EP1080612A1

EP1080612A1 - Method for modulating a magnetic field configuration

Info

Publication number: EP1080612A1
Application number: EP99920917A
Authority: EP
Inventors: Pascal Sortais; Claude Bieth
Original assignee: Pantechnik
Current assignee: Pantechnik
Priority date: 1998-05-26
Filing date: 1999-05-26
Publication date: 2001-03-07
Also published as: FR2779317A1; FR2779317B1; AU3831599A; WO1999062306A1

Abstract

The invention concerns a method for modulating the configuration of a magnetic field (B) defined by its axial component (Bz) and its radial component (Br) for confining a plasma generated by electronic cyclotronic resonance at a value RECR of the field (B), and having symmetry with respect to an axis or revolution (z). The invention is characterised in that it consists in continuously adjusting at least locally the magnetic field (B) intensity and/or direction to modulate its configuration in a domain where, the axial component (Bz) module takes on values located on either side of the resonance value (RECRZ) and which is delimited between a first configuration wherein said module variations along the axis of revolution (z) have a low gradient, and a second configuration, wherein said module variations have a high gradient, the value of the magnetic field maximum module/magnetic field minimum module ratio being more than 1.5 and preferably more than two.

Description

METHOD FOR MODULATING THE CONFIGURATION OF A MAGNETIC FIELD

The present invention relates to a method for continuously modulating the configuration of a magnetic field intended for the confinement of a plasma generated by electronic cyclotron resonance, as well as a source allowing the implementation of this method.

Sources with electronic cyclotron resonance, called ECR sources, are commonly used to produce mono-charged or multi-charged ions (that is to say atoms from which one or more electrons have been torn off).

The principle of these ECR sources is to couple, inside a vacuum chamber supplied with atoms (these atoms can come from a gas or a metal), a high-frequency wave with a magnetic field B, so as to obtain the conditions under which, a cyclotron resonance is likely to appear and to ionize the atoms present, thus generating a plasma. Conventionally, R _ECR denotes the value of the modulus of the magnetic field B for which the electronic cyclotron resonance is obtained. Generally, the chamber containing the plasma has a symmetry of revolution with respect to an axis which will be called z.

The magnetic field B is produced by means external to the vacuum chamber. These means may consist of a set of coils traversed by an electric current or a set of permanent magnets. The coils used, if they are made of superconductive materials, must be cooled to a determined temperature by an appropriate cryogenic system.

In cylindrical coordinates, the field B is defined by its module B and by the angle θ which it forms with the axis of revolution z. One can then define two components of the field B, one of which is the projection of the vector field B on the axis z, called axial component and will be noted B _z thereafter; and the other is the projection of the vector B onto a plane perpendicular to the z axis, called the radial component and conventionally denoted B _r .

The configuration of the magnetic field inside the vacuum chamber determines the number of charges carried by the plasma ions. In particular, the configuration of the axial component of the magnetic field is decisive.

Whatever the type of ECR source, one can define, along the z axis, two extreme zones inside the chamber: the so-called injection zone, where the high-frequency wave is introduced and where gas or metal atoms to be ionized are also introduced. Opposite this injection zone is the so-called extraction zone. This extraction zone corresponds to the exit of the ion beam from the chamber.

There are ECR sources allowing to produce strong flows of mono-charged ions (having an energy of the order of 200 KeV). In the case of these sources, the configuration of the module of the axial component B _z , inside the vacuum chamber, is as shown in FIG. 1. The curve has two maxima M1 and M2 at abscissas located respectively , in the extraction and injection zones and an intermediate minimum M3, located between the two maxima, at an abscissa corresponding roughly to the center of the chamber. These two maxima generally have a value greater than the value R _ECR z of the axial component B _z for which the electronic cyclotron resonance is obtained. The maximum value of the differences M1-M3 and M2-M3 represents the maximum gradient of the axial component. This gradient is small, generally of the order of a few percent of the maximum value of the axial component.

