Heat Shield

Abstract

To provide a heat shield that can measure temperature to evaluate the temperature distribution of a cathode during heating.SOLUTION: A heat shield 10 includes a cylindrical portion 11 that surrounds the outer periphery of a cathode 20 that extends in the axial direction, extends in the axial direction, and has heat insulating properties, and a slit 13A is formed in a region R of the circumferential surface of the cylindrical portion 11 that overlaps with the cathode in the axial direction, and the slit 13A penetrates the cylindrical portion 11 toward the cathode 20 and extends in a predetermined direction.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present disclosure relates to a heat shield used to evaluate the temperature distribution of a cathode. [Background technology]

[0002] Electrostatic accelerator thrusters mounted on spacecraft are a type of electric thruster that obtains thrust by electrically ejecting ions from plasma. Electrostatic accelerator thrusters generate high-temperature plasma from a supply gas through electron collisions, and generate thrust by accelerating the ions in the plasma using an electric field. To prevent charging of the electrostatic accelerator thruster, the emitted ion beam is neutralized by an electron beam. A hollow cathode, which can obtain a large current, is generally used as the electron source (see Patent Document 1). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2017-016795 Summary of the Invention [Problem to be solved by the invention]

[0004] The hollow cathodes described above are required to emit electrons at high density and with a large current. They also need to be stable during operation. For this reason, compounds such as lanthanum hexaboride (LaB6), which has a low work function and is structurally stable, are often used as cathode materials. However, because electron emission is generally sensitive to temperature, in order to obtain the desired current and current density, it is necessary to measure the temperature distribution of the cathode during heating and evaluate the performance of the cathode and heater based on the results.

[0005] The present disclosure has been made in consideration of the above circumstances, and aims to provide a heat shield that is capable of measuring temperature to evaluate the temperature distribution of a cathode during heating. [Means for solving the problem]

[0006] A heat shield according to one aspect of the present disclosure includes a cylindrical portion that surrounds an outer periphery of a cathode extending in an axial direction and extends in the axial direction, the cylindrical portion having thermal insulation properties, and a slit formed in a region of the circumferential surface of the cylindrical portion that overlaps with the cathode in the axial direction, the slit penetrating the cylindrical portion toward the cathode and extending in a predetermined direction. The cylindrical portion includes a plurality of metal plates stacked in the radial direction of the cylindrical portion and surrounding the outer periphery of the cathode. .

[0007] each The metal plate may have a plurality of protrusions protruding in its thickness direction. The cylindrical portion may include a pair of accommodating plates spaced apart in the radial direction and accommodating the plurality of metal plates therebetween, and a plurality of connecting pieces spaced apart along edges of the pair of accommodating plates and connecting the pair of accommodating plates. The slit may extend in the axial direction of the cylindrical portion. The slit may extend in the circumferential direction of the cylindrical portion. [Effects of the Invention]

[0008] According to the present disclosure, it is possible to provide a heat shield capable of measuring temperature to evaluate the temperature distribution of a cathode during heating. [Brief explanation of the drawings]

[0009] [Figure 1] FIG. 1 is a perspective view of a heat shield according to an embodiment of the present disclosure. [Figure 2] FIG. 2 is a cross-sectional view of an example of a cathode to be measured. [Figure 3] 1A and 1B are diagrams showing an example of a heater, in which (a) is a front view of the heater, (b) is a side view of the heater as seen from direction A in (a), and (c) is a side view of the heater as seen from direction B in (a). [Figure 4] 1A and 1B are diagrams showing the configuration of a heat shield, where (a) is a side view of the heat shield, (b) is a front view of the heat shield, and (c) is a cross-sectional view of CC in (b). [Figure 5]FIG. 3 is a cross-sectional view showing a stacked state of metal plates. [Figure 6] FIG. 10 is a diagram showing a state in which temperature measurement is performed using a heat shield. [Figure 7] 1A and 1B are diagrams showing modified slits according to an embodiment of the present disclosure, in which (a) is a side view of a heat shield having slits according to the modified example, and (b) is a DD cross-sectional view of (a). DETAILED DESCRIPTION OF THE INVENTION

