Ion source

Abstract

The invention relates to an ion source (1), in particular an ion thruster for propelling a spacecraft, comprising: a reservoir (2) for a propellant (3), which has a solid state and can be liquefied into a liquid state; a heater (4) for liquefying the propellant (3) in the reservoir (2); a transmitter (5) in fluid communication with the reservoir (2) for receiving a flow (S) of liquefied propellant (3) from the reservoir (2); an extractor (7) facing the emitter (5) for extracting ions (3 ') of the liquefied propellant (3) from the emitter (5) and accelerating the extracted ions (3') away from the emitter (5) wherein at least one baffle (11) is arranged upstream of the emitter (3) in a flow (S) of propellant (3) to the emitter (5).

Description

Technical Field

[0001] The present invention relates to an ion source, comprising: a reservoir for a propellant, the propellant having a solid state and being capable of being liquefied into a liquid state; a heater for liquefying the propellant in the reservoir; an emitter, which is in fluid communication with the reservoir and is used to receive a flow of the liquefied propellant from the reservoir; and an extractor, which faces the emitter and is used to extract ions of the liquefied propellant from the emitter and accelerate the extracted ions away from the emitter. Background Art

[0002] Ion sources are used, for example, for ion implantation or for producing focused ion beams in the semiconductor industry, metal finishing, materials science and / or analysis, or in ion thrusters for propelling spacecraft. In a liquid metal ion source ("LMIS"), the propellant is a metal (typically cesium, indium, gallium, mercury or bismuth). In so-called colloidal or electrospray ion sources, the propellant is typically a molten salt or the like. In either case, the propellant may be heated by a heater to liquefy to its liquid state in a reservoir and received from the reservoir by an emitter. From the emitter, ions of the liquefied propellant are electrically extracted and accelerated by an extractor to form a directed ion beam, which, in the case of an ion thruster, provides thrust.

[0003] In order to achieve the strong electric field required for ion extraction between the emitter and the extractor, the emitter has one or more emission points, which are usually protrusions in the shape of cones, pyramids, triangular prisms, needles, etc. The emission point is pointed or sharp-edged to take advantage of the field concentration effect of the tip or edge. Applying an electric field to such a sharp tip or edge causes the formation of a so-called Taylor cone on the top of the tip or edge of the protrusion of the emitter, which enhances the field concentration effect.

[0004] In order to transport the liquid propellant from the reservoir to the sharp tip or edge of each protrusion of the emitter, passive forces, such as capillary effects generated by a capillary penetrating the emitter (as described, for example, in AT500412A1 or US4328667B) or by a porous emitter (as described, for example, in US 2016 / 0297549A1 or EP3724497A1) and / or by an adhesion effect on the wetted surface of the protrusion of the emitter (as described, for example, in US2009 / 114838A1 or US2011 / 192968A1), are usually used in ion sources. However, under certain conditions, such as when the ion emission and the heating of the reservoir are suspended so that the propellant solidifies in the reservoir, the propellant retracts from the emitter into the reservoir due to the strong retraction force within the reservoir during the solidification of the propellant. In this case of propellant retraction, when the ion source is reheated, the passive force described above may not be sufficient to restart the propellant supply to the launcher. As a result, the ion source may fail after the pause. For reasons of safety, reliability and complexity, countermeasures such as applying an external force, such as pressurizing the reservoir from a separate pressure reservoir or by a mechanical pump or piston are undesirable, especially in a spacecraft. Summary of the invention

[0005] An object of the present invention is to provide a safe, reliable and efficient ion source.

[0006] This object is achieved with the ion source specified at the beginning, characterized in that at least one baffle is arranged in the stream of propellant to the launcher upstream of the launcher. The at least one baffle is a mechanical obstacle that limits the cross-sectional area of ​​the stream of propellant and deflects the stream of propellant. This reduces the cohesive force between the small volume of propellant on the launcher side of the baffle and the large volume of propellant on the reservoir side of the baffle. When the propellant solidifies (and in other cases where the propellant is retracted into the reservoir, for example due to heavy gravity or acceleration forces), the retraction force applied to the propellant is deflected by the baffle and is significantly reduced thereby. At least at the launcher side of the baffle, the passive (e.g. capillary) supply of the propellant can be prevented from being terminated due to the retraction of the propellant into the reservoir. However, the baffle does not significantly hinder the stream of the propellant from the reservoir to the launcher by a weak passive force, because the flow rate of the stream is relatively small, resulting in a smaller hydraulic resistance.

