EP0362947B1 - Sealed neutron tube equipped with a multicellular ion source with magnetic confinement - Google Patents
Sealed neutron tube equipped with a multicellular ion source with magnetic confinement Download PDFInfo
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- EP0362947B1 EP0362947B1 EP89202465A EP89202465A EP0362947B1 EP 0362947 B1 EP0362947 B1 EP 0362947B1 EP 89202465 A EP89202465 A EP 89202465A EP 89202465 A EP89202465 A EP 89202465A EP 0362947 B1 EP0362947 B1 EP 0362947B1
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- holes
- ion source
- neutron tube
- anode
- ion
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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
- H05H3/00—Production or acceleration of neutral particle beams, e.g. molecular or atomic beams
- H05H3/06—Generating neutron beams
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01J—ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
- H01J27/00—Ion beam tubes
- H01J27/02—Ion sources; Ion guns
- H01J27/04—Ion sources; Ion guns using reflex discharge, e.g. Penning ion sources
Definitions
- the invention relates to a sealed neutron tube containing a low-pressure deuterium-tritium gas mixture from which an ion source with two electrodes, an anode and a cathode, forms an ionized gas channeled by a confining magnetic field created by magnets or by any other means of creating said field, said source emitting from emission channels made in said cathode ion beams which pass through an extraction-acceleration electrode and are projected at high energy onto a target electrode for producing therein a fusion reaction resulting in the emission of neutrons, in which said ion source is of the multicellular type consisting of a structure of elementary cells of the Penning type comprising for all of said cells a cathode cavity inside which is disposed a multi-hole anode, the axes of said holes being aligned respectively on the corresponding axes desd its broadcast channels.
- Such a tube is known from NL-A- 7707357.
- Neutron tubes of the same kind are used in techniques for examining matter by fast, thermal, epithermal or cold neutrons: neutronography, analysis by activation, analysis by spectrometry of inelastic diffusions or radiative captures, neutron scattering, etc. .
- the fusion reaction d (3 H , 4 He ) n delivering 14 MeV neutrons is usually the most used because of its large cross section for relatively low ion energies.
- the number of neutrons obtained per unit of charge passing through the beam is always increasing as the energy of the ions directed towards a thick target is itself increasing and this largely at the beyond the energies of the ions obtained in the sealed tubes currently available and supplied by a THT not exceeding 250 kV.
- the erosion of the target by ion bombardment is one of the most determining.
- Erosion is a function of the chemical nature and structure of the target on the one hand, the energy of the incident ions and their density distribution profile on the impact surface on the other.
- the target consists of a hydrurable material (Titanium, Scandium, Zirconium, Erbium etc ...) capable of fixing and releasing large quantities of hydrogen without significant disturbance of its mechanical strength; the total quantity set is a function of the target temperature and the hydrogen pressure in the tube.
- the target materials used are deposited in the form of thin layers, the thickness of which is limited by problems of adhesion of the layer to its support.
- One way to delay erosion of the target is, for example, to form the absorbent active layer of a stack of identical layers isolated from each other by a diffusion barrier. The thickness of each of the active layers is of the order of the depth of penetration of the deuterium ions coming to strike the target.
- Another way to protect the target and therefore increase the life of the tube is to act on the ion beam so as to improve its density distribution profile on the impact surface.
- this improvement will result from a distribution as uniform as possible of the current density over the entire surface offered by the target to the bombardment of the ions.
- the object of the invention is to provide a source device enabling these disadvantages to be overcome.
- the invention is remarkable in that, the number of said holes is optimized so as to increase the extracted ion beam for an equivalent bulk of said ion source, and the shape and / or dimensions and / or positioning of said holes are adapted to the topology of said magnetic field , so that the radius of said anode holes of said ion source is gradually increased from the center to the periphery of the structure.
- a multicellular type neutron tube comprising, for all of the cells a cathode cavity inside which is arranged a multi-hole anode, the axes of the holes respectively on the corresponding axes of the emission channels in the cathode.
- an additional gain in the discharge current may result from the increase in length of the structure of the multicellular ion source. This gain can go up to a factor of 2.
- the increase in current resulting from the new source configuration can then be used to reduce the operating pressure of the neutron tube and thus limit the harmful impact of ion-gas reactions.
- the feasibility of the multicell structure assumes that a magnetic field is suitable for the proper functioning of a Penning structure, in particular at the level of the relationship between the magnetic induction and the hole radius of the multi-hole anode.
- the variation of the magnetic field in level and according to the shape of the lines of force can be corrected by an increase in said radius, which amounts to making structures with a variable anode radius.
- better adaptation of the shape of the anode to the main lines magnetic can be obtained by replacing the cylindrical structures with circular or square section by frustoconical structures so as to make the generators of truncated cones coincide with the lines of force which rest on the contours of the holes.
- the ions of the various structures are emitted through channels made in the cathode acting as an emission electrode. These channels, the number of which is identical to that of the elementary cells, are arranged respectively along the same axes of symmetry. In the case of circular section structures, the diameter is a function of the applied electric field and the thickness of the electrode.
- a variant of this system consists in introducing an expansion chamber below the cathodes in order to standardize the densities in the vicinity of the emission which then takes place through orifices the arrangement of which can be almost independent of that of the elementary cells.
- the extraction-acceleration electrode can be constituted by an electrode provided with n orifices having axes corresponding respectively to those of the n elementary cells, or with j orifices smaller than the number of n elementary cells and therefore diameters greater than those of the emission channels and whose arrangement avoids any interception of the beams.
- This extraction-acceleration electrode can be increased in order to improve the mechanical strength and to allow cooling by forced circulation of fluid.
- Figure 1 shows the block diagram of a sealed neutron tube according to the state of the prior art.
- Figure 2 shows the effects of target erosion at depth and the radial profile of ion bombardment density.
- FIG. 3 represents the diagram of a neutron tube of a known type, compatible with the invention, provided with a multicellular ion source of the Penning type and with an extraction-acceleration electrode comprising as many orifices than cells.