[0010] Below, we will explain the heat shield 10 according to several embodiments of the present disclosure. Note that common parts in each drawing are given the same reference numerals, and redundant explanations will be omitted. Hereinafter, for convenience of explanation, the Z axis is defined as the reference axis of the entire heat shield 10, and its extension direction is referred to as the axial direction AD. The axial direction AD is also the extension direction (axial direction) of the cylindrical portion 11 and cathode 20 of the heat shield 10, which will be described later. Furthermore, the circumferential direction CD and the radial direction RD are defined based on the Z axis.

[0011] FIG. 1 is a perspective view of a heat shield 10 according to this embodiment. For ease of explanation, the left front side in FIG. 1 is defined as the "front" and the right rear side as the "rear." As shown in FIG. 1, an insert (emitter) 21 of a cathode 20 is mounted on a support 22 and positioned on the Z axis. A heater 30 is installed so as to surround the outer periphery of the cathode 20 and heats the cathode 20. The heat shield 10 covers the cathode 20 and the heater 30 so as to surround the outer periphery of each of the cathode 20 and the heater 30. The cathode 20, heater 30, and heat shield 10 are supported, for example, by a substrate (not shown) or a current input terminal (not shown) on the substrate.

[0012] The heat shield 10 according to this embodiment is a simulated heat shield attached to the electron source of an ion engine such as an electrostatic accelerator thruster or an electromagnetic accelerator. The heat shield 10 blocks radiant heat generated within the heat shield 10. The source of the radiant heat is a heater 30 (see FIGS. 1 and 3) that heats the cathode 20, and the cathode 20 heated by the heater 30. However, the heater 30 may not be provided. In this case, the cathode 20 is heated by high-temperature plasma that is continuously generated due to discharge between the cathode 20 and a keeper electrode (not shown) provided in front of the cathode 20. Therefore, the source of the radiant heat is the cathode 20 and the high-temperature plasma.

[0013] The heat shield 10 according to this embodiment is used for temperature measurement to evaluate the temperature distribution of the cathode 20. The temperature measurement is performed by a non-contact temperature measuring device 40 (see FIG. 6), such as a thermograph, a radiation thermometer, or a pyrometer, on at least the portion of the cathode 20 where the insert 21 is located, to obtain a one-dimensional temperature distribution. When the cathode 20 is heated by a heater 30 (see FIGS. 1 and 3), the performance of the heater 30 can also be evaluated from the obtained temperature distribution.

[0014] First, the cathode 20 and heater 30 to be evaluated will be described. Fig. 2 is a cross-sectional view showing an example of the cathode 20. Fig. 3 shows an example of a heater 30, in which (a) is a front view of the heater 30, (b) is a side view of the heater 30 seen from direction A in (a), and (c) is a side view of the heater 30 seen from direction B in (a).

[0015] The cathode 20 includes at least an insert (emitter) 21, which is a hot cathode, and a support 22 (hereinafter referred to as an insert support) that supports the insert 21. The insert 21 has a cylindrical shape that extends in the axial direction AD, centered on the Z axis, and has a hole penetrating through it with the Z axis as its central axis. In other words, the insert 21 is a so-called hollow cathode. The insert 21 is made of an electron-emitting material such as lanthanum hexaboride (LaB6) or barium oxide (BaO).

[0016] The insert 21 is attached to the front end 22a of the insert support 22. The insert support 22 is a tubular member formed of a heat-resistant metal (high-melting point metal) such as molybdenum and extending in the axial direction AD. The insert support 22 is formed with an attachment hole 23 extending in the axial direction AD. The insert 21 is inserted into this attachment hole 23 and is positioned on the front end 22a side of the insert support 22. In addition, members such as an orifice 25 that constitutes an electron emission port 24 are attached to the front end 22a of the insert support 22.

