without iron. One obtains thus a focusing that is substantially equivalent to that supplied by the known system illustrated in FIG- URE 3.

In the modified embodiment illustrated in FIGURE 6, the

hollow tubes

5 and 6 are filled with ferromagnetic cores along the entire length thereof except within the central zone of the accelerating chamber, indicated by the circle shown in dash lines in the drawing.

This embodiment does not show a sector focusing such as FIGURES 4 and 5 but the arrangement of FIGURE 6 is of great simplicity and permits production of a magnetic field with alternating gradients or zones furnishing a very satisfactory focusing action in relativistic cyclotrons.

It should also be noted that there also exists an interest with the embodiment of FIGURE 6 to diminish progressively the transverse cross section of the ferromagnetic cores at the end or extremities adjacent the central zone of the chamber in order to render progressive the variation of the field between the zone with iron and the zone without iron.

Irrespective of the particular construction, it may be readily seen that the present invention permits utilization of shorter air gaps than those constituted by the pole pieces according to FIGURE 3. However, it is known that the reduction of the air gap permits a reduction also of the general dimensions of the magnet and further leads to an appreciable economy in the cost of production and ovenall dimensions of the installation.

While We have shown and described several embodiments in accordance with the present invention, it is understood that the same is not limited thereto but is susceptible of numerous modifications and changes as known to a person skilled in the art, and we therefore do not wish .to be limited to the detail shown and described herein but intend to cover all such changes and modifications as are encompassed by the scope of the appended claims.

We claim:

1. A cyclotron comprising: an acceleration chamber,

a source of charged particles located substantially within the center of said chamber, first means for establishing within said chamber a constant unidirectional magnetic field, and second means for establishing a high frequency electric field substantially perpendicularly to said magnetic field substantially within the entire interor space of said chamber including a wave delaying structure disposed within said chamber, and a source of high frequency coupled to said delay structure, said delay structure including two series of substantially parallel bars disposed adjacent to substantially the entire path of said charged particles in planes on either sides thereof substantially perpendicular to said magnetic field.

2. A cyclotron comprising: an acceleration chamber, a source of charged particles located substantially Within the center of said chamber, first means for establishing within said chamber a constant magnetic field, and second means for establishing a high frequency electric field substantially perpendicularly to said magnetic field substantially within the entire interior space of said chamber including a wave delaying structure disposed within said chamber, and a source of high frequency energy coupled tosaid delay structure, said delay structure including two series of substantially parallel bars made of a nonferrons metal and disposed in two planes substantially perpendicular to said magnetic field, said bars being hollow, and predetermined portions thereof being filled with ferromagnetic cores to form within the acceleration chamber zones with iron alternating with zones without iron whereby the magnetic field configuration has alternate zones of relatively high and low intensities, respectively.

3. A cyclotron comprising: an acceleration chamber, a source of charged particles located substantially Within the center of said chamber, first means for establishing within said chamber a constant magnetic field, and second means for establishing a high frequency electric field substantially perpendicularly to said magnetic field substantially within the entire interior space of said chamber including a wave delaying structure disposed within said chamber, and a source of high frequency energy coupled to said delay structure, said delay structure including two series of substantially parallel bars made of a nonferrons metal and disposed in two planes substantially perpendicular to said magnetic field, said bars being hollow, and predetermined portions thereof being filled with ferromagnetic cores to form within the acceleration chamber zones with iron alternating with zones without iron whereby the magnetic field configuration has alternate zones of relatively high and low intensities, respectively, and said zones being substantially sector-shaped. so as to provide a sector-type focusing suitable for use in relativistic cyclotrons.

4. A cyclotron comprising an acceleration chamber, a source of charged particles located substantially within the center of said chamber, first means for establishing within said chamber a constant magnetic field, and second means for establishing .a high frequency electric field substantially perpendicularly to said magnetic field substantially Within the entire interior space of said chamber including a wave delaying structure disposed within said chamber, and a source of high frequency energy coupled to said delay structure, said delay structure including two series of substantially parallel bars made of a nonferrons metal and disposed in two planes perpendicular to said magnetic field, said bars being hollow, and predetermined portions thereof disposed outside of the central area of said chamber being filled with ferromagnetic cores to form within the acceleration chamber zones with iron and at least one zone without iron whereby the magnetic field configuration has zones of relatively high and low intensities, respectively.

