EP0781921B1 - Ionenquelle mit geschlossener Elektronendrift - Google Patents

Ionenquelle mit geschlossener Elektronendrift Download PDF

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Publication number
EP0781921B1
EP0781921B1 EP96402873A EP96402873A EP0781921B1 EP 0781921 B1 EP0781921 B1 EP 0781921B1 EP 96402873 A EP96402873 A EP 96402873A EP 96402873 A EP96402873 A EP 96402873A EP 0781921 B1 EP0781921 B1 EP 0781921B1
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EP
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Prior art keywords
ion source
annular channel
source according
channel
main annular
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EP96402873A
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English (en)
French (fr)
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EP0781921A1 (de
Inventor
Dominique Valentian
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Safran Aircraft Engines SAS
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Societe Nationale dEtude et de Construction de Moteurs dAviation SNECMA
SNECMA SAS
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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
    • H01J27/08—Ion sources; Ion guns using arc discharge
    • H01J27/14—Other arc discharge ion sources using an applied magnetic field
    • H01J27/143—Hall-effect ion sources with closed electron drift
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F03—MACHINES OR ENGINES FOR LIQUIDS; WIND, SPRING, OR WEIGHT MOTORS; PRODUCING MECHANICAL POWER OR A REACTIVE PROPULSIVE THRUST, NOT OTHERWISE PROVIDED FOR
    • F03H—PRODUCING A REACTIVE PROPULSIVE THRUST, NOT OTHERWISE PROVIDED FOR
    • F03H1/00—Using plasma to produce a reactive propulsive thrust
    • F03H1/0037—Electrostatic ion thrusters
    • F03H1/0062—Electrostatic ion thrusters grid-less with an applied magnetic field
    • F03H1/0075—Electrostatic ion thrusters grid-less with an applied magnetic field with an annular channel; Hall-effect thrusters with closed electron drift
    • 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
    • H05H1/54—Plasma accelerators

Definitions

  • the present invention relates to closed drift ion sources electrons that can be used as propellants, plus particularly for spacecraft, or as sources of ions for industrial treatments such as, in particular, vacuum deposition, ion-assisted deposition (I.A.D., "Ion Assisted Deposition”) or dry etching of microcircuits.
  • vacuum deposition ion-assisted deposition
  • I.A.D. ion Assisted Deposition
  • dry etching of microcircuits dry etching of microcircuits.
  • Industrial ion beam treatments can bring play of ion sources with a grid or a closed electron drift. These two types of ion sources were originally developed for use space (ionic thrusters or plasma thrusters).
  • These sources produce relatively high energy ions (500 to 1000 eV) with relatively low beam densities (2 to 6 mA / cm 2 at the grid). They are well suited for certain applications such as deep fine etching or uniform ion erosion of targets.
  • the latter source is described in the European patent. 0 265 365. It uses a conical anode and an axial counter electrode. This source is mainly used for the I.A.D.
  • Figure 1 depicts a closed drift plasma thruster of electrons as proposed in an article by L. H. Artsimovitch et al. published in 1974 in "Machinostroenie", pp. 75-84, about the program development of the stationary thruster and its tests on the satellite "METEOR”.
  • Such propellants of the "closed electron drift" type, or stationary plasma thrusters different from other categories by the fact that ionization and acceleration are not differentiated and that the acceleration zone has an equal number of ions and electrons, which eliminates any space charge phenomenon.
  • annular channel 1 defined by a part 2 made of insulating material and placed in an electromagnet comprising parts external 3 and internal 4 polar annulars placed respectively at outside and inside of part 2 made of insulating material, a cylinder head magnetic 12 arranged upstream of the motor and the coils solenoid 11 which extend over the entire length of channel 1 and are mounted in series around magnetic cores 10 connecting the pole piece external 3 to the cylinder head 12.
  • a hollow cathode 7, connected to ground, is coupled with a xenon supply device to form a cloud of plasma in front of the downstream outlet of channel 1.
  • An annular anode 5 connected to the positive pole of an electrical power source, for example 300 volts, is arranged in the closed upstream part of the annular channel 1.
  • the ionization and neutralization electrons come from the hollow cathode 7. Ionization electrons are drawn into the channel annular insulator 1 by the electric field prevailing between the anode 5 and the plasma cloud from cathode 7.
  • the ionization electrons take a trajectory of drift in azimuth necessary to maintain the electric field in the channel.
  • the ionization electrons then drift along trajectories closed inside the insulating channel, hence the name of the propellant.
