JP7338450B2 - Electric propulsion test equipment - Google Patents

Description

The present disclosure relates to electric propulsion machine test equipment.

An electric propulsion device such as a Hall thruster generates a plasma as a propellant and accelerates ions in the plasma to obtain thrust. With respect to this thrust, electric propulsion machines are known to have higher energy conversion efficiencies than other propulsion mechanisms.

The electric propulsion machine is housed in the vacuum vessel of the test equipment for performance evaluation such as energy conversion efficiency. Inside the vacuum vessel, a pump such as a cryopump capable of obtaining a high pumping speed maintains a degree of vacuum equivalent to an ultra-high vacuum, forming a pseudo outer space (see Patent Document 1).

Japanese Unexamined Patent Application Publication No. 2010-71103

A large amount of plasma is generated from the electric propulsion machine while it is operating inside the vacuum vessel. Ions in the plasma are accelerated to obtain thrust and ejected from the electric propulsion machine. Direct entry of ions with sufficient energy into the pump tends to excessively increase the operating temperature of the pump and reduce pumping speed. In particular, the cryopump operates at extremely low operating temperatures, which makes this problem more pronounced.

The present disclosure has been made in view of the above situation. That is, an object of the present disclosure is to provide an electric propulsion machine test apparatus capable of suppressing a decrease in exhaust speed due to a large amount of ions emitted from the electric propulsion machine.

An electric propulsion machine test apparatus according to the present disclosure includes a vacuum vessel having an exhaust port, and a vacuum vessel provided in the vacuum vessel, arranged in at least one row facing each other at a predetermined interval, and discharged from the electric propulsion machine. a plurality of panels for reflecting ions, each panel having a plurality of through-holes extending in a thickness direction thereof, and at least one row of the plurality of panels lined up toward the exhaust port. there is

The aperture ratio of the through-holes in each panel may be larger in the panel closer to the wall of the vacuum vessel. The plurality of panels may be radially arranged in a plurality of rows with reference to the central axis of the ion flow. The panels of each row may be positioned annularly with the panels of other circumferentially adjacent rows. A spacing between the panels in a row may be set to a value that causes multiple reflections of the ions between the panels.

Advantageous Effects of Invention According to the present disclosure, it is possible to provide an electric propulsion machine test apparatus capable of suppressing a decrease in exhaust speed due to a large amount of ions emitted from an electric propulsion machine.

1 is a conceptual diagram for explaining the configuration of an electric propulsion machine testing device according to an embodiment; FIG. FIG. 4 is a cross-sectional view showing an example of the configuration and arrangement of a panel according to one embodiment; It is a figure which shows the modification of one Embodiment, (a) is sectional drawing which shows the modification of arrangement|sequence of a panel, (b) is sectional drawing which shows the modification of a panel. It is a figure which shows the modification of the arrangement|sequence of the panel which concerns on one Embodiment. FIG. 5 is a cross-sectional view taken along the line VV in FIG. 4;

Several exemplary embodiments are described below with reference to the drawings. In addition, the same code|symbol is attached|subjected to the part which is common in each figure, and the overlapping description is abbreviate|omitted.

FIG. 1 is a schematic diagram showing the configuration of an electric propulsion device testing device (hereinafter abbreviated as testing device) 10 according to the embodiment. The test device 10 is used to test the operation of the electric propulsion machine 11 . As shown in FIG. 1, the test apparatus 10 includes a vacuum vessel 12 that houses an electric propulsion machine 11, and a plurality of panels 14 that are provided in the vacuum vessel 12 and reflect ions 13 emitted from the electric propulsion machine 11. Prepare.

