EP0128052A1 - Cyclotron with defocusing system - Google Patents

Cyclotron with defocusing system Download PDF

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Publication number
EP0128052A1
EP0128052A1 EP84400682A EP84400682A EP0128052A1 EP 0128052 A1 EP0128052 A1 EP 0128052A1 EP 84400682 A EP84400682 A EP 84400682A EP 84400682 A EP84400682 A EP 84400682A EP 0128052 A1 EP0128052 A1 EP 0128052A1
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Prior art keywords
coils
narrow
air gap
gap
zones
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German (de)
French (fr)
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EP0128052B1 (en
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Gabriel Meyrand
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CGR MEV SA
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CGR MEV SA
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    • H—ELECTRICITY
    • H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
    • H05H—PLASMA TECHNIQUE; PRODUCTION OF ACCELERATED ELECTRICALLY-CHARGED PARTICLES OR OF NEUTRONS; PRODUCTION OR ACCELERATION OF NEUTRAL MOLECULAR OR ATOMIC BEAMS
    • H05H13/00—Magnetic resonance accelerators; Cyclotrons
    • H05H13/005—Cyclotrons
    • H—ELECTRICITY
    • H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
    • H05H—PLASMA TECHNIQUE; PRODUCTION OF ACCELERATED ELECTRICALLY-CHARGED PARTICLES OR OF NEUTRONS; PRODUCTION OR ACCELERATION OF NEUTRAL MOLECULAR OR ATOMIC BEAMS
    • H05H13/00—Magnetic resonance accelerators; Cyclotrons