In the vacuum chamber, the axial component has a module whose value remains close to the value R _ECRZ . Such an axial component makes it possible to obtain an efficient coupling between the high-frequency wave and the magnetic field B. The atoms are thus rapidly ionized and their diffusion inside the chamber is rapid. The extraction of the ions is also carried out at a value of B _z close to the value R _ECRZ of resonance. In the case of a source producing multi-charged ions, the configuration of the axial component B _z is as shown in FIG. 2. The axial component B _z has two maxima N1 and N2 corresponding to values greater than the value R _ECRZ and located near the injection and extraction zones. The minimum value noted N3, lower than the value R _ECRZ , is reached inside the vacuum chamber. Unlike the configuration shown in Figure 1, the maximum value of the differences N2-N3 or N1-N3 which represents the maximum gradient of the axial component is relatively large, in general of the order of 1.5 to 2.5. In addition, the maximum values obtained at points N1 and N2 are higher than the maximum values M1 and M2 of the configuration shown in FIG. 1; they are about 1.5 times higher.

When the axial component of the magnetic field, inside the vacuum chamber, has a configuration corresponding to FIG. 2, it is possible to obtain multi-charged ions as has already been described in the French patent application N ° 91-09945. The initially charged ions remain confined in the chamber, in the zone where the axial component of the magnetic field has its minimum N3, that is to say, between the two maxima N1 and N2. The electrons in the plasma of mono-charged ions are "heated" and progressively reach high energies (of the order of 1 MeV). The shocks between these high energy electrons and the mono-charged ions cause the deep ionization of the electronic layers; electrons located on the layers closest to the atom's nucleus are torn off, leading to the formation of multi-charged ions. These multi-charged ions are then extracted in the so-called extraction zone where the axial component of the magnetic field has a value greater than the value R _ECRz .

The production of single-charged ions and the production of multi-charged ions therefore require two distinct types of ECR source having different configurations of the axial component B _z inside the vacuum chamber.

However, from an industrial point of view, for the production of radioactive ions, it is generally easier to ionize a large number of mono-charged ions, but, for reasons of ease of acceleration, it is sometimes necessary to produce multi-charged ions. Similarly, for ion implantation, used in particular for the manufacture of integrated circuits, intense beams of mono-charged ions are generally used. Nevertheless, a deeper local implantation of the ions requires the use of ions having a higher energy and therefore multi-charged ions. The fact of having to have two separate ECR sources for the production of the two types of ions implies on the one hand, a high cost of production and on the other hand, operations from one source to another. Under these conditions, it is necessary at each change of source to carry out a new installation which can be extremely long and tedious and also presents risks, any manipulation of a source may indeed damage it.

The present invention therefore proposes to solve the technical problems posed by the prior art, previously exposed.

This object is achieved by a method of modulating the configuration of the magnetic field B defined by its axial component B _z and its radial component B _r) intended for the confinement of a plasma generated by electronic cyclotron resonance at a value R _ECR of field B, and having a symmetry with respect to an axis of revolution z. According to this method, the intensity and / or the direction of the magnetic field B is continuously and at least locally adjusted to modulate its configuration in a domain where, the module of the axial component B _z takes values located on both sides and d other of the resonance value R _ECR2 and which is delimited, between a first configuration in which the variations of said module along the axis of revolution z have a weak gradient, and a second configuration, in which the variations of said module have a gradient strong, the value of the ratio: maximum modulus of the magnetic field / minimum modulus of the magnetic field, being greater than 1.5 and preferably greater than 2.

This method has the advantage of being able to create a magnetic field B, inside the chamber, having any configuration intermediate to the two extreme configurations defined above. This method can be applied to all kinds of magnetic field generating means, namely, a permanent magnet, a coil, a system using superconductors, or a combination of two or more of these means. According to this method, it is possible to pass continuously from a magnetic field configuration intended to produce single charged ions to a configuration allowing the production of multi-charged ions.

Advantageously, the field B is created inside a vacuum chamber, using generator means arranged outside the chamber. Advantageously, the intensity and / or the direction of the magnetic field B in said chamber is adjusted continuously and at least locally by moving at least part of the generating means.

For example, one can move the magnetic field generating means in a direction parallel to the axis of revolution z of the B field.

