Device and method for generating a beam of charged particles

Abstract

The invention relates to a device (1) for generating charged particles, the device (1) comprising: - at least one emission module comprising an emission electrode (11) and a conductive liquid (17) deposited on the emission electrode (11), - an extraction electrode (12) arranged facing the at least one emission module, and - at least one high-voltage electrical generator (20, 22) configured to apply an emission potential to the emission electrode (11) suitable for applying an electric field to the conductive liquid (17), the device (1) being characterized in that it comprises a high-frequency modulator (M, M1, M2) that can be connected to the supply circuit of the device (1) and configured to modulate the electric field at high frequency, each emission module being configured to emit a beam of charged particles when an electric field is applied to the conductive liquid (17), the device (1) being configured to operate in a first mode, called purely ionic mode, in which the emission potential is equal to or greater than a threshold emission potential necessary for the formation of a Taylor cone and less than a limit emission potential, the high-frequency modulator (M, M1, M2) is disconnected from the supply circuit of the device (1) and the at least one emission module emits a beam of pure ions, and in a second mode, called droplet mode, in which the emission potential is greater than a limit emission potential, the high-frequency modulator is connected to the supply circuit of the device (1) and the at least one emission module emits a beam of charged clusters, the limit emission potential being defined as a function of the surface tension of the conductive liquid (17) such that the apex of the Taylor cone is subjected to a break for the limit emission potential.

Description

Device and method for generating a beam of charged particles

[0001] The present invention relates to a device for generating charged particles. It also relates to a method for generating charged particles.

[0002] The field of the invention is, in a non-limiting manner, that of ion beam generators. State of the art

[0003] Charged particle generators, and more specifically ion generators, are based on the principle of electro-hydro-dynamic (EHD) emission, in which a strong constant electric field (in the order of a billion volts per meter) is applied to the surface of a conductive liquid, such as a molten metal or an ionic liquid. Ion generators essentially consist of an emission electrode comprising an emitter or a set of emitters, an extraction electrode, a reservoir of a conductive liquid and, in some cases, an accelerating electrode. An emitter typically consists of a tip onto which the conductive liquid is applied. To apply the electric field to the surface of the conductive liquid, a potential difference of the order of 1-10 kV is applied between the emission electrode and the extraction electrode.When the electric field is applied to the surface of the conductive liquid covering a tip, it deforms the tip into a conical structure called a "Taylor cone". Under the effect of the intense local electric field present at the top of the Taylor cone, its terminal outgrowth, called the apex or terminal jet, emits a jet, or beam, of free ions. The charged particles are then accelerated to high speeds of the order of a few tens of kilometers per second by the applied electric field.

[0004] Ion generators can be used, in particular, as ion thrusters in spacecraft, such as satellites. The ion beam, or plume, provides thrust to the thruster. The propulsion produced by the beam can be characterized by a thrust vector.

[0005] The emitted beam of charged particles can be characterized by the flux, or emission currentI, and the velocity of the ejected ions. The operation of an ion thruster in particular can then be characterized by an I / V function.

[0006] An example of an ion propulsion system is described in P.C. Lozano, "LessinSpace," American Scientist, Volume 104, Page 270 (2016). The transmitting electrode has a plurality of aligned emitters in the form of porous tips infused with ionic liquid, as well as an extraction electrode and an accelerating electrode whose respective openings are aligned with the tips.

[0007] Another example of an ion propulsion system is described in S. Dandavino et al., “Microfabricated electrosprayemitterarrayswithintegratedextractorandacceleratorelectrodesforthepropulsionofsmallspacecraft,” J. Micromech. Microeng., 24, 075011 (2014), in which the emitters include a microcapillary tube to deliver the propellant liquid to its end where it is ionized.

[0008] In a low emitted current range, the ion flux torn from the Taylor cone apex is relatively stable. When the current is increased by applying a proportionally increased electric field, instabilities in the emitted beam appear. Beyond an emission flux of the order of ten µA, the force exerted by the electric field induces turbulent instabilities in the conducting liquid and the terminal jet of the Taylor cone, leading to rupture effects in the end of the cone apex. This stability limit corresponds to the emission potential from which the emitted beam no longer contains only ions, but also charged clusters or charged droplets. The geometric dimensions of the droplets are similar to the jet diameter, i.e. sizes of a few nanometers.

[0009] High current regime can degrade the performance of the ion generator, and in particular the propulsive performance of an ion thruster.

[0010] First, the tips of the emitting tips can be damaged. Indeed, the tips are no longer covered with conductive liquid following the instabilities produced. From then on, the electric field, of several Volts / nm, can erode the solid support tip generally chosen in a refractory material and cause material tearing, strong electric discharges and a significant release of energy over a very short time (µs).

[0011] Second, the coexistence of ions and droplets in the same beam or propellant plume produces disturbances in it. Indeed, the emitted droplets containing several hundred to several thousand atoms are much slower than the fast simple or molecular ions which accompany them with a speed v = (2eU / m) 1 / 2 . Due to this velocity differential, the droplets are then atomized in flight by the fast-moving ions, creating scattering centers for the ions that strike them. As a result, the opening angle of the plume is widened. As a result, the directivity and magnitude of the thrust vector are reduced, leading to a loss of propellant efficiency and a waste of the conductive liquid as fuel.

[0012] Finally, the in-flight spraying of droplets is also a significant source of pollution for the generator engine and its environment, due to the redeposition of ionized material, commonly referred to as "backsputtering", which can lead to failure through the surface metallization of electrical insulators.

[0013] The very high current operating mode (> 100 µA per emitter), called "degraded" mode, allows maximum thrust values ​​to be achieved. However, operation with the appearance of droplets is a regime to be avoided for reasons detailed above.

[0014] An aim of the present invention is to provide a device and a method for the stimulated, selective and reversible emission of charged particles.