Definitions

  • the invention relates to a cyclotron with a focus-defocus system making it possible to substantially increase the limit of admissible power when the target is placed inside the accelerating structure.
  • An isochronous cyclotron is an accelerator of charged particles (generally protons) which consists of an electromagnet comprising two pole pieces occupying the two axial faces, that is to say perpendicular to the axis, of an accelerating cavity, cylindrical and relatively flat.
  • a source of charged particles is placed in the center of this cavity so that the magnetic field perpendicular to the trajectory of the particle beam gives it a circular trajectory.
  • a conventional acceleration system has two flat electrodes, each consisting of two parallel plates in the shape of a disc portion. These electrodes are brought to a high alternating voltage, making it possible to apply to the particles four successive accelerations per revolution.
  • the energy of the particles increases and the beam trajectory is no longer a circle but a divergent spiral which brings the particles to the periphery of the accelerating cavity.
  • a curved electro-static channel brought to a high voltage is used to tear off the beam from the attraction of the magnetic field and extract it tangentially from the cavity.
  • This organ is one of the most exposed in the cyclotron and needs to be particularly well positioned relative to the incident beam to have the best possible extraction efficiency and also to prevent it from being bombarded by too large a fraction of the beam. incident.
  • pole pieces comprising a succession of thick sectors, spaced apart and distributed circumferentially to define in the cavity an alternating succession of zones with a wide air gap and zones with a narrow air gap.
  • This arrangement ensures, under certain conditions, vertical focusing.
  • the power of the extracted beam is defined by an extraction efficiency which depends to a large extent on the thermal dissipation limits of the aforementioned electro-static extraction channel and more particularly of a thin strip of copper thereof, known in the art under the name "septum".
  • the invention therefore relates to a cyclotron comprising two pole pieces occupying the two axial faces of a cylindrical and relatively flat accelerating cavity, at the center of which is placed a source of charged particles and comprising means for positioning a target inside said cavity, of the type in which said pole pieces comprise a succession of thick sectors spaced apart and regularly distributed circumferentially to define in said cavity an alternating succession of zones with a narrow gap and zones with a wide gap for focusing said vertical, characterized in that it further carries an arrangement of elongated coils arranged circularly in the vicinity of the periphery of said cavity and means of electrical supply thereof, to vary the conditions of vertical focusing in the vicinity a circular path corresponding to the radial positioning of the aforementioned target.
  • the main part of the cyclotron comprises means for generating a strong magnetic field in a cylindrical accelerating cavity 12 and of relatively flat shape.
  • These means consist of an external metal carcass (not shown) and two coils (not shown) supplied with direct current and located in the vicinity of two pole pieces 13, 14 spaced opposite one another for define an air gap.
  • the two pole pieces occupy the two axial faces of the cavity 12, the latter coincides with the air gap.
  • the latter houses accelerating electrodes, not shown for clarity in the drawing but whose structure with two parallel plates in the shape of a disc portion and well known to the skilled in the art.
  • the source of particles 16 is placed in the center of the cavity 12.
  • an electro-static extraction channel 19, curved is placed, to the peripheral part of the cavity 12.
  • This is composed of a curved electrode 20 brought to a high direct voltage and of an electrode parallel 21 to the ground potential.
  • This electrode called “septum” must be very effectively cooled by conduction by means of copper blocks arranged in thermal contact with it.
  • the assembly is mounted on a radially movable support, shown diagrammatically by a jack 22, in order to be able to remove the extraction channel from the cavity 12 and place a target 23 there, at another location but substantially at the same radial distance from the source 16.
  • the height of the air gap is not circumferentially constant, this is due to the presence of four thick sectors 24 on each pole piece 13, 14, spaced and regularly distributed circumferentially to define in the cavity 12 an alternating succession of narrow airgap zones 25 and wide airgap zones 26.
  • the sectors 24 belonging respectively to the poles 13 and 14 are arranged two by two opposite one another so as to be exactly superimposed in the direction of the axis of the cavity 12.
  • the charged particles, turning in the plane of Figure 1 therefore successively meet weak fields (wide air gap) and strong fields (narrow air gap) which are t the condition of a good vertical focusing.
  • the edges of the sectors are spiraled and the particles rotate clockwise while looking at FIG. 1, that is to say so as to meet a concave transition profile between two zones 25 and 26 neighbors.
  • the cyclotron further comprises an arrangement of elongated coils 28, 29 arranged circularly in the vicinity of the periphery of the cavity 12 as well as means of electrical supply of said coils (not shown since it does not it is only one or more direct current sources) to vary the vertical focusing conditions in the vicinity of a circular path 30 corresponding to the radial positioning of the target 23.
  • the circular path 30 is that which corresponds to the extraction radii (that is to say the radial distance where the electro-static channel 19 is placed) which path is that of the particles making their last turn in the cavity and therefore having reached an energy maximum.
  • the coils 28 are arranged on the sectors 24, that is to say in the zones with a narrow gap and face each other in pairs.
  • each coil 28 and 29 is made up of several narrow turns parallel to the pole pieces and these turns are curved to closely match the circular path 30.
  • Each pole piece comprises a coil 28 or 29 per zone with a narrow or wide air gap, respectively.
  • the coils 29 are connected to the supply means with a direction tending to strengthen the magnetic field locally in the areas with a wide air gap while the coils 28 are connected to the supply means with a direction tending to decrease the magnetic field locally in the narrow gap areas.
  • uz must be positive, a negative value of uz physically signifying a defocusing, that is to say a widening of the beam. This is precisely what the invention does, and this by reducing the standard deviation 2 2 since neither the number of sectors, nor their shape, nor the horizontal focus can be modified.
  • This defocusing must take place while the particles perform the few turns which precede the circular path 30 defined above, this is why the coils 28 and 29 are arranged to come substantially to tangent inside a fictitious cyclindric surface passing through said circular path 30.
  • connection several types of connection are possible.
  • the number of amp-turns of the coils 29 located in the areas with a wide air gap is greater than the number of amp-turns of the coils 28 located in the areas with a narrow air gap since the magnetic field correction in these areas should be performed over a shorter airgap distance.
  • all the coils 29 located in the zones with a wide air gap are connected to a first source of food.
  • adjustable electrical power while all the coils 28 located in the narrow air gap areas are connected to a second adjustable electrical power source with a reverse connection direction.
  • This variant uses additional power, but is more flexible in that the field corrections in zones 25 and 26 can be adjusted independently.
  • FIG. 3 illustrates a variant in which the zones with a wide air gap 26 are provided with projecting circular portions 32 (called “shims") locally reducing the air gap in the vicinity of the circular path 30 and / where the zones with a narrow air gap are provided with grooves 34 locally increasing the air gap in the vicinity of this same path.
  • the dimensional characteristics of the parts have been modified to place the cyclotron at the lower limit of correct vertical focusing and it suffices to insert polarity reversal means between the coils 28, 29 and the supply means.
  • the fields developed by said coils come, in one case, to increase the standard deviation ⁇ - and therefore to reinforce the focusing to allow a correct extraction of the beam and, in the other case, to decrease this same standard deviation for ensure vertical defocusing and allow operation with internal target.
  • the electric power consumed by the coils 28, 29 is approximately half of that which is necessary with the previous embodiment.
  • the grooves 34 can be used for the integration of the coils in the areas with a narrow gap where the space for accommodating them is most limited.

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  • Physics & Mathematics (AREA)
  • Engineering & Computer Science (AREA)
  • Plasma & Fusion (AREA)
  • Spectroscopy & Molecular Physics (AREA)
  • Particle Accelerators (AREA)

Abstract

Cyclotron permettant une meilleure utilisation de la puissance dans un cas d'utilisation à cible interne. Selon l'invention on dispose des bobines de défocalisation verticale (28, 29) le long d'un trajet circulaire (30) en travers duquel on dispose la cible (23); ces bobines allongées et courbes ayant pour effet de détruire la focalisation verticale, donc d'élargir le faisceau, avant l'impact sur la cible, de façon que cette dernière ne soit pas détériorée. Application à la production de radioisotopes.Cyclotron allowing better use of power in an internal target use case. According to the invention there are vertical defocus coils (28, 29) along a circular path (30) across which the target (23) is arranged; these elongated and curved coils having the effect of destroying the vertical focusing, therefore of widening the beam, before impact on the target, so that the latter is not deteriorated. Application to the production of radioisotopes.

