Surface thermocouple system suitable for actively water-cooled full-tungsten divertor of magnetic confinement device

Abstract

The application discloses a surface thermocouple system suitable for a full-tungsten divertor of a magnetic confinement device, and relates to the field of plasma diagnosis of magnetic confinement devices, and comprises a box-shaped support structure and a thermocouple assembly. The tungsten-copper string tube of the divertor is fixedly connected with the box-shaped support structure through fixing pins. The thermocouple assembly is composed of a thermocouple probe, a pyrolytic graphite shell, a base, a screw, a nut, a spring washer, a fixing support plate and a lead wire, and is installed in a cylindrical through hole between adjacent tungsten-copper string tubes and a gap between the tungsten-copper string tube and the box-shaped support structure. The application enables the surface thermocouple to be normally disassembled and maintained, and provides a direct means for measuring the surface temperature of the target plate of the full-tungsten divertor.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of magnetic confinement device plasma diagnosis, and in particular to a surface thermocouple system suitable for a main water-cooled full-tungsten divertor of a magnetic confinement device. BACKGROUND

[0002] A magnetic confinement device uses a special structure of magnetic field to confine a plasma in a vacuum vessel, uses an external neutral beam or a radio frequency wave to improve the temperature of the plasma, and uses a gas filling, an ultrasonic molecular beam or a projectile to improve the density of the plasma, so that the ion temperature, the density and the confinement time of the core plasma reach the ignition condition of fusion, and self-sustaining combustion is achieved, and energy is continuously outputted to the outside. The magnetic confinement device is considered to be an effective way to utilize fusion energy for peaceful purposes. The magnetic confinement fusion energy is a clean energy, and the raw material is abundant in nature, which is a feasible way to solve the future energy problem of human beings. The magnetic confinement device includes a tokamak, a stellarator, a magnetic mirror and a pinch fusion device. At present, the tokamak and the stellarator are considered to be the two devices most likely to achieve controlled thermonuclear fusion.

[0003] The divertor is one of the core components of the tokamak device, is a main area where the plasma directly contacts and interacts with the surface of a solid material, and has important functions of removing heat energy, particles and fusion products helium ash transported from the plasma, shielding impurities generated by the interaction between the plasma and the material, and avoiding impurity pollution of the core plasma. In the magnetic confinement fusion device, a huge amount of energy is transported from the plasma, most of which is deposited on the surface of the divertor target plate, which brings a very high heat load, may erode the target plate material, shorten the service life of the material, and produce a large amount of impurities to pollute the core plasma, so that the nuclear reaction condition is difficult to maintain stably. The measurement and control of the heat load on the surface of the divertor target plate are crucial for the safe operation of the magnetic confinement device. The divertor designs of major international tokamaks are different from each other. The divertor structure of the future fusion reactor ITER is a modular structure of a main water-cooled tungsten divertor based on a box-shaped support structure, and the EAST tokamak in China currently uses a similar divertor structure to ITER.

[0004] Traditional thermocouples are installed inside the divertor target plate. Temperature changes on the target surface must penetrate the target material to be detected by the thermocouple, resulting in an excessively long response time and making real-time measurement of the target surface temperature impossible. Surface thermocouples overcome this slow response time limitation, allowing direct measurement of plasma particle and heat flows. They operate even under high-energy transient thermal pulses thanks to a special welding technique that enables the hot junction to automatically renew itself after plasma erosion. Furthermore, the thermoelectrodes, employing a strip-film structure and layered assembly technology, significantly reduce the volume, mass, and heat capacity of the hot junction, enabling a much faster response to changes in target surface temperature and heat flow. Devices like the C-Mod and DIII-D can provide experimental data for studies related to the thermal load on divertor target surfaces. However, the surface thermocouples on the C-Mod device use non-standard molybdenum / tungsten-rhenium as thermoelectrodes, and the thermocouple installation structure is relatively complex, with multiple uncompensated hot junctions between the thermocouple probe and the wires, affecting temperature measurement results. The divertor on the DIII-D device uses graphite tiles, eliminating the need to consider the potential fusion welding problem between the thermocouple protective shell material and the target plate material under extremely high temperatures; therefore, its surface thermocouples use metallic molybdenum as the protective shell material. The surface thermocouple system on the domestic tokamak device EAST is installed on an actively water-cooled all-tungsten divertor structure similar to the future fusion reactor ITER. Under the extremely high temperature environment on the tokamak divertor target plate surface, the surface metal material of the divertor target plate may fused with the thermocouple protective shell metal material, making it impossible to disassemble and maintain the surface thermocouple normally. Summary of the Invention