[0007] During the uniform cooling of the propellant, solidification begins at the point of lowest thermal mass. Compared to the reservoir, the propellant mass and therefore the thermal mass at the location where the cross-sectional area is restricted by the baffle is significantly smaller. As a result, the propellant solidifies earlier at this location. This leads to a blocking effect on the solidified propellant at the baffle, which further prevents the retraction of the propellant from the launcher towards the reservoir.

[0008] By introducing the shutter, the ion source can be safely shut down when not in operation, allowing the propellant to solidify to reduce power consumption and improve efficiency, and when the ion source is reactivated and the propellant is liquefied, operation will be reliably resumed. In addition, the ion source is safer and more reliable than ion sources that use pressurized reservoirs and / or mechanical pumps or pistons to force the propellant supply to the emitter.

[0009] In an advantageous embodiment, at least two baffles are spaced apart in the direction from the reservoir to the launcher and are staggered to cause a tortuous flow of the propellant to the launcher. Thereby, the cohesion of the propellant in and around the launcher and in the reservoir is further reduced and the withdrawal of the propellant from the launcher is even better prevented. In a particularly advantageous variant thereof, which improves the effect of reducing the cohesion and preventing the withdrawal of the propellant from the launcher, two adjacent baffles, seen in a longitudinal section of the ion source, are L-shaped with two legs, one leg of each baffle facing the other baffle.

[0010] In a further advantageous embodiment, the at least one baffle is a truncated cone or a cage. A truncated cone, i.e. a section of a pyramid or a cone, constitutes a particularly robust embodiment of a baffle. On the other hand, a cage-type baffle allows a flexible adaptation to different requirements. Of course, two or more baffles of the same type, of similar type or of different types can be combined.

[0011] In an advantageous embodiment, the at least one baffle is mounted on a plurality of spaced-apart pins, which are located in an annular wall surrounding the launcher. Alternatively, the at least one baffle can be mounted on a rod extending from the launcher towards the reservoir. Such mounting pins or rods increase the design freedom of the reservoir, the launcher and the baffle and facilitate the introduction of the baffle. The rod can also optionally be supported on an end wall of the reservoir. Thus, the rod can not only mount the baffle, but also the launcher, from which the rod extends.

[0012] In an advantageous embodiment, the fluid communication is established via a channel, which connects the launcher to the reservoir, wherein the at least one baffle protrudes into the channel. The channel already limits the cross-sectional area of ​​the flow of the propellant, which further enhances the effect of reducing the cohesion and retraction forces of the propellant. Furthermore, one or more baffles can be mounted on the lateral walls of the channel, thereby producing a particularly secure mounting. The channel can simply be formed by the neck of the bottle-shaped reservoir.

[0013] The channel can have any cross section and extension, for example, it can be cylindrical, prismatic or even curved. In an advantageous embodiment, the channel tapers towards the launcher. This ensures an efficient supply of propellant from the reservoir to the launcher and facilitates a particularly small volume of propellant on the launcher side of the baffle to achieve the effect of reducing the withdrawal force from the reservoir.

[0014] The cross-sectional shape of the channel can be, for example, square, rectangular, polygonal, elliptical, etc. In an advantageous embodiment, the channel has a circular cross-section. Thus, the maximum area through which the propellant passes is achieved on the smallest circumference. In addition, the baffle can also be circular or disc segment shaped with internal through holes, etc., and can be mounted on the channel wall or using the above-mentioned rods or pins. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] The present invention will now be explained in more detail below based on exemplary embodiments of the invention with reference to the accompanying drawings, in which: Figure 1a and 1b Two embodiments of an ion source according to the invention are shown in respective longitudinal sections, each with two baffles ( Figure 1a ) or a baffle ( Figure 1b ); Figures 2a to 2c Further embodiments of an ion source according to the invention are shown in each case in a partial longitudinal section, which have a plurality of baffles; Figure 3 A further embodiment of an ion source according to the invention is shown in a partial longitudinal section, having an emitter with an array of emission points and two baffles; Figures 4a to 4c Further embodiments of an ion source according to the invention are shown in each case in a partial longitudinal section, which have a plurality of baffles in the form of truncated cones; Figure 5a A further embodiment of an ion source according to the invention with a cage-shaped baffle is shown in a partial longitudinal section. Figure 5b Shown in perspective side view Figure 5a Cage baffles; and Figure 6a A further embodiment of the ion source of FIG. 1 is shown in partial longitudinal section, having mounting pins for a baffle, Figure 6b Shown in perspective side view Figure 6a pin and baffle. DETAILED DESCRIPTION