The electric propulsion device 11 is an ion thruster (ion engine), a hall thruster, or the like having a well-known configuration. The electric propulsion device 11 generates a large amount of plasma from gas as a propellant, accelerates ions 13 in the plasma to about several hundred eV to several keV, and emits them backward. The emitted ions 13 form a flow that is generally axially symmetrical with respect to the central axis 16, and spreads in the radial direction RD while traveling backward (to the right in the drawing). The central axis 16 of this flow of ions (hereinafter, ion flow 13a) substantially coincides with the axis of rotational symmetry of the shape or position of the ion emission ports 11a of the electric propulsion device 11 (when there are a plurality of ion emission ports 11a).

The vacuum vessel 12 is a metal vessel that accommodates the electric propulsion device 11, the panel 14, devices for measurement and control, and the like. The vacuum vessel 12 has, for example, a cylindrical wall portion 19 centered on a central axis 17 . The electric propulsion device 11 is installed on one side of the internal space of the vacuum vessel 12, and the plurality of panels 14 are arranged on the other side of the internal space together with an exhaust port 18 described later, in other words, the ion emission port 11a of the electric propulsion device 11. installed on the downstream side of the For convenience of explanation, it is assumed that the central axis 17 of the vacuum vessel 12 and the central axis 16 of the ion flow 13a are aligned.

Vacuum vessel 12 has an exhaust port 18 . The inner diameter of the exhaust port 18 is appropriately set according to the volume of the vacuum vessel 12, the required exhaust speed, and the like. Exhaust port 18 has a flange (not shown) at its end. Exhaust port 18 extends outwardly from wall 19 of vacuum vessel 12 . The extending direction of the exhaust port 18 is not limited to the direction orthogonal to the central axis 17 of the vacuum vessel 12 (for example, the radial direction RD), and may be inclined with respect to the central axis 17 of the vacuum vessel 12 .

An inlet of pump 20 is attached to a flange (not shown) of exhaust port 18 . A valve (not shown) such as a gate valve may be attached between the pump 20 and the exhaust port 18 .

A plurality of exhaust ports 18 may be provided at different positions in the circumferential direction of the vacuum vessel 12 . For example, two exhaust ports 18, 18 may be provided on both sides of the central axis 17 of the vacuum vessel 12 (see FIG. 4).

The electric propulsion machine 11 generates a large amount of plasma over a long period of time. As a result, a large amount of gas (atoms or molecules) originating from the ions 13 in the plasma is generated inside the vacuum vessel 12 . The pump 20 according to the present embodiment is required to have a high exhaust speed enough to sufficiently exhaust this large amount of gas and suppress an excessive pressure rise in the vacuum vessel 12 . A cryopump is an example of a pump 20 that satisfies such requirements.

A cryopump is a reservoir pump that causes the baffle and cryopanel to condense or adsorb gases within the vacuum vessel 12 . The baffles and cryopanels are cryogenically cooled for evacuation using condensation or adsorption.

A panel 14 is provided near the exhaust port 18 . The panel 14 is a flat plate having conductivity and reflects the ions 13 emitted from the electric propulsion device 11 . Panel 14 is electrically conductive at least on surface 21 (see FIG. 2). That is, the panel 14 may be a metal plate such as stainless steel, or an insulating plate having a metal layer on the surface 21 . As a simple example, panel 14 may be a perforated metal sheet or metal mesh sheet. In either case, the panel 14 is electrically connected to the vacuum vessel 12 and the like.

The panels 14 are facing each other with a predetermined distance D therebetween. The interval D may be a constant value (see FIG. 1) or may vary (see FIG. 3(a)). Also, as shown in FIG. 1 , at least one row of the plurality of panels 14 is aligned toward the exhaust port 18 . Panels 14 may be parallel or non-parallel to each other. For example, as shown in FIG. 1, each panel 14 may be arranged parallel to the central axis 17 of the vacuum vessel 12 .

The interval D between the panels 14 in a row may be set to a value that causes multiple reflections of the ions 13 between the panels 14 . This interval D can be set based on the length of the panel 14 along the central axis 17 of the vacuum vessel 12, the emission angle of the ions 13, and the like. In this case, non-colliding ions 13 emitted from the electric propulsion device 11 toward the installation space of the panel 14 can collide with any of the panels 14 in the space.