- FIG. 4 represents a neutron tube of a known type compatible with the invention, provided with a multicellular ion source and with an extraction-acceleration electrode comprising a number of orifices different from the number of cells.
- FIG. 5 represents a first variant of the neutron tube of the invention, provided with an ion source whose anode holes are of variable radii.
- FIG. 6 represents a second variant of the neutron tube of the invention provided with a source whose anode holes are of frustoconical shape.
- FIG. 7 represents a third variant of the neutron tube of the invention according to the first variant or according to the first and second variants, provided with a source with expansion chamber.
- FIG. 1 shows the main basic elements of a sealed neutron tube 11 containing a gaseous mixture under low pressure to be ionized such as deuterium-tritium and which comprises an ion source 1 and an extraction-acceleration electrode 2 between which there is a very high potential difference allowing the extraction and acceleration of the ion beam 3 and its projection on the target 4 where the fusion reaction takes place resulting in an emission of neutrons at 14 MeV for example.
- a sealed neutron tube 11 containing a gaseous mixture under low pressure to be ionized such as deuterium-tritium and which comprises an ion source 1 and an extraction-acceleration electrode 2 between which there is a very high potential difference allowing the extraction and acceleration of the ion beam 3 and its projection on the target 4 where the fusion reaction takes place resulting in an emission of neutrons at 14 MeV for example.
- the ion source 1 secured to an insulator 5 for the passage of the THT supply connector is a Penning type source for example, consisting of a cylindrical anode 6, a cathode cavity 7 to which is incorporated a magnet 8 with an axial magnetic field which confines the ionized gas 9 around the axis of the anode cylinder and whose lines of force 10 show a certain divergence.
- An ion emission channel 12 is formed in said cathode cavity opposite the anode
- FIG. 2a shows the profile of the density J of bombardment of the ions in any radial direction Or, from the point of impact O of the central axis of the beam on the target surface.
- the shape of this profile highlights the inhomogeneous nature of this beam whose very high density in the central part decreases rapidly when one moves away from it.
- erosion takes place as a function of the bombardment density and the entire layer of hydrurable material of thickness e deposited on a substrate S is saturated with a deuterium-tritium mixture.
- the depth of penetration of the deuterium-tritium energetic ions represented in dotted lines takes place over a depth which is a function of this energy.
- the erosion of the layer is such that the penetration depth l2 is greater than the thickness e in the most bombarded part; a part of the incident ions is implanted in the substrate and very quickly the atoms of deuterium and tritium are in supersaturation.
- FIG. 3 shows a neutron tube provided with a multicellular ion source of the Penning type consisting of a cathode cavity 7 and a multi-hole anode 6, brought to a potential 4 to 8 kV higher than that of the cathode cavity itself brought to a very high voltage of 250 kV for example.
- a multicellular ion source of the Penning type consisting of a cathode cavity 7 and a multi-hole anode 6, brought to a potential 4 to 8 kV higher than that of the cathode cavity itself brought to a very high voltage of 250 kV for example.
- the magnet 8 provides a magnetic field for confining the ionized gas of the order of a thousand gauss.
- the invention consists in exploiting, in a first known step, the property of multicellular discharge structures with confinement of magnetic type, namely that for the same anode section, the discharge current as well as the current of the ion beam extracted from this discharge are respectively greater in the case of a multicellular source structure than the same currents obtained in the case of a single-cell structure. Similarly, it is more advantageous to use a multicell structure with n anode holes than a multicell structure with m holes if n> m.
- Each section of the structure with n holes is then smaller than each of the sections of the structure with m holes; but the aforementioned advantage is only ensured if the anode section remains equivalent for said structures, which makes it possible to reduce the pressure of the gaseous mixture and therefore the probability of ion-gas reactions.
- a new structure with n cells has thus been constituted in known manner comprising the multi-hole anode 6 having n holes 61, 62, ... 6 n and the cathode 7 in which the anode holes have been practiced.
- These multi-beams 3 are projected onto the target 4 by means of the extraction-acceleration electrode 2 having the same number of orifices 21, 22, ... 2 n as that of said beams and arranged along the same axes.
- the number of orifices made in the extraction-acceleration electrode is less than that of the beams coming from the source: for example each orifice 13 of this electrode 2 delivers passage to two beams from the source as shown in the figure.
- the divergence of the lines of force of the magnetic field shows that it is very high in the central area and gradually decreases to a very low value on the periphery.
- the anode holes 6′1, 6′2, ..., 6 ′ n are, according to the invention, constituted as shown in FIG. 5 with radii varying in opposite directions to the magnetic field so that the product of magnetic induction by the anode radius remains substantially constant. This arrangement tends to standardize the density of ion current.
- the device shown in Figure 6 provides a significant improvement in that the anode holes 6 ⁇ 1, 6 ⁇ 2, ..., 6 ⁇ n have frustoconical shapes which approximate the lines of force of the magnetic field.
- an expansion chamber 14 is arranged below the cathodes in order to standardize the ion densities.
- the emission is carried out through orifices 15 the number of which can be independent of that of the holes of the multi-hole anode.
Description
L'invention concerne un tube neutronique scellé contenant un mélange gazeux deutérium-tritium sous faible pression à partir duquel une source d'ions à deux électrodes, une anode et une cathode, forme un gaz ionisé canalisé par un champ magnétique de confinement créé par des aimants ou par tout autre moyen de création dudit champ, ladite source émettant à partir de canaux d'émission pratiqués dans ladite cathode des faisceaux d'ions qui traversent une électrode d'extraction-accélération et sont projetés à grande énergie sur une électrode cible pour y produire une réaction de fusion entraînant une émission de neutrons, dans lequel ladite source d'ions est de type multicellulaire constitué d'une structure de cellules élémentaires de type Penning comportant pour l'ensemble desdites cellules une cavité cathodique à l'intérieur de laquelle est disposée une anode multitrous, les axes desdits trous étant alignés respectivement sur les axes correspondants desdits canaux d'émission.The invention relates to a sealed neutron tube containing a low-pressure deuterium-tritium gas mixture from which an ion source with two electrodes, an anode and a cathode, forms an ionized gas channeled by a confining magnetic field created by magnets or by any other means of creating said field, said source emitting from emission channels made in said cathode ion beams which pass through an extraction-acceleration electrode and are projected at high energy onto a target electrode for producing therein a fusion reaction resulting in the emission of neutrons, in which said ion source is of the multicellular type consisting of a structure of elementary cells of the Penning type comprising for all of said cells a cathode cavity inside which is disposed a multi-hole anode, the axes of said holes being aligned respectively on the corresponding axes desd its broadcast channels.