Another possibility, which does not exclude being used in combination with that set out above, consists in adjusting at least locally the intensity and / or the direction of said magnetic field B by adjusting the generating means. The generator means can be adjusted by varying, for example, the intensity of their supply current.

Advantageously, the field B is modulated so that its module is between 0.1 and 3 times the value of the module of the magnetic field for which the resonance is obtained. Preferably, the direction of said magnetic field is varied so that the angle θ formed by said field vector B with the axis of revolution z is between 0 ° and 90 °.

Another object of the present invention is to provide a device for implementing the method described above. This object is achieved by means of a source of mono- and multi-charged ions of the type comprising:

- means generating a magnetic field B located outside of said vacuum chamber; this magnetic field B, defined by its axial component B _z and its radial component B _r ; is intended for confining the plasma generated by electronic cyclotron resonance to an R _ECR value and has symmetry with respect to an axis of revolution z,

- a vacuum chamber intended to contain a plasma;

- means for propagating a high-frequency wave inside the chamber;

means for injecting the atoms to be ionized into said chamber

- means for extracting the constituent ions from the plasma; this source further comprises means for modulating the configuration of the magnetic field B by adjusting, at least locally, the direction and / or the intensity of said magnetic field B. It is then possible to use the same source to produce mono-charged ions and multi-charged ions. This has many advantages, in particular, great flexibility of use since a single device then allows the production of the two types of ions, which considerably reduces the cost of production of these ions.

Any type of magnetic field generating means can be used, coils, superconductive materials or the like. A combination of two or more of these means can also be envisaged. For example, the generating means comprise at least one magnetic dipole having symmetry with respect to an axis of revolution parallel to the z axis and surrounding the chamber. This embodiment has the advantage of easily creating the two types of configuration for the axial component B _z of the field B. Advantageously, this dipole is carried by at least one permanent magnet. Since permanent magnets are inexpensive, their use makes it possible to further reduce the cost price of the source.

Advantageously, the means for modulating the magnetic field B comprise means for moving the generating means. The displacement of the generator means can be carried out in any direction, by translation or by rotation about any axis.

For example, according to a particular embodiment, these displacement members comprise at least one frame fixed in a position parallel to said axis of revolution z and now at least part of said generator means; the armature is provided with a tapped hole passing through it parallel to the axis of revolution z and is capable of cooperating with a threaded rod disposed parallel to the axis of revolution z, so as to cause it to move parallel to the 'z axis. According to another embodiment, the generator means comprise at least one coil traversed by a current of determined intensity.

Advantageously, the means for modulating said magnetic field B then further comprise means for adjusting the intensity of the supply current to the coil. The invention will be better understood and its advantages will appear better on reading the detailed description which follows, of an embodiment shown by way of nonlimiting example. The description refers to the appended drawings in which - FIG. 1 represents the variations in the modulus of the axial component of the magnetic field prevailing in the vacuum chamber in the case of production of mono-charged ions,

FIG. 2 represents the variations in the modulus of the axial component of the magnetic field prevailing in the vacuum chamber in the case of the production of multi-charged ions,

- Figure 3 shows a particular embodiment of the present invention, in which the field generating means are arranged so as to form, in the vacuum chamber, the magnetic configuration suitable for the production of multi-charged ions, - FIG. 4 represents a section of FIG. 3 along the axis IV-IV on which the field generating means are arranged so as to form, in the chamber, the magnetic configuration adapted to the production of mono-charged ions,

FIG. 5 is a detail of the particular embodiment shown in FIGS. 3 and 4,

FIG. 6 is a left view of FIG. 3,

FIG. 7 represents a bottom view of part of FIG. 3,

FIG. 8a represents another possible arrangement of the field generating means and FIG. 8b represents the corresponding configuration of the axial component of the field,

- Figure 9 shows a perspective view of the source corresponding to the embodiment shown in Figures 3 to 6

Referring to Figure 3, the main elements of the present invention will now be described