FIG. 2 is a cross-sectional view showing an example of the configuration and arrangement of the panel 14. As shown in FIG. As shown in this figure, each panel 14 is provided with a plurality of through holes 22 . The through-holes 22 extend in the thickness direction of the panel 14 and are two-dimensionally distributed on the surface 21 with a predetermined interval (pitch) P therebetween. Accordingly, the through holes 22 of the panels 14 arranged toward the exhaust port 18 are generally opened toward the exhaust port 18 . Each through hole 22 has the same inner diameter and is evenly distributed over surface 21 of panel 14 . However, the inner diameter and distribution of the through-holes 22 may be changed according to their positions.

As shown in FIG. 1, the electric propulsion device 11 accelerates ions 13 in the plasma backward (rightward in the drawing) and emits them. The emitted ions 13 spread rearward and generally travel along the central axis 16 of the ion flow 13a. The energy of the accelerated ions 13 is, for example, several hundred eV to several keV.

A plurality of panels 14 described above are arranged downstream of the ion flow 13a. Ions 13 strike any one of these panels 14 and are reflected repeatedly between the panel 14 they struck and the other panel 14 facing this panel 14 . The ions 13 may pass through the through holes 22 while being repeatedly reflected. Although the ions 13 are neutralized after several collisions, the neutralized ions 13 are also called "ions" for convenience of explanation.

Viewed at the atomic level, the surface 21 of the panel 14 is rough. Therefore, the reflection of the ions 13 is diffuse reflection (irregular reflection) that leaves the influence of specular reflection to some extent. On the other hand, the kinetic energy of the ions 13 is lost each time the ions 13 are reflected from the panel 14 . That is, the ions 13 are decelerated each time they are reflected. When reflection and deceleration are repeated, the influence of specular reflection on the reflection is diminished and the tendency of diffuse reflection is strengthened.

As the tendency of diffuse reflection increases, the reflection angle distribution (probability density distribution) of the ions 13 becomes closer to a distribution according to the cosine law. That is, due to multiple reflections, the ions 13 are decelerated, and the velocity component along the normal direction ND increases from the velocity component along the surface direction of the panel 14 . As a result, the ions 13 tend to stay between the panels 14 .

Also, the through hole 22 of the panel 14 extends in the normal direction ND of the panel 14 . Therefore, the ions 13 move toward the exhaust port 18 through the through hole 22 while being decelerated while repeating reflections between the panels 14 .

In this way, the ions 13 tend to stay between the panels 14 due to multiple reflections between the panels 14 , and are guided to the exhaust port 18 by passing through the through holes 22 . A large amount of ions 13 are introduced near the exhaust port 18, and the pump 20 can take in (exhaust) them. That is, the installation of the panel 14 can promote the evacuation of the pump 20 .

As described above, the ions 13 immediately after being emitted from the electric propulsion device 11 have an energy of several hundred eV to several keV. On the other hand, the energy of the ions 13 after passing through the panel 14 is reduced due to repeated reflections. For example, the energy of ions 13 decreases to a value close to thermal motion. Therefore, the temperature rise of the pump 20 caused by the collision of the ions 13 during evacuation is suppressed, and the reduction in the pumping speed of the pump 20 can be suppressed.

3A and 3B are diagrams showing a modification of the embodiment, FIG. 3A being a cross-sectional view showing a modification of the arrangement of the panel 14, and FIG. 3B being a cross-sectional view showing a modification of the panel 14. As shown in FIG. 3( a ), the distance D between the panels 14 may narrow toward the central axis 17 of the vacuum vessel 12 and away from the wall 19 (exhaust port 18 ) of the vacuum vessel 12 . The farther away the panel 14 is from the wall 19 (exhaust port 18), the shallower the angle at which the ions 13 enter the panel 14, and the higher the probability of the ions 13 passing downstream of the panel 14 in the ion flow 13a. By arranging the panels 14 at a distance D that narrows with distance from the wall 19 (exhaust port 18 ), the probability (frequency) of the ions 13 colliding with the panel 14 can be increased.