[0015] It is in particular an aim of the present invention to propose a device and a method for the stimulated, selective and reversible emission of simple or rapid molecular ions or charged droplets, also called charged clusters, of variable mass, while preventing the mixing of the two types of charged particles.

[0016] At least one of these aims is achieved with a device for generating charged particles, the device comprising:at least one emission module comprising an emission electrode and a conductive liquid deposited on the emission electrode,an extraction electrode arranged opposite the at least one emission module, andat least one high voltage electric generator configured to apply an emission potential to the emission electrode adapted to apply an electric field to the conductive liquid,

[0017] the device being characterized in that it comprises a high-frequency modulator connectable to the power supply circuit of the device and configured to modulate the electric field at high frequency when it is connected,

[0018] each emission module being configured to emit a beam of charged particles when an electric field is applied to the conductive liquid,

[0019] the device being configured to operate in a first mode, called purely ionic mode, in which the emission potential is equal to or greater than a threshold emission potential necessary for the formation of a Taylor cone and less than a limit emission potential, the high-frequency modulator is disconnected from the power supply circuit of the device and the at least one emission module emits a beam of pure ions, and in a second mode, called droplet mode, in which the emission potential is equal to or greater than the limit emission potential, the high-frequency modulator is connected to the power supply circuit of the device and the at least one emission module emits a beam of charged clusters,

[0020] the limiting emission potential being defined as a function of the surface tension of the conducting liquid so that the apex of the Taylor cone is subject to a breakdown for the limiting emission potential.

[0021] The charged particle generating device according to the present invention provides a configuration for operating the device in a first operating mode and a second operating mode.

[0022] More particularly, the architecture for generating the electrical potential applied to the emission module, comprising a single tip or a set of tips on which the conductive liquid is deposited, makes it possible to switch from the first operating mode to the second operating mode, and vice versa. The switch is achieved by connecting or disconnecting an additional electrical circuit comprising a high-frequency modulator, and adapting the value of the emission current. The second operating mode can therefore be activated and deactivated on demand.

[0023] In the first operating mode, corresponding to the classical operation of ion generators, a constant electric field is applied to the surface of the conductive liquid, allowing the formation of the Taylor cone. For the formation of the Taylor cone, the applied emission potential must be equal to or greater than the threshold emission potential. Under the effect of the intense electric field present at the apex of the Taylor cone, the apex emits a jet of free ions. This is a beam of pure ions. To obtain this regime, the emission potential ensuring the formation of the Taylor cone is lower than a limiting potential, the potential allowing a stable emission of ions thus being between the threshold emission potential and the limiting potential. In this regime, the emission current is also lower than a limiting emission current.

[0024] In the second operating mode, according to the invention, the value of the electric field creating the conical structure is modulated at high frequency (> MHz). For this, thanks to the high-frequency modulator, the emission potential is modulated periodically when it reaches its limit value, corresponding to the stability limit of the Taylor cone. This modulation causes ruptures and reconstructions of the apex or terminal jet of the Taylor cone, the emission potential being modulated subtractively from the limit potential.

[0025] Once a droplet is emitted, it shields the electric field applied to the emitter, this shielding effect diminishing as the droplet moves away from the emitter. The apex of the Taylor cone reforms after the rupture, and will be completely reformed when the electric field value has returned to that of before the rupture. A new rupture then takes place as well as a new reconstruction, and so on. The apex of the Taylor cone is therefore subjected to a series of ruptures and reconstructions at high frequency when the emission potential is equal to or greater than the limiting emission potential and the electric field applied to the conductive liquid is modulated.

[0026] During the apex reconstruction phases, no emission of simple or molecular ions can be established.

[0027] The formation of charged droplets or clusters or aggregates is then stimulated. The dimensions of these droplets correspond to that of the apex of the cone. The droplets are made up, depending on the applied voltage and therefore the emission current, of several tens to several thousand atoms or molecules. In the emitted beam there are only charged droplets or clusters, also called "clusters", but no ions. To obtain this regime, the emission potential is greater than a limiting potential, the emission current also being greater than a limiting emission current.

[0028] The limiting emission potential is defined as a function of the surface tension of the conductive liquid used in the device. The limiting emission potential corresponds to the emission potential at which the apex of the Taylor cone is subject to rupture. From this limiting potential, stable emission of pure ions is no longer possible.

[0029] As a result, the device according to the invention allows the generation of either a beam of pure ions or a beam of charged clusters. These two types of charged particles are not mixed in the same beam. The problems of reduced directivity of a beam mixing these types of charged particles can be avoided.

[0030] The generator according to the present invention can make it possible to have, in the same device, a fast ion emitter having a high specific impulse (ISP) regime, and a charged droplet emitter having a lower ISP regime but with a higher ejected momentum.

[0031] The charged particle generator of the invention can be advantageously implemented as an ionic or spatial thruster, for example in a satellite.

[0032] The high ISP mode is a low fuel consumption mode (conductive liquid) leading to maximum autonomy, for example for station keeping of a satellite. In this purely ionic mode or regime, the ISP value can be very high (for example, > 8000s), favoring propulsive efficiency. The thrust in this mode is low. Also, the divergence of the ion beam is reduced compared to a beam mixing pure ions and charged clusters, which improves the propulsive efficiency as well as the directivity of the thrust vector.

[0033] In low ISP mode, the ISP value is reduced compared to the purely ionic mode. The ISP value can be optimized so as not to fall below a certain value (e.g., 3000s). The thrust increases very strongly compared to the purely ionic mode, due to the fact that the mass of ejected material is greater in charged clusters.

[0034] If charged droplets in an ion beam are an operating regime to be avoided, the device according to the invention allows stimulated and selective emission of one or other type of charged particles.

[0035] In this document, the term "charged particle generation device" means a device for generating simple ions, molecular ions, charged clusters, also called charged droplets.

[0036] The term "device power supply circuit" means any component enabling the device to be powered up, or supplied with power. It includes in particular at least one high-voltage electric generator as well as the emission and extraction electrodes.