The source of the present invention conventionally comprises a cylinder head 11 having a symmetry of revolution with respect to an axis z This cylinder head 11 is made with a material such as aluminum and contains the field generating means The cylinder head 11 comprises in its center, a cylindrical opening partially delimiting the chamber 13 which will be evacuated In the present case, the chamber 13 and the yoke 11 have the same axis of revolution z as the magnetic field itself. Any other geometry of the cylinder head 11 and of the chamber 13 can also be envisaged without any relation whatsoever to the geometry of the magnetic field prevailing in this chamber 13. A side wall 15 made of any non-magnetic metal such as, for example, aluminum or stainless steel, is tightly fixed on the walls of the cylindrical opening of the cylinder head 11 constitutes the external lateral surface of the chamber 13 serving as a plasma chamber. Referring to FIG. 3, at the left end of the chamber 13, is located the extraction zone connected to the extraction system 16, part of which 18 penetrates inside the chamber 13. The part 18 penetrates up to a determined abscissa z1 at which the axial component B ₂ of the magnetic field B has the value required for the extraction of the ions. Preferably, z1 is equal to a few centimeters depending on the extraction voltage.

At the opposite end of the extraction zone is located the high-frequency (HF) wave guidance system 19 and the atom injection system 20. The wave guidance system 19 comprises an HF window 19a, permeable to the wave but making it possible to maintain the vacuum in the chamber 13, and a wave guide 19b which guides the high-frequency wave to the interior of the chamber 13. The system atom injection system 20 will be explained in more detail below, with reference to FIG. 7. The extraction system 16, the wave guiding system 19b and the atom injection system 20 are connected perfectly sealed to the chamber 13 by means of appropriate seals. The chamber 13 extends from the end of the part 20 to the internal wall of the cylinder head 11.

In the example presented, the generating means are permanent magnets, respectively, A1, A2, A3, A4 and A5 having a ring shape and arranged so that their axis of revolution substantially merges with the axis of revolution z of the chamber 13. The substantially equal diameters of the magnets A1 and A2 are greater than the diameters of the magnets A3, A4 and A5.

The respective dimensions of the magnets, i.e. their internal diameters, their external diameters and their widths (LA1, LA2, LA3, LA4 and LA5) are determined according to the dimensions of the chamber 13 The dimensions of chamber 13 are themselves defined as a function of the wavelength of the high-frequency wave

As shown in Figure 3, magnets A1 and A5 can be the same width, as well as magnets A2 and A3 Preferably, magnets A1 and A5 are wider than magnets A2 and A3 Magnet A4 can be chosen wider than the others

The magnets A1, A2, A3, A4 and A5 are mounted on armatures 21, 22, 23, 24 and 25 respectively. The armatures are such that they are firmly fixed, by stamping, to the magnets so as not to prevent the establishment of the magnetic field generated by each magnet, inside the chamber 13 These armatures can have various shapes In the case of the present embodiment, they have a ring shape such that their external diameter is substantially equal to the diameter of the yoke 11 The particular shape of the armature 23 is intended to support the magnet A3 separately from the magnet A2 which is capable of being superimposed above the same Similarly, the armature 25 has a shape adapted to superimposition of magnet A1 on magnet A5

In FIG. 3, it can be noted that the armature 25 is placed in abutment against the internal wall of the cylinder head 11 and is fixed there using screws or any other fixing means.

In the particular embodiment shown, the magnet A5 is therefore fixed but one can also imagine a movable armature. The displacement of the magnet A5 would, for example, make it possible to adapt the dimensions of the confining magnetic field prevailing in the chamber. at the wavelength of the high-frequency wave used to obtain the electronic cyclotron resonance It would then be possible for a given configuration to vary the dimensions of the confining magnetic field so as to use a high-frequency wave of length d different wave to obtain the electronic cyclotron resonance Similarly, it would be possible by adapting the dimensions of the confining magnetic field to pass from one configuration to another, while modifying the wavelength of the high-frequency wave used , i.e. to obtain the electronic cyclotron resonance for different values R _E CRZ and R ' _ECRZ of the axial component of the field, as shown in Figures 1 and 2