Un tel tube est connu de NL-A- 7707357.Such a tube is known from NL-A- 7707357.
Les tubes neutroniques du même genre sont utilisés dans les techniques d'examen de la matière par neutrons rapides, thermiques, épithermiques ou froids : neutronographie, analyse par activation, analyse par spectrométrie des diffusions inélastiques ou des captures radiatives, diffusion des neutrons etc...Neutron tubes of the same kind are used in techniques for examining matter by fast, thermal, epithermal or cold neutrons: neutronography, analysis by activation, analysis by spectrometry of inelastic diffusions or radiative captures, neutron scattering, etc. .
L'obtention de la pleine efficacité de ces techniques nucléaires nécessite d'avoir, pour les niveaux d'émission correspondants, des durées de vie de tubes plus longues.Obtaining the full effectiveness of these nuclear techniques requires having, for the corresponding emission levels, longer tube lifetimes.
La réaction de fusion d(3H, 4He)n délivrant des neutrons de 14 MeV est habituellement la plus utilisée en raison de sa grande section efficace pour des énergies d'ions relativement faibles. Toutefois, quelle que soit la réaction utilisée, le nombre de neutrons obtenu par unité de charge transitant dans le faisceau est toujours croissant au fur et à mesure que l'énergie des ions dirigés vers une cible épaisse est elle-même croissante et ceci largement au delà des énergies des ions obtenus dans les tubes scellés actuellement disponibles et alimentés par une THT n'excédant pas 250 kV.The fusion reaction d (3 H , 4 He ) n delivering 14 MeV neutrons is usually the most used because of its large cross section for relatively low ion energies. However, whatever the reaction used, the number of neutrons obtained per unit of charge passing through the beam is always increasing as the energy of the ions directed towards a thick target is itself increasing and this largely at the beyond the energies of the ions obtained in the sealed tubes currently available and supplied by a THT not exceeding 250 kV.
Parmi les principaux facteurs limitatifs de la durée de vie d'un tube neutronique, l'érosion de la cible par le bombardement ionique est l'un des plus déterminants.Among the main factors limiting the life of a neutron tube, the erosion of the target by ion bombardment is one of the most determining.
L'érosion est fonction de la nature chimique et de la structure de la cible d'une part, de l'énergie des ions incidents et de leur profil de répartition en densité sur la surface d'impact d'autre part.Erosion is a function of the chemical nature and structure of the target on the one hand, the energy of the incident ions and their density distribution profile on the impact surface on the other.
Dans la plupart des cas, la cible est constituée par un matériau hydrurable (Titane, Scandium, Zirconium, Erbium etc...) capable de fixer et de relâcher des quantités importantes d'hydrogène sans perturbation notable de sa tenue mécanique ; la quantité totale fixée est fonction de la température de la cible et de la pression d'hydrogène dans le tube. Les matériaux cibles utilisés sont déposés sous forme de couches minces dont l'épaisseur est limitée par des problèmes d'adhérence de la couche sur son support. Un moyen de retarder l'érosion de la cible consiste par exemple à former la couche active absorbante d'un empilage de couches identiques isolées les unes des autres par une barrière de diffusion. L'épaisseur de chacune des couches actives est de l'ordre de la profondeur de pénétration des ions deutérium venant frapper la cible.In most cases, the target consists of a hydrurable material (Titanium, Scandium, Zirconium, Erbium etc ...) capable of fixing and releasing large quantities of hydrogen without significant disturbance of its mechanical strength; the total quantity set is a function of the target temperature and the hydrogen pressure in the tube. The target materials used are deposited in the form of thin layers, the thickness of which is limited by problems of adhesion of the layer to its support. One way to delay erosion of the target is, for example, to form the absorbent active layer of a stack of identical layers isolated from each other by a diffusion barrier. The thickness of each of the active layers is of the order of the depth of penetration of the deuterium ions coming to strike the target.
Une autre façon de protéger la cible et donc d'accroître la durée de vie du tube consiste à agir sur le faisceau d'ions de manière à améliorer son profil de répartition en densité sur la surface d'impact. A courant d'ions total constant sur la cible ce qui entraîne une émission neutronique constante, cette amélioration résultera d'une répartition aussi uniforme que possible de la densité de courant sur l'ensemble de la surface offerte par la cible au bombardement des ions.Another way to protect the target and therefore increase the life of the tube is to act on the ion beam so as to improve its density distribution profile on the impact surface. At a constant total ion current on the target, which results in a constant neutron emission, this improvement will result from a distribution as uniform as possible of the current density over the entire surface offered by the target to the bombardment of the ions.
Dans un tube neutronique scellé, les ions sont en général fournis par une source d'ions de type Penning qui a l'avantage d'être robuste, d'être à cathode froide (d'où une longue durée d'utilisation), de donner des courants de décharge importants pour de faibles pressions (de l'ordre de 10 A/torr; 1 torr = 133,3 Pa), d'avoir un rendement d'extraction élevé (de 20 à 40 %) et d'être de faibles dimensions.In a sealed neutron tube, the ions are generally supplied by a Penning-type ion source which has the advantage of being robust, of being cold cathode (hence a long service life), of give large discharge currents for low pressures (of the order of 10 A / torr; 1 torr = 133.3 Pa), to have a high extraction yield (from 20 to 40%) and to be of small dimensions.