Description

L'invention concerne un cyclotron à système de focalisation- défocalisation permettant d'augmenter sensiblement la limite de 'puissance admissible lorsque l'on place la cible à l'intérieur de la structure accélératrice.The invention relates to a cyclotron with a focus-defocus system making it possible to substantially increase the limit of admissible power when the target is placed inside the accelerating structure.

Un cyclotron isochrone est un accélérateur de particules chargées (généralement des protons) qui se compose d'un électroaimant comprenant deux pièces polaires occupant les deux faces axiales, c'est-à-dire perpendiculaires à l'axe, d'une cavité accélératrice, cylindrique et relativement plate. Une source de particules chargées est disposée au centre de cette cavité de sorte que le champ magnétique perpendiculaire à la trajectoire du faisceau de particules donne à celui-ci une trajectoire circulaire. Un système d'accélération classique comporte deux électrodes plates constituées chacune de deux plaques parallèles en forme de portion de disque. Ces électrodes sont portées à une haute tension alternative, permettant d'appliquer aux particules quatre accélérations successives par tour. Dans ces conditions, l'énergie des particules augmente et la trajectoire du faisceau n'est plus un cercle mais une spirale divergente qui amène les particules jusqu'à la périphérie de la cavité accélératrice. Dans le cas où on désire faire sortir le faisceau de la cavité accélératrice (par exemple pour bombarder une cible de façon à créer un isotope radioactif) on utilise un canal électro-statique courbe porté à une haute tension pour arracher le faisceau de l'attraction du champ magnétique et l'extraire tangentiellement de la cavité. Cet organe est l'un des plus exposés du cyclotron et nécessite d'être particulièrement bien positionné par rapport au faisceau incident pour avoir le meilleur rendement d'extraction possible et aussi pour éviter qu'il ne soit bombardé par une fraction trop importante du faisceau incident. Ceci nécessite une très grande finesse du faisceau, autrement dit une bonne focalisation dans toutes les directions. On caractérise le faisceau par sa focalisation horizontale (ou radiale) dans le plan de la spirale et par sa focalisation verticale dans la direction perpendiculaire aux pièces polaires. On sait que la focalisation horizontale peut être obtenue en augmentant la valeur du champ magnétique en fonction du rayon. Ce gradient de champ dans la cavité permet aussi de compenser l'effet de l'augmentation de la masse de la particule au cours de son accélération (effet relativiste). En revanche, ce gradient est nuisible pour la focalisation verticale. On a résolu ce problème en soumettant la particule, à chaque tour, à une succession alternée de champs forts et de champs faibles. Ceci est obtenu grâce à des pièces polaires comprenant une succession de secteurs épais, espacés et répartis circonférentiellement pour définir dans la cavité une succession alternée de zones à entrefer large et de zones à entrefer étroit. Cet agencement assure, sous certaines conditions, la focalisation verticale. La puissance du faisceau extrait est définie par un rendement d'extraction qui dépend pour beaucoup des limites de dissipation thermique du canal électro-statique d'extraction précité et plus particulièrement d'une fine bande de cuivre de celui-ci, connue dans la technique sous le nom "septum".An isochronous cyclotron is an accelerator of charged particles (generally protons) which consists of an electromagnet comprising two pole pieces occupying the two axial faces, that is to say perpendicular to the axis, of an accelerating cavity, cylindrical and relatively flat. A source of charged particles is placed in the center of this cavity so that the magnetic field perpendicular to the trajectory of the particle beam gives it a circular trajectory. A conventional acceleration system has two flat electrodes, each consisting of two parallel plates in the shape of a disc portion. These electrodes are brought to a high alternating voltage, making it possible to apply to the particles four successive accelerations per revolution. Under these conditions, the energy of the particles increases and the beam trajectory is no longer a circle but a divergent spiral which brings the particles to the periphery of the accelerating cavity. In the case where it is desired to bring out the beam from the accelerating cavity (for example to bombard a target so as to create a radioactive isotope), a curved electro-static channel brought to a high voltage is used to tear off the beam from the attraction of the magnetic field and extract it tangentially from the cavity. This organ is one of the most exposed in the cyclotron and needs to be particularly well positioned relative to the incident beam to have the best possible extraction efficiency and also to prevent it from being bombarded by too large a fraction of the beam. incident. This requires very great fineness of the beam, in other words good focusing in all directions. We characterize the beam by its focusing horizontal (or radial) in the plane of the spiral and by its vertical focus in the direction perpendicular to the pole pieces. It is known that horizontal focusing can be obtained by increasing the value of the magnetic field as a function of the radius. This field gradient in the cavity also makes it possible to compensate for the effect of the increase in the mass of the particle during its acceleration (relativistic effect). On the other hand, this gradient is detrimental for vertical focusing. This problem has been solved by subjecting the particle, at each turn, to an alternating succession of strong and weak fields. This is obtained by means of pole pieces comprising a succession of thick sectors, spaced apart and distributed circumferentially to define in the cavity an alternating succession of zones with a wide air gap and zones with a narrow air gap. This arrangement ensures, under certain conditions, vertical focusing. The power of the extracted beam is defined by an extraction efficiency which depends to a large extent on the thermal dissipation limits of the aforementioned electro-static extraction channel and more particularly of a thin strip of copper thereof, known in the art under the name "septum".