5. A cyclotron comprising: an acceleration chamber, means providing a source of charged particles within said chamber, and means for accelerating the particles within said chamber while simultaneously therewith producing a phase focusing action including first means for establishing within said chamber a magnetic field and second means having a wave guiding structure for establishing a high frequency electric field substantially perpendicularly to said magnetic field with said electric field prevailing at least throughout the major portion of the interior space of said chamber through which move said particles, and means including said wave guiding structure for produc ing strong and weak Zones in said magnetic field.

6. A cyclotron comprising: an acceleration chamber, means effectively providing a source of charged particles approximately within the center of said chamber, first means for establishing within said chamber -a magnetic field, and second means for establishing a high frequency electric field substantially perpendicularly to said magnetic field throughout at least a major portion of the interior space of said chamber including a wave guiding structure made of a material that is substantially non-magnetic and good electrical conductor, and means associated with said wave guiding structure for effectively providing within the acceleration chamber zones of relatively high and low magnetic field intensities.

7. A cyclotron comprising: an acceleration chamber, mean-s providing a source of charged particles within said chamber, and means for accelerating the particles within said chamber while simultaneously therewith producing a phase focusing action including first means for establishing within said chamber a magnetic field and second means having a wave guiding structure for establishing a high frequency electric field substantially perependicularly to said magnetic field with said electric field prevailing at least throughout the major portion of the interior space of said chamber through which move said particles, and means including said wave guiding structure for producing strong and weak zones in said magnetic field with substantially uniform air gaps.

8. A cyclotron comprising: an acceleration chamber, means for establishing within said chamber a constant unidirectional magnetic field, a wave guiding structure composed of two arrays of straight, substantially parallel, metallic bars disposed within said chamber in two planes substantially perependicular to said magnetic field, a source of charged particles located substantially within the center of said chamber between said two planes, and a source of high-frequency energy coupled to said wave guiding structure for establishing between the bars of each array a highfrequency electric field perpendicular to the bars and substantially perependicular to said magnetic field.

References Cited by the Examiner UNITED STATES PATENTS 2,229,572 1/1941 Jonas 313-62 X 2,579,315 12/1951 Gurewitsch 3 l362 X 2,881,348 4/1959 Palluel 3153.6 2,926,279 2/1960 Gallop 31539.3 X 2,933,639 4/1960 Lally 315-3.6 3,129,356 4/1964 Phillips 315--3.5 X

JAMES W. LAWRENCE, Primary Examiner.

DAVID J. GALVIN, GEORGE N. WESTBY, Examiners.

R. DZIURGOT, R. JUDD, Assistant Examiners.

Claims

1. A CYCLOTRON COMPRISING: AN ECCELERATION CHAMBER, A SOURCE OF CHANGED PARTICLES LOCATED SUBSTANTIALLY WITHIN THE CENTER OF SAID CHAMBER, FIRST MEANS FOR ESTABLISHING WITHIN SAID CHAMBER A CONTANT UNDIRECTIONAL MAGNETIC FIELD, AND SECOND MEANS FOR ESTABLISHING A HIGH FREQUENCY ELECTRIC FIELD SUBSTANTIALLY PERPENDICULARLY TO SAID MAGNETIC FIELD SUBSTANTIALLY WITHIN THE ENTIRE INTERIOR SPACE OF SAID CHAMBER INCLUDING A WAVE DELAYIUNG STRUCTURE DISPOSED WITHIN SAID CHAMBER, AND A SOURCE OF HIGH FREQUENCY COUPLED TO SAID DELAY STRUCTURE, SAID DELAY STRUCTURE INCLUDING TWO SERIES OF SUBSTANTIALLY PARALLEL BARS DISPOSED ADJACENT TO SUBSTANTIALLY THE ENTIRE PATH OF SAID CHARGED PARTICLES IN PLANES ON EITHER SIDES THEREOF SUBSTANTIALLY PERPENDICULAR TO SAID MAGNETIC FIELD.