Ce type de source présente par contre l'inconvénient de nécessiter un champ magnétique de l'ordre du millier de gauss (1Gs = 10⁻⁴T), parallèle à l'axe de la chambre d'ionisation, introduisant une inhomogénéité transverse importante de densité de courant des ions à l'intérieur de la décharge et au niveau de l'extraction qui s'effectue suivant l'axe commun du champ et de la source.However, this type of source has the disadvantage of requiring a magnetic field of the order of a thousand gauss (1Gs = 10⁻⁴T), parallel to the axis of the ionization chamber, introducing significant transverse inhomogeneity in density. current of the ions inside the discharge and at the level of the extraction which is carried out along the common axis of the field and the source.
Un autre inconvénient résulte du fait que les ions extraits et accélérés vers la cible vont réagir avec les molécules du gaz contenu dans le tube à une pression au premier ordre constante pour produire des effets d'ionisation, de dissociation et d'échange de charges entraînant d'une part une diminution de l'énergie sur la cible, c'est-à-dire une réduction de la production de neutrons et d'autre part la formation d'ions et d'électrons qui sont ensuite accélérés et vont bombarder la source d'ions ou les électrodes du tube.Another disadvantage results from the fact that the ions extracted and accelerated towards the target will react with the molecules of the gas contained in the tube at a constant first order pressure to produce effects of ionization, dissociation and charge exchange resulting on the one hand a reduction in the energy on the target, that is to say a reduction in the production of neutrons and on the other hand the formation of ions and electrons which are then accelerated and will bombard the ion source or the tube electrodes.
Il en résultera des dépôts d'énergie qui vont accroître la température des matériaux des électrodes tels que le molybdène ou l'acier inoxydable. L'échauffement de ces matériaux va provoquer la désorption d'impuretés telles que l'oxyde de carbone qu'ils renferment et perturber ainsi la qualité de l'atmosphère du tube. Les ions d'impuretés formés dans le tube, Co⁺ par exemple, vont bombarder la cible avec un coefficient de pulvérisation supérieur d'un facteur 10² à 10³ à celui des ions deutérium-tritium, d'où une accentuation importante de l'érosion. Ces effets croissent avec la pression de fonctionnement dans le tube neutronique.This will result in energy deposits which will increase the temperature of the electrode materials such as molybdenum or stainless steel. The heating of these materials will cause the desorption of impurities such as the carbon monoxide which they contain and thus disturb the quality of the atmosphere of the tube. The impurity ions formed in the tube, Co⁺ for example, will bombard the target with a spray coefficient higher by a factor of 10² to 10³ than that of the deuterium-tritium ions, resulting in a significant increase in erosion . These effects increase with the operating pressure in the neutron tube.
Le but de l'invention est de procurer un dispositif de source permettant de pallier lesdits inconvénients.The object of the invention is to provide a source device enabling these disadvantages to be overcome.
A cet effet l'invention est remarquable en ce que, le nombre desdits trous est optimisé de façon à accroître le faisceau d'ions extrait pour un encombrement équivalent de ladite source d'ions, et la forme et/ou les dimensions et/ou le positionnement desdits trous sont adaptés à la topologie dudit champ magnétique, de façon telle que le rayon desdits trous d'anode de ladite source d'ions est augmenté progressivement du centre vers la périphérie de la structure.To this end, the invention is remarkable in that, the number of said holes is optimized so as to increase the extracted ion beam for an equivalent bulk of said ion source, and the shape and / or dimensions and / or positioning of said holes are adapted to the topology of said magnetic field , so that the radius of said anode holes of said ion source is gradually increased from the center to the periphery of the structure.
On notera qu'il est connu, de la demande de brevet NL-A 77 07357 un tube neutronique de type multicellulaire comportant, pour l'ensemble des cellules une cavité cathodique à l'intérieur de laquelle est disposée une anode multitrous, les axes des trous étant respectivement sur les axes correspondants des canaux d'émission, dans la cathode.Note that it is known, from patent application NL-A 77 07357, a multicellular type neutron tube comprising, for all of the cells a cathode cavity inside which is arranged a multi-hole anode, the axes of the holes respectively on the corresponding axes of the emission channels in the cathode.
Il faut noter en outre qu'un gain complémentaire du courant de décharge peut résulter de l'accroissement de longueur de la structure de la source d'ions multicellulaire. Ce gain peut aller jusqu'à un facteur 2.It should also be noted that an additional gain in the discharge current may result from the increase in length of the structure of the multicellular ion source. This gain can go up to a factor of 2.
L'accroissement de courant résultant de la nouvelle configuration de source peut alors être utilisé pour diminuer la pression de fonctionnement du tube neutronique et limiter ainsi l'incidence nocive des réactions ions-gaz.The increase in current resulting from the new source configuration can then be used to reduce the operating pressure of the neutron tube and thus limit the harmful impact of ion-gas reactions.
La faisabilité de la structure multicellulaire suppose qu'un champ magnétique est adapté au bon fonctionnement d'une structure Penning en particulier au niveau de la relation entre l'induction magnétique et le rayon de trou de l'anode multitrous.The feasibility of the multicell structure assumes that a magnetic field is suitable for the proper functioning of a Penning structure, in particular at the level of the relationship between the magnetic induction and the hole radius of the multi-hole anode.
La variation du champ magnétique en niveau et suivant la forme des lignes de force peut être corrigée par un accroissement dudit rayon, ce qui revient à faire des structures à rayon d'anode variable. De plus, une meilleure adaptation de la forme de l'anode aux lignes de force magnétiques peut être obtenue en remplaçant les structures cylindriques à section circulaire ou carrée par des structures tronconiques de façon à faire coïncider les génératrices de troncs de cône avec les lignes de force qui s'appuient sur les contours des trous.The variation of the magnetic field in level and according to the shape of the lines of force can be corrected by an increase in said radius, which amounts to making structures with a variable anode radius. In addition, better adaptation of the shape of the anode to the main lines magnetic can be obtained by replacing the cylindrical structures with circular or square section by frustoconical structures so as to make the generators of truncated cones coincide with the lines of force which rest on the contours of the holes.