  • the electron drift movement increases considerably the probability of collision of electrons with neutral atoms, phenomenon producing ions (here, xenon).
  • the specific pulse obtained by ion propellants closed electron drift classics operating with xenon, is around 1000 to 2500 seconds.
  • Figure 2 is an axial section of an example of a thruster developed by Professor Morozov having been the subject of a publication in document FR-A-2 693 770.
  • This propellant 20 comprises, like the propellant of FIG. 1, an annular channel 21 defined by a piece 22 of insulating material, a magnetic circuit comprising annular pieces external 24 a and internal 24 b , a magnetic yoke 32 disposed upstream of the propellant and a central core 28 connecting the annular parts 24 a , 24 b and the magnetic yoke 32.
  • Coils 31 make it possible to create a magnetic field and an electric field in the annular channel.
  • the hollow cathode 40 is coupled to a xenon supply device to form a plasma cloud in front of the downstream outlet of the channel 21.
  • This motor is characterized by the presence of a still chamber 23 which has a dimension in the radial direction larger than that of the main annular channel 21.
  • An anode 25 is disposed on the insulating pieces 22 delimiting the annular channel 21, in an area located immediately downstream of the stilling chamber 23.
  • An annular ionizable gas distributor 27 is disposed at the bottom of the ple
  • the anode layer propellants known as ALT
  • ALT have been described in Russian publications, for example: Fizika Plasmi, Plasmennie uckoriteli i ionnie injectori, Moscow 1984: Plasmennie uckoriteli c anodnim cloem, V.I. Garkusha, L. V. Leckov, E. A. Lyapin and, more recently, in international conferences
  • Figure 3 shows the section through an ALT anode layer propellant.
  • the magnetic circuit is very close to that of a stationary thruster at first generation SPT plasma. It includes a central pole piece 54 around which is wound an internal coil 61 serving as a support to the propellant, and an external annular pole piece 53, these two pieces grounded poles being connected by magnetic cores 60 supporting external coils 62.
  • the walls 56 of the acceleration channel 51 of the ALT anode layer thrusters are made of a metallic conductive material.
  • a massive anode 55 and a cathode 59 also serve to distribute the propellant gases.
  • the anode massive 55 occupies most of the acceleration chamber, the channel acceleration 51 being reduced to a very thin area between the anode massive 55 and the conductive walls 56 (hence the name anode layer). In fact, all parts of the propellant in contact with the discharge are metallic.
  • FIG. 4A which relates to a thruster conventional plasma with acceleration channel fully defined by a insulating part 62
  • the internal surface delimiting the acceleration channel is divides into two zones under the influence of the operation of the propellant.
  • the downstream zone 67 of length L (the length L may have values of the order of 5 to 7 mm for a thruster with a diameter of 100 mm), corresponds to an area permanently eroded by bombardment ionic.
  • the upstream zone 68 corresponds on the contrary to a deposition zone eroded products.
  • FIG. 4B shows the evolution of the value of the radial component of the magnetic induction B r as a function of the axial position Z on the imaginary cylindrical surface 65 corresponding to an average radius of the acceleration channel.
  • Figure 4C represents the value of the potential V as a function of the axial position Z on the same imaginary cylindrical surface 65 corresponding to an average radius of the acceleration channel.
  • the deposition zone 68 corresponds to an almost zero potential gradient (Figure 4C) and to a relatively weak radial magnetic field B r ( Figure 4B).
  • the functioning of the propellant is linked to plasma-wall interactions and in particular the secondary emission characteristics of the wall. Secondary emission properties may be different in zones 67 and 68.
  • the plasma thruster channel comprising boron nitride
  • erosion of this channel can cause boron atoms on the substrate to treat. This can be particularly troublesome for applications microelectronics because boron is a dopant of silicon.
  • the stationary plasma thrusters such as film thrusters anode
  • plasma thrusters with an acceleration channel defined by fully ceramic parts as described with reference to Figures 1, 2 and 4A have drawbacks insofar as the ceramic channel must obey contradictory imperatives: resistance to sputtering, mechanical strength, resistance to gradient thermal and thermal shock.
  • the object of the present invention is to remedy the drawbacks known electron drift ion sources and, more particularly, to modify them to allow greater flexibility of use.
  • the improvements of the invention are aimed at particular to reduce the mass of these sources while increasing their longevity, to simplify the manufacture of these sources while facilitating their disassembly and increase their mechanical resistance.
  • the invention also aims to reduce the emission of particles resulting of the erosion of the walls of the acceleration channel so that these sources may be likely to be used effectively as ion sources in large-scale industrial treatments, while their structure has so far limited their use essentially for the propulsion of satellites or other spacecraft.