[0016] Figure 1a and 1b Two different exemplary embodiments of an ion source 1 are shown. The ion source 1 comprises a reservoir 2 for a propellant 3. The propellant 3 generally has a solid state and can be liquefied from its solid state to a liquid state. To this end, the ion source 1 comprises a heater 4 which, when activated, heats and liquefies the propellant 3 in the reservoir 2. The heater 4 is connected to or irradiates the reservoir 2.

[0017] The ion source 1 further comprises an emitter 5 in fluid communication with the reservoir 2. The fluid communication is such that the emitter 5 receives a flow S of liquefied propellant 3 from the reservoir 2 during operation of the ion source 1. Figure 1a and 1b In the example of , the ion source 1 comprises an optional channel 6 connecting the emitter 5 to the reservoir 2 to establish fluid communication therebetween. The channel 6 may be a neck of the substantially bottle-shaped reservoir 2. However, the reservoir 2 may be of a different shape, and the channel 6 may be attached to the reservoir 2 in any other form or may be omitted.

[0018] In order to extract ions 3' of the liquefied propellant 3 from the emitter 5 and accelerate the extracted ions 3', the ion source 1 includes an extractor 7 facing the emitter 5. By connecting a voltage source of several kilovolts (kV), a strong electric field is applied to the emitter 5 and the extractor 7. The emitter 5 may have a ( Figure 1a ) or more ( Figure 1b ) emission points 8, each of which is a protrusion in the shape of a cone, pyramid, triangular prism, needle, etc., and has a sharp tip or edge on the side of the emitter 5 pointing away from the reservoir 2. Applying a strong electric field to such a sharp tip or edge causes a so-called Taylor cone to be formed on the top of the tip or edge of each emission point 8. At the apex of the Taylor cone, the ions 3' are extracted and accelerated by the strong electric field between the extractor 7 and the emitter 5, thereby generating an ion beam 9, which points away from the emitter 5 and - as in this example when the extractor 7 is installed in, for example, a housing 10 of the ion source 1 - away from the ion source 1.

[0019] The ion source 1 can be used, for example, for ion implantation or for producing a focused ion beam in the semiconductor industry, metal finishing, materials science and / or analysis, and in particular as an ion thruster for propelling a spacecraft. In addition, as known in the art, the ion source 1 can include or be connected to other elements, such as a controller, a power supply, a voltage source, a neutralizer, etc.

[0020] Figure 1a and 1b The propellant 3 in the embodiment of is a metal, such as cesium, indium, gallium, mercury or bismuth, etc. In this "liquid metal ion source" ("LMIS"), the neutral atoms of the liquefied metal propellant 3 are field evaporated at the apex of the Taylor cone, and the negative electrons tunnel back to the surface, leaving the positively charged ions 3' of the liquid metal propellant 3 for extraction. Therefore, the propellant 3 is ionized, extracted and accelerated by the same electric field between the extractor 7 and the emitter 5. On the other hand, in an ion source 1 of the "colloid" or "electrospray" type, the propellant 3 is, for example, a salt, which is ionized in its liquefied state so that positively or negatively charged ions are extracted from the emitter 5 and accelerated by the electric field.

[0021] In order to receive the liquefied propellant 3 from the reservoir 2 in the launcher 5 and convey it to the launch point 8, passive forces (here: capillary effect) are usually used. For this purpose, the launcher 5 is penetrated by a capillary (not shown) or (in the present example) is made of a porous material. The launch points 8 are likewise penetrated by a capillary or are made of a porous material and / or they have a wetted surface to which the liquefied propellant 3 adheres.

[0022] When the operation of the ion source 1 is not required, the heating of the reservoir 2 and the emission of ions 3' can be suspended. The propellant 3 will then freeze (solidify) in the emitter 5, the optional channel 6 and the reservoir 2. During solidification, the propellant 3 can be retracted from the emitter 5 towards the reservoir 2 due to the strong retraction force inside the reservoir 2 with a larger propellant volume and due to the cohesive force of the propellant 3.