[0017] The insert 21 is inserted into the mounting hole 23 with the sleeve 26 attached. The sleeve 26 is made of carbon and is attached, for example, to the front end and rear end of the cathode 20 so as to form a radial gap between the insert 21 and the insert support 22. This protects the insert 21 from chemical reaction between the insert 21 and the insert support 22.

[0018] The heater 30 is a heating element that generates heat when energized, and heats the cathode 20 from the outer periphery of the cathode 20. The heater 30 has a roughly cylindrical outer shape centered on the Z axis, and its inner diameter is larger than the outer diameter of the insert support 22. The heater 30 is made of a heat-generating member containing carbon or the like. Furthermore, the heat-generating member is provided in at least an area surrounding the outer periphery of the insert 21 so that the entire insert 21 can be heated.

[0019] 3, the heat-generating member of the heater 30 extends in the circumferential direction CD while meandering in the axial direction AD (while reciprocating in the axial direction AD) on an imaginary cylindrical surface centered on the Z axis. The heater 30 is also arranged concentrically with the cathode 20 (insert 21) about the Z axis. However, the heater 30 is not formed in a position that overlaps with the slit 13A (see FIG. 1) of the heat shield 10 when viewed from the radial direction RD. In other words, the heater 30 is formed so as not to interfere with optical temperature measurement of the insert 21 or the insert support 22 via the slit 13A.

[0020] The shapes of the insert 21 and the insert support 22 are not limited to those shown in FIG. 2 and may be other well-known shapes. The same applies to the materials. For example, the insert 21 is not limited to the hollow cathode described above, and depending on the specifications of the insert, the insert may be exposed from the cathode support or the like. Similarly, the shape of the heater 30 shown in FIG. 3 is not limited to the shape shown in FIG. 3 and its material may be a material other than the tantalum described above. For example, it may be a metal heater using a high-melting-point metal (alloy) such as tungsten, or a ceramic heater using graphite as a heat-generating material.

[0021] Next, the heat shield 10 according to this embodiment will be described. 4 is a structural diagram of the heat shield 10, where (a) is a side view of the heat shield 10, (b) is a front view of the heat shield 10, and (c) is a CC cross-sectional view of (b). As shown in FIGS. 1 and 4, the heat shield 10 includes a cylindrical portion 11 and a support portion 12 that supports the cylindrical portion 11.

[0022] The cylindrical portion 11 is a hollow cylindrical member that surrounds at least the outer periphery of the cathode 20. The cylindrical portion 11 has thermal insulation properties against the above-mentioned radiant heat and shields it. As shown in FIG. 4(a), the length of the cylindrical portion 11 along the axial direction AD is sufficiently longer than that of the insert 21. As shown in FIGS. 4(b) and 4(c), the cylindrical portion 11 has a substantially annular cross section and extends in the axial direction AD. This substantially annular cross section is formed around a point on the Z axis, has a predetermined length (thickness) in the radial direction RD, and extends in the circumferential direction CD. Therefore, when viewed from the axial direction AD, the cathode 20, the heater 30, and the cylindrical portion 11 are arranged substantially concentrically.

[0023] As shown in FIGS. 4(b) and 4(c), the cylindrical portion 11 includes multiple metal plates 14, a pair of housing plates 15 and 16, and multiple connecting pieces 17. The metal plates 14 are stacked in the radial direction RD and surround the outer periphery of the cathode 20. The metal plates 14 may be formed of a high-melting-point metal such as tantalum or molybdenum, and reflect radiant heat from a heat source such as a heater 30 inside the cylindrical portion 11. Each metal plate 14 may have multiple protrusions 14a protruding in its thickness direction (see FIG. 5). In this case, two adjacent metal plates 14 are stacked so that the positions of the protrusions 14a formed on each plate are offset relative to each other. This maintains an appropriate spacing between the metal plates 14, and the point contact between them improves the thermal insulation of the cylindrical portion 11. The multiple protrusions 14a can be formed by pressing the metal plates 14, such as embossing.