  • an ion source at closed electron drift comprising a main annular channel ionization and acceleration open at its downstream end, at least one hollow compensation cathode disposed outside the annular channel main, means of creating a magnetic field in the channel main annular, adapted to produce a field in said channel essentially radial magnetic with a gradient with a maximum induction at the downstream end of the canal, a first means supply of ionizable gas associated with the hollow cathode and a second means for supplying ionizable gas located upstream of the canal main annular, and polarization means cooperating with a anode, characterized in that the main annular channel of this source consists of an electrically conductive material, and in that guard rings brought to a lower potential than that of the anode extend the annular channel downstream of it, these guard rings protecting central and peripheral pole pieces that are part said means for creating a magnetic field and delimiting a air gap in which the radial magnetic field acts with an induction Max.
  • the downstream part extending the channel can be produced using a material different from that of the upstream part of the main annular canal which must be essentially compatible with plasma gas partially ionized.
  • a part at less of the main annular channel is electrically polarized by the polarization means so that at least part of the wall internal of the main annular channel directly constitutes said anode.
  • the channel main ring of ionization and acceleration is a set monobloc made of an electrically conductive material.
  • the main annular channel constitutes a main annular canal block closed upstream by a tranquilization supplied with plasma gas by said second means gas supply which includes an annular distributor connected to a supply line.
  • the means of creation of a magnetic field include a magnetic circuit consisting of a cylinder head on which is fixed the main annular channel block, said cylinder head comprising an axial core supporting a pole piece lower central and concentric upper central pole piece with the main annular channel block, said cylinder head comprising other share a plurality of tie rods arranged around the annular channel block a once it is mounted on the cylinder head, said tie rods supporting a peripheral upper pole piece, said upper pole pieces central and peripheral constituting said pole pieces defining a air gap in which the radial magnetic field acts with an induction maximum, said guard rings protecting the pole pieces from ion erosion of the plasma.
  • the guard rings arranged at the mouth of the main annular canal are removable.
  • the main annular channel block is isolated electrically and thermally by vacuum with respect to the elements of the rest of the ion source including electrostatic screens, the space between the annular canal block and the elements of the rest of the source of ions being between 1 and 5 mm.
  • the annular channel block removable is fixed to the magnetic yoke by a plurality of balusters made of thermal insulating material and held in place by removable insulators.
  • the pole pieces upper include removable guard rings arranged at the mouth of the main annular canal.
  • the guard rings are made of one of the following conductive materials: carbon, carbon-carbon composite, nickel alloy, noble metal, composite ceramic consisting of nitrides bonded by silicon, silicon, stainless steel, aluminum.
  • the guard rings are made in one of the following insulating materials: boron nitride, alumina, quartz.
  • the main annular channel block is made in one of the following conductive materials: refractory nickel alloy, molybdenum, carbon-carbon composite.
  • the internal wall of the annular channel block is plated with a noble metal such as platinum, gold or rhodium in order to eliminate chemical attacks due to the gases present in said channel.
  • a noble metal such as platinum, gold or rhodium
  • the wall of the main annular channel is made of a material electrically conductive, and is electrically isolated from the rest of the structural elements of the source, including the anode.
  • the guard rings are made of dielectric material partially covering the channel main ring finger.
  • guard rings are produced under form of inserts made of ceramic material which are fixed by means of supports on the pole pieces.
  • the electrically conductive walls of the annular channel and the plenum are at slightly lower floating potential to that of the anode. This arrangement reduces interactions plasma-wall, therefore the heating of the channel.
  • the latter can by therefore be made of relatively thin sheet metal.
  • the channel block is held vis-à-vis the magnetic circuit by columns made of weakly conductive material.
  • the anode is held opposite of the channel block by insulators and supplied by a conductor in the axis of one of the columns.
  • the gas supply is at the potential of the channel block.
  • Figure 5 shows a view overall view, in axial section, of a first example of an ion source at closed electron drift according to the invention.
  • annular channel design and construction of an annular channel are significantly simplified compared to the case of a source for space use like the one in Figure 2.
  • a 123 plenum, which is of dimensions reduced, and the upstream part of a main annular acceleration channel form a one-piece metallic assembly 122 which will be referred to below "channel block" and which plays in particular the role of an anode 125.
  • a magnetic circuit consisting of a yoke 136, a core axial 138, a pole piece 132, an internal pole piece 135, tie rods 137 and an external pole piece 134, determines a magnetic field maximum in the air gap defined by the pole pieces 134, 135.