Cependant, de nombreux utilisateurs de cyclotron, notamment pour la production de certains radioisotopes, désirent obtenir un faisceau le plus puissant possible. On a alors proposé de placer la cible à l'intérieur de la cavité accélératrice, sensiblement à la même distance du centre que le canal électro-statique d'extraction, ce dernier étant provisoirement retiré de la cavité. Dans ce nouveau mode d'utilisation du cyclotron, la focalisation poussée du faisceau, nécessaire pour l'extraction, devient un inconvénient car la cible ne peut assurer une dissipation thermique pour une zone d'impact aussi localisée et risque donc d'être endommagée. Par conséquent, la puissance du faisceau doit être limitée dans ce mode d'utilisation à cible interne et il n'est pas possible d'utiliser le cyclotron à sa puissance nominale de sorte que le gain de puissance est inférieur à ce qui pouvait être attendu d'une utilisation avec cible interne. L'invention vise à résoudre cet inconvient ; son principe de base consiste à jouer localement sur la focalisation verticale précitée.However, many cyclotron users, particularly for the production of certain radioisotopes, want to obtain the strongest possible beam. It has then been proposed to place the target inside the accelerating cavity, substantially at the same distance from the center as the electro-static extraction channel, the latter being temporarily removed from the cavity. In this new mode of use of the cyclotron, the focused focusing of the beam, necessary for the extraction, becomes a drawback because the target cannot provide thermal dissipation for such a localized impact zone and therefore risks being damaged. Consequently, the beam power must be limited in this mode of use with internal target and it is not possible to use the cyclotron at its nominal power so that the power gain is less than what could be expected of use with internal target. The invention aims to solve this drawback; its basic principle consists in playing locally on the aforementioned vertical focusing.

Plus précisément, l'invention concerne donc un cyclotron comprenant deux pièces polaires occupant les deux faces axiales d'une cavité accélératrice cylindrique et relativement plate, au centre de laquelle est placée une source de particules chargées et comportant des moyens de positionnement d'une cible à l'intérieur de la dite cavité, du type dans lequel lesdites pièces polaires comprennent une succession de secteurs épais espacés et régulièrement répartis circonférentiellement pour définir dans ladite cavité une succession alternée de zones à entrefer étroit et de zones à entrefer large pour assurer la focalisation dite verticale, caractérisé en ce qu'il com porte en outre un agencement de bobines allongées disposées circulairement au voisinage de la périphérie de ladite cavité et des moyens d'alimentation électrique de celles-ci, pour faire varier les conditions de focalisation verticale au voisinage d'un trajet circulaire correspondant au positionnement radial de la cible précitée.More specifically, the invention therefore relates to a cyclotron comprising two pole pieces occupying the two axial faces of a cylindrical and relatively flat accelerating cavity, at the center of which is placed a source of charged particles and comprising means for positioning a target inside said cavity, of the type in which said pole pieces comprise a succession of thick sectors spaced apart and regularly distributed circumferentially to define in said cavity an alternating succession of zones with a narrow gap and zones with a wide gap for focusing said vertical, characterized in that it further carries an arrangement of elongated coils arranged circularly in the vicinity of the periphery of said cavity and means of electrical supply thereof, to vary the conditions of vertical focusing in the vicinity a circular path corresponding to the radial positioning of the aforementioned target.

L'invention sera mieux comprise et d'autres avantages de celle-ci apparaitront mieux à la lumière de la description qui va suivre de deux modes de réalisation possibles d'un cyclotron selon l'invention, donnée uniquement à titre d'exemple et faite en référence au dessin annexé dans lequel :

  • - la figure 1 est une vue schématique en plan des parties essentielles d'un cyclotron selon l'invention ;
  • - la figure 2 est une section II - II de la figure 1 ; et
  • - la figure 3 est une vue analogue à la figure 2, illustrant une variante de l'invention.
The invention will be better understood and other advantages thereof will appear better in the light of the following description of two possible embodiments of a cyclotron according to the invention, given solely by way of example and made with reference to the attached drawing in which:
  • - Figure 1 is a schematic plan view of the essential parts of a cyclotron according to the invention;
  • - Figure 2 is a section II - II of Figure 1; and
  • - Figure 3 is a view similar to Figure 2, illustrating a variant of the invention.