[0037] The term "a conductive liquid deposited on the emission electrode" is to be understood in a broad sense. In particular, the conductive liquid does not only cover the emission electrode like a sheet. The conductive liquid can also be supplied or conveyed from the interior of the electrode, for example, by a capillary in emission tips or by a porous tip structure. The conductive liquid is in all cases deposited on one or more emission sites from which the beam of single ions, molecular ions or droplets is emitted.

[0038] Advantageously, the device according to the invention may comprise a high voltage electric generator linked to the emission electrode operating as a current generator.

[0039] A high voltage generator operated in “current source” mode is particularly suitable for rapidly delivering a desired flow of charged particles.

[0040] According to one embodiment, the device may further comprise a second high voltage electrical generator linked to the extraction electrode.

[0041] A high voltage generator operated in “voltage source” mode is suitable for delivering a stable output voltage and minimizing its variations.

[0042] Preferably, the high-frequency modulator may comprise an avalanche diode, the avalanche diode being disconnected in the purely ionic mode and connected in the droplet mode. The orientation of the diode depends on the polarization between the electrodes and the type of charged particles.

[0043] An avalanche diode is configured to clip a signal very quickly, thus preventing the propagation of noise and destructive overvoltages. An avalanche diode typically consists of a silicon chip and a PIN junction. These diodes are designed to operate in avalanche mode with a very low clipping time, on the order of picoseconds. Avalanche diodes also have a very low dynamic resistance, resulting in a very good clipping factor.

[0044] Such a high-frequency modulator does not supply an additional voltage to the device but modulates its potential by periodically subtracting a voltage corresponding to the avalanche threshold of the diode. The modulation period and the voltage value can be chosen.

[0045] The avalanche diode can be connected in series with the current generator or with the extraction electrode.

[0046] Alternatively, the high-frequency modulator may comprise two avalanche diodes, one of the avalanche diodes being connected in series with the current generator and the other of the avalanche diodes being connected in series with the second high-voltage electrical generator.

[0047] Two avalanche diodes provide redundancy for the high-frequency modulator.

[0048] According to one embodiment, the device may further comprise at least one resistor connected in series with the avalanche diode(s) and configured to limit the current flowing in the avalanche diode(s).

[0049] The conductive liquid may include one of an ionic liquid, a conductive liquid, and a liquid or molten metal.

[0050] The ionic liquid may comprise one of an onium salt, phosphate, ammonium, sulfate, chloride, bromide, tetrafluoroborate, or hexafluorophosphate. Ionic liquids are particularly adept at generating positively or negatively charged molecular ions depending on the sign of the voltage applied to the electrodes.

[0051] The liquid or molten metal may include one of gallium, indium, gold, an alkali metal, or an alkali alloy.

[0052] The conductive liquid may comprise a conductive glycerol type liquid.

[0053] According to another aspect of the same invention, there is provided a method for generating ions implemented in a device for generating charged particles, the device comprising at least one emission module comprising an emission electrode and a conductive liquid deposited on the emission electrode, an extraction electrode arranged opposite the at least one emission module, at least one high-voltage electrical generator configured to apply an emission potential to the emission electrode adapted to apply an electric field to the conductive liquid, and at least one high-frequency modulator connectable to a power supply circuit of the device, each emission module being configured to emit a beam of charged particles when an electric field is applied to the conductive liquid, the method comprising the following steps:setting an ion emission current to a first setpoint valueI cby applying a threshold emission potentialV seuil to the emission electrode by means of the at least one high-voltage electrical generator, the threshold emission potential being necessary for the formation of a Taylor cone;in a first operating mode, called purely ionic mode, in which the emission potential is lower than a limit emission potential, the high-frequency modulator is disconnected from the power supply circuit of the device and the at least one emission module emits a beam of pure ions,adjustment of the emission potential to keep the first setpoint valueI cconstant, in a second operating mode, called droplet mode, in which the emission potential is equal to or greater than the limit emission potential, the high-frequency modulator is connected to the power supply circuit of the device and the at least one emission module emits a beam of charged clusters, adjustment of the emission current to a second setpoint value I limit from the first setpointI c , Yes c limit , by applying a limiting emission potentialV limit at the emission electrode, the limiting emission potential being defined as a function of the surface tension of the conductive liquid so that the Taylor cone is subject to a breakdown for the limiting emission potential,high-frequency modulation, by means of the high-frequency modulator, of the electric field applied to the conductive liquid,

[0054] ​in the first mode, the at least one emission module emitting a beam of pure ions, and in the second mode, the at least one emission module emitting a beam of charged clusters.

[0055] To enter the second operating mode, the steps of adjusting the emission current to the second setpoint valueI limit and electric field modulation can be initiated at the same time or one after the other. In the latter case, the current adjustment step can be performed before or after the modulation is started.

[0056] To switch back from the second operating mode to the first operating mode, the emission current is set to a value lower than the second setpoint value I limit , while remaining greater than or equal to the first setpoint value I c, and the modulation of the electric field is stopped. It is possible to carry out these steps simultaneously or one after the other. In the latter case, one can either reduce the emission current below the limit valueI limit and then turn off the high frequency modulator, or turn off the modulator and then reduce the current.

[0057] According to one embodiment of the invention, the method may further comprise, in the second operating mode, a step of adjusting the emission current to a third setpoint value I c3 , Yes limit c3 , by applying an emission potential called dropletsV seuil2 at the emission electrode, whereV seuil2 >V limit .

[0058] According to an example, the step of adjusting the emission current to the first setpoint value I c ​can be achieved by gradually increasing the value of the potential applied to the emission electrode from 0 to the threshold valueV seuil for which the emission current I em reaches the first setpoint valueI c .

[0059] The step of adjusting the emission current to the second set valueI limit can be achieved by gradually increasing the value of the potential applied to the emission electrode ofV seuil to the limit valueV limit for which the emission current reaches the second setpoint value I limit .

