Classifications

• • 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
  • F03H1/0006—Details applicable to different types of plasma thrusters
  • F03H1/0025—Neutralisers, i.e. means for keeping electrical neutrality
• • 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
  • F03H1/0006—Details applicable to different types of plasma thrusters
  • F03H1/0012—Means for supplying the propellant
• • 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 invention lies in the field of plasma thrusters. These thrusters may for example be used in satellites or in spacecraft whose propulsion requires low thrusts over long periods, such as probes.
• Plasma thrusters achieve these high ejection speeds.
• the principle of the plasma thrusters (conventional) described in the diagram illustrated in FIG. 1 is as follows: the "fuel" (gas) X is first ionized to form positive ions X + and electrons e " . Positive are accelerated by an electric field E, created by accelerating gates, and are thus ejected from the system, before being neutralized by an electron beam Fe " annex, positioned downstream of the accelerator zone, generated by a cathode . Neutralization is essential to prevent space vehicles from charging electrically.
• the various prototypes of plasma propellants existing to date generally use an ionization stage to generate a source of positively charged material (positive ions), an acceleration stage and a neutralization structure. Sources of ionization, accelerating and neutralizing structures can be varied. But, all the propellers existing today use only the positively charged material (positive ions) for propulsion, the negative charge (the electrons) serving only for ionization and neutralization.
• an electronegative gas gas with high electron affinity
• an electropositive gas gas with high electron affinity
• the two gases are different and it is two separate ion sources, or be used alone and, in the latter case, the flow of negative ions and the flow of positive ions are generated from this same electronegative gas.
• FIG. 2 illustrates this type of thruster configuration. More precisely, this thruster comprises a structure fed with electronegative gas and:
• An electronegative gas flow A 2 is introduced into the ionization stage 1. Under the action of an electrical power schematized by the arrow Pe, the electronegative gas generates positive ions A + , negative ions
• the ionization stage 1 is coupled to a filter stage
• the filtering means which can be for example a static magnetic field.
• Plasma extraction is ensured, in the case schematized here, by two grids polarized negatively 4 and positively 5, according to a first possible extraction method.
• the extraction of the plasma can also be ensured by a polarized grid alternately positively and negatively according to a second extraction method.
• the first and second extraction methods can also be combined or arranged in a matrix (for example to increase the size of the system).
• the thrust is therefore ensured by the two types of ions (the negative charge and the positive charge). Downstream neutralization is no longer necessary because the ion beams neutralize downstream (recombination) to form a beam of fast neutral molecules.
• the plasma thruster has a single ionization stage in which a positive ion and negative ion plasma is created.
• the Applicant proposes to exploit the temperature difference of the electrons within the ionization stage: the so-called "hot” electrons favor the positive ionization of the electronegative gas, thus creating positive ions, while the so-called less "hot” electrons favor the creation of negative ions, by attachment of these electrons.
• the subject of the present invention is a plasma thruster comprising the extraction of a positive ion flux and a negative ion flux characterized in that it comprises:
• ionizable gas injection means of said ionization stage said means comprising at least first injection means of a first gas and second injection means of a second electronegative gas;
• means for creating an electric power so as to produce the ionization of the gases in the ionization stage said means creating a first so-called hot zone at the level of the ionization stage; - the first gas being distributed in the first so-called hot zone, the second gas being distributed in a second zone less hot than said first zone;
• first means for extracting a flow of negative ions second means for extracting a flow of positive ions, connected to the ionization stage; the extraction of a flow of positive ions and the extraction of a flow of negative ions ensuring the electrical neutrality of the propellant.
• first gas and the second gas are identical.
• the thruster comprises two constituent compartments of the first and second zones.
• the first injection means of the first gas are located at a first face of the ionization stage, the second injection means being distributed along a second transverse face. to said first face, so as to dispense a series of second gas streams into the ionization stage.
• the second second gas injection means distribute different flow rates in the ionization stage.