[0023] Excessive retraction of the propellant 3 from the emitter 5 would prevent the subsequent formation of a Taylor cone after heating the reservoir 2 to restart operation. To avoid this, the ion source 1 has at least one baffle 11, which is arranged in the flow S of the propellant 3 to the emitter 5 upstream of the emitter 3. The at least one baffle 11 is a mechanical obstacle which limits the cross-sectional area of ​​the flow S and deflects the flow S of the propellant. Possible retraction forces exerted on the propellant 3 in and near the emitter 5, in particular in the small volume 12 of the propellant 3 on the emitter side of the baffle 11, for example due to solidification of the propellant 3 (or due to other reasons), are significantly reduced and also redirected around the baffle 11.

[0024] exist Figure 1a In the example of the embodiment of the invention, the channel 6 is cylindrical or prismatic, with a circular, polygonal or elliptical cross section, and has two baffles 11 arranged in the flow S upstream of the launcher 5 (here: protruding from the lateral channel wall 13 into the channel 6). The two baffles 11 are spaced apart in the direction d from the reservoir 2 to the launcher 5. As shown, the individual baffles 11 may be staggered to cause a tortuous flow of the propellant 3 through the channel 6 to the launcher 5. However, the channel 6 is not essential, as will be described below with reference to Figure 5a and 6a Explain that in more detail.

[0025] exist Figure 1b In the example, channel 6 has Figure 1a The same cross section, but tapers towards the emitter 5. The ion source 1 comprises only one baffle 11 arranged in the flow S (here: protruding into the channel 6). Furthermore, the baffle 11 is mounted on a rod 14 extending from the emitter 5 towards the reservoir 2. The baffle 11 is thus annular around the rod 14. The rod 14 optionally also extends through the entire reservoir 2 to its end wall 15 opposite the emitter 5. Figure 1bIn the example of FIG. 4 , the transmitter 5 is mounted at the end of a rod 14 and is crown-shaped with a plurality of emission points 8 arranged in a ring.

[0026] Figure 2a-2c Different arrangements of (here: three) baffles 11 are shown. Figure 1a In the example of FIG. 1 , the baffles 11 in these embodiments are spaced apart from each other along the direction d. Figure 2a In a variant of , all baffles 11 are mounted on a rod 14 extending from the launcher 5 substantially in the center of the reservoir 2 and the channel 6. The channel 6 may optionally be as described above with respect to Figure 1b The tapering; and accordingly, the baffles 11 may increase in size as they distance from the emitter 5, however, this is optional.

[0027] exist Figure 2b In a variant of , the individual baffles 11 are staggered, resulting in a tortuous flow S of the propellant 3 to the launcher 5. Here, two baffles 11 are mounted on a rod 14 and protrude from it into the channel 6, while the remaining intermediate baffle 11 protrudes from a lateral channel wall 13 into the channel 6.

[0028] Figure 2c Examples and Figure 1a The embodiment of is also similar in that, when seen in direction d, successive baffles 11 protrude from different sides of the lateral channel wall 13 into the channel 6. The baffles 11 may alternatively be mounted on the rod 14 and on one of the individual lateral channel walls 13.

[0029] Figure 3 An embodiment is shown in which the emitter 5 has a plurality of emission points 8 arranged in an array on the emitter 5. (At least) two baffles 11 are staggered and L-shaped (seen in a longitudinal section of the ion source 1), each baffle having two legs 11', 11", one leg 11' of each baffle 11 facing the other baffle 11. Thereby, the flow S of the propellant 3 is more tortuous.

[0030] exist Figure 4a-4c In the embodiment of the invention, the (at least one) baffle 11 is a truncated cone, ie a part of a pyramid or a cone, the axis of which is generally substantially parallel to the direction d. Figure 4a In the embodiment of the invention, the truncated cone tapers away from the emitter 5. Alternatively, the truncated cone may taper toward the emitter 5 ( Figure 4b ). When the channel 6 also tapers towards the emitter 5 , the lateral surfaces of the truncated cone are optionally parallel to the lateral channel walls 13 .

