WO1998022970A1 - Source a resonance cyclotronique electronique pour la production d'ions multicharges en milieu hostile - Google Patents
Source a resonance cyclotronique electronique pour la production d'ions multicharges en milieu hostile Download PDFInfo
- Publication number
- WO1998022970A1 WO1998022970A1 PCT/FR1997/002081 FR9702081W WO9822970A1 WO 1998022970 A1 WO1998022970 A1 WO 1998022970A1 FR 9702081 W FR9702081 W FR 9702081W WO 9822970 A1 WO9822970 A1 WO 9822970A1
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- WO
- WIPO (PCT)
- Prior art keywords
- coils
- enclosure
- ions
- ion source
- confinement
- Prior art date
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Classifications
-
- 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 invention relates to an electron cyclotron resonance (ECR) ion source for the production of multicharged ions, usable in hostile environments where neutron radiation deteriorates certain elements of conventional ECR ion sources (sources comprising permanent magnets).
- ECR electron cyclotron resonance
- the invention finds numerous applications as a function of the different values of the kinetic energy of the ions produced, in the field of ion implantation, microgravure, and more particularly in the equipment of the particle accelerators used both in the scientific than medical.
- the ion source of the invention can be used in a hostile environment for the ionization of unstable elements for the production of a beam of multicharged radioactive ions, for example, in nuclear physics.
- the ions are obtained by ionization, in a closed enclosure (such as a microwave cavity), of a gaseous medium consisting of one or more gases or metallic vapors, by means of electrons strongly accelerated by electronic cyclotron resonance.
- HF high frequency electromagnetic field
- the quantity of ions that can be produced results from the competition between two processes: on the one hand, the formation of ions by electronic impact on neutral atoms constituting the gas to be ionized and, on the other hand , the destruction of these same ions by recombination, single or multiple, during a collision of the latter with a neutral atom; this neutral atom can come from the gas not yet ionized or else be produced on the walls of the enclosure, by impact of an ion on these walls.
- This drawback is avoided by confining, in the enclosure constituting the source, the ions formed, as well as the electrons used for their ionization. This is achieved by creating inside the enclosure radial and axial magnetic fields, defining a so-called "equimagnetic" surface which has no contact with the walls of the enclosure and on which the condition of electronic cyclotron resonance is satisfied.
- This equimagnetic surface has substantially the shape of a rugby ball.
- This surface equimagnetic also makes it possible to confine the ions and the electrons produced by ionization of the gas. Thanks to this confinement, the electrons created have the time to bombard the same ion several times and fully ionize it.
- FIG. 1 there is shown schematically a conventional RCE ion source.
- This source comprises an enclosure 1 constituting a resonant cavity which can be excited by a high frequency electromagnetic field (HF).
- HF high frequency electromagnetic field
- This electromagnetic field is produced by a generator 3 of electromagnetic waves and introduced inside the enclosure 1 via a wave guide 5 and a transition cavity 20.
- This ion source also includes an externally shielded magnetic structure (7, 9, 11), the shielding 11 of which makes it possible to magnetize only the volume useful for electronic cyclotron resonance in the enclosure 1.
- this magnetic structure comprises permanent magnets 7 and solenoids 9 (or electromagnetic coils), arranged around the enclosure 1 and respectively creating a radial magnetic field and an axial magnetic field. These two magnetic fields are superimposed and distributed throughout the enclosure; they thus form a resulting magnetic field which defines the resonant equimagnetic surface S inside the enclosure 1.
- First and second pipes 21 and 23 connect the opening 19 of the shield 11 to respective openings 25 and 27 of the transition cavity 20, these openings being located on the lateral faces of the cavity 20.
- said gas is introduced into the enclosure 1 by means of a gas pipeline 30 connected to the opening 27 of the transition cavity 20.
- the gas and the electromagnetic waves introduced into the cavity 20 are transmitted to enclosure 1 by the first and second pipes 21 and 23, the role of which is precisely to ensure the transmission of waves to the enclosure and to inject them there along the longitudinal axis 15.
- enclosure 1 the combination of the axial magnetic field and the radial magnetic field makes it possible to strongly ionize the gas introduced.
- the electrons produced are then strongly accelerated by electronic cyclotron resonance, which leads to formation of a plasma of hot electrons confined in the volume limited by the equimagnetic surface S.
- the ions then formed in enclosure 1 are extracted therefrom by an electric extraction field generated by a potential difference applied between an electrode 31 and enclosure 1.