L'émission des ions des différentes structures s'effectue à travers des canaux pratiqués dans la cathode faisant office d'électrode d'émission. Ces canaux, dont le nombre est identique à celui des cellules élémentaires, sont disposés respectivement suivant les mêmes axes de symétrie. Dans les cas de structures à section circulaire, le diamètre est fonction du champ électrique appliqué et de l'épaisseur de l'électrode.The ions of the various structures are emitted through channels made in the cathode acting as an emission electrode. These channels, the number of which is identical to that of the elementary cells, are arranged respectively along the same axes of symmetry. In the case of circular section structures, the diameter is a function of the applied electric field and the thickness of the electrode.
Une variante de ce système consiste à introduire en dessous des cathodes une chambre d'expansion afin d'uniformiser les densités au voisinage de l'émission qui se fait alors à travers des orifices dont la disposition peut être quasi indépendante de celle des cellules élémentaires.A variant of this system consists in introducing an expansion chamber below the cathodes in order to standardize the densities in the vicinity of the emission which then takes place through orifices the arrangement of which can be almost independent of that of the elementary cells.
Dans un tube neutronique de l'invention, l'électrode d'extraction-accélération peut être constituée par une électrode munie de n orifices ayant des axes correspondant respectivement à ceux des n cellules élémentaires, ou de j orifices inférieurs au nombre de n cellules élémentaires et donc des diamètres supérieurs à ceux des canaux d'émission et dont la disposition évite toute interception des faisceaux.In a neutron tube of the invention, the extraction-acceleration electrode can be constituted by an electrode provided with n orifices having axes corresponding respectively to those of the n elementary cells, or with j orifices smaller than the number of n elementary cells and therefore diameters greater than those of the emission channels and whose arrangement avoids any interception of the beams.
L'épaisseur de cette électrode d'extraction-accélération peut être augmentée afin d'améliorer la tenue mécanique et de permettre un refroidissement par circulation forcée de fluide.The thickness of this extraction-acceleration electrode can be increased in order to improve the mechanical strength and to allow cooling by forced circulation of fluid.
La description suivante en regard des dessins annexés, le tout donné à titre d'exemple, fera bien comprendre comme l'invention peut être réalisée.The following description with reference to the appended drawings, all given by way of example, will make it clear how the invention can be implemented.
La figure 1 représente le schéma de principe d'un tube neutronique scellé selon l'état de l'art antérieur.Figure 1 shows the block diagram of a sealed neutron tube according to the state of the prior art.
La figure 2 montre les effets de l'érosion en profondeur de la cible et le profil radial de densité de bombardement d'ions.Figure 2 shows the effects of target erosion at depth and the radial profile of ion bombardment density.
La figure 3 représente le schéma d'un tube neutronique d'un type connu, compatible avec l'invention, muni d'une source d'ions multicellulaire de type Penning et d'une électrode d'extraction-accélération comportant autant d'orifices que de cellules.FIG. 3 represents the diagram of a neutron tube of a known type, compatible with the invention, provided with a multicellular ion source of the Penning type and with an extraction-acceleration electrode comprising as many orifices than cells.
La figure 4 représente un tube neutronique d'un type connu compatible avec l'invention, muni d'une source d'ions multicellulaire et d'une électrode d'extraction-accélération comportant un nombre d'orifices différent du nombre de cellules.FIG. 4 represents a neutron tube of a known type compatible with the invention, provided with a multicellular ion source and with an extraction-acceleration electrode comprising a number of orifices different from the number of cells.
La figure 5 représente une première variante du tube neutronique de l'invention, munie d'une source d'ions dont les trous d'anode sont de rayons variables.FIG. 5 represents a first variant of the neutron tube of the invention, provided with an ion source whose anode holes are of variable radii.
La figure 6 représente une deuxième variante du tube neutronique de l'invention muni d'une source dont les trous d'anode sont de forme tronconique.FIG. 6 represents a second variant of the neutron tube of the invention provided with a source whose anode holes are of frustoconical shape.
La figure 7 représente une troisième variante du tube neutronique de l'invention selon la première variante ou selon les première et deuxième variantes, muni d'une source avec chambre d'expansion.FIG. 7 represents a third variant of the neutron tube of the invention according to the first variant or according to the first and second variants, provided with a source with expansion chamber.
Les éléments identiques sur lesdites figures seront indiqués par les mêmes signes de référence.Identical elements in said figures will be indicated by the same reference signs.
Le schéma de la figure 1 montre les principaux éléments de base d'un tube neutronique scellé 11 renfermant un mélange gazeux sous faible pression à ioniser tel que deutérium-tritium et qui comporte une source d'ions 1 et une électrode d'extraction-accélération 2 entre lesquelles existe une différence de potentiel très élevée permettant l'extraction et l'accélération du faisceau d'ions 3 et sa projection sur la cible 4 où s'effectue la réaction de fusion entraînant une émission de neutrons à 14 MeV par exemple.The diagram in FIG. 1 shows the main basic elements of a sealed
La source d'ions 1 solidaire d'un isolateur 5 pour le passage du connecteur d'alimentation en THT (non représenté) est une source de type Penning par exemple, constituée d'une anode cylindrique 6, d'une cavité cathodique 7 à laquelle est incorporé un aimant 8 à champ magnétique axial qui confine le gaz ionisé 9 aux alentours de l'axe du cylindre d'anode et dont les lignes de force 10 accusent une certaine divergence. Un canal d'émission des ions 12 est pratiqué dans ladite cavité cathodique en vis-à-vis de l'anodeThe ion source 1 secured to an
Les schémas de la figure 2 représentent les effets de l'érosion sur la cible au fur et à mesure que s'accentue le phénomène.The diagrams in Figure 2 represent the effects of erosion on the target as the phenomenon increases.