En se reportant aux figures 1 et 2, la partie principale du cyclotron Il comporte des moyens pour générer un puissant champ magnétique dans une cavité accélératrice 12 cylindrique et de forme relativement plate. Ces moyens se composent d'une carcasse métallique externe (non représentée) et de deux bobines (non représentées) alimentées en courant continu et situées au voisinage de deux pièces polaires 13, 14 espacées en regard l'une de l'autre pour définir un entrefer. Comme les deux pièces polaires occupent les deux faces axiales de la cavité 12 celle-ci coïncide avec l'entrefer. En fonctionnement, on fait le vide dans la cavité 12. En outre , cette dernière abrite des électrodes accélératrices, non représentées pour plus de clarté dans le dessin mais dont la structure à deux plaques parallèles en forme de portion de disque et bien connue de l'homme du métier. Comme mentionné précédemment, la source de particules 16 est placée au centre de la cavité 12. Lorsque l'on désire extraire le faisceau tangentiellement (voir trajectoire 18 sur la figure 1) on place un canal électro-statique d'extraction 19, courbe, à la partie périphérique de la cavité 12. Celui-ci est composé d'une électrode courbe 20 portée à une haute tension continue et d'une électrode parallèle 21 au potentiel de la masse. Cette électrode appelée "septum" doit être très efficacement refroidie par conduction au moyen de blocs de cuivre disposés en contact thermique avec elle. L'ensemble est monté sur un support mobile radialement, schématisé par un vérin 22, pour pouvoir retirer le canal d'extraction de la cavité 12 et y placer une cible 23, à un autre endroit mais sensiblement à la même distance radiale par rapport à la source 16. Comme mentionné précédemment, la hauteur de l'entrefer n'est pas constante circonférentiellement, ceci est dû à la présence de quatre secteurs épais 24 sur chaque pièce polaire 13, 14, espacés et régulièrement répartis circonférentiellement pour définir dans la cavité 12 une succession alternée de zones à entrefer étroit 25 et de zones à entrefer large 26. Pour ce faire, les secteurs 24 appartenant respectivement aux pôles 13 et 14 sont disposés deux à deux en regard l'un de l'autre de façon à être exactement superposés dans la direction de l'axe de la cavité 12. Les particules chargées, en tournant dans le plan de la figure 1 rencontrent donc successivement des champs faibles (entrefer large) et forts (entrefer étroit) ce qui est la condition d'un bonne focalisation verticale. De façon connue, les bords des secteurs sont spiralés et les particules tournent dans le sens des aiguilles d'une montre en regardant la figure 1, c'est-à-dire de façon à rencontrer un profil de transition concave entre deux zones 25 et 26 voisines.Referring to Figures 1 and 2, the main part of the cyclotron It comprises means for generating a strong magnetic field in a cylindrical accelerating cavity 12 and of relatively flat shape. These means consist of an external metal carcass (not shown) and two coils (not shown) supplied with direct current and located in the vicinity of two pole pieces 13, 14 spaced opposite one another for define an air gap. As the two pole pieces occupy the two axial faces of the cavity 12, the latter coincides with the air gap. In operation, there is a vacuum in the cavity 12. In addition, the latter houses accelerating electrodes, not shown for clarity in the drawing but whose structure with two parallel plates in the shape of a disc portion and well known to the skilled in the art. As mentioned previously, the source of particles 16 is placed in the center of the cavity 12. When it is desired to extract the beam tangentially (see trajectory 18 in FIG. 1) an electro-static extraction channel 19, curved, is placed, to the peripheral part of the cavity 12. This is composed of a curved electrode 20 brought to a high direct voltage and of an electrode parallel 21 to the ground potential. This electrode called "septum" must be very effectively cooled by conduction by means of copper blocks arranged in thermal contact with it. The assembly is mounted on a radially movable support, shown diagrammatically by a jack 22, in order to be able to remove the extraction channel from the cavity 12 and place a target 23 there, at another location but substantially at the same radial distance from the source 16. As mentioned previously, the height of the air gap is not circumferentially constant, this is due to the presence of four thick sectors 24 on each pole piece 13, 14, spaced and regularly distributed circumferentially to define in the cavity 12 an alternating succession of narrow airgap zones 25 and wide airgap zones 26. To do this, the sectors 24 belonging respectively to the poles 13 and 14 are arranged two by two opposite one another so as to be exactly superimposed in the direction of the axis of the cavity 12. The charged particles, turning in the plane of Figure 1 therefore successively meet weak fields (wide air gap) and strong fields (narrow air gap) which are t the condition of a good vertical focusing. In known manner, the edges of the sectors are spiraled and the particles rotate clockwise while looking at FIG. 1, that is to say so as to meet a concave transition profile between two zones 25 and 26 neighbors.