• the propellant further comprises means for filtering the electrons released in the ionization stage, during the ionization of the gas.
• the means for creating an electric field comprise two conductive elements placed at the ends of the ionization stage to place said stage under tension.
• the means for creating an electric field comprise a coil supplied with a radiofrequency current.
• the means for creating an electric field comprise a helicon antenna powered by a radio frequency (RF) current.
• the electronegative gas is a dihalogen.
• the electronegative gas is of the diode type.
• the electronegative gas is oxygen
• the electronegative gas is sulfur hexafluoride (SF 6 ).
• the thruster comprises means for creating a pulsed plasma.
• the thruster comprises means for generating a static magnetic field within the ionization stage, so as to filter the electrons.
• the thruster comprises permanent magnets placed at the periphery of the ionization stage to create the magnetic field within said ionization stage.
• the thruster comprises means for extracting negative and / or positive ion fluxes in a direction perpendicular to the direction of the magnetic field applied at the level of the ionization stage.
• the thruster comprises a temporal modulation system of the ion extraction means.
• the positive and negative ions are extracted alternately by the same extraction means.
• the ion flux extraction means comprise at least one polarized gate.
• FIG. 1 schematizes a conventional plasma thruster according to the prior art comprising an electropositive gas for generating a positive ion flux which is neutralized with an electron beam downstream of the accelerating zone;
• FIG. 2 schematizes a plasma thruster according to the prior art comprising an electronegative gas for simultaneously generating a flow of positive ions and a flow of negative ions;
• FIG. 3 illustrates an example of a thruster according to the invention comprising the injection of two different gases at dissociated and optimized locations;
• FIG. 4 illustrates the evolution of the electron temperature as a function of a distance away from electric field generating means perpendicular to an applied magnetic field creating an electron heating zone
• FIG. 5 illustrates the evolution of the ratio of negative ions per electron, generated by attachment collision, as a function of a distance away from electrical field creation means perpendicular to an applied magnetic field, creating a zone electron heating
• FIG. 6 illustrates the rate of generation of negative ions by collision with electrons (attachment) as a function of temperature and the ionization rate creating positive ions by collision with electrons as a function of temperature;
• FIG. 7 schematizes a second variant of the invention comprising a series of means for injecting the second gas into the ionization stage;
• FIGS. 8a, 8b and 8c illustrate an example of a thruster according to the invention.
• the propellant of the invention comprises a single ionization stage coupled to means for ionizing one or more gases intended for propulsion, said stage comprising at least first injection means of a first gas and second means for injecting a second gas.
• the second injected gas is an electronegative gas and is diffused in the ionization stage in a so-called colder region, with respect to a so-called hot zone located near the means for creating an electric field necessary for the ionization of the ions. gas.
• These means for coupling the electrical energy to the plasma may be of the type of two plates polarized continuously, at low frequency or radiofrequency, radiofrequency supplied coil for inductive coupling, or even microwave source.
• FIG. 3 schematizes a first example of an ionization stage comprising a gas supply Gi and an electronegative gas supply G 2 , the coupling means of the electrical energy being represented by a power Pe of supply and generating electrons represented e " .
• the so-called hot region of the ionization stage is referenced Zi close to the RF source, the so-called colder region and remote from the RF source being referenced Z 2 .
• the electronegative gas is injected into the least hot region.
• the first gas may be an electropositive or electronegative gas, introduced into the so-called hot region Zi at the plasma core in which the RF power is coupled with the electrons.
• the second gas is introduced into a region Z 2 close to the extraction means in which the electrons have a lower temperature.
• the second gas is electronegative and ensures efficient generation of negative ions.
• Extraction means Me are provided for extracting the positive ions and the negative ions.
• FIG. 4 illustrates in this respect the evolution of the electron temperature as a function of a distance X within the ionization stage, the distance being located from the zone located near the electric field creation (reference 0) along the horizontal axis shown in FIG. 4.
