EP0374011B1 - Verfahren und Vorrichtung unter Benutzung einer ECR-Quelle für die Herstellung von hochgeladenen, schweren Ionen - Google Patents

Verfahren und Vorrichtung unter Benutzung einer ECR-Quelle für die Herstellung von hochgeladenen, schweren Ionen Download PDF

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Publication number
EP0374011B1
EP0374011B1 EP19890403384 EP89403384A EP0374011B1 EP 0374011 B1 EP0374011 B1 EP 0374011B1 EP 19890403384 EP19890403384 EP 19890403384 EP 89403384 A EP89403384 A EP 89403384A EP 0374011 B1 EP0374011 B1 EP 0374011B1
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Prior art keywords
electrode
electrons
frequency
cavity
aperture
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English (en)
French (fr)
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EP0374011A1 (de
Inventor
Bernard Jacquot
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Commissariat a lEnergie Atomique et aux Energies Alternatives CEA
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Commissariat a lEnergie Atomique CEA
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    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01J—ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
    • H01J27/00—Ion beam tubes
    • H01J27/02—Ion sources; Ion guns
    • H01J27/16—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
    • 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

Definitions

  • the subject of the present invention is a method and a device using a source of electronic cyclotron resonance type for the production of highly charged heavy ions.
  • Heavy atoms are understood to mean atoms which include several electrons; the ions formed from these atoms are used in particular in atomic and nuclear physics.
  • the obtaining of ions can be carried out from a gas or a metallic vapor whose neutral atoms are ionized by impacts of energetic electrons.
  • the axial component has symmetry of revolution and has a gradient along an axis crossing the cavity.
  • the magnetic field is adjusted so that there is in the cavity at least one completely closed magnetic sheet and having no contact with the walls of the cavity.
  • the ions formed are extracted from the cavity by the effect of an electric field obtained by maintaining a potential difference between two electrodes. These electrodes are attached to the cavity and pierced with an opening allowing the passage of ions. A pumping circuit ensures the evacuation of the residual neutral atoms continuously. These electrodes are made of material which cannot be magnetized (generally made of stainless steel) so as not to disturb the distribution of magnetic field inside the cavity.
  • the closed sheet allows the ionization of the gas and the second favors the confinement of the plasma of ions and electrons.
  • Figure 1 represents approximately a Maxwell distribution.
  • the abscissas represent the energies of the electron populations noted in keV.
  • the ordinates represent the distribution D of the electron density H.
  • the asymmetrical bell curve in solid lines represents the energy distribution obtained with an electromagnetic excitation f1 (of the order of 10 GHz).
  • the curve passes through a maximum for an Eo value of low electronic energy.
  • the dashed curve in Figure 1 is obtained using a frequency f2 greater than f1.
  • the electrons favorable to the ionization of the strong states of charge are always located in the "tail" of the distribution which was slightly raised.
  • This technique involves a significant increase in the overall energy supplied to the plasma electrons by the electromagnetic wave, and raising the operating frequency quickly becomes very expensive (because of the need to use a higher power microwave generator).
  • the aim of the present invention is to increase the number of energetic electrons favorable to the ionization of strong charge states without resorting to an expensive increase in the frequency and the power of the microwave electromagnetic wave.
  • the present invention relates to a process for producing highly charged heavy ions.
  • This process consists in injecting a gas of atoms to be ionized into an ion source of the type "with several magnetic layers of electronic cyclotron resonance", a first fundamental magnetic layer being closed, a second the harmonic magnetic sheet being open, this source comprising a microwave confinement cavity and injecting an electron beam inside the microwave confinement cavity, these electrons having an energy at least equal to the energy of the ionization threshold atoms making up the gas.