[0024] The pair of storage plates 15, 16 are positioned on concentric circles centered on the Z axis and are cylindrically shaped. Therefore, the pair of storage plates 15, 16 define the outer shape of the cylindrical portion 11. The pair of storage plates 15, 16 are spaced apart in the radial direction RD and store multiple metal plates 14 therebetween. That is, the storage plate 15 is located at the innermost position in the radial direction, and the storage plate 16 is located at the outermost position in the radial direction, with the aforementioned spacing therebetween. Like the metal plates 14, each storage plate 15, 16 is formed of a high-melting-point metal such as tantalum or molybdenum and reflects radiant heat from a heat source such as the heater 30. To maintain the outer shape of the cylindrical portion 11, the storage plates 15, 16 may be thicker than the metal plates 14.

[0025] The diameter of the cylinder formed by the receiving plate 15 is set to a value larger than at least the outer diameter of the insert support 22. Furthermore, if a heater 30 is provided, this diameter is set to a value larger than the outer diameter of the heater 30. The diameter of the cylinder formed by the receiving plate 16 is set to a value that allows the stacked multiple metal plates 14 to be accommodated between the receiving plate 15 and the receiving plate 16.

[0026] The connecting pieces 17 are provided at intervals along the edges of the pair of storage plates 15, 16 and connect the pair of storage plates 15, 16. The connecting pieces 17 maintain the relative positions of the storage plates 15, 16 and prevent the metal plate 14 from falling out from between the storage plates 15, 16. The connecting pieces 17 are joined to each of the storage plates 15, 16 by, for example, spot welding.

[0027] The heat shield 10 has a support portion 12. The support portion 12 is provided at the rear of the cylindrical portion 11 and supports the cylindrical portion 11. The support portion 12 is, for example, a circular flange perpendicular to the Z axis. The support portion 12 has a plurality of holes (not shown) formed at intervals in the circumferential direction CD. Fastening parts such as screws are inserted into these holes to fix the heat shield 10 to a substrate (not shown).

[0028] As shown in FIG. 4(a), at least one slit 13A is provided in the cylindrical portion 11. The slit 13A is formed in a region R of the circumferential surface of the cylindrical portion 11 that overlaps with the cathode 20 in the axial direction AD. The slit 13A penetrates the cylindrical portion 11 toward the cathode 20 and extends in the axial direction AD. The length (i.e., width) of the slit 13A in the circumferential direction CD is set to a value that allows temperature measurement by the temperature measuring device 40 via the slit 13A and prevents excessive leakage of radiant heat from the slit 13A. The slit 13A may extend from the region R to the support portion 12. The number of slits 13A is arbitrary as long as heat leakage does not cause any problems. However, when multiple slits 13A are provided, it is desirable to provide them at positions symmetrical with respect to the Z axis to prevent excessive deformation of the cylindrical portion 11 due to thermal expansion.

[0029] As long as heat leakage does not cause any problems, the cylindrical portion 11 may be made of ceramic, in which case the receiving plates 15 and 16, the plurality of metal plates 14, and the connecting piece 17 are not necessary.

[0030] FIG. 6 shows the state in which temperature measurement is being performed using the heat shield 10. The cathode 20, heater 30, and heat shield 10 are placed in a vacuum chamber (not shown) in advance. The heat shield 10 is also positioned so that the slit 13A faces the observation window 41. The temperature measuring instrument 40 is placed in the atmosphere, with the measurement point aligned with the slit 13A. Once the pressure in the vacuum chamber has sufficiently decreased, power is applied to the heater 30 to heat the cathode 20. The temperature measuring instrument 40 measures the infrared or visible light that passes through the slit 13A and the observation window 41 and calculates the temperature.