  • This field includes a minimum in the vicinity of the pole piece 132.
  • the control is created by an internal coil 133 and one or more external coils 131, which makes it possible to adjust its distribution and adjust thus the divergence of the ion beam.
  • the channel block 122 comprises, at its upstream part, a tranquilization 123 which is equipped with a gas injection manifold 127 supplied by a pipe 126.
  • This channel block 122 serving as anode 125 is held by at least three balusters 121, one of which can be constituted by the line 126 itself.
  • These balusters 121, 126 are fixed on insulators 145 by nuts 146.
  • the balusters 121, 126 can thus be separated from the insulators 145 to allow the disassembly of the annular channel block 122.
  • Electrostatic covers 147, 148, 154 make it possible to prevent discharges.
  • the gas supply is performed using ground tubing 150, isolator 151 and a fitting comprising a gasket 152 and a nut 153.
  • This assembly is housed in a base 130 which serves as a support for the source.
  • the electric discharge producing the ion beam is established between a hollow cathode 140 supplied with rare gas and the channel block 122 forming anode 125, supplied with pure gas or a mixture of gases, at least one of these gases can be reactive.
  • the nature of the material of the channel 122 can be adapted to the gas to be ionize while the nature of the guard rings 164, 165 which are placed in the extension of the channel block 122, downstream of it and which are subject to ion erosion, can be adapted to both the nature of the gas and the requirements of the substrate to be treated (for example semiconductor or layer thin optic).
  • these removable guard rings 164, 165 which are arranged respectively in the outer pole pieces 134 and internal 135, can be made of carbon (with a low rate of erosion), ceramic composite materials (such as a composite consisting of silicon, silicon nitride and titanium nitride) in aluminum, stainless steel, noble metal (such as platinum or gold).
  • Screens 139, 159, 160 arranged outside the channel block 122, play both a thermal and electrostatic role vis-à-vis the channel block 122. They prevent excessive heating of the pole pieces and the coils and determine, around the channel block 122, a field preventing landfills.
  • the main annular channel 122 is thus electrically isolated and thermally from the rest of the source 139, 159, 160 by vacuum, space between the annular channel 122 and the rest of the source being included typically between 1 and 5mm.
  • Tests show that with a channel block 122 produced entirely of conductive material cooperating downstream with end pieces 134, 135, 164, 165 brought to a lower different potential, in this case to mass, we get a profile of the plasma potential along the median axis of channel 122 (Figure 6B) practically identical to that of the thrusters first generation stationary plasma (SPT) ( Figure 4C). It is therefore possible to generate a progressive acceleration of the ions in a channel formed by two zones brought to different potentials.
  • the profile of magnetic field in plasma is determined by the thickness of guard rings 164, 165 protecting the pole pieces from erosion ionic plasma.
  • Determining the nature of the wall of the canal according to the nature of industrial treatment using ions produced by the source is basically a chemical problem due to the reaction of the wall with the partially ionized plasma gas.
  • an ion source conforming to the invention it is now possible, thanks to the material walls driver, to use this source for a whole range of treatments for which conventional channel sources made of ceramic material were disreputable.
  • the electrical insulation of the channel block 122 with respect to the cylinder head is carried out by means of the three balusters 121 provided with insulators 145.
  • the electrical insulation of the front, side and rear faces of the channel block 122 from the grounded parts (i.e. pole pieces 134 and 135 and heat shields 139 and 159) is provided by vacuum. Indeed, the small distance between these walls (of the order of a millimeter) and the low pressure (2.10 -4 to 5.10 -4 mbar) lead to a discharge voltage much higher than the operating voltage (according to Paschen's law ).
  • Channel block 122 receives the heat flow, radiated and dissipated (resulting from inelastic collisions of ions and electrons) by the plasma. This corresponds to a power of a few hundred watts for a 1.5 kW source. To avoid overheating of the parts polar (whose temperature must always remain below the point of Curie) coils and dismountable connecting members 145, 153, 152, the heat losses from the channel block 122 forming the anode 125, to the rest from the source, are limited by specific constructive provisions.
  • the only conductive link with the source is constituted by the hollow support columns 121 and the gas inlet duct 126.
  • These columns can be made of weak material conductor (stainless steel, Inconel), so that the heat flow leads can be greatly reduced.
  • balusters and / or the inlet duct allow a differential expansion of the channel block 122 forming the anode 125 with respect to the magnetic yoke 136.