  • the energy of these electrons is in a range from three times to four times the energy of the ionization threshold of the atoms making up the gas.
  • these electrons when entering the cavity, are provided with a gyrating movement following a helix, so that these electrons emit an electromagnetic wave of frequency close to twice the resonance frequency fce substantially equal to fHF .
  • the Maxwellian distribution of the energy of the electrons confined in the cavity is enriched by the energetic electrons of the injected beam.
  • the latter increase the density of the population of electrons having the energy favorable to the ionization of the gas.
  • the ionization efficiency is improved by printing to the electrons of the beam injected a movement of gyration following a propeller.
  • the electrons then emit an electromagnetic wave (cyclotronic emission due to the gyrotron effect) in a frequency spectrum around f′ce.
  • the present invention also relates to a device for implementing the method.
  • This device comprises an ion source of the type "with several magnetic layers of electronic cyclotronic resonance".
  • This source comprises a microwave confinement cavity inside which there is a magnetic field having an axial component and a radial component.
  • the source comprises a first electrode brought to a positive potential V1 and having an opening in the cavity.
  • the source is also provided, outside the cavity with a second electrode brought to a potential V2 lower than the potential V1 and pierced with an opening opposite the opening of the first electrode.
  • the second electrode is made of a material capable of being magnetized.
  • the magnetic field lines are then modified: it appears between the electrodes (outside the cavity) a sheet of magnetic field corresponding to an electronic cyclotron frequency f′ce double of fce. This layer closes the inner layer corresponding to the same frequency f′ce.
  • the potential difference V1-V2 between the electrodes allows the extraction of the ions formed inside the cavity.
  • the ions exit the cavity through the openings. In the process, electrons are torn off when peripheral ions collide with the edge of the opening in the second electrode.
  • the second electrode is made of iron, a material used when the magnetic fields present do not exceed 1 T.
  • the material capable of being magnetized is chosen from cobalt and an alloy of cobalt and iron.
  • the second electrode has the shape of a cone pierced by the opening at its pointed end.
  • the opening of the first electrode, the opening of the second electrode and the distance separating the electrodes are such that electrons traveling the distance separating the electrodes are provided with a gyrating movement in a helix so as to that these electrons emit an electromagnetic wave of frequency close to double the resonance frequency fce substantially equal to fHF.
  • the electrons are provided with a movement of gyration following a helix.
  • the presence of a radial acceleration component then produces the emission of an electromagnetic wave (gyrotron emission of electrons).
  • FIG. 2 schematically represents the distribution D of the energy of the electrons inside the microwave cavity, the energy being noted in keV. Thanks to the injection of an electron beam having an energy spectrum centered on Ei (value between three and four times the energy of the ionization threshold), the distribution is enriched without being forced to increase the electronic cyclotronic frequency of the injected wave.
  • FIG. 3A schematically represents an ion source according to the invention, seen in section and FIG. 3B the corresponding axial magnetic profile.
  • the invention uses an ion source of the "electron cyclotron resonance” (ECE) type known and of which only the elements necessary for understanding the invention have been shown.
  • ECE electron cyclotron resonance
  • the atomic gas to be ionized is injected inside the microwave confinement cavity 10 in the direction symbolized by the arrow. There is shown inside this cavity a closed sheet of magnetic field corresponding to the electronic cyclotron frequency fce in agreement with the frequency fHF of the wave injected into the cavity 10.
  • fHF fce is equal to 10 GHz for example.
  • a second non-closed sheet of magnetic field associated with an electronic cyclotron frequency f′ce multiple of fce surrounds the closed sheet.
  • the frequency f′ce can be equal to 2fce for example.
  • the cavity 10 is provided with an electrode 12 pierced with an opening 14.