La figure 2a montre le profil de la densité J de bombardement des ions suivant une direction radiale quelconque Or, à partir du point d'impact O de l'axe central du faisceau sur la surface de la cible. La forme de ce profil met en valeur le caractère inhomogène de ce faisceau dont la densité très élevée dans la partie centrale décroît rapidement lorsqu'on s'en éloigne.FIG. 2a shows the profile of the density J of bombardment of the ions in any radial direction Or, from the point of impact O of the central axis of the beam on the target surface. The shape of this profile highlights the inhomogeneous nature of this beam whose very high density in the central part decreases rapidly when one moves away from it.
Sur la figure 2b l'érosion s'effectue en fonction de la densité de bombardement et toute la couche de matériau hydrurable d'épaisseur e déposée sur un substrat S est saturée en mélange deutérium-tritium. La profondeur de pénétration des ions énergétiques deutérium-tritium représentée en traits pointillés s'effectue sur une profondeur l₁ fonction de cette énergie.In FIG. 2b, erosion takes place as a function of the bombardment density and the entire layer of hydrurable material of thickness e deposited on a substrate S is saturated with a deuterium-tritium mixture. The depth of penetration of the deuterium-tritium energetic ions represented in dotted lines takes place over a depth which is a function of this energy.
Sur la figure 2c, l'érosion de la couche est telle que la profondeur de pénétration l₂ est supérieure à l'épaisseur e dans la partie la plus bombardée ; une partie des ions incidents s'implante dans le substrat et très rapidement les atomes de deutérium et de tritium sont en sursaturation.In FIG. 2c, the erosion of the layer is such that the penetration depth l₂ is greater than the thickness e in the most bombarded part; a part of the incident ions is implanted in the substrate and very quickly the atoms of deuterium and tritium are in supersaturation.
Sur la figure 2d, les atomes de deutérium et de tritium se sont rassemblés pour donner des bulles qui, en éclatant ont formé des cratères et accru très rapidement l'érosion de la cible sur la profondeur l₃.In FIG. 2d, the atoms of deuterium and of tritium have gathered to give bubbles which, when they burst, formed craters and very quickly increased the erosion of the target at depth l₃.
Ce dernier processus précède de peu la fin de vie du tube en entraînant soit un accroissement drastique des claquages (présence de microparticules résultant des éclatements de bulles), soit une pollution de la surface de la cible par les atomes pulvérisés absorbant l'énergie des ions incidents.This last process just precedes the end of the tube's life by causing either a drastic increase in breakdowns (presence of microparticles resulting from the bursting of bubbles), or pollution of the target surface by atomized atoms absorbing the energy of the ions. incidents.
On a schématisé sur la figure 3 un tube neutronique muni d'une source d'ions multicellulaire de type Penning constituée d'une cavité cathodique 7 et d'une anode multitrous 6, portée à un potentiel supérieur de 4 à 8 kV à celui de la cavité cathodique portée elle-même à une très haute tension de 250 kV par exemple.FIG. 3 shows a neutron tube provided with a multicellular ion source of the Penning type consisting of a
L'aimant 8 fournit un champ magnétique de confinement du gaz ionisé de l'ordre du millier de gauss.The
L'invention consiste à exploiter dans une première étape connue, la propriété des structures de décharge multicellulaire avec confinement de type magnétique, à savoir que pour une même section d'anode, le courant de décharge ainsi que le courant du faisceau d'ions extraits de cette décharge sont respectivement supérieurs dans le cas d'une structure de source multicellulaire aux mêmes courants obtenus dans le cas d'une structure monocellulaire. De même il est plus avantageux d'utiliser une structure multicellulaire à n trous d'anode qu'une structure multicellulaire à m trous si n > m. Chaque section de la structure à n trous est alors plus réduite que chacune des sections de la structure à m trous ; mais l'avantage précité n'est assuré que si la section d'anode reste équivalente pour lesdites structures, ce qui permet de diminuer la pression du mélange gazeux et de ce fait, la probabilité des réactions ions-gaz.The invention consists in exploiting, in a first known step, the property of multicellular discharge structures with confinement of magnetic type, namely that for the same anode section, the discharge current as well as the current of the ion beam extracted from this discharge are respectively greater in the case of a multicellular source structure than the same currents obtained in the case of a single-cell structure. Similarly, it is more advantageous to use a multicell structure with n anode holes than a multicell structure with m holes if n> m. Each section of the structure with n holes is then smaller than each of the sections of the structure with m holes; but the aforementioned advantage is only ensured if the anode section remains equivalent for said structures, which makes it possible to reduce the pressure of the gaseous mixture and therefore the probability of ion-gas reactions.
On a ainsi constitué de façon connue une nouvelle structure à n cellules comportant l'anode multitrous 6 ayant n trous 6₁, 6₂,... 6n et la cathode 7 dans laquelle on a pratiqué en vis-à-vis desdits trous anodiques les canaux d'émission 7₁, 7₂,... 7n à partir desquels n faisceaux ioniques sont extraits. Ces multifaisceaux 3 sont projetés sur la cible 4 au moyen de l'électrode d'extraction-accélération 2 comportant le même nombre d'orifices 2₁, 2₂,... 2n que celui desdits faisceaux et disposés suivant les mêmes axes.A new structure with n cells has thus been constituted in known manner comprising the
Dans un autre dispositif de tube neutronique schématisé sur la figure 4 le nombre d'orifices pratiqué dans l'électrode d'extraction-accélération est moindre que celui des faisceaux issus de la source : par exemple chaque orifice 13 de cette électrode 2 livre passage à deux faisceaux de la source comme il est représenté sur la figure.In another neutron tube device shown diagrammatically in FIG. 4, the number of orifices made in the extraction-acceleration electrode is less than that of the beams coming from the source: for example each
Dans une structure de source d'ions multicellulaire, la divergence des lignes de force du champ magnétique montre que celui-ci est très élevé dans la zone centrale et diminue progressivement jusqu'à une valeur très faible sur la périphérie. Pour compenser cette variation, les trous d'anode 6′₁, 6′₂,..., 6′n sont, selon l'invention, constitués comme indiqué sur la figure 5 avec des rayons variables en sens inverse du champ magnétique de telle façon que le produit de l'induction magnétique par le rayon d'anode reste sensiblement constant. Cette disposition tend à uniformiser la densité de courant ionique.In a multicellular ion source structure, the divergence of the lines of force of the magnetic field shows that it is very high in the central area and gradually decreases to a very low value on the periphery. To compensate for this variation, the anode holes 6′₁, 6′₂, ..., 6 ′ n are, according to the invention, constituted as shown in FIG. 5 with radii varying in opposite directions to the magnetic field so that the product of magnetic induction by the anode radius remains substantially constant. This arrangement tends to standardize the density of ion current.