Selon un aspect essentiel de l'invention, le cyclotron comporte en outre un agencement de bobines allongées 28, 29 disposées circulairement au voisinage de la périphérie de la cavité 12 ainsi que des moyens d'alimentation électrique desdites bobines (non représentés puisqu'il ne s'agit que d'une ou plusieurs sources de courant continu) pour faire varier les conditions de focalisation verticale au voisinage d'un trajet circulaire 30 correspondant au positionnement radial de la cible 23. Dans l'exemple, le trajet circulaire 30 est celui qui correspond aux rayons d'extraction (c'est-à-dire la distance radiale ou l'on place le canal électro-statique 19) lequel trajet est celui des particules effectuant leur dernier tour dans la cavité et ayant par conséquent atteint une énergie maximum. Les bobines 28 sont disposées sur les secteurs 24, c'est-à-dire dans les zones à entrefer étroit et se font face deux à deux. Par ailleurs, les bobines 29 sont disposées dans les zones à entrefer large et se font également face deux à deux. Chaque bobine 28 et 29 est constituée de plusieurs spires étroites parallèles aux pièces polaires et ces spires sont courbées pour épouser au plus près le trajet circulaire 30. Chaque pièce polaire comporte une bobine 28 ou 29 par zone à entrefer étroit ou large, respectivement. Les bobines 29 sont connectées aux moyens d'alimentation avec un sens tendant à renforcer le champ magnétique localement dans les zones à entrefer large tandis que les bobines 28 sont connectées aux moyens d'alimentation avec un sens tendant à diminuer le champ magnétique localement dans les zones à entrefer étroit.According to an essential aspect of the invention, the cyclotron further comprises an arrangement of elongated coils 28, 29 arranged circularly in the vicinity of the periphery of the cavity 12 as well as means of electrical supply of said coils (not shown since it does not it is only one or more direct current sources) to vary the vertical focusing conditions in the vicinity of a circular path 30 corresponding to the radial positioning of the target 23. In the example, the circular path 30 is that which corresponds to the extraction radii (that is to say the radial distance where the electro-static channel 19 is placed) which path is that of the particles making their last turn in the cavity and therefore having reached an energy maximum. The coils 28 are arranged on the sectors 24, that is to say in the zones with a narrow gap and face each other in pairs. Furthermore, the coils 29 are arranged in the zones with a wide air gap and also face each other in pairs. Each coil 28 and 29 is made up of several narrow turns parallel to the pole pieces and these turns are curved to closely match the circular path 30. Each pole piece comprises a coil 28 or 29 per zone with a narrow or wide air gap, respectively. The coils 29 are connected to the supply means with a direction tending to strengthen the magnetic field locally in the areas with a wide air gap while the coils 28 are connected to the supply means with a direction tending to decrease the magnetic field locally in the narrow gap areas.

Le développement mathématique qui suit permet de mieux comprendre l'action de ce jeu de bobines sur la focalisation verticale du faisceau.The following mathematical development allows us to better understand the action of this set of coils on the vertical focusing of the beam.

L'effet de focalisation verticale obtenue par les pièces polaires définies ci-dessus s'exprime par un coefficient v z tel que :

Figure imgb0001
uz represente le nombre de "noeuds" de focalisation du faisceau par tour (dans la pratique on recherche uz = 0,4, par exemple) et dans la formule ci-dessus :

  • - N est le nombre de secteurs 24 (quatre dans l'exemple)
  • - a est un coefficient lié à la géométrie (spiralisation) des secteurs.
  • - k =
    Figure imgb0002
    Figure imgb0003
    , caractérise le gradient de focalisation horizontale, R étant le rayon d'une orbite considérée et B la valeur du champ magnétique au voisinage de ce rayon
    Figure imgb0004
    représente une sorte d'écart-type de variation de champ magnétique sur une orbite donnée.
The vertical focusing effect obtained by the pole pieces defined above is expressed by a coefficient vz such that:
Figure imgb0001
 uz represents the number of "nodes" of focusing of the beam per revolution (in practice one seeks uz = 0.4, for example) and in the above formula:
  • - N is the number of sectors 24 (four in the example)
  • - a is a coefficient linked to the geometry (spiraling) of the sectors.
  • - k =
    Figure imgb0002
    Figure imgb0003
     , characterizes the horizontal focusing gradient, R being the radius of a considered orbit and B the value of the magnetic field in the vicinity of this radius
    Figure imgb0004
     represents a kind of standard deviation of magnetic field variation on a given orbit.

Or, pour que la focalisation verticale soit effective, il faut que uz soit positif, une valeur de uz négative signifiant physiquement une défocalisation c'est-à-dire un élargissement du faisceau. C'est précisément ce que réalise l'invention et ceci en réduisant l'écart-type 22 puisqu'on ne peut modifier ni le nombre de secteurs, ni leur forme, ni la focalisation horizontale. Cette défocalisation doit s'opérer pendant que les particules effectuent les quelques tours qui précédent le trajet circulaire 30 défini plus haut, c'est pourquoi les bobines 28 et 29 sont disposées pour venir sensiblement tangenter l'intérieur d'une surface cyclindrique fictive passant par ledit trajet circulaire 30.However, for vertical focusing to be effective, uz must be positive, a negative value of uz physically signifying a defocusing, that is to say a widening of the beam. This is precisely what the invention does, and this by reducing the standard deviation 2 2 since neither the number of sectors, nor their shape, nor the horizontal focus can be modified. This defocusing must take place while the particles perform the few turns which precede the circular path 30 defined above, this is why the coils 28 and 29 are arranged to come substantially to tangent inside a fictitious cyclindric surface passing through said circular path 30.