In FIG. 3, the magnet A5 is placed at a distance H5 from the wall of the cylinder head 11 This distance H5 is preferably equal to a few millimeters Similarly, the magnet A1 is placed at a distance H1 from the internal wall of the cylinder head 11 The magnets A2 and A3 are moved to a respective distance H'2 and H'3, from the wall of the cylinder head 11

The magnet A1 has an internal diameter such that it can be superimposed on the magnet A5, the magnet A5 being integral with the frame 25 The frame 21 has an opening 26 of cylindrical section passing through it parallel to the axis z and capable of sliding along a cylindrical guide 27 The guide 27 is fixed parallel to the axis z, at one of these ends on the frame 25 and, at the other end, on the frame 24 , the magnets A4 and A5 being placed side by side This fixing can be carried out using screws or any other fixing means The guide 27 makes it possible to ensure the exact parallelism, or even the superposition of the axis of revolution of the magnet A1 and the z axis Preferably, the length of the guide 27 is equal to the total width LA4 + LA5

According to this embodiment, the magnet A5 being fixed, the magnet A4 is also it It would however be possible to imagine a mobile magnet A4 whose movements would be coupled or not with the movements of the magnet A5 The advantages provided by such an embodiment would be the same as those exposed for a mobile A5 magnet

The frame 21 supporting the magnet A1 further comprises a through hole 28, parallel to the axis z This hole 28 is capable of sliding around a guide 29 fixed parallel to the axis z, on the wall of cylinder head 11 and on frame 25

The frames 22, 23 and 24 are also provided with openings 30a and 30b passing through them parallel to the axis z The frames 22 and 23 are capable of sliding around this guide 29 The frames are thus all perfectly positioned relative to the z axis, thanks to the presence of these two guides 27 and 29 The presence of these two guides 27 and 29 also prevents any rotation of the magnets around the z axis It is also possible to provide a plurality of guides equipping the circumference of the armatures Conventionally, the holes 28, 30a and 30b are fitted with rings so as to facilitate the sliding of the armature on the guide 29

The magnets A2 and A3 are thus capable of moving along the axis between the magnet A4 and the internal wall of the cylinder head 11 The magnets A2 and A3 can move respectively up to distances H2 and H3 from the wall internal of the cylinder head 11 Preferably, the distance H2 will be of the order of a few centimeters and the distance H3 will be of the order of a few centimeters (distances shown in FIG. 4)

An example of means for translational movement of the magnets will now be described with reference to FIGS. 4 and 5

The magnet A1 is moved using a screw 61 placed on the wall of the yoke 11 The frame 21 also includes a threaded hole 31 whose thread is capable of cooperating with the complementary thread 51 of the threaded rod 41 Preferably, the length L1 of the possible translation of the magnet A1 along the axis z is between 0 and a few centimeters

By screwing or unscrewing the screw 61 located on the cylinder head 11, this causes the displacement of the assembly formed by the armature 21 and the magnet A1. This displacement is carried out in translation relative to the axis of revolution z of the chamber Again, the guides 27 and 29 ensure the parallelism of this translation with the axis z

Likewise, the plates 22 and 23 respectively supporting the magnets A2 and A3 also include tapped holes 32 and 33 capable of cooperating with the rods 42 and 43, the ends of which include threads 52 and 53 The rod 42 ends in the screw 62 located on the cylinder head 11 This rod passes through a recessed part located on the frame 23 and 24 The threaded end 52 of the rod 42 then cooperates with the threading of the tapped hole 32 In the same way as before, the operation of the screw 62 allows the magnet A2 to be advanced or moved back along the z axis. The length of the thread of the threaded rod 32 determines the length L2 of the displacement of the magnet A2. The length of the displacement L2 will preferably be equal to a few centimeters

5 shows the rod 43 terminated by the screw 63 located on the wall of the cylinder head 11 The rod 43 has a thread 53 only on its through end opposite the screw 63 This thread 53 is capable of cooperating with the tapped hole 33 formed in the frame 23 The rod 43 is placed parallel to the z axis The operation of the screw 63 allows, as explained above, to move the magnet A3, parallel to the z axis The rod 43 also passes through three hollow zones located on the frames 21, 24 and 22 Likewise, the length of the thread 53 of the rod 43 determines the length L3 of the translational movement of the magnet A3 Preferably, this length L3 will be between 0 and a few centimeters

We have just described an example of means allowing a displacement in translation of the magnetic field generating means which in the previous example are represented by permanent magnets It is obviously possible to imagine this same device applied to coils traversed by a current or to superconductive materials. This device can also be coupled allowing displacement in translation with any other device allowing other displacements, in other directions, of the field-generating means (translation in another direction, rotation, etc.).

