Classifications

• • 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
  • H05H1/00—Generating plasma; Handling plasma
  • H05H1/02—Arrangements for confining plasma by electric or magnetic fields; Arrangements for heating plasma
  • H05H1/16—Arrangements for confining plasma by electric or magnetic fields; Arrangements for heating plasma using externally-applied electric and magnetic fields
  • H05H1/18—Arrangements for confining plasma by electric or magnetic fields; Arrangements for heating plasma using externally-applied electric and magnetic fields wherein the fields oscillate at very high frequency, e.g. in the microwave range, e.g. using cyclotron resonance
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01J—ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
  • H01J27/00—Ion beam tubes
  • H01J27/02—Ion sources; Ion guns
  • H01J27/16—Ion sources; Ion guns using high-frequency excitation, e.g. microwave excitation
  • H01J27/18—Ion sources; Ion guns using high-frequency excitation, e.g. microwave excitation with an applied axial magnetic field

Definitions

• 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.
• ECR sources 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).
• ECR ECR denotes the value of the modulus of the magnetic field B for which the electronic cyclotron resonance is obtained.
• 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.
• the field B is defined by its module B and by the angle ⁇ which it forms with the axis of revolution z.
• the configuration of the magnetic field inside the vacuum chamber determines the number of charges carried by the plasma ions.
• the configuration of the axial component of the magnetic field is decisive.
• the so-called injection zone where the high-frequency wave is introduced and where gas or metal atoms to be ionized are also introduced.
• this injection zone is the so-called extraction zone. This extraction zone corresponds to the exit of the ion beam from the chamber.
• ECR sources allowing to produce strong flows of mono-charged ions (having an energy of the order of 200 KeV).
• 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.
• 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.
• 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.
• N3 The minimum value noted N3, lower than the value R ECRZ , is reached inside the vacuum chamber.
• 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.
• 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.
• 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.
• 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
• 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.
• the field B is created inside a vacuum chamber, using generator means arranged outside the chamber.
• 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.
• 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.
• 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.
• the direction of said magnetic field is varied so that the angle ⁇ 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:
• this 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,
• 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.
• 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.
• 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.
• 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.
• 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.
• the generator means comprise at least one coil traversed by a current of determined intensity.
• 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
• FIG. 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,
• FIG. 9 shows a perspective view of the source corresponding to the embodiment shown in Figures 3 to 6
• 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
• 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.
• 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.
• z1 is equal to a few centimeters depending on the extraction voltage.
• 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.
• 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
• 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
• the armature 25 has a shape adapted to superimposition of magnet A1 on magnet A5
• 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
• 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
• the length of the guide 27 is equal to the total width LA4 + LA5
• 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
• 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
• 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)
• 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
• the length L1 of the possible translation of the magnet A1 along the axis z is between 0 and a few centimeters
• 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 threaded end 52 of the rod 42 then cooperates with the threading of the tapped hole 32
• 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
• FIG. 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
• 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.
• 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
• 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.
• FIG. 4 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.
• 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.
• 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.
• the electronic cyclotron resonance will be obtained with a high-frequency wave of frequency greater than 6.4 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 centimeters.
• M3 is substantially equal to the resonance value.
• the axial component B z increases in modulus to reach a maximum value M2 in the zone where the magnets
• the length N will be equal to a few millimeters.
• 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.
• H'5 equal to H5 and H'1 is of the order of a few millimeters.
• 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.
• 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.
• 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.
• 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.
• 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.
• 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 .
• 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.
• 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.
• 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.
• 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.

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Citations (5)

• 1998
  • 1998-05-26 FR FR9806578A patent/FR2779317B1/fr not_active Expired - Fee Related
• 1999
  • 1999-05-26 AU AU38315/99A patent/AU3831599A/en not_active Abandoned
  • 1999-05-26 EP EP99920917A patent/EP1080612A1/de not_active Withdrawn
  • 1999-05-26 WO PCT/FR1999/001225 patent/WO1999062306A1/fr not_active Application Discontinuation

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