[0060] The step of adjusting the emission current to the third set valueI c3 can be achieved by gradually increasing the value of the potential applied to the emission electrode ofV limit to the droplet valueV seuil2 for which the emission current reaches the third setpoint value I c3 .

[0061] According to one embodiment, the method may further comprise a step of adjusting a rate of emission of pure ions by applying an extraction potential V ext to the conductive liquid once the set valueI c of the emission current reached, so as to bring the emission potentialV em to a predetermined valueV empr =V seuil +V ext .

[0062] Advantageously, the device and the method according to the invention can be implemented in a satellite, in particular of the CubeSat type, in which the beam of charged particles emitted by the device is adapted to provide thrust to the satellite.

[0063] The device and method according to the invention can also be implemented in a nanofabrication system, configured for the transfer and deposition of droplets on a surface of an object.

[0064] For example, clusters of conductive particles can be deposited on the surface of a substrate to make conductive structures.

[0065] In another example, reactive or non-reactive chemical species can be created, transported and deposited out of equilibrium on a surface of a sample.

[0066] Also, the device and the method according to the invention can be implemented in a mass spectrometer, configured for the acceleration of charged particles.

[0067] Charged droplets of selected sizes can be produced by electrospray ionization (ESI), allowing access to the mass and certain structural elements of heavy and polar molecules by spectrometric analyses. Description of figures and embodiments

[0068] Other advantages and characteristics will become apparent upon examination of the detailed description of non-limiting examples, and the appended drawings in which:is a schematic representation of a device for generating charged particles according to one embodiment of the invention,is a schematic representation of examples of emitters that can be implemented in a device according to the invention,is a schematic representation of a device for generating charged particles according to another embodiment of the invention,is a schematic representation of a device for generating charged particles according to another embodiment of the invention,is a schematic representation of a device for generating charged particles according to another embodiment of the invention,is a schematic representation of a device for generating charged particles according to another embodiment of the invention,lais a block diagram with an avalanche diode,lais a schematic representation of a non-limiting example of a method for generating charged particles according to the present invention, andlashows a timing diagram of the method for generating charged particles according to one embodiment of the invention.,

[0069] It is understood that the embodiments which will be described below are in no way limiting. In particular, it is possible to imagine variants of the invention comprising only a selection of characteristics described below isolated from the other characteristics described, if this selection of characteristics is sufficient to confer a technical advantage or to differentiate the invention compared to the state of the prior art. This selection includes at least one preferably functional characteristic without structural details, or with only part of the structural details if this part alone is sufficient to confer a technical advantage or to differentiate the invention compared to the state of the prior art.

[0070] In particular, all the variants and embodiments described can be combined with each other if there is no technical obstacle to this combination.

[0071] In the figures, elements common to several figures retain the same reference.

[0072] This is a schematic representation of a non-limiting exemplary embodiment of a device for generating charged particles that can be implemented within the framework of the present invention. The device can in particular be used to implement the method of the invention.

[0073] The device 1, shown in the, is arranged to produce a beam of charged particles.

[0074] The device 1 comprises an emission unit 10, comprising an emission electrode 11 and an extraction electrode 12.

[0075] The emission electrode 11 comprises one or more emitters 14, for example in the form of tips. The end of the emitter 14 is covered by a conductive liquid. This conductive liquid may be, for example, an ionic liquid, a liquid made conductive or a liquid or molten metal.

[0076] The ionic liquid may comprise, for example, an onium, phosphate, ammonium, sulfate, chloride, bromide, tetrafluoroborate, or hexafluorophosphate salt.

[0077] The liquid or molten metal may include, for example, gallium, indium, gold, an alkali metal or an alkali alloy.

[0078] The conductive liquid may comprise, for example, a conductive glycerol type liquid.

[0079] When an electric field is generated between the two electrodes 11, 12, a very strong local electric field (of the order of 10 9V / m) is generated at the tip(s), causing the conductive liquid to form a Taylor cone located at the tip end 14. Ions are then emitted at the apex of each cone. The charged particles are then accelerated to high speeds of the order of a few tens of kilometers per second by the applied electric field.

[0080] Each emission electrode 11 – conductive liquid assembly can be considered as an emission module.

[0081] The emitter 14 of the emission electrode 11 and the provision of the conductive liquid on or in the emitter 14 may take different forms. Examples of different types of emission tips and deposition of a conductive liquid on said tip are shown in the.

[0082] La(a) shows a solid tip 14 on which the conductive liquid 17 is deposited. The conductive liquid 17 can be diffused onto the emission electrode 11 passively from a reservoir of conductive liquid. This then forms a layer of liquid 17 on the upper surface of the emission electrode 11 and in particular the tip 14 or all of the tips 14.

[0083] La(a) also shows, in enlargement, the Taylor cone formed at the end of the tip 14 by the conductive liquid 17. The apex, or jet, of the Taylor cone is also visible.

[0084] La(b) shows a hollow tip 14' provided with a capillary 15 inside. The conductive liquid 17 can rise to the end of the tip 14' by capillarity from a reservoir of conductive liquid.

[0085] La(c) shows a 14'' tip having a porous structure. The porous material is soaked with conductive liquid 17. The porous material may be a porous metal such as nickel, tungsten, etc.

[0086] With reference to the, the extraction electrode 12 may consist, for example, of a metal plate arranged opposite the emission electrode 11 and having openings 16 for allowing the flow of ions or charged particles to pass through.

[0087] The device 1 as shown in the also comprises a first high voltage power supply 20 for powering the emission electrode 11. The first power supply 20 is a high voltage generator operating in current source mode. This means that the generator 20 is adapted to deliver a constant current corresponding to a set value and to minimize variations therein.

[0088] The device 1 also comprises a high frequency (HF) modulator M. The HF modulator M can be connected to the current source 20 or disconnected from the current source 20. As shown in the, the modulator M is connected between the current source 20 and ground. The modulator M is adapted to modulate at high frequency the electric field applied to the conductive liquid.