We will now describe the method applied to the particular embodiment described above, making it possible to pass from the configuration of B _z represented in FIG. 1, to the configuration of B ₂ represented in FIG. 2

The field B prevailing in the chamber 13 is the superposition of all the fields created by the different magnets

The magnet A4 can be a multipole, that is to say that it comprises a plurality of magnets whose poles are oriented in different directions. It is disposed substantially at a position corresponding to the middle of the length of the chamber and at a distance of the order of a few millimeters from the side wall 15

The field generated by the magnet A4 is essentially radial, that is to say that it generates a field represented by a vector B of any direction, located in a plane perpendicular to the direction of the axis z Figure 6 represents, in more detail, this magnet A4 II is composed of several dipoles creating magnetic fields having different directions A4 can thus be composed of an even number of dipoles oriented four by four The dipoles of the same direction but of opposite directions are diametrically opposed. In a plane perpendicular to the z axis, we can define two perpendicular directions in which are located dipoles having a centripetal orientation (along the vertical axis) and a centrifugal orientation (along the horizontal axis). The dipoles are ordered according to the following pattern: centripetal dipole, dipole tangent to the circumference of the multipole A4 and directed towards the preceding centripetal dipole, centrifugal dipole, dipole having a direction tangent to the circumference of the multipole A4 and directed in the opposite direction of the dipole tangent to the circumference of the multipole A4 and directed towards the centripetal dipole. The fields generated by each of the magnets A1, A2 A3 and A5 have a symmetry of revolution with respect to the z axis. They can advantageously also be substantially symmetrical with respect to the middle of the chamber 13. Each of these fields consists of an axial component B _z and a radial component B _r whose modules decrease along the z axis, when we move away from the center of the magnet considered

As shown in Figure 3, the magnet A1 produces a magnetic field having a radial component oriented, in Figure 3, from top to bottom towards the z axis. The same is true for the A3 magnet. The magnets A1 and A5 produce a magnetic field whose radial component is oriented from bottom to top towards the z axis.

FIG. 4 shows the arrangement of the magnets to obtain a configuration of B _z identical to that shown in FIG. 1.

We now describe Figure 4, starting with the area near the extraction system. The magnets A2 and A3 are offset from each other, but are superimposed on a length M. This length M has a determined value to obtain, near the extraction device, the appropriate value of the field B. For a magnetic resonance obtained by a wave of frequency greater than 1 GHz, the chamber advantageously has dimensions equal to 1.5 times the wavelength in the vacuum of the heating wave, and the length M advantageously has a value of a few tens of centimeters.

Advantageously, the magnet A2 is placed at a distance H "2 from the axis, of the order of a few centimeters and the magnet A3 is placed at a distance H" 3 from the internal wall of the cylinder head 11, H ' 3 being of the order of a few centimeters. It will be noted that, in the particular case of FIG. 4, the distance H "3 is equal to the distance H3.

Advantageously, the electronic cyclotron resonance will be obtained with a high-frequency wave of frequency greater than 6.4 GHz. In this case, the chamber advantageously has dimensions equal to 1.5 times the wavelength in the vacuum of the heating wave, and the length M advantageously has a value of a few centimeters.

When one moves away from this superposition zone, one moves away from the respective centers of the magnets A2 and A3, the field which results therefrom has an axial component B ₂ which decreases and passes through a minimum value M3 lower than the value of resonance R _ECRz then believes again when one approaches the magnets A1 and A5. Preferably, M3 is substantially equal to the resonance value.