[0005] To address the aforementioned technical issues, this invention provides a surface thermocouple system suitable for an active water-cooled all-tungsten divertor in a magnetic confinement device. Pyrolytic graphite is used as the thermocouple protective shell material, effectively avoiding the problem of surface thermocouples being unable to be properly disassembled and maintained. Furthermore, in the vacuum environment inside a tokamak device, pyrolytic graphite exhibits stronger temperature resistance than molybdenum, ensuring the thermocouple protective shell can withstand higher temperatures to protect the surface thermocouple probe. Since the surface thermocouple directly faces the plasma for measurement, impurities may sputter from the surface of the measuring end under plasma bombardment, affecting the core plasma confinement performance. Low-charge-number carbon impurities have a smaller impact on core plasma confinement performance compared to high-charge-number molybdenum impurities. Therefore, selecting pyrolytic graphite as the thermocouple protective shell material can reduce the impact of surface impurity sputtering on the core plasma confinement performance. In addition, the EAST device uses type C standard tungsten-rhenium thermocouples and dedicated compensating wires, avoiding the formation of new hot junctions in the measurement circuit that could affect temperature measurement.

[0006] To achieve the above objectives, the present invention adopts the following technical solution:

[0007] A surface thermocouple system suitable for an actively water-cooled all-tungsten divertor in a magnetically confined device includes a box-shaped support structure and a thermocouple assembly. The box-shaped support structure securely supports the tungsten-copper series tubes of the divertor. The thermocouple assembly includes a thermocouple probe, a pyrolytic graphite shell, a base, a fixing support plate, screws, nuts, spring washers, and leads. The thermocouple probe is entirely encapsulated in the pyrolytic graphite shell, with the measuring end surface of the probe flush with the front end surface of the pyrolytic graphite shell. The leads extend from the bottom end face of the pyrolytic graphite shell. The base is located adjacent to the tungsten-copper series tubes. Below the cylindrical through-hole between the thermocouples; after the thermocouple probe, pyrolytic graphite shell and base are assembled, they are inserted from the rear end of the cylindrical through-hole between the tungsten copper tubes and screwed in. The screw passes through the fixed support plate, spring washer and nut and is screwed in. The base is fixed to the fixed support plate by tightening the nut. The two ends of the fixed support plate are welded to the box-shaped support structure. The thermocouple probes of multiple thermocouple assemblies are distributed along the surface of the divertor target plate with the poles of the surface thermocouple system facing upward. The front end surface of the pyrolytic graphite shell is flush with the surface of the divertor target plate.

[0008] Furthermore, the divertor target plate is composed of multiple sets of parallel tungsten copper tubes, with gaps between adjacent tungsten copper tubes and cylindrical through holes.

[0009] Furthermore, the rear half of the pyrolytic graphite shell is machined with external threads for connection with the internal threads of the tubular extension of the base.

[0010] Furthermore, the thermocouple probe is a type C tungsten-rhenium thermocouple.

[0011] Furthermore, the base is made of stainless steel.

[0012] Furthermore, the base consists of a cuboid base and a cylindrical extension, and the base has an inner cavity with openings at the top and bottom of the cavity.

[0013] Furthermore, the base has a circular inner cavity opening at its bottom, and two internally threaded blind holes are opened on both sides of the circular inner cavity opening at the bottom of the base for screwing in with screws; the base has a tubular extension at its top that communicates with the inner cavity of the base, and the tubular extension extends into the cylindrical through hole between adjacent tungsten copper tubes, with the lower end plane of the tubular extension closely attached to the outer wall of the tungsten copper tube.

[0014] Furthermore, the fixed support plate is made of stainless steel and has three cylindrical through holes machined on it.

[0015] Furthermore, the lead wire is led out through the bottom end face of the pyrolytic graphite shell, passes through the inner cavity of the base, and exits from the circular inner cavity opening at the bottom of the base.

[0016] Furthermore, the surface thermocouple system applicable to the active water-cooled all-tungsten divertor of the magnetic confinement device is characterized in that the lead wire is a compensating wire of a type C tungsten-rhenium thermocouple, and the positive and negative poles are insulated with glass fiber and wrapped with a stainless steel braided mesh to shield external interference signals.

[0017] Beneficial effects:

[0018] This invention's surface thermocouple system fully utilizes the limited space on an all-tungsten divertor to securely mount the surface thermocouple probe. Because the base is tightly fitted to the divertor target plate, and the target plate contains internal water-cooling pipes, heat deposited on the thermocouple probe during discharge can be removed. Therefore, this thermocouple system is capable of operating under steady-state long-pulse discharge conditions. This invention uses pyrolytic graphite as a protective shell, enabling operation in high-temperature environments. Furthermore, the front surface of the protective shell is flush with the measuring end surface of the thermocouple probe, preventing direct plasma bombardment of the probe's measuring edge and increasing its lifespan. The components are connected and fixed using threads, making installation simple and easy, ensuring the stability of the thermocouple probe installation, enabling stable operation under high-temperature conditions, and facilitating disassembly or replacement of the thermocouple assembly during maintenance. Attached Figure Description

[0019] Figure 1 This is a front sectional view of the surface thermocouple system of the present invention, applicable to an active water-cooled all-tungsten divertor for a magnetically confined device.

