EP1080613B1 - Device for generating a magnetic field inside a chamber - Google Patents

Description

The present invention relates to a device for creating a magnetic field inside an enclosure.

More particularly, the present invention relates to a device intended to create a magnetic field in order to confine a plasma inside an enclosure.

Plasmas are ionized gases, electrically mixed neutral ions and electrons, used in industry, in particular, for make very thin deposits on surfaces.

Plasma can be created by various methods, for example, from non-ionized atoms which we bring, in the form of vapor, in an enclosure containing a magnetic field having a configuration determined. The term configuration takes into account both the spatial geometry of the magnetic field and its intensity at any point the space where he reigns.

The configuration of the control mainly depends on the arrangement of magnetic field generating means around the enclosure. By placing them appropriately, we can achieve in the enclosure a field having the desired configuration.

The atoms are ionized, for example, by energetic electrons called "heated by a high frequency wave propagating in the enclosure and coupled with the magnetic field B reigning in the enclosure, according to the relation: B = (2πmf) / e where m and e are respectively the mass and the charge of the electron and f the frequency of the high-frequency wave.

The electrons, torn from the nuclei of atoms under the effect of the high frequency wave, are subjected to the magnetic field B and describe then spiral movements while colliding with the other atoms surrounding, thus causing their ionization.

The ions and electrons constituting the plasma cannot describe as spiral trajectories, the plasma is thus confined in a restricted volume delimited by the magnetic field B, that is to say that this serves, in a way, as an intangible plasma container. The shocks between atoms and electrons accelerate the ionization of gas atoms not ionized or already ionized. It is thus possible to tear off several electrons to the same atom and form multi-charged ions.

The magnetic field prevailing in the enclosure is produced by permanent magnets or coils placed outside of the enclosure. In general, the intensity of the field used is between 0.01 T and several Teslas. The fields generated by these magnets or coils do create a configuration magnetic field determined, that in very small volumes, of the order of a few liters.

When it comes to creating magnetic fields in larger volumes, coils of superconductive materials are used. These windings must be cooled to temperatures of the order of 4 K, helium liquefaction temperature.

These windings are surrounded by several envelopes containing sufficient liquid helium to keep them at the desired temperature. This cooling device requires having the superconductive coils at a distance of at least 5 cm from the walls of the enclosure, which considerably hinders the establishment of a field magnetic of arbitrary configuration inside the enclosure.

There are already devices for creating a field magnetic inside an enclosure such as those described in the Patent Abstracts of Japan, vol. 013, n ° 220 (E-762) of May 23, 1989 or in Patent Abstracts of Japan, vol. 013, n ° 184 (E-751) of April 28 1989 or even in DE 12 44 975 B, which in particular use a winding made with a material having properties superconductive and arranged around the enclosure.

Under these conditions, two problems arise: either all the interior space of the enclosure cannot be properly magnetized, i.e. that the intensity of the magnetic field does not reach the desired value at all points in the space inside the enclosure, i.e. the intensity of the field is high enough but then it is impossible to get the desired configuration of the field inside the enclosure.

The aim of the present invention is to solve the problems techniques posed by the prior art.

• des moyens générateurs de champ magnétique susceptibles d'entourer au moins partiellement ladite enceinte, en étant placés à une distance de la paroi de ladite enceinte, comprise entre 1 mm et 50 mm de la paroi de ladite enceinte, et comprenant au moins un bobinage réalisé avec un matériau présentant des propriétés supraconductrices entre 16 K et 273 K ainsi qu'un système cryogénique destiné à maintenir lesdits moyens générateurs de champ magnétique à cette température, caractérisé en ce qu'il comporte en outre des organes de déplacement d'au moins une partie des moyens générateurs de champ magnétique permettant de moduler la configuration du champ magnétique régnant dans l'enceinte pour produire différents types d'ions et obtenir pour chacun d'eux la résonance cyclotronique électronique (ECR).