Similarly, in the zone where the magnets A1 and A5 are superimposed on a length N, the axial component B _z increases in modulus to reach a maximum value M2 in the zone where the magnets

A1 and A5 are superimposed. Advantageously, the length N will be equal to a few millimeters.

Advantageously, the magnet A5 is placed at a distance H'5 from the internal wall of the cylinder head and the magnet A1 is placed at a distance H'1 from the wall of the cylinder head. We have for example, H'5 equal to H5 and H'1 is of the order of a few millimeters.

By moving the magnets A1, A2 and A3 simultaneously or successively, by actuating the screws 61, 62, 63 disposed on the yoke 11, it is possible to arrange said magnets so as to obtain a field having an axial component whose configuration is identical to that shown in FIG. 2. Such an arrangement of the magnets is represented in FIG. 3.

Starting with the extraction zone, we note that the magnets A2 and A3 are superimposed over their entire length and located at a respective distance H'2 and H'3 from the wall of the cylinder head 11. An axial component is therefore obtained which is the superposition of the two maximum axial components obtained at the center of the magnets of the fields generated by the magnets A1 and A2 and which therefore reaches a maximum value at the combined centers of the two magnets. In the area where the magnet A4 is located, the resulting field B has an axial component B _z which results from the superposition of the axial components of the fields generated by the magnets A1, A2, A3 and A5. This area being further from the center of magnets A2 and A3 and from the centers of magnets A5 and A1 than in the arrangement shown in Figure 3, the axial component has a module lower than the module it has when the magnets are arranged as in FIG. 3. The minimum value N3 of the modulus of the axial component is of the order of 1.5 times the magnetic field of resonance. Generally, the minimum value of the component B _z is reached at an abscissa z representing half the length of the multipole A4, assuming that the fields generated by the magnets A1 and A2 are the symmetric of the fields generated by the magnets A3 and A5 relative to the middle of the chamber 13. Symmetrically, a maximum is obtained in module of the component B _z for the zone where the two magnets A1 and A5 are superimposed. The magnets A1 and A5 being superimposed along their entire length, the maximum obtained with this arrangement is greater than the maximum obtained when a determined length is superimposed. FIG. 7 represents a bottom view of FIG. 3, in which the input device 75 for the gaseous ions as well as the input device 77 for the metal ions, connected to an oven 78, appears.

FIG. 8a represents another possible arrangement of the field generating means. According to this arrangement, the magnets A1 and A5 remain placed, for example, as in the arrangement shown in FIG. 3. The magnets A2 and A3 are arranged at a distance H from the internal wall of the cylinder head 11 and superimposed along their entire length .

As a result, the axial component Bz of the field has the profile along z shown in FIG. 8b. Bz therefore has a maximum at the center combined of the two magnets A2 and A3, then decreases to a minimum value between A3 and A4 to increase again in the area close to the superimposed magnets A4 and A1 and A1 and A5. The magnets A1 and A5 being disposed respectively at a distance H "1 and H5 from the wall of the cylinder head. There are a multitude of magnetic configurations that can be obtained by moving a single magnet or by moving several magnets simultaneously.

Figure 9 is a perspective representation of the source according to the present invention. The three screws 61, 62 and 3 are arranged on the cylinder head. The displacement of the magnets is adjusted by measuring their respective displacement using the graduated openings 71, 72 and 73.

FIG. 9 represents the device for entering the gaseous ions 75 as well as the device for entering the metal ions 77. The present source can in fact be connected to an oven 78 intended to generate metal atoms.

The source according to the present invention also adapts to any ion extraction system.

One can also imagine replacing the permanent magnets with coils traversed by current; these coils being produced with a superconductive material or not. In the case of coils, the magnetic field can be modulated by simple variation of the intensity which traverses the coil. The modulation means for this purpose will include intensity variators placed inside or outside the cylinder head. One can also imagine a device whose generator means would include both coils and magnets and whose modulation means include displacement means and means for regulating the intensity of the current flowing through the coils.