- the electrode 31 and enclosure 1 are all two connected to a power source 33.
- a pulse generator 35 itself located upstream of a power source 37 connected to the generator d 'electromagnetic waves.
- This pulse generator 35 controls said power source 37 by adjusting the useful cycle, namely the ratio between the duration of a pulse and the period of the pulses.
- An adaptation piston 45 connected to a third lateral opening 29 of the cavity 20, makes it possible to adjust the internal volume of said cavity 20.
- the adjustment of this piston 45 is used to tune all of the internal volumes of cavity 20 on the frequency of electromagnetic waves in order to obtain a minimum of reflected waves, that is to say waves which return to the wave generator 3.
- these internal volumes wave generator 3.
- the waves injected into the cavity 20 by the generator 3 are almost completely transmitted, via the pipes 21 and 23, to the enclosure 1 containing the plasma, then absorbed by the equimagnetic surface S.
- the second pipe 23 is transparent to electromagnetic waves at its end 23a situated opposite the shielding 11.
- this transparent part 23a there is a magnetic field axial from solenoids 9, an electromagnetic field and a high gas pressure.
- the electromagnetic field comes from the electromagnetic waves transmitted between the first pipe 21 and a non-transparent part 23b of the second pipe 23, and which pass through the transparent part 23a of the second pipe 23. Therefore, an electronic cyclotron resonance can take place at inside the end 23a of the second pipe 23 in a volume where there is a high gas pressure.
- This transparent end to the electromagnetic waves therefore constitutes a self-regulated pre-ionization stage, where the excess incident power of the electromagnetic waves is transmitted without reflection to the zone of electronic cyclotron resonance constituted by the equimagnetic surface S.
- the denser the plasma produced by electronic cyclotron resonance (or pre-ionized plasma) inside the end 23a of the pipe the better the transmission of electromagnetic waves, this pre-ionized plasma itself becoming conductive .
- the pre-ionized plasma carries a potential which is imposed on it by the immediate presence of the part 23b conductor of the line 23, itself subjected, via the line 21 and the enclosure 1, to the voltage of the power source 33.
- the plasma confined in the equimagnetic surface naturally carries a potential positive compared to enclosure 1. Indeed, the electrons of this confined plasma are heated by the cyclotronic resonance of the electrons and some of these electrons, too energetic, escape from the confinement. They will then strike enclosure 1 which, under this effect, charges negatively.
- the confined plasma therefore has a more positive polarity than that of the enclosure 1.
- the potential difference created between the enclosure 1 and the confined plasma is at the origin of an electric field E.
- This electric field E allows , in particular, the transfer of confined ions to the opening 17 of the enclosure 1.
- the magnetic structure of such an ion source comprises permanent magnets 7. However, the magnetic properties of the permanent magnets deteriorate rapidly when they are in the presence of neutron radiation. It is therefore difficult to envisage using such an ion source in a nuclear environment.
- permanent magnets do not tolerate neutron bombardment or overheating; for example, a Fe Nd B magnet does not tolerate a temperature above 80 ° C.
- magnetic structures comprising only electromagnetic coils. Since they do not have permanent magnets, these structures can withstand neutron radiation.
- An example of an electromagnetic coil structure is described by K. SUDLITZ in the article "The cusp ECR ion source", Journal de Physique, Colloque Cl, supplement to number 1, volume 50, January 1989.
- the ion yield multicharged obtained from such a magnetic structure is relatively weak, since it corresponds to a current of the order of the nanoampere, with weak states of charge.
- the yields which can be obtained from sources of ions with permanent magnets correspond to a current of the order of the microampere with high states of charge.
- the object of the invention is precisely to propose a source of multicharged ions which can be used in a hostile environment and having a yield substantially equivalent to the yields of ion sources with permanent magnets.
- the invention relates to an ion source with electronic cyclotron resonance comprising:
- the magnetic structure comprises:
- the pair of electrodes is negatively polarized so as to increase the electrostatic confinement.
- the magnetic structure also includes a negatively polarizable target electrode.
- the magnetic structure comprises several electromagnetic coils grouped in two sets, the two coils of the same set operating in an identical manner, the two sets operating in opposition with respect to the other.
- the two sets of coils are grouped in two sets, the two coils of the same set operating in an identical manner, the two sets operating in opposition with respect to the other.
- 1 invention include identical power supplies, as well as a number of identical coils, these coils being of identical size and made up of the same number of turns.