This object is achieved by means of a device intended to create a magnetic field inside the enclosure capable of receiving at least one material in the atomic state, in vapor phase in order to extract the ions, electrons there. or electromagnetic radiation from the ionization of this material, comprising in particular:

• magnetic field generating means capable of at least partially surrounding said enclosure, being placed at a distance from the wall of said enclosure, between 1 mm and 50 mm from the wall of said enclosure, and comprising at least one coil produced with a material having superconductive properties between 16 K and 273 K as well as a cryogenic system intended to maintain said magnetic field generating means at this temperature, characterized in that it further comprises displacement members of at least one part of the magnetic field generating means for modulating the configuration of the magnetic field prevailing in the enclosure to produce different types of ions and obtain for each of them the electronic cyclotron resonance (ECR).

Preferably, the magnetic field generating means are arranged at a distance from the wall of the enclosure between 1 mm and 50 mm.

The device using superconductive materials between 16 K and 273K, it is then possible to get rid of the refrigeration using liquid helium. We can for example use a "Cryocooler" type cryogenic system which not only allows the approximation of the coils, but also, has the advantage of being less bulky, less expensive and more flexible and safer to use than helium cryogenic system. The cost of installation is so greatly reduced and the safety of the installation improved.

For example, a device using a conventional helium cryogenic system generally occupies a volume of 1 m ³ and weighs several hundred kilos. On the contrary, a device using a cryogenic system of the "Cryocooler" type occupies a volume of only a few tens of liters.

In addition, the use of superconductive materials allows significantly reduce the amount of electricity consumed reducing thus the cost of using any device comprising the device according to the present invention.

Such a device can be used, for example, to confine a plasma produced in another device.

The very small distance between the wall and the generating means allows to establish, at any point located inside a volume enclosure any magnetic field of the order of 1 to 5 T sufficient to multiple applications.

Advantageously, this device also comprises a system injecting atoms into the enclosure and an ion extraction system and electrons from the plasma contained in the enclosure. Such a device can then be integrated into the structure of various devices.

Advantageously, this device will also comprise a ionization system of the atoms injected into the enclosure.

Advantageously, the device will also comprise a device for guiding a high frequency wave inside said wave pregnant. Such a device then makes it possible to achieve ionization of the atoms by generating electronic cyclotron resonance (ECR), as exposed in the prior art. This method has the advantage of not using of filament which, when consumed, reduce the life of the device whole.

Advantageously, such a device can further comprise an extraction system making it possible to obtain a wide beam delimiting an area of approximately 1 m ² . It could then be used, for example, for the production of wide beams, or the production of an apparatus intended to treat surfaces on an industrial scale. Since the volume magnetized by the device according to the present invention can be very large, the part to be treated can be completely immersed in the plasma. Its processing is then much easier and faster than with a beam that must be moved on the surface of said part. The deposit thus made is perfectly uniform.

Advantageously, the device according to the present invention further includes a heavy element extraction system likely to be contained in plasma.

Advantageously, the device according to the present invention, further comprises means for regulating the intensity of the current electric traversing at least one winding. These means of regulation can be, for example, simple potentiometers. It is possible to combine means for regulating the intensity of the current in the winding with one or more displacement members of said winding or other magnetic field generating means.

One use of the device according to the present invention is production of devices for the production of plasmas.

Another possible example of using the device according to the invention is the production of an apparatus intended for the production of rays X using the ECR atom ionization method, previously exposed.

A third example of application of the device according to the invention is the implementation of a surface treatment device.