As shown in FIG. 3(b), the aperture ratio of the through holes 22 in each panel 14 may be larger in the panel closer to the wall 19 (exhaust port 18) of the vacuum vessel 12. As shown in FIG. The aperture ratio referred to here is the ratio of the aperture area of the through-holes 22 per unit area. As described above, by causing multiple reflections of the ions 13 between the panels 14, the proportion of the ions 13 traveling in the normal direction ND of the panel 14 increases. On the other hand, according to this modification, the closer the panel is to the wall 19 (exhaust port 18), the higher the ion 13 passage rate, and the farther the panel 14 from the wall 19 (exhaust port 18), the higher the ion 13 reflectance. Therefore, it becomes easier to guide the multiple-reflected ions 13 toward the wall portion 19 (exhaust port 18), and the evacuation of the pump 20 can be facilitated. In addition, you may combine the above-mentioned modification. That is, the arrangement of the through holes 22 shown in FIG. 3(b) may be combined with the arrangement of the panel 14 shown in FIG. 3(a).

FIG. 4 is a diagram showing a modification of the arrangement of panels according to the embodiment, and FIG. 5 is a cross-sectional view taken along line VV in FIG. As shown in these figures, a plurality of panels 14 may be arranged radially in a plurality of rows with reference to the central axis 16 of the ion flow 13a. As described above, the ions 13 form an approximately axially symmetrical flow and travel while expanding in the radial direction RD. The rows of panels 14 are arranged radially on a plane perpendicular to the central axis 16 of the flow, with the central axis 16 of the flow as a reference. By arranging the panels 14 radially, the amount of ions 13 passing behind the panels 14 can be reduced and the ions 13 can be guided toward the wall 19 of the vacuum vessel 12 . It is also possible to arrange a plurality of exhaust ports 18 on a plane including the row of panels 14 to further promote exhaust. As shown in FIG. 5, each row of panels 14 may be arranged in a ring together with other rows of panels 14 adjacent in the circumferential direction. In this case, the ions 13 staying between the panels 14 other than the panels 14 arranged toward the exhaust port 18 can be easily guided between the panels 14 arranged toward the exhaust port 18 by multiple reflection.

It should be noted that the present disclosure is not limited to the above-described embodiments, but is indicated by the description of the scope of claims, and further includes all modifications within the meaning and scope equivalent to the description of the scope of claims.

DESCRIPTION OF SYMBOLS 10... Electric propulsion machine test apparatus (test apparatus), 11... Electric propulsion machine, 11a... Ion discharge port, 12... Vacuum vessel, 13... Ions, 13a... Ion flow, 14... Panel, 16... Central axis of ion flow, 17 Central axis of vacuum container 18 Exhaust port 19 Wall 20 Pump 21 Surface 22 Through hole D Spacing P Spacing (pitch) ND Normal direction RD radial direction

Claims (5)

a vacuum vessel having an exhaust port;
a plurality of panels provided in the vacuum vessel, arranged in at least one row facing each other at predetermined intervals, and reflecting ions emitted from the electric propulsion machine;
Each panel is provided with a plurality of through holes extending in its thickness direction,
at least one row of the plurality of panels aligns toward the exhaust port;
Electric propulsion test equipment. The opening ratio of the through-holes in each panel is larger for the panel closer to the wall of the vacuum vessel,
The electric propulsion machine testing device according to claim 1. The plurality of panels are radially arranged in a plurality of rows with reference to the central axis of the ion flow,
The electric propulsion machine testing device according to claim 1 or 2. the panels of each row are annularly positioned with the panels of other circumferentially adjacent rows;
The electric propulsion machine testing device according to claim 3. The interval between the panels in a row is set to a value that causes multiple reflections of the ions between the panels.
The electric propulsion machine testing device according to any one of claims 1 to 4.

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