- FIG. 1, already described, schematically represents a source of conventional RCE ions;
- - Figure 2 schematically shows the magnetic coil structure, according to one invention.
- FIG. 3 shows the different field lines and equimagnetic surfaces obtained in the structure of the invention.
- the invention relates to an RCE source of multicharged ions, intended for use in nuclear environments where neutron radiation rapidly degrades the magnetic properties of permanent magnets used in conventional RCE sources.
- the RCE source of the invention therefore does not include permanent magnets; it only includes electromagnetic coils which create the magnetic fields in the enclosure.
- solenoids makes it possible to work at high temperature (several hundred degrees Celsius).
- the use of solenoids has the following advantage: when the power supply is cut, the magnetic field is zero. Consequently, the type of device of the invention can be carried, for example, in an aircraft.
- the ion source of the invention comprises an enclosure 1 in which there is an ion and electron plasma formed by electronic cyclotron resonance, a magnetic structure 6 which surrounds the enclosure 1 and which creates inside it two magnetic fields intended to ensure confinement in the enclosure, an ion extraction system 31 from the enclosure 1, a transition cavity 20 connected to an electromagnetic wave generator and a double pipe 21, 23 connecting the enclosure and the cavity.
- FIG. 2 shows only part of the ion source, and in particular an embodiment of the magnetic structure of the invention, surrounding the enclosure containing the plasma of ions and electrons.
- This magnetic structure comprises, according to the embodiment shown in Figure 2, two coils or two sets of two coils each; these coils, or sets of coils, operate in opposition to each other.
- the embodiment in which two sets of two coils are used is described; another embodiment (in which only two coils are used, operating in opposition to one another) being simpler and therefore easily understood from the explanation of FIG. 2.
- the magnetic structure of the ion source of the invention comprises two sets of coils 8 and 10, each set itself comprising two coils 8a, 8b and 10a, 10b (for the embodiment described); the two coils of the same assembly operate in a similar fashion; on the other hand, the two sets of coils operate in opposition to one another. In other words, each set of coils is traversed by an electric current in the opposite direction to the electric current flowing through the other set of coils.
- This magnetic coil structure is a “SPINDLE CUSP” type structure, in which the lines of magnetic fields come into contact, without touching. In this structure, the difference between the two sets of coils is chosen optimally, so that the modulus of the magnetic field is maximum; in fact, if these sets of coils are too far apart, the module of the magnetic field decreases.
- the sets of coils of the magnetic structure are identical, that is to say that they comprise the same current supply, as well as the same number of coils all the same. size and the same number of turns.
- the cusp obtained with such a structure is then a symmetrical cusp.
- the sets of coils may not be identical: they may comprise a different number of coils or else coils of different sizes or made up of a different number of turns; they can also be supplied with currents whose absolute values differ.
- the cusps obtained are asymmetrical.
- the magnetic field produced by the structure of the invention defines several equimagnetic surfaces S, including an external equimagnetic surface Se, also called “last equimagnetic surface”.
- This external equimagnetic surface Se is the largest equimagnetic surface not touching the enclosure.
- the ratio between the magnetic field of the external equimagnetic surface and the magnetic field of resonance is called "mirror relationship". The greater the mirror ratio, the greater the confinement.
- sets of electrodes consist of:
- Electrodes Two pairs of electrodes: these electrodes are called “confinement electrodes”, mounted face to face, perpendicular to the axis of the coils, at a radial distance from each other
- these confinement electrodes are made, for example, from a material which can be easily vaporizable, such as molybdenum, tantalum, refractory metals, etc.
- This set of confinement electrodes 12 therefore makes it possible to improve the confinement of the magnetic field created by the coils; the electric field necessary for this improvement of confinement can be evaluated from the expression of the electrical pressure ⁇ E 2 - which compensates for the axial pressure of the lost plasma Ne.kT e with Ne of the order of 10 10 cm “ 3 and T e of the order of 1 KeV, ie approximately 6 kV for a distance of 1 cm between the electrodes.
- the target electrode is made of a material which allows, when an electron hits it, that there is a production of several electrons which leave towards the medium.
- this target electrode can be made of a metal with secondary emission, such as an oxidized metal, oxidized aluminum, stainless steel coated with silica, etc. ;
- the magnetic structure of the ion source of the invention can be produced by choosing: an internal diameter of the coils of the order of 100 mm; with 20 m of copper / coil, five coils per set, + 1000 amps on one set, - 1000 amps on the other; - optimal spacing of the coil assemblies, so as to obtain an external equimagnetic surface Se of 0.36 Tesla;
- the volume of the chamber determining the quantity of multicharged ions.