[0031] In this embodiment, the insert support 22 is visible through the slit 13A. Therefore, the calculated temperature indicates the surface temperature of the insert support 22. If the temperature measuring device 40 is a thermography camera, the one-dimensional temperature distribution of the insert support 22 visible through the slit 13A can be acquired all at once by observing the entire slit 13A. If the temperature measuring device 40 is a spot radiation thermometer, the temperature is measured while its focus is moved stepwise over a predetermined distance from near one end of the slit 13A to near the other end. This makes it possible to acquire the one-dimensional temperature distribution of the insert support 22, in other words, the one-dimensional temperature distribution of the cathode 20.

[0032] Since it can be assumed that there is almost no difference between the one-dimensional temperature distribution of the insert support 22 and the temperature distribution of the insert 21, the temperature distribution of the portion of the obtained temperature distribution where the insert 21 is located can be considered the temperature distribution of the insert 21. Therefore, the temperature distribution of the insert 21 during heating can be evaluated from this temperature measurement. Furthermore, if only the heater 30 is replaced without changing the insert 21 and the insert support 22, it is also possible to evaluate the performance of the heater 30 by comparing the temperature distributions before and after the heater 30 replacement. Furthermore, temperature measurement using the heat shield 10 according to this embodiment is performed without contact. That is, unlike temperature measurement using a thermocouple, heat is not lost due to contact with the temperature sensor. In other words, measurement errors due to heat leakage can be suppressed.

[0033] FIG. 7 shows a modified example of the slit 13A. (a) is a side view of a heat shield having a modified slit 13B, and (b) is a DD cross-sectional view of (a). In the modified heat shield 10, the slit 13B extends in the circumferential direction CD of the cathode 20. In this case, the heater 30 also has a shape that does not interfere with the slit 13B. In other words, when viewed from the radial direction, the heater 30 does not overlap with the slit 13B. This modified example allows the circumferential temperature distribution of the portion of the cathode 20 where the insert 21 is located to be evaluated. Similarly, the performance of the heater 30 can also be evaluated.

[0034] Alternatively, slits 13A and 13B may be provided in cylindrical portion 11. For example, slit 13A is provided on one side of the Z axis, and slit 13B is provided on the other side. In this case, the temperature distribution in the axial and circumferential directions can be measured with a single heating.

[0035] The present disclosure is not limited to the above-described embodiments, but is defined by the claims, and includes all modifications within the meaning and scope equivalent to the claims. [Explanation of symbols]

[0036] 10...heat shield, 11...cylindrical portion, 12...support portion, 13A, 13B...slit, 14...metal plate, 14a...protrusion, 15...accommodating plate, 16...accommodating plate, 17...connecting piece, 20...cathode, 21...insert (emitter), 22...support (insert support), 23...mounting hole, 24...discharge port, 25...orifice, 26...sleeve, 30...heater, 40...temperature measuring instrument, 41...observation window, AD...axial direction, CD...circumferential direction, RD...radial direction, R...area

Claims

1. a cylindrical portion that surrounds the outer periphery of the cathode extending in the axial direction and that extends in the axial direction and has thermal insulation properties; a slit is formed in a region of the circumferential surface of the cylindrical portion that overlaps with the cathode in the axial direction, the slit penetrates the cylindrical portion toward the cathode and extends in a predetermined direction, The cylindrical portion includes a plurality of metal plates stacked in a radial direction of the cylindrical portion and surrounding the outer periphery of the cathode. Heat shield.

2. Each of the metal plates has a plurality of protrusions protruding in the thickness direction. The heat shield of claim 1 .

3. The cylindrical portion is a pair of receiving plates spaced apart in the radial direction and receiving the plurality of metal plates therebetween; a plurality of connecting pieces provided at intervals along the edges of the pair of receiving plates and connecting the pair of receiving plates; Contains The heat shield of claim 2 .

4. The slit extends in the axial direction of the cylindrical portion. A heat shield according to any one of claims 1 to 3.

5. The slit extends in the circumferential direction of the cylindrical portion. A heat shield according to any one of claims 1 to 3.

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