• la figure 1a représente un mode de réalisation particulier de la présente invention et la figure 1b représente les différentes configurations qu'il est possible d'obtenir en utilisant le dispositif de la figure 1a ;
• la figure 2a représente un mode de réalisation particulier, utilisé pour la production d'un plasma ; la figure 2b représente un exemple de configuration du champ magnétique à l'intérieur de l'enceinte ;
• la figure 3a représente un second mode de réalisation de la présente invention, utilisé pour produire des ions multi-chargés ; la figure 3b représente un exemple de configuration du champ utilisé ;
• la figure 4 représente schématiquement un troisième mode de réalisation utilisé dans un système de production de plasma larges et uniformes pour le traitement industriel de grandes surfaces ;
• la figure 5a représente schématiquement un quatrième mode de réalisation utilisé, par exemple, pour la fabrication d'un appareil destiné à produire des rayons X ; la figure 5b représente un exemple d'une configuration préférée du champ magnétique utilisé dans ce dispositif ;

The invention will be clearly understood and its advantages will appear better on reading the detailed description which follows, of the embodiments shown by way of nonlimiting examples. All the embodiments must include displacement members as defined in claim 1. The description refers to the appended drawings in which:

• Figure 1a shows a particular embodiment of the present invention and Figure 1b shows the different configurations that can be obtained using the device of Figure 1a;
• FIG. 2a represents a particular embodiment, used for the production of a plasma; FIG. 2b represents an example of configuration of the magnetic field inside the enclosure;
• Figure 3a shows a second embodiment of the present invention, used to produce multi-charged ions; FIG. 3b represents an example of configuration of the field used;
• FIG. 4 schematically represents a third embodiment used in a system for producing large and uniform plasma for the industrial treatment of large areas;
• FIG. 5a schematically represents a fourth embodiment used, for example, for the manufacture of an apparatus intended to produce X-rays; FIG. 5b represents an example of a preferred configuration of the magnetic field used in this device;

Figure 1a shows a particular embodiment to obtain a magnetic field B prevailing in an enclosure 10 and having a cylindrical geometry with respect to an axis of symmetry z. Five coils, 20, 21, 22, 23 and 24 create an axial magnetic field Bz, i.e. parallel to the z axis.

Placed in the center of these coils are two multipoles 26 and 28 intended to create a radial field Br. The resulting magnetic field, prevailing in the enclosure will therefore have a radial component Br and a axial component Bz. The coils 20, 21, 22, 23 and 24 are contained in an envelope 30 connected, for example, to a Cryocooler (not shown in Figure 1a), so as to maintain them at a temperature between 16K and 273K. These windings are connected to potentiometers to regulate the intensity of the current passing through them and therefore adjust the intensity of the axial component, which allows modify the configuration of the prevailing field in enclosure 10. You can also arrange each winding in an envelope connected to a Cryocooler type cryocooler, for example.

Figure 1b shows the different configurations of the axial component that it is possible to obtain with such a device, in varying the intensity of the current flowing through the windings. Each curve represents the shape of the module of the axial component of the field magnetic reigning in the enclosure as a function of the position on the z axis. The maximum intensity of this component is of the order of a few teslas and depends on the cyclotron resonance frequency. The curves 100, 101 and 102 all have two maximum values different and a minimum value that can form a plateau, as is the case on curve 102. Curve 103 is almost flat. The curves 104 and 105 only have a maximum value whose position on the z axis is adjustable by adjusting the intensity of the current in the windings, for example, using potentiometers. The intensity of current in said coils will, for example, be of the order of a few hundreds of amps.

FIG. 2a schematically represents an embodiment of the present invention. Five coils 20, 22, 24, 26 and 28 of superconductive materials maintained at a temperature between 16 K and 273 K are arranged respectively in a connected envelope 30 to a suitable cryogenic system 40, for example, a Cryocooler which maintains them at a temperature of the order of 30 K; envelope 30 being itself at room temperature. We can also imagine separate envelopes for each of the windings connected to systems independent cryogenic.

These two windings surround the enclosure 10 comprising an orifice 12 input of the material in the form of a gas consisting of atoms and a plasma outlet 14 capable of being generated or injected into enclosure 10.

This device can also be provided with an ionization system 46 atoms introduced into the enclosure. This ionization system is by example, either a filament, a waveguide, or an optical system allowing to bring a high frequency wave in the enclosure 10. On can also provide a number of windings suitable for dimensions of the enclosure to be magnetized.