Claims

claims

1. Method for modulating the configuration of a magnetic field (B) defined by its axial component (B _z ) and its radial component (B _r ), intended for the confinement of a plasma generated by electronic cyclotron resonance at an R value _ECR of the field (B), and having a symmetry with respect to an axis of revolution (z), characterized in that: - the intensity and / or the direction of the magnetic field (B) is continuously and at least locally adjusted ) to modulate its configuration in a domain where, the module of the axial component (B _z ) takes values located on either side of the resonance value (R _ECRZ ) ^e t which is delimited between a first configuration in which the variations of said module along the axis of revolution (z) have a weak gradient; and a second configuration, in which the variations of said module have a strong gradient, the value of the ratio: maximum module of the magnetic field / minimum module of the magnetic field, being greater than 1.5 and preferably greater than 2.

2. Method according to claim 1, characterized in that said field (B) is created inside a vacuum chamber (13), using magnetic field generating means (A1, A2, A3, A4, A5), said means being arranged outside of said chamber (13).

3. Method according to claim 2, characterized in continuously and at least locally adjusts the intensity and / or direction of the magnetic field (B) in said chamber (13) by moving at least part of the generating means (A1, A2, A3, A4, A5).

4. Method according to claim 3, characterized in that one moves said generating means (A1, A2, A3, A4, A5) in a direction parallel to the axis of revolution (z) of said field (B).

5. Method according to any one of claims 2 to 4, characterized in that one adjusts at least locally the intensity and / or the direction of said magnetic field (B) by adjusting the generating means (A1, A2. A3, A4, A5).

6. Method according to claim 5, characterized in that said generating means (A1, A2, A3, A4, A5) are adjusted by varying the intensity of the supply current of said means.

7. Method according to any one of claims 1 to 6, characterized in that one modulates said field (B) so that its module is between 0.1 and 3 times the value of the module of the magnetic field of resonance.

8. Method according to any one of claims 1 to 7, characterized in that the direction of said magnetic field is varied so that the angle θ formed by said field vector (B) with the axis of revolution (z) is between 0 ° and 90 °.

9. Source of mono- and multi-charged ions of the type comprising:

- Generating means (A1, A2, A3, A4, A5) of a magnetic field (B) located outside of a vacuum chamber (13), said magnetic field (B) being defined by its axial component (B _z ) and its radial component (B _r ), intended for the confinement of said plasma generated by electronic cyclotron resonance at a value R _{ËCR of} said field (B), and having a symmetry with respect to an axis of revolution (z), - a vacuum chamber (13) for containing said plasma;

- means of propagation (19, 19a, 19b) of a high-frequency wave inside the chamber (13);

- means for injecting (20) the atoms to be ionized into said chamber (13); - Extraction means (16, 18) of the constituent ions of said plasma; characterized in that, said source also comprises means for modulating (61, 62, 63) the configuration of the magnetic field (B) by adjusting at least local the direction and / or the intensity of said magnetic field (B ).

10. Device according to claim 9, characterized in that said generating means (A1, A2, A3, A4, A5) comprise at least one magnetic dipole having symmetry with respect to an axis of revolution parallel to said axis of revolution (z) of said field (B) and surrounding said chamber (13).

11. Device according to claim 10, characterized in that said dipole is carried by at least one permanent magnet (A1, A2, A3, A4, A5).

12. Device according to any one of claims 9 to 11, characterized in that said means for modulating (61, 62, 63) of said magnetic field (B), comprise displacement members (41, 42, 43) of said means generators.

13. Device according to claim 12, characterized in that said displacement members (51, 52, 53) comprise at least one fixed frame (21, 22, 23) in a position parallel to said axis of revolution (z) and now at at least part of said generating means, said armature being provided with a threaded hole (31, 32, 33) passing through it parallel to the axis of revolution (z) and capable of cooperating with a threaded rod arranged parallel to the axis of revolution (z) so as to drive said armature in displacement parallel to said axis of revolution (z).

14. Device according to one of claims 9 to 13, characterized in that said generating means (A1, A2, A3, A4, A5) comprise at least one coil traversed by a current of determined intensity.

15. Device according to claim 14, characterized in that said means for modulating said magnetic field (B), further comprise means for adjusting the intensity of the supply current of said coil.