[0089] When the HF modulator M is disconnected from the power supply 20, the device 1 can operate in a first mode, called purely ionic mode, in which the emission potential is lower than a limit emission potential. The device 1 then emits a beam of pure ions.

[0090] When the HF modulator M is connected to the power supply 20, the device can operate in a second mode, called droplet mode, in which the emission potential is greater than a limit emission potential. The device 1 then emits a beam of charged droplets or charged clusters.

[0091] The operation of the device according to the invention in the first and second modes will be described in more detail later.

[0092] This is a schematic representation of another non-limiting exemplary embodiment of a device for generating charged particles that can be implemented within the framework of the present invention.

[0093] The device 2, as shown in the, comprises the same elements as the device 1 according to the embodiment illustrated in the.

[0094] In the embodiment of the, the HF modulator M can be connected between the emission electrode 11 and the first high voltage power supply 20. In particular, the HF modulator M is connected to the high voltage output of the current generator 20. The modulator M can be controlled from the controller 24 by an isolation transformer. The isolation transformer makes it possible to obtain galvanic isolation between a primary control circuit with a reference to the “earth” potential and a secondary circuit referenced to the high voltage output voltage of the current generator 20. This galvanic isolation can be several tens of kilovolts.

[0095] This is a schematic representation of another non-limiting exemplary embodiment of a device for generating charged particles that can be implemented within the framework of the present invention.

[0096] The device 3, as shown in the, comprises the same elements as the devices 1 according to the embodiments illustrated in Figures 1 and 3.

[0097] In the embodiment of the, the HF modulator M can be connected between the extraction electrode 12 and the ground.

[0098] Figures 5 and 6 are schematic representations of other non-limiting exemplary embodiments of a device for generating charged particles that can be implemented within the framework of the present invention.

[0099] The device 4, 5, as shown respectively in Figures 5 and 6, comprises the same elements as the devices 1, 2, 3 described in relation to Figures 1, 3 and 4.

[0100] The device 4, 5 of Figures 5 and 6 further comprises a second high voltage power supply 22, for powering the extraction electrode 12.

[0101] The second power supply 22 is a high voltage generator operating in voltage source mode. This means that the generator 22 is adapted to deliver a stable output voltage and to minimize its variations.

[0102] In the embodiment of the, the HF modulator M can be connected between the high voltage generator 22 and ground.

[0103] In the embodiment of the, the device 5 comprises two HF modulators M1, M2. The first modulator M1 can be connected between the emission electrode 11 and the ground. The second modulator M2 can be connected between the extraction electrode 12 and the ground.

[0104] In the device according to the embodiments shown in Figures 1 and 3 to 5, the high frequency modulator preferably comprises an avalanche diode.

[0105] The avalanche diode M can be connected in series either with the current generator 20 or with the extraction electrode 12. It can also be connected in series with the high voltage generator 22 when it is present.

[0106] In the device according to the embodiments shown in the, the high frequency modulator comprises two avalanche diodes.

[0107] One of the avalanche diodes, M1, is connected in series with the current generator 20, and the other of the avalanche diodes, M2, is connected in series with the second high-voltage electric generator 22.

[0108] Of course, other configurations of one or two avalanche diodes in the device according to the invention are possible and conceivable.

[0109] More than two avalanche diodes can also be provided. For example, several diodes can be connected in parallel.

[0110] The avalanche diode(s) can be connected or disconnected using a switch. The direction of the diode is chosen according to the polarity of the electrodes to allow the emission of positively or negatively charged particles as appropriate.

[0111] The avalanche diode(s) can be connected in series with at least one resistor. This resistor protects the avalanche diode(s) by limiting the current flowing through them.

[0112] The following represents a schematic diagram of an avalanche diode 40, connected in series with a resistor 41 and a switch 42. The avalanche diode may be a Transil diode (formerly a brand of the Thomson company) or transient voltage suppression diode. As implemented in the present invention, and shown in the, the avalanche diode 40 is a unidirectional diode, that is to say, conducting in one direction and clipping in the other direction. In the example shown, the diode 41 is connected between a "low" point which is the reference potential or "earth", or "ground", and a high point which is the "0 Volts" or reference potential of the power supply. Due to the presence of the circuit, this reference potential of the power supply is continuously modulated to the clipping value of the diode.

[0113] An avalanche diode has very abrupt current / voltage characteristics and very low response times (of the order of picoseconds). It allows electrical charges to be discharged in a very short time, as soon as the potential applied to the terminals of the diode exceeds a specific value, called the clipping voltage (V écrêtage ), to the chosen diode (for example, from a few Volts to several hundred Volts).

[0114] In the figure, diode 40' is shown to illustrate the other direction of the diode compared to that of diode 40.

[0115] Finally, the device according to the embodiments shown in Figures 1 and 3 to 6 comprises a controller 24 linked to the power supply 20 or to the high voltage power supplies 20, 22. The controller 24 makes it possible to control the power supply 20 or the power supplies 20, 22, for example, according to a method of generating charged particles with this device within the framework of the present invention.

[0116] The controller 24 is configured to control the emission of ions or charged clusters, such as the flow and velocity of the emitted particles, as well as to monitor the chemical characteristics of the conductive liquid. The controller 24 may comprise, for example, an on-board platform, such as a microcomputer, a digital electronic circuit and / or software means. The controller 24 may also comprise a communication means in order to communicate with a base station 30 (for example, when the device is implemented in a satellite as an ion thruster). The data exchanged between the controller 24 and the base station 30 may comprise, for example, setpoints (current and potential for example) as well as measurements.

[0117] In Figures 1 and 3 to 6, the arrows between the different components designate the communication of instructions or measurements between these components.

[0118] The device according to the invention, as for example shown in Figures 1 and 3 to 6, can be operated in a first operating mode and a second operating mode.