• FIG. 5 illustrates the evolution of the ratio of negative ions by an electron as a function of the same distance X. It appears that the generation of negative ions is very marked beyond a distance in the case considered of about 40 mm. Curve 5a is relative to a gas O 2 , the curve
• the rate of creation of negative ions is a decreasing function of the electron temperature
• the ionization rate, creating positive ions, by collision with electrons is an exponential function of the electron temperature
• FIG. 6 illustrates these behaviors for an electronegative gas, curve 6a being respectively relative to the first phenomenon (attachment reaction), curve 6b being relative to the second phenomenon (ionization reaction).
• Negative ions are created in the low temperature region and become dominant when the temperature is typically below 1 -2 eV, whereas positive ions are created in a region of high temperature for the electrons and become dominant for energies higher than about 4-5 eV (the threshold values vary greatly according to the type of gas).
• the electronegative gas used may advantageously be a dihalogen of the type I 2 .
• Such a gas has several interests, it is cheap compared to other electronegative gases and has the great advantage of being solid at room temperature which can strongly favor all packaging and storage operations.
• the propellant can use as a first gas, a Xenon type gas for generating positive ions and as a second gas, a dihalogen capable of generating negative ions.
• the thruster comprises two zones respectively called hot and cold in which, respectively, are injected a first gas and a second electronegative gas via two injection means.
• the thrust is ensured by the two types of ions (positive and negative). Downstream neutralization is no longer necessary because the ion beams neutralize downstream (recombination) to form a beam of fast neutral molecules.
• the previously described ionization stage can be coupled to a filtering stage like that illustrated in FIG.
• the filtering stage can be realized in at least two ways: - (i) by modulating the creation of the plasma (pulsed plasmas: ON-OFF alternation of the electric power) and by using the OFF period for the extraction, period during which the electrons disappeared by attachment on the molecules. According to this configuration, the ionization and filtering stages are common. - (ii) by using a static magnetic field to trap the electrons, the ions, much heavier, are not.
• the thruster of the invention also comprises an extraction stage that can consist of accelerating grids whose dimensions are not necessarily similar to those of conventional grid thrusters, because the properties of the space charge sheaths are different in the absence of electrons.
• the plasma is created by an RF radio frequency antenna whose active surface is optimized and sized according to the intended applications.
• FIGS. 8a and 8b illustrate different views of the RF antenna and of the two hot and cold zones Z 1 and Z 2 in which the plate 80 is respectively inserted and closes the enclosure into which the gas is introduced.
• the temperature is sufficiently high in the Zi volume to create positive ions by ionization, and thus obtain a high density of positive ions in this region.
• a second electronegative gas G 2 is injected into the volume Z 2 to produce the negative ions.
• the extraction volume is separated into two regions by permanent magnets, the installation of two acceleration grids is also provided at the output of volume Z 2 .
• Permanent magnets 70 are placed on one side and in the middle of the volume Z 2 to filter the electrons so as to keep in the medium only positive ions and negative ions at the output of volume Z 2 . In this region the temperature of the electrons decreases and the negative ions are produced by collision of attachment with electrons.
• the applied magnetic field has two functions:
• Extraction means 40 and 50 shown in FIG 8c are used to accelerate the ions and cause the output of the propellant, the ionic entities A " and A + are thus extracted from the propellant.
• These means can typically be grid type, a grid that can be used to accelerate the negative ions, another grid that can be used to accelerate the positive ions.
• the two extracted ion beams neutralize each other downstream (in space). Neutralization is therefore automatic and does not require additional electron beam.
• the two beams can also recombine to form a beam of fast neutral molecules.

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• 2008
  • 2008-11-28 FR FR0858077A patent/FR2939173B1/fr not_active Expired - Fee Related
• 2009
  • 2009-11-24 WO PCT/EP2009/065688 patent/WO2010060887A1/fr active Application Filing
  • 2009-11-24 EP EP09756319.1A patent/EP2359001B1/de not_active Not-in-force
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