Dans la pratique, plusieurs types de branchement sont possibles. On peut par exemple faire en sorte que toutes les bobines soient reliées (par exemple en série) à une unique source d'alimentation électrique réglable, le sens d'enroulement des bobines 29 situées dans les zones à entrefer large étant inverse du sens d'enroulement des bobines 28 situées dans les zones à entrefer étroit. Dans ce cas particulièrement (mais non exclusivement), le nombre d'ampère-tours des bobines 29 situées dans les zones à entrefer large est plus grand que le nombre d'ampère-tours des bobines 28 situées dans les zones à entrefer étroit puisque la correction de champ magnétique dans ces zones doit être effectuée sur une distance d'entrefer plus faible.In practice, several types of connection are possible. One can for example ensure that all the coils are connected (for example in series) to a single adjustable electrical power source, the winding direction of the coils 29 located in the wide air gap areas being opposite to the direction of winding of the coils 28 located in the areas with a narrow air gap. In this case in particular (but not exclusively), the number of amp-turns of the coils 29 located in the areas with a wide air gap is greater than the number of amp-turns of the coils 28 located in the areas with a narrow air gap since the magnetic field correction in these areas should be performed over a shorter airgap distance.

On peut aussi prévoir que toutes les bobines 29 situées dans les zones à entrefer large soient reliées à une première source d'alimentation électrique réglable tandis que toutes les bobines 28 situées dans les zones à entrefer étroit soient reliées à une seconde source d'alimentation électrique réglable avec un sens de branchement inversé. Cette variante fait appel à une alimentation supplémentaire mais est d'une utilisation plus souple dans la mesure où les corrections de champ dans les zones 25 et 26 peuvent être réglées indépendamment.It can also be provided that all the coils 29 located in the zones with a wide air gap are connected to a first source of food. adjustable electrical power while all the coils 28 located in the narrow air gap areas are connected to a second adjustable electrical power source with a reverse connection direction. This variant uses additional power, but is more flexible in that the field corrections in zones 25 and 26 can be adjusted independently.

La figure 3 illustre une variante dans laquelle les zones à entrefer large 26 sont munies de portions circulaires saillantes 32 (appelés "shims") réduisant localement l'entrefer au voisinage du trajet circulaire 30 et/où les zones à entrefer étroit sont pourvues de rainures 34 augmentant localement l'entrefer au voisinage de ce même trajet. Dans ces conditions on a modifié les caractéristiques dimensionnelles des pièces pour placer le cyclotron à la limite inférieure d'une focalisation verticale correcte et il suffit d'intercaler des moyens d'inversion de polarité entre les bobines 28, 29 et les moyens d'alimentation correspondants pour que les champs développés par lesdites bobines viennent, dans un cas, augmenter l'écart-type γ- et donc renforcer la focalisation pour permettre une extraction correcte du faisceau et, dans l'autre cas, diminuer ce même écart-type pour assurer la défocalisation verticale et permettre le fonctionnement avec cible interne. Avec cette variante, la puissance électrique consommée par les bobines 28, 29 est environ la moitié de celle qui est nécessaire avec le mode de réalisation précédent. En outre, les rainures 34 peuvent être mises à profit pour l'intégration des bobines dans les zones à entrefer étroit où la place pour les loger est la plus restreinte.FIG. 3 illustrates a variant in which the zones with a wide air gap 26 are provided with projecting circular portions 32 (called "shims") locally reducing the air gap in the vicinity of the circular path 30 and / where the zones with a narrow air gap are provided with grooves 34 locally increasing the air gap in the vicinity of this same path. Under these conditions, the dimensional characteristics of the parts have been modified to place the cyclotron at the lower limit of correct vertical focusing and it suffices to insert polarity reversal means between the coils 28, 29 and the supply means. corresponding so that the fields developed by said coils come, in one case, to increase the standard deviation γ- and therefore to reinforce the focusing to allow a correct extraction of the beam and, in the other case, to decrease this same standard deviation for ensure vertical defocusing and allow operation with internal target. With this variant, the electric power consumed by the coils 28, 29 is approximately half of that which is necessary with the previous embodiment. In addition, the grooves 34 can be used for the integration of the coils in the areas with a narrow gap where the space for accommodating them is most limited.

Bien entendu l'invention n'est pas limitée aux modes de réalisation qui viennent d'être décrits, elle comprend tous les équivalents techniques des moyens mis en jeu si ceux-ci le sont dans le cadre des revendications qui suivent.Of course, the invention is not limited to the embodiments which have just been described, it includes all the technical equivalents of the means brought into play if these are in the context of the claims which follow.

Claims (7)