Le dispositif représenté sur la figure 6 apporte une amélioration sensible par le fait que les trous d'anode 6˝₁, 6˝₂,..., 6˝n ont des formes tronconiques qui épousent approximativement les lignes de force du champ magnétique.The device shown in Figure 6 provides a significant improvement in that the
Sur la figure 7 une chambre d'expansion 14 est disposée en dessous des cathodes afin d'uniformiser les densités ioniques. L'émission est effectuée par des orifices 15 dont le nombre peut être indépendant de celui des trous de l'anode multitrous.In FIG. 7, an
Ainsi, l'augmentation du rapport de l'intensité du faisceau à la pression dans le tube neutronique, résultant de la structure de source multicellulaire de l'invention peut être exploitée de diverses manières :
- A parcours ionique identique, les créations de paires ions/électrons sur le trajet du faisceau d'ions sont moins nombreuses et l'énergie déposée dans la source d'ions par les électrons réaccélérés est moindre ; l'échauffement de la source d'ions est plus faible et par conséquent le dégazage des matériaux constitutifs est réduit. Les ions lourds résultant de ce dégazage sont moins nombreux et leur contribution à l'érosion de la cible plus faible. Par ailleurs l'énergie moyenne des ions deutérium-tritium est accrue, ce qui peut permettre de réduire le courant tube.
- A courant de faisceau identique, il est possible d'accroître les distances interélectrodes et de diminuer ainsi le champ électrique afin de réduire les phénomènes d'émission froide.
- A courant de faisceau intégré (sur l'unité de temps) identique, on peut accroître le courant maximal en mode pulsé dans le rapport des pressions Pmax/P, Pmax étant la pression maximale de fonctionnement n'entraînant pas un changement du régime de fonctionnement du tube (passage de la décharge en régime d'arc).
- En outre la répartition du courant sur la cible est beaucoup plus homogène en raison d'une part de l'homogénéité de la décharge au niveau des canaux d'émission et d'autre part de la multiplication du nombre de faisceaux élémentaires. Il en résulte une décroissance de la densité ionique maximale et à courant de faisceau identique un accroissement de durée de vie.
- With an identical ion path, the creations of ion / electron pairs on the path of the ion beam are less numerous and the energy deposited in the ion source by the re-accelerated electrons is less; the heating of the ion source is lower and consequently the degassing of the constituent materials is reduced. The heavy ions resulting from this degassing are less numerous and their contribution to the erosion of the target weaker. In addition, the average energy of the deuterium-tritium ions is increased, which can make it possible to reduce the tube current.
- At identical beam current, it is possible to increase the interelectrode distances and thus reduce the electric field in order to reduce the cold emission phenomena.
- With the same integrated beam current (over the time unit), the maximum current can be increased in pulsed mode in the pressure ratio Pmax / P, Pmax being the maximum operating pressure not causing a change in the operating regime of the tube (passage of the discharge in arc mode).
- In addition, the distribution of the current on the target is much more homogeneous due on the one hand to the homogeneity of the discharge at the level of the emission channels and on the other hand to the multiplication of the number of elementary beams. This results in a decrease in the maximum ion density and at the same beam current an increase in lifetime.
Claims (6)
- A sealed neutron tube which contains a low-pressure gaseous deuteriumtritium mixture wherefrom an ion source comprising two electrodes, an anode and a cathode, forms an ionised gas which is guided by a magnetic confinement field produced by magnets (8) or any other means for producing said field, which source emits, via emission channels formed in said cathode, ion beams which traverse an extraction-acceleration electrode (2) and which are projected with high energy onto a target electrode (4) in order to produce therein a fusion reaction which causes an emission of neutrons, said ion source being a multi-cell type which is formed by a structure of Penning-type elementary cells comprising, for said cells together, a cathode cavity (7) in which there is arranged a multi-hole anode (6), the axes of said holes being aligned with the corresponding axes of said emission channels, characterized in that the number of said holes is optimised so as to enlarge the extracted ion beam for equivalent coverage of said ion source, and the shape and/or the dimensions and/or the position of said holes are adapted to the topology of said magnetic field, in such a manner that the radius of said anode holes (6′₁, 6′₂, ..., 6′n) of said ion source progressively increases from the centre towards the periphery of the structure in order to take into account the topology of the magnetic field.
- A neutron tube as claimed in Claim 1, characterized in that said holes (6˝₁, 6˝₂, 100, 6˝n) of said ion source have a truncated shape so as to be adapted to the topology of the magnetic field.
- A neutron tube as claimed in Claim 1 or 2, characterized in that an expansion chamber (14) is arranged underneath said ion source in order to enhance the uniformity of the densities at the area of the ion emission, formed in the wall of the chamber which faces the target, via orifices (15) whose disposition and number may be quasiindependent of those of said elementary cells.
- A neutron tube as claimed in the Claims 1 to 3, characterized in that said extraction-acceleration electrode (2) comprises a number of orifices (2₁, 2₂, ..., 2n) equal to the number of anode holes, which orifices are disposed along the axes of said emission channels.