- the frequency of the high-frequency generator is fixed so that the module of the magnetic field of the external equimagnetic surface (B ⁇ as ) divided by the module of the magnetic field of the source (B ECR ) is, for example, equal to 2, that is:
- FIG. 3 shows the lines of force L of the magnetic field, as well as the various equimagnetic surfaces S obtained within the enclosure of the ion source of the invention.
- this figure 3 shows the external equimagnetic surface S e , that is to say the last closed equimagnetic surface located at the edge of the coils, including the magnetic field module IB
- This FIG. 3 also shows the confinement electrodes 12, as well as the target electrode 14; a dotted Z zone shows the effect of electrostatic confinement on the plasma particles which tend to flee along the magnetic field force field lines: the confinement electrodes associated with the target electrode act on these particles preventing their escape.
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- Chemical & Material Sciences (AREA)
- Engineering & Computer Science (AREA)
- Combustion & Propulsion (AREA)
- Particle Accelerators (AREA)
- Plasma Technology (AREA)
Abstract
Description
Claims
Priority Applications (2)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
JP52328598A JP2001504266A (ja) | 1996-11-20 | 1997-11-19 | 有害環境下で多重荷電イオンを生成するためのサイクロトロニック電子共鳴源 |
EP97947091A EP0939968A1 (fr) | 1996-11-20 | 1997-11-19 | Source a resonance cyclotronique electronique pour la production d'ions multicharges en milieu hostile |
Applications Claiming Priority (2)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
FR9614149A FR2756097B1 (fr) | 1996-11-20 | 1996-11-20 | Source a resonance cyclotronique electronique pour la production d'ions multicharges en milieu hostile |
FR96/14149 | 1996-11-20 |
Publications (1)
Publication Number | Publication Date |
---|---|
WO1998022970A1 true WO1998022970A1 (fr) | 1998-05-28 |
Family
ID=9497813
Family Applications (1)
Application Number | Title | Priority Date | Filing Date |
---|---|---|---|
PCT/FR1997/002081 WO1998022970A1 (fr) | 1996-11-20 | 1997-11-19 | Source a resonance cyclotronique electronique pour la production d'ions multicharges en milieu hostile |
Country Status (4)
Country | Link |
---|---|
EP (1) | EP0939968A1 (fr) |
JP (1) | JP2001504266A (fr) |
FR (1) | FR2756097B1 (fr) |
WO (1) | WO1998022970A1 (fr) |
Citations (1)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
EP0252845A1 (fr) * | 1986-07-10 | 1988-01-13 | Commissariat A L'energie Atomique | Source d'ions à résonance cyclotronique électronique |
-
1996
- 1996-11-20 FR FR9614149A patent/FR2756097B1/fr not_active Expired - Fee Related
-
1997
- 1997-11-19 JP JP52328598A patent/JP2001504266A/ja active Pending
- 1997-11-19 WO PCT/FR1997/002081 patent/WO1998022970A1/fr not_active Application Discontinuation
- 1997-11-19 EP EP97947091A patent/EP0939968A1/fr not_active Withdrawn
Patent Citations (1)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
EP0252845A1 (fr) * | 1986-07-10 | 1988-01-13 | Commissariat A L'energie Atomique | Source d'ions à résonance cyclotronique électronique |
Non-Patent Citations (2)
Title |
---|
SUDLITZ K: "THE CUSP ECR ION SOURCE", JOURNAL DE PHYSIQUE. COLLOQUE, vol. 50, no. 1 (SUPPL.), January 1989 (1989-01-01), pages 779 - 781, XP000617182 * |
YABE E ET AL: "LARGE VOLUME RADIO-FREQUENCY PLASMA SOURCE USING A MAGNETIC LINE-CUSP FIELD", REVIEW OF SCIENTIFIC INSTRUMENTS, vol. 65, no. 4, PART 02, 1 April 1994 (1994-04-01), pages 1365 - 1367, XP000453929 * |
Also Published As
Publication number | Publication date |
---|---|
FR2756097B1 (fr) | 1998-12-11 |
FR2756097A1 (fr) | 1998-05-22 |
EP0939968A1 (fr) | 1999-09-08 |
JP2001504266A (ja) | 2001-03-27 |
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