  • the electrode 12 is brought to a positive potential V1 of between 10 and 20 kV, for example.
  • the opening 14 has a diameter of 8 mm, for example.
  • the geometry of the electrode 12 is produced in a known manner so as to allow the extraction of the ions formed in the cavity 10.
  • a second electrode 16 in the form of a cone for example, is opposite the first electrode.
  • This electrode 16 is brought to a potential V2 lower than V1, zero volts for example.
  • An opening 18 is drilled in the pointed end of the cone.
  • the first electrode 12 and the second electrode 16 are separated by a distance of 40 mm for example.
  • the openings 14 and 18 are centered on the same axis which can be the axis of the cavity 10 for example.
  • the ions formed inside the cavity 10 are extracted through these openings 14 and 18 under the action of the electric field generated by the potential difference V1-V2.
  • the second electrode 16 is made of a material capable of being magnetized, preferably, of iron.
  • the opening 18 has a diameter of at least 15 mm, for example.
  • the opening 14 of the first electrode 12, the opening 18 of the second electrode 16 and the distance between the electrodes 12, 16 are adjusted so as to create a component of the B field perpendicular to the electric field generated by the potential difference V1 -V2, this in the vicinity of the second electrode 16.
  • the diameter of the opening 14 of the first electrode determines the quantity of ions which will lick the edge of the opening 18 of the second electrode 16.
  • the diameter of the opening 18 of the second electrode determines to what extent the lines of magnetic forces will flourish on the edges of the second electrode 16. It therefore determines the intensity and the location of the magnetic field gradient created in the vicinity of the second electrode. The magnetic field lines are therefore modified.
  • the electrode 16 is made of a material capable of being magnetized, the lines of force leaving the cavity 10 (magnetic leaks) terminate inevitably on the end of the electrode 16.
  • the magnetic induction B is very high just in front of the electrode 16 and between electrodes 16 and 12.
  • the magnetic induction B along the axis of the cavity, decreases and then increases, so as to form a bowl, the minimum of which is located in the center of the cavity.
  • peripheral ions extracted from the cavity 10 strike the edge of the opening 18 of the electrode 16; the latter then emits electrons which are channeled under the effect of the magnetic field and accelerated between the electrodes 16 and 12.
  • the energy communicated to these electrons allows them to strike the atoms of the gas and ionize them.
  • FIG. 4 schematically illustrates the injection of the electrons inside the cavity 10.
  • the electrons are torn from the electrode 16 and a kinetic energy is communicated to them due to the potential difference V1-V2.
  • This energy is at least equal to the ionization threshold energy of the atoms of the gas.
  • this energy is close to Ei, energy having a value 3 to 4 times higher than the threshold energy and allowing optimal ionization.
  • the electrons are wound around the lines of magnetic forces and are accelerated in a spiral movement.
  • the electrons with a turning motion describe a straight or curved trajectory.
  • they emit an electromagnetic wave whose frequency is around 2fce. In this way the electrons are reflected on the open sheet of magnetic field associated with the frequency 2fce which forms a dynamic magnetic mirror.
  • the multiple reflections on this sheet multiply by a factor of about 1000 the intensity of the electron current from the electrode 16. Without this, the device described in this exemplary embodiment would not work: the current of the injected electrons does not not more than a few milliamps, which is insufficient to achieve significant ionization of the atoms.
  • High energy electrons can also be injected into the cavity using a simple electron gun.
  • the electron current must be around a hundred amperes since the electrons having no gyratory movement make only one pass through the cavity.
  • the method according to the invention makes it possible to strongly ionize atoms of a gas without having to resort to costly increases in the frequency of the injected wave.
  • the external electrode has been modified, the electrons injected into the cavity coming from the shocks occurring between the peripheral ions of the beam extracted from the source and the edges of this electrode.