[0119] In the first operating mode of the device according to the invention, called purely ionic mode, the high-frequency modulator is disconnected from the power supply circuit of the device. A beam of pure ions is emitted, and the emission potential is lower than a limit emission potential.

[0120] In the second operating mode of the device according to the invention, called droplet mode, the high-frequency modulator is connected to the power supply circuit. A beam of droplets, or charged clusters, is emitted, and the emission potential is greater than the limit emission potential.

[0121] The limit emission potentialV limitis defined as a function of the surface tension of the conductive liquid used in the device. This is the emission potential at which the apex of the Taylor cone is subject to rupture. For an emission potential lower than the limiting potentialV limit , the device stably emits a beam of pure ions, whereas for an emission potential greater than the limit potentialV limit , the operation of the device becomes unstable and the particle beam contains not only pure ions, but also charged clusters, or droplets, the latter being of variable sizes and much slower than pure ions. To avoid these instabilities, the value of the electric field applied to the conductive liquid and forming the Taylor cone is modulated at high frequency (> MHz). For this, when the emission potential is higher than the limit emission potentialV limit, the emission potential is modulated periodically by a few hundred volts around the potential allowing stable ion emission, therefore subtractively from the limit value V limit .

[0122] In particular, when an avalanche diode is implemented as a high-frequency modulator, the modulation allows the voltage to collapse very quickly. Indeed, as soon as the clipping voltage V écrêtage is reached, the potential applied to the device rapidly decreases by a value corresponding to the clipping voltage. When the voltage seen by the diode is lower than its clipping voltage V écrêtage , it becomes non-conducting / blocking. The initial potential is restored to the emitter(s), corresponding to the emission regime.

[0123] The modulation thus causes ruptures and reconstructions of the apex of the Taylor cone at defined time intervals, without reaching the electric field value necessary for the field evaporation mechanism (typically of the order of V / A), thus generating charged droplets or clusters. These emitted droplets or clusters keep the dimensions of the apex, or jet, of the Taylor cone (of the order of a few nanometers for example).

[0124] This is a schematic representation of a non-limiting exemplary embodiment of a method for generating charged particles according to the invention.

[0125] The device according to the invention, and in particular according to one of the embodiments shown in Figures 1 and 3 to 6, can be implemented in the method according to the invention.

[0126] When the device according to the invention is put into operation, from the stop, the device is in the first operating mode 120, that is to say, the high frequency modulator is disconnected and the electric field applied to the conductive liquid is not modulated.

[0127] The method, shown in the, comprises a step 102 of adjusting the ion emission current to a first setpoint value I c The emission current corresponds to the flow of ions emitted by the emitter(s) 14.

[0128] The set value can be, for example, in the order of 50 to 80 µA per tip or emissive site.

[0129] The emission current is adjusted by applying a threshold emission voltage V seuil to the emission electrode 11 by means of the current generator 20. By means of the current generator 20, the emitted ion current can be precisely regulated.

[0130] This adjustment step 102 can be considered as an activation phase during which the ion ejection is initiated. By applying the threshold emission potential to the emission electrode, the Taylor cone necessary for the ion ejection is formed. The flux, or the number of ejected ions, is determined by the emission current setpoint, this emission current setpoint being reached with the threshold emission potential.

[0131] To perform step 102 of adjusting the emission current, the voltage applied to the emission electrode V em is gradually increased from 0 V until the current emitted by the current generator 20 reaches its set value I c .

[0132] At a step 104, in the purely ionic mode, the emission potentialV em is adjusted to keep the first setpoint valueI cconstant. The adjustment step 104 can be carried out automatically thanks to the control of the emission current. To do this, the device according to the invention can comprise a means for measuring the emission current in order to carry out a control of this current value. The measuring means can comprise, for example, a micro-ammeter placed in the current generator 20, or an ammeter placed at the extraction electrode 12.

[0133] The value of V em corresponds to the threshold value V seuil the potential for which a stable emission of pure ions is obtained, this value being characteristic of each device for generating charged particles. This value can be, for example, of the order of 5000 V.

[0134] At the end of step 102 of adjusting the emission current, or step 104 of adjusting the emission current, the device emits a flow of ions corresponding to a certain mass of ejected material.

[0135] The method 100 according to the embodiment shown in the further comprises a step 106 of adjusting the transmission speed. During this step 106, an extraction voltage V ext is applied to the extraction electrode 12. The extraction voltage can be applied, for example, by means of a voltage generator 22 for embodiments of the device having two power supplies as shown in Figures 5 and 6. Thus, the emission potential between the electrodes 11, 12 is brought to a programmed value V empr , so thatV empr =V seuil +V ext .

[0136] The programmed potentialV emprmay, for example, correspond to a predetermined beam potential for which the thrust provided by the ion beam reaches a required value. The value V empr may be predetermined, for example, by calculation by the on-board controller 24 or by a remote base station 30 and sent to the controller 24.

[0137] According to an exemplary embodiment, the voltage V ext applied to the extraction electrode 12 can be increased gradually from 0V, for example, in steps of 50 V. The sign of the voltageV ext is the same as that of the voltageV seuil . The increase in the value of the voltage V ext at the extraction electrode is governed by a time-dependent law, of the asymptotic type, which makes it possible to progressively polarize the conductive surfaces and to avoid electrical discharge or breakdown phenomena.V ext is increased until the emission potential reaches the programmed value Vempr .

[0138] According to other embodiments, the voltage V ext can be 0, or of the opposite sign to that of the emission voltage V em .

[0139] At the end of step 106 of adjusting the emission speed, the value of the emission current still corresponds to the set value I c .

[0140] The device according to the invention can be switched into the second operating mode 121 after step 102 of setting the first setpoint value I c , after step 104 of adjusting the emission potential or after step 106 of adjusting the emission speed. The device cannot be directly operated in the second operating mode, i.e., directly from standstill, because the first operating mode is necessary for the formation of the Taylor cone.