- A neutron tube as claimed in the Claims 1 to 4, characterized in that said extraction-acceleration electrode (2) comprises a number of orifices which is smaller than the number of anode holes, the disposition of said orifices on the extraction-acceleration electrode precluding interception of the beams.
- A neutron tube as claimed in the Claims 4 and 5, characterized in that the thickness of said extraction-acceleration electrode (2) is increased in order to improve its mechanical strength and to enable cooling of the electrode by forced circulation of liquids.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| FR8813187 | 1988-10-07 | ||
| FR8813187A FR2637726A1 (en) | 1988-10-07 | 1988-10-07 | SEALED NEUTRON TUBE EQUIPPED WITH A MULTICELLULAR ION SOURCE WITH MAGNETIC CONTAINMENT |
Publications (2)
| Publication Number | Publication Date |
|---|---|
| EP0362947A1 EP0362947A1 (en) | 1990-04-11 |
| EP0362947B1 true EP0362947B1 (en) | 1995-04-26 |
Family
ID=9370794
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| EP89202465A Expired - Lifetime EP0362947B1 (en) | 1988-10-07 | 1989-10-02 | Sealed neutron tube equipped with a multicellular ion source with magnetic confinement |
Country Status (5)
| Country | Link |
|---|---|
| US (1) | US5078950A (en) |
| EP (1) | EP0362947B1 (en) |
| JP (1) | JP2825025B2 (en) |
| DE (1) | DE68922364T2 (en) |
| FR (1) | FR2637726A1 (en) |
Families Citing this family (11)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| FR2666477A1 (en) * | 1990-08-31 | 1992-03-06 | Sodern | HIGH FLOW NEUTRONIC TUBE. |
| FR2710782A1 (en) | 1993-09-29 | 1995-04-07 | Sodern | Neutron tube with magnetic confinement of electrons by permanent magnets and its manufacturing process. |
| JP3122081B2 (en) * | 1998-11-25 | 2001-01-09 | 石油公団 | Neutron generator tube |
| US6441569B1 (en) | 1998-12-09 | 2002-08-27 | Edward F. Janzow | Particle accelerator for inducing contained particle collisions |
| US20100301196A1 (en) * | 2007-05-02 | 2010-12-02 | Wei-Kan Chu | portable/mobile fissible material detector and methods for making and using same |
| US8891721B1 (en) | 2011-03-30 | 2014-11-18 | Sandia Corporation | Neutron generators with size scalability, ease of fabrication and multiple ion source functionalities |
| CN102243900A (en) * | 2011-06-28 | 2011-11-16 | 中国原子能科学研究院 | Primary neutron source component for starting nuclear reactor |
| CN102709140B (en) * | 2012-05-23 | 2014-09-17 | 四川大学 | Gas discharging type ion source for neutron pipe |
| RU2634483C1 (en) * | 2016-12-09 | 2017-10-31 | Федеральное государственное бюджетное научное учреждение "Федеральный исследовательский центр Институт прикладной физики Российской академии наук" (ИПФ РАН) | Source of neutrons of limited dimensions for neutron tomography |
| IL281747B2 (en) | 2021-03-22 | 2024-04-01 | N T Tao Ltd | High efficiency plasma creation system and method |
| RU209936U1 (en) * | 2021-11-24 | 2022-03-24 | Федеральное Государственное Унитарное Предприятие "Всероссийский Научно-Исследовательский Институт Автоматики Им.Н.Л.Духова" (Фгуп "Внииа") | Pulse neutron generator |
Family Cites Families (10)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US2806161A (en) * | 1952-07-08 | 1957-09-10 | Jr John S Foster | Coasting arc ion source |
| GB980947A (en) * | 1961-06-30 | 1965-01-20 | Atomic Energy Authority Uk | Neutron generator |
| FR1369531A (en) * | 1963-06-12 | 1964-08-14 | Commissariat Energie Atomique | Penning type ion source |
| DE1303276B (en) * | 1964-08-18 | Philips Nv | ||
| JPS594819B2 (en) * | 1975-10-08 | 1984-02-01 | 双葉電子工業株式会社 | ion source |
| NL7707357A (en) * | 1977-07-04 | 1979-01-08 | Philips Nv | Anode for neutron generator ion source - has holes aligned to outlets in cathode converging beams on target |
| US4423355A (en) * | 1980-03-26 | 1983-12-27 | Tokyo Shibaura Denki Kabushiki Kaisha | Ion generating apparatus |
| US4447773A (en) * | 1981-06-22 | 1984-05-08 | California Institute Of Technology | Ion beam accelerator system |
| GB2136328B (en) * | 1983-02-17 | 1986-02-12 | Marconi Co Ltd | A method of making a grid |
| FR2550681B1 (en) * | 1983-08-12 | 1985-12-06 | Centre Nat Rech Scient | ION SOURCE HAS AT LEAST TWO IONIZATION CHAMBERS, PARTICULARLY FOR THE FORMATION OF CHEMICALLY REACTIVE ION BEAMS |
-
1988
- 1988-10-07 FR FR8813187A patent/FR2637726A1/en not_active Withdrawn
-
1989
- 1989-10-02 EP EP89202465A patent/EP0362947B1/en not_active Expired - Lifetime
- 1989-10-02 DE DE68922364T patent/DE68922364T2/en not_active Expired - Fee Related
- 1989-10-04 US US07/416,811 patent/US5078950A/en not_active Expired - Fee Related
- 1989-10-06 JP JP1260309A patent/JP2825025B2/en not_active Expired - Lifetime
Also Published As
| Publication number | Publication date |
|---|---|
| US5078950A (en) | 1992-01-07 |
| JP2825025B2 (en) | 1998-11-18 |
| JPH02276198A (en) | 1990-11-13 |
| DE68922364D1 (en) | 1995-06-01 |
| FR2637726A1 (en) | 1990-04-13 |
| DE68922364T2 (en) | 1995-12-14 |
| EP0362947A1 (en) | 1990-04-11 |
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