  • This screen can be for example either a solid block 139, such as can see it in Figure 5, discharging the heat flow over a large surface, i.e. a screen fitted with screened windows 179, represented on the Figure 7, allowing direct radiation from the channel block 122 forming the anode 125 in a certain solid angle.
  • the part which extends the channel block 122 downstream thereof is divided into two removable and interchangeable rings.
  • the outer ring 164 is screw mounted on the outer pole piece 134, while the ring internal 165 is locked in position by the internal pole piece 135.
  • the gas distributor 127 is an integral part of the tranquillization 123.
  • the channel block 122 also constitutes a metal part easily interchangeable. To dismantle the channel block 122, you must first remove the assembly constituted by the external pole piece 134, the ring of guard 164 and the screen 139 and the assembly constituted by the internal pole piece 135 and the guard ring 165. This first level of disassembly can be done without adjustment by keeping the source in place.
  • connection between the gas supply and the tube 126 is hermetic.
  • a flat seal 152 seals between the two parts. He is crushed by the nut 153.
  • the base 130 is removable ( Figure 5). It is provided with a degassing 176 screened, in order to prohibit the entry of the plasma prevailing in the vacuum chamber inside the space formed by the base 130 and the magnetic yoke 136.
  • the cable 143 for polarizing the anode 125 and the gas supply 150 pass advantageously through the interface between cylinder head 136 and base 130 so as not to hinder disassembly of the latter.
  • Figure 9 shows a device for supplying the channel block 122 in particles 195 of a sublimable solid under vacuum (metals with strong vapor pressure, volatile oxides). This ionizes these vapors (partially) to carry out vacuum deposition, reactive or not.
  • the external screen 139 may provide the external screen 139 with a heating element 191. It will be noted that the shape of the plenum affects that of a crucible which helps to standardize the flow of steam. If necessary, we can introduce this room a conical cornice 192.
  • Figure 10 shows a variant of the channel block 122 provided with a internal insulating deposit 193 delimiting the conductive area 198 constituting the anode 125 opposite the minimum field.
  • Figure 11 shows an overall view, in axial section, of a second example of a closed electron drift ion source conforming to the invention.
  • This ion source includes the following components: a hollow compensation cathode 240 disposed outside the source itself, downstream of it; a magnetic circuit comprising a cylinder head 236 disposed upstream from the source and from the bars 237, 238 connecting the cylinder head 236 to external pole pieces 234 and inner 235 in the form of rings, arranged downstream of the ion source; means 231, 233 for creating a magnetomotive force constituted by coils can be arranged for example around some of the connecting bars 237, 238 and auxiliary pole pieces 232, 239 determining a minimum of field in the vicinity of the anode; a channel block ring 222 of ionization and acceleration, delimited downstream by walls cylindrical external 281 and internal 282 metallic, and extended in the acceleration zone by two annular pieces 264, 265 of material dielectric (ceramic) held against internal pole pieces 235 and external 234, either by mechanical mounting (positioning between the pole piece and a metal holding piece), either by brazing each ceramic ring 264, 265 on
  • the bottom of the plenum receives a cylindrical anode 225 and a gas distributor 227, the anode 225 being held in place by insulators 283, compressed by the distributor 227 against the bottom of the chamber using tie rods 221 and spacers 221 a .
  • tie rod-spacer assemblies 221, 221a are mounted on 245 insulators ensuring positioning with respect to the magnetic circuit (and more particularly the cylinder head 236).
  • the distributor 227 is supplied with gas by a line 226 and a connector 252 mounted on an insulator 245.
  • the polarization of the anode is ensured by a tie rod 221b and a wire polarization 243.
  • the anode 225 and the distributor 227 remain easily removable.
  • the ion source further includes electrostatic screens conductors 259, 339 which surround the annular channel 222.
  • Screens 259, 339 can slide at their downstream end respectively on the outer ceramic ring 264 and the ceramic ring internal 265.
  • channel 222 It is the same for channel 222, the ends of which can be fitted with a metal wire eliminating peak effects, therefore the risks of dump.
  • Free space created between electrically conductive screens 259, 339 and the metal walls 281, 282 have a width approximately constant (typically between 1 and 5mm) so as to avoid risk of electric shock between the walls 281, 282 and the screens 259, 339.
  • the screens 259, 339 can be provided with a grid so as to allow the degassing of the space between these screens and the walls 281, 282.
  • the end pieces 264, 265 have a length along the acceleration channel 222 which extends at least over an area corresponding to the length L of Figure 4, i.e. over the erosion zone due to ions.
  • the walls electrically conductive 281, 282 define a width of the acceleration channel 222, in the radial direction, which can be greater than the width of the channel acceleration 222 defined in the radial direction by the end pieces 264, 265 of dielectric material.