[0141] Switching the device to the second operating mode is achieved by connecting the high-frequency modulator to the power supply, or power-up, circuit. As detailed above, several locations for placing the modulator are possible.

[0142] In the second operating mode, the method according to the invention comprises a step 108 of adjusting the emission current to a second setpoint value I limit from the first setpointI c , Yes c limit . This second step 108 of adjusting the emission current is carried out by applying the limit emission potential V limit to the emission electrode 11 by means of the current generator 20.

[0143] To carry out the second step 108 of adjusting the emission current, the voltage applied to the emission electrode V em is gradually increased by its threshold value V seuil to the limit valueV limit ​for which the current emitted by the current generator 20 reaches its second set value I limit .

[0144] The emitted particle beam then becomes unstable and reaches a mixed regime, in which the beam no longer contains only ions, but also charged droplets.

[0145] Once the second setpoint value of the emission current is reached, during a modulation step 110 of the method 100, the electric field applied to the conductive liquid is modulated at high frequency by means of the high frequency modulator.

[0146] It is also possible to activate the modulator first and then increase the transmit current as described.

[0147] By modulating the electric field around the Taylor cone stability boundary, the rupture and reconstruction of the Taylor cone apex is induced in a controlled manner, allowing the emission of charged clusters or droplets, without the emission of ions.

[0148] Illustrates a timing diagram of the method according to one embodiment of the invention. The diagram shows the evolution of the emission potential ("peak potential") as a function of time (in arbitrary units). Initially (time = 0), the high-frequency modulator is deactivated.

[0149] The different phases of the process are as follows:

[0150] (a) polarization of the emitter to reach the threshold emission potential (time from 0 to 250),

[0151] (b) pure ion emission for the threshold emission potential (time 250 to 450),

[0152] (c) increase of the emission potential to the limiting potentialV limitto reach the mixed regime of emission of pure ions and charged clusters (times from 450 to 500),

[0153] (d) mixed emission of ions and charged clusters (times 500 to 750),

[0154] (e) modulator activated: modulation of the emission potential below the value V limit , and emission of charged clusters only (time from 750 to 1050),

[0155] (f) stopping the modulator and decreasing the emission potential to the threshold value (time from 1050 to 1100),

[0156] (g) pure ion emission (time 1100 to 1300),

[0157] (h) stopping the device.

[0158] The method 100 according to the embodiment shown in the further comprises, in the second operating mode, a step 112 of adjusting the emission current to a third setpoint value I c3 , Yes limit c3 ​. This third step 112 of adjusting the emission current is carried out by applying an emission potential called droplets, V seuil2 at the emission electrode, with V seuil2 >V limit . The emission potential is gradually increased by V limit to the “droplet” value V seuil2 for which the emission current reaches its third setpoint value I c3 .

[0159] This step 112 makes it possible to increase the emission current of droplets or charged clusters and to stabilize it, so that the device emits a stable and regular beam of droplets.

[0160] To switch back from the second operating mode to the first operating mode, the emission current is set to a value lower than the second setpoint value I limit, and the modulation of the electric field is stopped. It is possible to carry out these steps simultaneously or one after the other. In the latter case, one can either reduce the emission current below the limit valueI limit (e.g., < 50 µA per emitter) and then turn off the high frequency modulator, or turn off the modulator and then reduce the current.

[0161] Examples of implementation of the device and method according to the invention will be described below.

[0162] According to a first example, the device and method according to the invention can be implemented in a satellite, in particular of the CubeSat type, for ionic propulsion. The beam emitted by the device is adapted to provide a more or less strong thrust to the satellite, depending on the type of beam emitted (pure ions or charged clusters). Such miniaturized satellites are used in particular for the transmission of information and space exploration. The device and method according to the invention can be implemented to control the placement, orientation and position of satellites.

[0163] According to a second example, the device and method according to the invention can be implemented in a nanofabrication system. With such a system, charged clusters can be transferred and deposited on a surface of an object. This can be, for example, a substrate, on which charged particles are deposited to manufacture conductive structures.

[0164] Also, reactive or non-reactive chemical species can be created, transported and deposited out of equilibrium on a surface of a sample.

[0165] For example, a complex molecular cation can be emitted, transported and deposited out of electrical equilibrium, carrying a fluorine or chlorine chemical function, or any other required chemical function, and deposited locally at a submicrometer scale in a miniaturized lab-on-chip assembly.

[0166] According to a third example, the device and the method according to the invention can be implemented in a mass spectrometer. In a mass spectrometer, ionized droplets of selected sizes can be produced by electrospray ionization (ESI) according to the method of the invention and accelerated, making it possible to access the mass and certain structural elements of heavy and polar molecules by spectrometric analyses.

[0167] Of course, the invention is not limited to the examples which have just been described and numerous adjustments can be made to these examples without departing from the scope of the invention.