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  • Physics & Mathematics (AREA)
  • Engineering & Computer Science (AREA)
  • Optics & Photonics (AREA)
  • Plasma & Fusion (AREA)
  • Spectroscopy & Molecular Physics (AREA)
  • Chemical & Material Sciences (AREA)
  • Combustion & Propulsion (AREA)
  • Particle Accelerators (AREA)

Claims (10)

  1. Verfahren zur Herstellung von Ionen, indem man eine Ionenquelle des Typs "mit mehreren Magnetmänteln der elektronischen Zyklotronresonanz" verwendet, wobei ein erster Grundmagnetmantel geschlossen wird, ein zweiter harmonischer Magnetmantel geöffnet wird, und diese Quelle einen Einschließungshochfrequenzresonator (10) umfaßt, in den man ein Gas von zu ionisierenden Atomen einführt, dadurch gekennzeichnet, daß es darin besteht, einen Elektronenstrahl ins Innere des besagten Einschließungshochfrequenzresonators (10) einzustrahlen, wobei diese Elektronen eine Energie von mindestens gleich der Energie der Ionisationsschwelle der das Gas bildenden Atome haben.
  2. Verfahren gemäß Anspruch 1, dadurch gekennzeichnet, daß die Energie der Elektronen des besagten Elektronenstrahls zwischen drei und vier mal der, der Ionisationsschwelle der das Gas bildenden Atome entsprechenden, Energie eingefaßt ist.
  3. Verfahren gemäß Anspruch 1, ein geöffneter Mantel des Magnetfeldes entsprechend einer elektronischen Zyklotronfrequenz f'ce, dem Doppelten der elektronischen Zyklotronfrequenz fce in Übereinstimmung mit der Frequenz fHF einer in den Hochfrequenzresonator eingestrahlten Welle, dadurch gekennzeichnet, daß die Elektronen des besagten Elektronenstrahls, indem sie in Resonator (10) durchdringen, mit einer, einer Helix entsprechenden, Kreisdrehungsbewegung versehen sind, so daß diese Elktronen eine elektromagnetische Welle der Frequenz nahe dem doppelten der Resonanzfrequenz fce aussenden.
  4. Vorrichtung für den Gebrauch des Verfahrens gemäß einem der Ansprüche 1 bis 3, ein nicht geschlossener Mantel des Magnetfeldes der mit einer Zyklotronfrequenz f'ce verbunden ist, dem Doppelten der Resonanzfrequenz fce, wobei die besagte Ionenquelle des Typs "mit mehreren Magnetmänteln der elektronischen Zyklotronresonanz", welche eine erste Elektrode (12), die bei einem positiven Potential V1 gehalten wird, die von einer Öffnung (14) durchdrungen ist, und eine zweite Elektrode (16), die bei einem Potential V2 kleiner V1 gehalten wird, die von einer Öffnung (18) gegenüber der Öffnung (14) der ersten Elektrode (12) durchdrungen ist, besitzt, dadurch gekennzeichnet, daß die zweite Elektrode (16) aus Material ist, das magnetisiert werden kann.
  5. Vorrichtung gemäß Anspruch 4, dadurch gekennzeichnet, daß das besagte Material, das magnetisiert werden kann, Eisen ist.
  6. Vorrichtung gemäß Anspruch 4, dadurch gekennzeichnet, daß das besagte Material, das magnetisiert werden kann, zwischen Kobalt und einer Legierung aus Kobalt und Eisen ausgewählt wird.
  7. Vorrichtung gemäß Anspruch 4, dadurch gekennzeichnet, daß die Öffnung (14) der ersten Elektrode (12), die Öffnung (18) der zweiten Elektrode (16) und der die Elektroden (12, 16) trennende Abstand so sind, daß Elektronen, die den, die Elektronden (12, 16) trennenden Abstand durchlaufen, mit einer Kreisdrehungsbewegung gemäß einer Helix versehen werden, so daß diese Elektronen eine elektromagnetische Welle der Frequenz nahe der doppelten Resonanzfrequenz fce emittieren.
  8. Vorrichtung gemäß Anspruch 4, dadurch gekennzeichnet, daß die zweite Elektrode (16) die Form eines Konus hat, der an seinem spitzigen Ende von der Öffnung (18) der zweiten Elektrode durchdrungen wird.
  9. Vorrichtung gemäß Anspruch 4, dadurch gekennzeichnet, daß die Frequenz fHF = fce
    Figure imgb0009
     ungefähr 10 GHz beträgt, die Öffnung (14) der ersten Elektrode (12) einen Durchmesser von 8 mm aufweist, die Öffnung (18) der zweiten Elektrode (14) einen Durchmesser größer 15 mm aufweist, der Abstand zwischen den Elektroden (12, 16) 40 mm beträgt.
  10. Vorrichtung gemäß Anspruch 4, dadurch gekennzeichnet, daß das Potential V2 gleich Null ist und daß das Potential V1 im Bereich zwischen 10 und 20 keV eingefaßt ist.
EP19890403384 1988-12-08 1989-12-06 Verfahren und Vorrichtung unter Benutzung einer ECR-Quelle für die Herstellung von hochgeladenen, schweren Ionen Expired - Lifetime EP0374011B1 (de)

Applications Claiming Priority (2)

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FR8816141 1988-12-08
FR8816141A FR2640411B1 (fr) 1988-12-08 1988-12-08 Procede et dispositif utilisant une source rce pour la production d'ions lourds fortement charges

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EP0374011A1 EP0374011A1 (de) 1990-06-20
EP0374011B1 true EP0374011B1 (de) 1994-04-06

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AU4705593A (en) * 1992-08-08 1994-03-03 Jurgen Andra Process and device for generating beams of any highly charged ions having low kinetic energy
ATA4694A (de) * 1994-01-13 1994-11-15 Ims Ionen Mikrofab Syst Projektionssystem fuer geladene teilchen

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US3634704A (en) * 1970-09-02 1972-01-11 Atomic Energy Commission Apparatus for the production of highly stripped ions
FR2475798A1 (fr) * 1980-02-13 1981-08-14 Commissariat Energie Atomique Procede et dispositif de production d'ions lourds fortement charges et une application mettant en oeuvre le procede
FR2595868B1 (fr) * 1986-03-13 1988-05-13 Commissariat Energie Atomique Source d'ions a resonance cyclotronique electronique a injection coaxiale d'ondes electromagnetiques

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EP0374011A1 (de) 1990-06-20
FR2640411B1 (fr) 1994-04-29
FR2640411A1 (fr) 1990-06-15
DE68914421T2 (de) 1994-11-10

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