  • this provision avoids the appearance of a discontinuity due to the deposition zone / erosion zone transition, the deposition producing progressively on surfaces 281 and 282.
  • the walls electrically conductive 281, 282 are electrically connected to each other by a bottom conductor 270 constituting, with the conductive walls 281, 282, a monobloc assembly which can itself be integral with the assembly 227 gas distributor.
  • the cylindrical surfaces 281 and 282 are connected to the bottom of chamber 270 by radii of curvature ensuring a smooth surface evolving gradually. So the electric field between the surfaces conductive 281, 282 and the conductive screens 259, 339, which are at the mass, does not undergo a significant increase which can cause a breakdown.
  • the upstream part of the acceleration channel 222 is separated from the parts polar 232, 239 as well as electrostatic screens 259, 339 by a empty space.
  • the main annular channel 222 is electrically and thermally insulated from the rest of the source 259, 339, 232, 239, 236 by the vacuum, the space between the main annular channel 222 and the rest of the source included typically between 1 and 5mm.
  • the walls 281, 282 of the annular channel 222 are electrically isolated from the rest of structural elements of the source, including anode 225.
  • the external surface of the walls 281, 282, 270 as well as the surfaces external and internal screens 259, 339 can be polished so that decrease the radial radiative losses. This allows in particular to decrease the heat flux on the central coil 233 ( Figure 11).
  • the outer surface of the wall external 281 of the chamber can be on the contrary covered with a high-emissivity coating, as well as the faces of the screen 339, the part of the screen 259, which faces the internal wall 282, remaining polished.
  • This arrangement improves radiation cooling of the conductive channel while preventing the heating of the central coil 233.
  • the life and efficiency of the ion source depends on the functional phenomena that occur within the layer ionization.
  • the main phenomenon that determines lifespan is erosion end pieces 264, 265 of the discharge chamber-channel assembly acceleration 222, due to the projection onto the walls of the ions which have been accelerated.
  • Integrity characteristics of the closed drift ion source of electrons are largely determined by the geometry and intensity of the magnetic field in the acceleration channel and remain stable even when the downstream outlet part of the discharge chamber has widened by further ion projection (see Figure 4A).
  • a significant degradation of the operating efficiency of the thruster is observed only when a complete projection of the ions was carried out on the walls of the chamber of discharge in the interpole space of the magnetic system and when the poles 234, 235 themselves have undergone significant projections. In this cases, changes in topology and intensity of the magnetic field are the main causes of performance degradation.
  • terminals 264, 265 of the walls of the discharge chamber-channel assembly acceleration inserts of sufficiently thick dielectric material which have increased resistance to spraying by accelerated ions, which increases the lifespan of the entire ion source.
  • the walls 281, 282 can however be also connected to the anode 225 by an electrical resistance.
  • electrically conductive walls 281, 282, made of metal or composite material leads to a reduction in the mass of the entire ion source.
  • the walls electrically conductive 281, 282 have a potential close to that of the anode while in operation the structural elements of the magnetic system (elements 236, 237, 238) are going to be at a potential close to that of the cathode. This is to avoid the appearance of electrical discharges between the magnetic system and the chamber that this is surrounded by conductive screens 339, 259 which are placed at an approximately constant small distance from the walls 281, 282 and 270.
  • Figure 12 gives an example of a brazed connection allowing to allow differential expansion between a part 264, respectively 265, and a metallic support 274, respectively 275, while respecting the electric field requirements between the screen 339 respectively 259 and the wall 281, respectively 282.
  • the support 274 has an inverted end 272 which is wetted by the solder 271 and the support 275 can be made of identical way.

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Claims (21)

  1. Ionenquelle mit geschlossener Elektronendrift, umfassend einen lonisierungs- und Beschleunigungs-Hauptringkanal (122), der an seinem stromabwärtigen Ende offen ist, mindestens eine hohle Kompensationskathode (140), die außerhalb des Hauptringkanals (122) angeordnet ist, Mittel (131, 132, 133, 134, 135, 137) zum Erzeugen eines Magnetfelds in dem Hauptringkanal, ausgebildet um in dem Kanal ein im Wesentlichen radiales Magnetfeld zu erzeugen, welches einen Gradienten bei maximaler Induktion am stromabwärtigen Ende des Kanals (122) aufweist, eine erste, der hohlen Kathode zugeordnete Zuführeinrichtung für ionisierbares Gas, und eine stromaufwärts bezüglich des Hauptringkanals (122) gelegene zweite Zuführeinrichtung (126, 150, 151) für ionisierbares Gas, und mit einer Anode (125) zusammenwirkende Polarisationsmittel (143, 121),
    dadurch gekennzeichnet, dass der Hauptringkanal (122) dieser Quelle aus elektrisch leitendem Material besteht, und dass auf einem Potential unterhalb des Potentials der Anode (125) gehaltene Schutzringe (164, 165) den Ringkanal (122) stromabwärts von diesem verlängern, wobei diese Schutzringe zentrale (135) sowie umfängliche (134) Polstücke, welche die Mittel zum Erzeugen eines Magnetfelds darstellen, schützen und einen Luftspalt begrenzen, in welchem das radiale Magnetfeld mit maximaler Induktion wirkt.