1. Cyclotron comprenant deux pièces polaires (13, 14) occupant les deux faces axiales d'une cavité accélératrice (I2) cylindrique et de forme relativement plate au centre de laquelle est placée une source (16) de particules chargées et comportant des moyens de positionnement d'une cible (23) à l'intérieur de la cavité, du type dans lequel lesdites pièces polaires comprennent une succession de secteur épais (24) espacés et régulièrement répartis circonférentiellement pour définir dans ladite cavité une succession alternée de zones à entrefer étroit (25) et de zones à entrefer large (26) pour assurer la focalisation verticale, caractérisé en ce qu'il comporte en outre un agencement de bobines allongées (28, 29) disposées circulairement au voisinage de la périphérie de ladite cavité et des moyens d'alimentation électrique de celles-ci pour faire varier les conditions de focalisation verticale au voisinage d'un trajet circulaire (30) correspondant au positionnement radial de ladite cible (23).1. Cyclotron comprising two pole pieces (13, 14) occupying the two axial faces of a cylindrical accelerating cavity (I2) and of relatively flat shape at the center of which is placed a source (16) of charged particles and comprising means for positioning of a target (23) inside the cavity, of the type in which said pole pieces comprise a succession of thick sectors (24) spaced apart and regularly distributed circumferentially to define in said cavity an alternating succession of zones with narrow airgaps (25) and of wide air gap zones (26) for ensuring vertical focusing, characterized in that it further comprises an arrangement of elongated coils (28, 29) arranged circularly in the vicinity of the periphery of said cavity and means power supply thereof to vary the vertical focusing conditions in the vicinity of a circular path (30) corresponding to the radial positioning of said target ( 23). 2. Cyclotron selon la revendication 1, caractérisé en ce que chaque pièce polaire comporte une bobine (28 ou 29) par zone à entrefer étroit ou large.2. Cyclotron according to claim 1, characterized in that each pole piece comprises a coil (28 or 29) per zone with a narrow or wide air gap. 3. Cyclotron selon la revendication 2, caractérisé en ce que les bobines (29) situées dans une zone à entrefer large (26) sont connectées aux moyens d'alimentation avec un sens tendant à renforcer le champ magnétique localement dans cette zone et en ce que les bobines (28) situées dans une zone à entrefer étroit (25) sont connectées auxdits moyens d'alimentation avec un sens tendant à diminuer localement le champ magnétique dans cette zone.3. Cyclotron according to claim 2, characterized in that the coils (29) located in a wide gap area (26) are connected to the supply means with a direction tending to strengthen the magnetic field locally in this area and in that that the coils (28) located in a narrow gap area (25) are connected to said supply means with a direction tending to locally decrease the magnetic field in this area. 4. Cyclotron selon la revendication 3, caractérisé en ce que les bobines précitées sont toutes reliées à une unique source d'alimentation électrique réglable, le sens d'enroulement des bobines situées dans les zones à entrefer large étant inverse du sens d'enroulement des bobines situées dans les zones à entrefer étroit.4. Cyclotron according to claim 3, characterized in that the aforementioned coils are all connected to a single adjustable electrical power source, the direction of winding of the coils located in the areas with a wide air gap being opposite to the direction of winding of the coils located in narrow air gap areas. 5. Cyclotron selon la revendication 3, caractérisé en ce que toutes les bobines situées dans les zones à entrefer large sont reliées à une première source d'alimentation électrique réglable tandis que toutes les bobines situées dans les zones à entrefer étroit sont reliées à une seconde source d'alimentation électrique réglable.5. Cyclotron according to claim 3, characterized in that all the coils located in the wide air gap zones are connected to a first adjustable electrical power source while all the coils located in the narrow air gap zones are connected to a second adjustable power source. 6. Cyclotron selon l'une des revendications 4 ou 5, caractérisé en ce que le nombre d'ampère-tours des bobines situées dans les zones à entrefer large (26) est plus grand que le nombre d'ampère- tours des bobines situées dans les zones à entrefer étroit (25).6. Cyclotron according to one of claims 4 or 5, characterized in that the number of ampere-turns of the coils located in the wide airgap areas (26) is greater than the number of ampere-turns of the coils located in areas with narrow air gaps (25). 7. Cyclotron selon l'une des revendications précédentes, caractérisé en ce que lesdites zones à entrefer large (26) sont munies de portions circulaires saillantes (32) réduisant localement l'entrefer au voisinage du trajet circulaire (30) précité et/où que lesdites zones à entrefer étroit (25) sont pourvues de rainures (34) augmentant localement l'entrefer au voisinage du même trajet circulaire (30).7. Cyclotron according to one of the preceding claims, characterized in that said wide gap zones (26) are provided with projecting circular portions (32) locally reducing the gap in the vicinity of the aforementioned circular path (30) and / or that said narrow gap zones (25) are provided with grooves (34) locally increasing the gap in the vicinity of the same circular path (30).
EP84400682A 1983-04-12 1984-04-06 Cyclotron with defocusing system Expired EP0128052B1 (en)

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FR8305939A FR2544580B1 (en) 1983-04-12 1983-04-12 FOCUS-DEFOCUS SYSTEM CYCLOTRON
FR8305939 1983-04-12

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EP1069809A1 (en) * 1999-07-13 2001-01-17 Ion Beam Applications S.A. Isochronous cyclotron and method of extraction of charged particles from such cyclotron
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US9895552B2 (en) * 2015-05-26 2018-02-20 Antaya Science & Technology Isochronous cyclotron with superconducting flutter coils and non-magnetic reinforcement
EP3496516B1 (en) * 2017-12-11 2020-02-19 Ion Beam Applications S.A. Superconductor cyclotron regenerator
CN114430607B (en) * 2022-01-21 2022-11-29 中国原子能科学研究院 Spiral magnetic pole structure for improving focusing force of central area of cyclotron
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FR2544580B1 (en) 1985-07-05
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FR2544580A1 (en) 1984-10-19
EP0128052B1 (en) 1988-06-08

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