Claims

Device (1) for generating charged particles, the device (1) comprising:at least one emission module comprising an emission electrode (11) and a conductive liquid (17) deposited on the emission electrode (11),an extraction electrode (12) arranged opposite the at least one emission module, andat least one high-voltage electric generator (20, 22) configured to apply an emission potential to the emission electrode (11) adapted to apply an electric field to the conductive liquid (17),the device (1) being characterized in that it comprises a high-frequency modulator (M, M1, M2) connectable to the power supply circuit of the device (1) and configured to modulate the electric field at high frequency when it is connected,each emission module being configured to emit a beam of charged particles when an electric field is applied to the conductive liquid (17),the device (1) being configured to operate in a first mode,said purely ionic mode, in which the emission potential is equal to or greater than a threshold emission potential necessary for the formation of a Taylor cone and less than a limit emission potential, the high-frequency modulator (M, M1, M2) is disconnected from the power supply circuit of the device (1) and the at least one emission module emits a beam of pure ions, and in a second mode, called droplet mode, in which the emission potential is greater than the limit emission potential, the high-frequency modulator is connected to the power supply circuit of the device (1) and the at least one emission module emits a beam of charged clusters, the limit emission potential being defined as a function of the surface tension of the conductive liquid (17) so that the apex of the Taylor cone is subject to a break for the limit emission potential., Device (1) according to claim 1, characterized in that it comprises a high voltage electric generator linked to the emission electrode functioning as a current generator (20). Device (1) according to claim 2, characterized in that it further comprises a second high voltage electric generator (22) linked to the extraction electrode (12). Device (1) according to any one of claims 2 and 3, characterized in that the high frequency modulator (M, M1, M2) comprises an avalanche diode (40), the avalanche diode (40) being disconnected in the purely ionic mode and connected in the droplet mode. Device (1) according to claim 3, characterized in that the avalanche diode (40) is connected in series with the current generator (20) or with the extraction electrode (12). Device (1) according to claim 3, characterized in that the high-frequency modulator (M, M1, M2) comprises two avalanche diodes (40), one of the avalanche diodes being connected in series with the current generator (20) and the other of the avalanche diodes being connected in series with the second high-voltage electric generator (22). Device (1) according to any one of claims 4 to 6, characterized in that it further comprises at least one resistor (41) mounted in series with the avalanche diode(s) (40) and configured to limit the current flowing in the avalanche diode(s) (40). Device (1) according to any one of the preceding claims, characterized in that the conductive liquid (17) comprises one of an ionic liquid, a conductive liquid and a liquid or molten metal. Device (1) according to the preceding claim, characterized in that the ionic liquid comprises one of an onium, phosphate, ammonium, sulfate, chloride, bromide, tetrafluoroborate or hexafluorophosphate salt. Device (1) according to claim 9, characterized in that the liquid or molten metal comprises one of gallium, indium, gold, an alkali metal, an alkali alloy. Device (1) according to claim 9, characterized in that the liquid made conductive comprises a glycerol type liquid made conductive. A method (100) for generating charged particles implemented in a device (1) for generating charged particles, the device (1) comprising at least one emission module comprising an emission electrode (11) and a conductive liquid (17) deposited on the emission electrode (11), an extraction electrode (12) arranged opposite the at least one emission module, at least one high-voltage electrical generator (20, 22) configured to apply an emission potential to the emission electrode (11) adapted to apply an electric field to the conductive liquid (17), and at least one high-frequency modulator (M, M1, M2) connectable to the power supply circuit of the device (1), each emission module being configured to emit a beam of charged particles when an electric field is applied to the conductive liquid (17), the method (100) comprising the following steps: adjusting (102) an ion emission current to a first value of instructionIc by applying a threshold emission potentialV seuil to the emission electrode (11) by means of the at least one high-voltage electric generator (20, 22), the threshold emission potential being necessary for the formation of a Taylor cone;in a first operating mode (120), called purely ionic mode, in which the emission potential is lower than a limit emission potential, the high-frequency modulator (M, M1, M2) is disconnected from the power supply circuit of the device (1) and the at least one emission module emits a beam of pure ions,adjustment (104) of the emission potential to keep the first setpoint valueI cconstant, in a second operating mode (121), called droplet mode, in which the emission potential is greater than the limit emission potential, the high-frequency modulator (M, M1, M2) is connected to the power supply circuit of the device (1) and the at least one emission module emits a beam of charged clusters, adjustment (108) of the emission current to a second setpoint value I limit from the first setpointI c , Yes c limit , by applying a limiting emission potentialV limit ​to the emission electrode (11), the limiting emission potential being defined as a function of the surface tension of the conductive liquid (11) so that the Taylor cone is subject to a breakdown for the limiting emission potential,modulation (110) at high frequency, by means of the high frequency modulator (M, M1, M2), of the electric field applied to the conductive liquid (17),in the first mode (120), the at least one emission module emitting a beam of pure ions, and in the second mode (121), the at least one emission module emitting a beam of charged clusters. Method (100) according to claim 12, characterized in that it further comprises, in the second operating mode (121), a step (112) of adjusting the emission current to a third setpoint value I c3 , Yes limit c3 , by applying an emission potential called dropletsV seuil2 at the emission electrode (11), whereV seuil2 >V limit . ​Method (100) according to claim 12 or 13, characterized in that the step (102) of adjusting the emission current to the first setpoint value I c is achieved by the progressive increase in the value of the potential applied to the emission electrode (11) from 0 to the threshold value V seuil for which the emission current I em reaches the first setpoint valueI c . Method (100) according to any one of claims 12 to 14, characterized in that the step of adjusting (108) the emission current to the second setpoint value I limit is achieved by the progressive increase in the value of the potential applied to the emission electrode (11) of V seuil to the limit value V limit for which the emission current reaches the second setpoint value I limit . Method (100) according to any one of claims 12 to 15, characterized in that the step of adjusting (112) the emission current to the third setpoint value I c3 is achieved by the progressive increase in the value of the potential applied to the emission electrode (11) of V limit to the droplet valueV seuil2 for which the emission current reaches the third setpoint value I c3 . A method (100) according to any one of claims 12 to 16, further comprising a step (106) of adjusting a pure ion emission rate by applying an extraction potentialV ext to the conductive liquid (17) once the set value I c of the emission current reached, so as to bring the emission potentialV em to a predetermined valueV empr =V seuil +V ext . Satellite, in particular of the CubeSat type, comprising a device (1) for generating charged particles according to any one of claims 1 to 11 and implementing a method (100) according to any one of claims 12 to 17, the beam of charged particles emitted by the device (1) being adapted to provide thrust to the satellite. Nanofabrication system, comprising a device (1) for generating charged particles according to any one of claims 1 to 11 and implementing a method (100) according to any one of claims 12 to 17, configured for the transfer and deposition of charged particles on a surface of an object. Mass spectrometer, comprising a device (1) for generating charged particles according to any one of claims 1 to 11 and implementing a method (100) according to any one of claims 12 to 17, configured for the acceleration of charged particles.

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