  2. lonenquelle nach Anspruch 1,
    dadurch gekennzeichnet, dass zumindest ein Teil des Hauptringkanals (122) elektrisch von den Polarisationsmitteln (143, 142) derart polarisiert wird, dass zumindest ein Teil der Innenwand des Hauptringkanals (122) die Anode (125) direkt bildet.
  3. lonenquelle nach Anspruch 1 oder Anspruch 2,
    dadurch gekennzeichnet, dass der Hauptringkanal (122) elektrisch und thermisch durch den Zwischenraum bezüglich den restlichen Elementen der lonenquelle isoliert ist, welche elektrostatische Abschirmungen (159, 160, 139; 259, 339) aufweisen, wobei der Raum zwischen dem Hauptringkanal (122; 222) und den übrigen Elementen der lonenquelle zwischen 1 und 5 mm ausmacht.
  4. lonenquelle nach Anspruch 2 oder Anspruch 3,
    dadurch gekennzeichnet, dass der lonisierungs- und Beschleunigungs-Hauptringkanal (122) eine Monoblockanordnung ist, gebildet aus einem elektrisch leitenden Material.
  5. lonenquelle nach Anspruch 4,
    dadurch gekennzeichnet, dass der Hauptringkanal (122) einen Hauptringkanalblock bildet, der stromaufwärts von einer Beruhigungskammer (123) abgeschlossen ist, die von der zweiten Gaszuführeinrichtung, welche einen mit einer Speiseleitung (126, 150) verbundenen Verteilerring (127) aufweist, mit plasmagenem Gas gespeist wird.
  6. Ionenquelle nach Anspruch 5,
    dadurch gekennzeichnet, dass die Mittel zum Erzeugen eines Magnetfelds einen magnetischen Kreis aufweisen, gebildet durch ein Joch (136), an dem der Hauptringkanalblock (122) fixiert ist, wobei das Joch (136) einen Axialkern (138) aufweist, der ein unteres zentrales Polstück (132) und ein oberes zentrale Polstück (135) trägt, die konzentrisch bezüglich des Hauptringkanalblocks (122) sind, wobei das Joch (136) andererseits eine Mehrzahl von Zugstäben (137) enthält, die um den Ringkanalblock nach dessen Anbringung an dem Joch angeordnet sind, wobei die Zugstäbe ein oberes Umfangs-Polstück (134) haltern, wobei das zentrale (135) sowie die umfänglichen (134) oberen Polstücke die erwähnten Polstücke bilden, welche einen Luftspalt begrenzen, in welchem das radiale Magnetfeld mit einer maximalen Induktion wirkt, während die Schutzringe (164, 165) die Polstücke vor lonenerosion durch Plasma schützen.
  7. lonenquelle nach Anspruch 6,
    dadurch gekennzeichnet, dass der abnehmbare Ringkanalblock (122) an dem magnetischen Joch (136) durch mehrere Säulchen (121, 126) fixiert ist, die aus einem Wärmeisoliermaterial bestehen und von abnehmbaren Isolatoren (145) gehalten werden.
  8. lonenquelle nach einem der Ansprüche 1 bis 7,
    dadurch gekennzeichnet, dass die Schutzringe (164, 165), die an der Mündung des Hauptringkanals angeordnet sind, lösbar sind.
  9. lonenquelle nach Anspruch 8,
    dadurch gekennzeichnet, dass die Schutzringe (164, 165) aus einem der folgenden leitenden Werkstoffe gebildet sind: Kohlenstoff, Kohlenstoff-Kohlenstoff-Verbundwerkstoff, Nickellegierung, Edelmetall, Keramik-Verbundwerkstoff, gebildet durch Nitride von Silicium, Silicium, nicht-oxidierbarer Stahl und Aluminium.