The use of superconductive materials at temperatures between 16 K and 273 K allows the windings to be placed at a distance L from the wall 11 of the enclosure 10. This distance L is of the order of a few millimeters instead of a few tens of centimeters for conventional superconductors.

Advantageously, a conventional extraction system 50 intended for extract the components of the plasma generated in the enclosure 10 and a injection system 52 will complete the device which can then receive a plasma or atoms inside the enclosure 10.

If we generate a plasma using a cyclotron resonance electronic, the field then advantageously has the configuration shown in Figure 2b. The magnetic field has at least a value at which the electronic cyclotron resonance is obtained with any field geometry.

Advantageously, the windings are arranged as close as possible to the plasma chamber to minimize the magnetized volume.

Figure 3a shows schematically an apparatus for generate multi-charged ion plasmas, that is to say comprising several positive charges.

Advantageously, in the case of an enclosure 10 having a geometry with cylindrical symmetry, the device further comprises a system for generating a multipolar magnetic field 60 comprising superconductive coils or permanent magnets and a high frequency wave guiding system (not shown in FIG. 3a) inside the enclosure 10 so as to generate the plasma by electronic cyclotron resonance.

The coils 20, 21 and 22 are preferably placed around the enclosure 10 and placed at a distance I of the order of a few millimeters. Each winding is contained in an envelope 30, 31, 32 connected to a cryogenic system. Several systems can also be provided cryogenic, one for each envelope.

Figure 3b shows a preferred configuration of the field magnetic along a section of the chamber along an axis perpendicular to the z axis located in the middle of the enclosure in the case of a magnetic field B having a cylindrical symmetry with respect to this z axis.

Note that the magnetic field module B has two maximums B1 and B2 surrounding a minimum value B3 intermediate to these two maxima. The value of these maxima is greater than the value B _ECR for which the cyclotronic resonance is obtained. This value B _ECR depends on the nature of the atoms used and the high frequency wave brought into the enclosure 10. The minimum value B3 is less than B _ECR · This type of configuration of the magnetic field is given only as indicative; it is obviously possible to establish a magnetic field of arbitrary configuration inside the enclosure 10.

Figure 4 shows an embodiment of the present invention for treating surfaces using large plasmas and uniform in density.

In FIG. 4, for simplicity, a single coil 20 has been represented. This coil 20 is contained in an envelope 30 connected to a suitable cryogenic system, keeping it at a temperature between 16 K and 273 K. The extraction system 70 comprises a grid 74 of so as to produce a wide plasma beam which will be applied to a fixed or mobile substrate S under the device. The surface to be treated of the substrate S is located at an adjustable distance R, of the order of several tens of centimeters, for example. We can also imagine diving directly the surface to be treated in the plasma. The guidance system of the wave has several waveguides 200, 201, 202, 203, 204, 205, 206, and 207 arranged along the enclosure 10 and intended to bring there a frequency wave higher than 900Mhz, with a distribution uniform power density of this HF wave

The magnetic field B prevailing in the enclosure 10 is intense and uniform preferably its intensity is greater than 0.01 T.

As the magnetizable volume can be extremely large, it is possible to extract long and wide beams representing an area of approximately 1 m ² . It is then possible to treat very large areas quickly and obtain a regular deposit.

FIG. 5a schematically represents a fourth mode of realization of the present invention which can be used for production X-rays.

The device comprises a system 58 for guiding a wave of frequency preferably greater than 2.45 Ghz, inside the enclosure 10.

The generator means comprising several windings, 20, 21, 22, 23, 24 are arranged along the z axis. The magnetic field generated in the enclosure, assuming that it has an axi-cylindrical geometry, to simplify its representation, has a configuration of preference similar to that shown in Figure 5b.

The magnetic field module, presents along the axis of symmetry z two maxima B1 and B2, at values greater than R _ECR and a plateau, B3, whose value is equal to R _ECR . The atoms confined between these two maxima undergo shocks between them and with the electrons which were torn from them.