[0031] Figure 4cA slightly different variation is shown in which the frustum has a substantially cylindrical or prismatic end section 16 at its larger diameter end. It will be appreciated that in this embodiment the frustum shaped baffle 11 may taper away from the emitter 5 as shown, or alternatively taper towards the emitter 5.

[0032] Figure 5a and 5b The baffle 11 shown in the embodiment of the invention is a cage which extends into the channel 6 as shown or, in particular in the absence of a channel 6, into the reservoir 2 (not shown). In any case, the baffle 11 is arranged in the flow S of the propellant 3 to the launcher 5 upstream of the launcher 5. The cage-shaped baffle 11 can be made of rods, blades or the like. In the present case, the baffle 11 is made of a perforated disk 17 and four rods 18 for mounting the disk 17 on the lateral channel wall 13 of the channel 6, on the wall of the reservoir 2, on the launcher 5 or elsewhere. It goes without saying that two or more cage-shaped baffles 11 can be arranged upstream of the launcher 5.

[0033] Figure 6a and 6b An embodiment without the channel 6 is shown by way of example. The baffle 11 shown in this example is mounted on a plurality of pins 19 which are spaced apart from one another and extend from an annular wall 20 surrounding the emitter 5 into the reservoir 2 (in other embodiments: into the channel 6). Figure 6b As shown, the baffle 11 may be a disk 21 mounted on the plurality of pins 19 . However, the baffle 11 may have a different shape and / or the plurality of pins 19 may have a different number, orientation, etc. Furthermore, more than one baffle 11 may be mounted on the plurality of pins 19 .

[0034] It should be understood that the embodiments shown in the drawings and described above are exemplary only. In particular, different types and / or shapes of launchers 5, for example with different numbers of launch points 8, can be combined with one or another shape of channel 6 and / or with one or another number, shape, size and / or arrangement of baffles 11. For example, the rod 14 can be used with any type of launcher 5 and can be hollow or solid. In addition, baffles 11 of different shapes and / or sizes can be combined in any way. Therefore, the present invention is not limited to the specific embodiments described in detail herein, but covers all variations, modifications and combinations thereof that fall within the scope of the appended claims.

Claims

1. An ion source, in particular an ion thruster for propelling a spacecraft, comprising a reservoir (2) for a propellant (3) which has a solid state and can be liquefied into a liquid state, a heater (4) for liquefying the propellant (3) in the reservoir (2), a launcher (5) in fluid communication with the reservoir (2) for receiving a flow (S) of liquefied propellant (3) from the reservoir (2), an extractor (7), facing the launcher (5), for extracting ions (3') of the liquefied propellant (3) from the launcher (5) and accelerating the extracted ions (3') away from the launcher (5), Features At least one baffle (11) is arranged in the flow (S) of the propellant (3) to the launcher (5) upstream of the launcher (5) and is a mechanical obstacle which limits the cross-sectional area of ​​the flow (S) of the propellant (3) and deflects the flow (S) of the propellant (3).

2. The ion source according to claim 1, characterized in that At least two baffles (11) are spaced apart in a direction (d) from the reservoir (2) to the launcher (5) and are staggered to cause a tortuous flow (S) of the propellant (3) to the launcher (5).

3. The ion source according to claim 2, characterized in that When viewed in a longitudinal section of the ion source (1), two adjacent baffles (11) are L-shaped and have two legs (11', 11"), with one leg (11') of each baffle (11) facing the other baffle (11).

4. The ion source according to claim 1 or 2, characterized in that: The at least one baffle (11) is a truncated cone.

5. The ion source according to claim 1 or 2, characterized in that: The at least one baffle (11) is a cage (17, 18).

6. The ion source according to any one of claims 1 to 5, characterized in that The at least one baffle (11) is mounted on a plurality of spaced apart pins (19) located on an annular wall (20) surrounding the emitter (5).

7. The ion source according to any one of claims 1 to 5, characterized in that The at least one baffle (11) is mounted on a rod (14) extending from the launcher (5) towards the reservoir (2).

8. The ion source according to any one of claims 1 to 7, characterized in that The fluid communication is established via a channel (6) connecting the emitter (5) to the reservoir (2), wherein the at least one baffle (11) protrudes into the channel (6).

9. The ion source according to claim 8, characterized in that The channel (6) tapers towards the emitter (5).

10. The ion source according to claim 8 or 9, characterized in that: The channel (6) has a circular cross section.

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