  10. lonenquelle nach Anspruch 8,
    dadurch gekennzeichnet, dass die Schutzringe (164, 165) aus einem der folgenden Isolierwerkstoffe gebildet sind: Bornitrid, Aluminiumoxid, Quartz.
  11. lonenquelle nach Anspruch 5,
    dadurch gekennzeichnet, dass der Hauptringkanalblock (122) aus einem der folgenden leitenden Werkstoffe gebildet ist: Refraktär-Nickellegierung, Molybdän, Kohlenstoff-Kohlenstoff-Verbundwerkstoff.
  12. lonenquelle nach Anspruch 5,
    dadurch gekennzeichnet, dass die Innenwand des Ringkanalblocks mit einem Edelmetall wie z.B. Platin, Gold oder Rhodium überzogen ist, um chemische Angriffe durch in dem Kanal vorhandene Gase auszuschalten.
  13. lonenquelle nach Anspruch 6,
    dadurch gekennzeichnet, dass die Mittel zum Erzeugen eines Magnetfelds außerdem Induktionsspulen (131, 133) oder Permanentmagneten aufweisen, die in den magnetischen Kreis eingefügt sind.
  14. lonenquelle nach Anspruch 13,
    dadurch gekennzeichnet, dass auf den Zugstäben (137) Induktionsspulen (131, 133) gelagert sind.
  15. lonenquelle nach Anspruch 13,
    dadurch gekennzeichnet, dass eine torusförmige Spule (133), die mit einer magnetischen ringförmigen Abschirmung ausgestattet ist, um den Axialkern (138) herum angeordnet ist.
  16. lonenquelle nach Anspruch 1,
    dadurch gekennzeichnet, dass die Wand (281, 282) des Hauptringkanals (222) aus einem elektrisch leitenden Material besteht und elektrisch vom Rest der Strukturelemente der Quelle, darunter die Anode (225), isoliert ist.
  17. lonenquelle nach Anspruch 16,
    dadurch gekennzeichnet, dass die Schutzringe (264, 265) aus einem dielektrischen Material bestehen, welches den Hauptringkanal (222) teilweise abdeckt.
  18. Ionenquelle nach Anspruch 17,
    dadurch gekennzeichnet, dass die Schutzringe (264, 265) in Form von Einsätzen aus Keramikmaterial ausgebildet sind, welche durch Halterungen (274, 275) an den Polstücken (234, 235) befestigt sind.
  19. Ionenquelle nach Anspruch 18,
    dadurch gekennzeichnet, dass die elektrisch leitende Wand (281, 282) eine Breite des Ringkanals (222) definiert, welche in radialer Richtung größer ist als die Breite des Ringkanals (222) in radialer Richtung in der Höhe der Schutzringe (264, 265).
  20. lonenquelle nach einem der Ansprüche 16 bis 19,
    dadurch gekennzeichnet, dass die einen größeren Durchmesser und die einen kleineren Durchmesser aufweisenden Bereiche der elektrisch leitenden Wand (281, 282) des Ringkanals (222) elektrisch miteinander durch einen leitenden Boden verbunden sind, der zusammen mit den erwähnten Teilen der elektrisch leitenden Wand (281, 282) eine Monoblockanordnung (281, 282, 270) bildet, die sich auf einem schwimmenden Potential etwas unterhalb von dem der Anode (225) befindet.
  21. lonenquelle nach Anspruch 20,
    dadurch gekennzeichnet, dass die einen größeren Durchmesser und die einen kleineren Durchmesser aufweisenden Bereiche der elektrisch leitenden Wand (281, 282) des Ringkanals (222) mit dem leitenden Boden (270) über Krümmungsradien verbunden sind, die eine glatte Oberfläche garantieren.
EP96402873A 1995-12-29 1996-12-23 Ionenquelle mit geschlossener Elektronendrift Expired - Lifetime EP0781921B1 (de)

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FR9515718 1995-12-29
FR9515718A FR2743191B1 (fr) 1995-12-29 1995-12-29 Source d'ions a derive fermee d'electrons

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EP0781921B1 true EP0781921B1 (de) 2002-05-29

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EP (1) EP0781921B1 (de)
DE (1) DE69621411T2 (de)
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EP0781921A1 (de) 1997-07-02
US5945781A (en) 1999-08-31
DE69621411T2 (de) 2003-01-09
FR2743191B1 (fr) 1998-03-27
FR2743191A1 (fr) 1997-07-04
DE69621411D1 (de) 2002-07-04
UA43863C2 (uk) 2002-01-15

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