An electron strongly linked to the nucleus is torn from the atom, a electron located near the nucleus but less linked to it than the electron previously torn off fills the void left by the electron before. This passage is carried out with an emission of photons at high energy like X-rays. This type of device also allows to obtain a magnetic field of arbitrary geometry in the enclosure 10.

Each embodiment previously exposed must additionally comprise displacement members of at least part magnetic field generating means. It is then possible to modulate the configuration of the magnetic field prevailing in the enclosure by moving the magnetic field generating means. We can thus modify, at any point inside the enclosure, the direction of the vector magnetic field and its intensity.

According to a particular embodiment, the coils are fixed on displacement members, for example in translation along the plasma chamber, comprising for example screws allowing a precise movement of the windings. This modulates the configuration of the magnetic field B prevailing in the enclosure. We can in addition to simultaneously providing the device with potentiometers intended for regulate the intensity of the current flowing through the windings.

The generator means being close to the wall, it is easy modify the configuration of the control with finesse and precision magnetic reigning in the enclosure, that is to say, its intensity and its geometry. We can thus create, in any volume, a field magnetic of any geometry.

In the case of devices generating plasmas by electronic cyclotron resonance, field modulation magnetic has several advantages. The bedroom has dimensions dependent on the high frequency wave which ionizes atoms. The magnetic field is also coupled to this wave. The fact of being able to modulate the intensity of the B field allows the use of different frequencies and thus get the cyclotron resonance electronics for several kinds of ions from different elements.

The shape of the windings can be variable, i.e., by example, circular or square, depending on the field to create in enclosure 10.

The magnetic configuration of the field also determines the type of ion formed. The device according to the present invention therefore makes it possible to produce different field configurations suitable for training different types of ions.

Claims (10)

1. Apparatus for creating a magnetic field (B) inside an enclosure (10) suitable for receiving at least one matter in the atomic state, in the vapour phase, with a view to extracting therefrom ions, electrons, or electromagnetic radiation (14) produced by ionising said matter, the apparatus comprising in particular:

   magnetic field generator means (20, 21, 22, 24, 26, 28) suitable for surrounding said enclosure (10) at least in part by being placed at a distance (L, I ) from the wall of said enclosure (10) lying in the range 1 mm to 50 mm from the wall (11) of said enclosure (10), and comprising at least one coil made of a material that presents superconductive properties in the range 16 K to 237 K together with a cryogenic system (40) for maintaining said magnetic field generator means at said temperature, the apparatus being characterised in that it further comprises displacement members for displacing at least a portion of the magnetic field generator means making it possible to modulate the configuration of the magnetic field that exists in the enclosure (10) in order to produce various types of ion and to obtain electron cyclotron resonance (ECR) for each of them.
2. Apparatus according to claim 1, characterised in that it further comprises:

   an injector system (52) for injecting atoms into said enclosure (10); and

   an extractor system (50) for extracting ions and electrons from the plasma formed inside said enclosure (10).
3. Apparatus according to claim 1 or 2, characterised in that it further comprises ionisation apparatus (46) for ionising atoms injected into said enclosure (10).
4. Apparatus according to any one of claims 1 to 3, characterised in that it further comprises waveguide apparatus (46) for guiding a high frequency wave inside said enclosure.
5. Apparatus according to any one of claims 1 to 4, characterised in that it further comprises:

   an extractor system (74) enabling a broad beam to be obtained defining a surface area of approximately 1 m².
6. Apparatus according to any one of claims 1 to 5, characterised in that it further comprises:

   an extractor system for extracting the heavy ions that may be contained in the plasma.
7. Apparatus according to any one of claims 1 to 6, characterised in that it further comprises means for regulating the magnitude of the electric current carried by said coil.
8. Use of the apparatus according to any one of claims 1 to 7 for making equipment for producing plasmas.
9. Use of the apparatus according to any one of claims 1 to 7 for making equipment for producing X-rays.
10. Use of the apparatus according to any one of claims 1 to 7 for making equipment for treating surfaces.

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