[0020] Figure 2 This is a left sectional view of the surface thermocouple system of the present invention applicable to an active water-cooled all-tungsten divertor for a magnetically confined device;

[0021] Figure 3 This is a top view of the surface thermocouple system of the present invention, applicable to an active water-cooled all-tungsten divertor for a magnetically confined device;

[0022] The attached figures are labeled as follows: 1 is the pyrolytic graphite shell, 2 is the thermocouple probe, 3 is the base, 4 is the tungsten copper tube, 5 is the fixing foot, 6 is the fixing seat, 7 is the box-shaped support structure, 8 is the fixing pin, 9 is the spring washer, 10 is the nut, 11 is the screw, 12 is the fixing support plate, and 13 is the lead wire. Detailed Implementation

[0023] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention. Furthermore, the technical features involved in the various embodiments of this invention described below can be combined with each other as long as they do not conflict with each other.

[0024] like Figure 1 , Figure 2 and Figure 3 As shown, the surface thermocouple system of the present invention, applicable to an active water-cooled all-tungsten divertor for a magnetically confined device, includes a tungsten-copper tube 4, a box-shaped support structure 7, and thermocouple assemblies. Multiple thermocouple probes 2 of the thermocouple assemblies are distributed along the surface of the divertor target plate in the polar direction of the surface thermocouple system. A fixing pin 8 passes through a pin hole in the side wall of a fixing foot 5 supporting the tungsten-copper tube 4 and a fixing seat 6 on the outer wall of the box-shaped support structure 7, thereby fixing the tungsten-copper tube 4 to the box-shaped support structure 7. The fixing foot 5 is welded to the tungsten-copper tube 4, and the fixing seat 6 is welded to the outer wall of the box-shaped support structure 7. The divertor target plate is composed of multiple sets of parallel tungsten-copper tubes 4, wherein there is a gap between two adjacent tungsten-copper tubes 4, and cylindrical through holes are machined therein.

[0025] The thermocouple assembly includes a thermocouple probe 2, a pyrolytic graphite shell 1, a base 3, a fixing support plate 12, screws 11, nuts 10, spring washers 9, and leads 13. The thermocouple probe 2 is integrally encapsulated and fixed in the pyrolytic graphite shell 1, so that the measuring end surface of the thermocouple probe 2 is flush with the front end surface of the pyrolytic graphite shell 1. The front end of the leads 13 is connected to the rear end of the thermocouple probe 2, and is led out through the bottom end face of the pyrolytic graphite shell 1, the bottom through hole of the base 3, and the central through hole of the fixing support plate 12. The rear end of the leads 13 is connected to the thermocouple acquisition system. The rear half of the pyrolytic graphite shell 1 is machined with external threads, which engage with the internal threads of the cylindrical extension of the base 3, and the thread engagement length can be adjusted. The surface of the thermocouple probe 2 at the measuring end and the front end of the pyrolytic graphite shell 1 are flush with the surface of the divertor target plate. After the thermocouple probe 2, pyrolytic graphite shell 1, lead wire 13 and base 3 are assembled, they are inserted into the rear end of the cylindrical through hole between the tungsten copper tubes 4 of the divertor. Threaded holes are machined on both sides of the bottom of the base 3, which are screwed into the base 11. The screw 11 passes through the through holes on both sides of the fixed support plate 12 and the spring washer 9, and is screwed into the nut 10. By tightening the nut 10, the base 3 is fixedly connected to the fixed support plate 12, and the upper surface of the cuboid base of the base 3 is tightly attached to the lower surface of the tungsten copper tube 4. The two ends of the fixed support plate 12 are welded to the box-shaped support structure 7.

[0026] The installation of the surface thermocouple system of the divertor must ensure the installation accuracy of the surface thermocouple, that is, the surface of the thermocouple probe measuring end is flush with the surface of the divertor target plate, while ensuring the firmness of the thermocouple probe installation and its removability for maintenance.

[0027] Preferably, thermocouple probe 2 uses a type C tungsten-rhenium thermocouple (positive electrode: 95% tungsten + 5% rhenium, negative electrode: 74% tungsten + 26% rhenium), with a maximum temperature range of approximately 2300 degrees Celsius. It can withstand the high-temperature environment in the magnetic confinement device. Thermocouple probe 2 has a temperature measurement accuracy of 1% of full scale, a frequency response of 50 kHz, and a thermal response time of approximately a few milliseconds. It employs an corrosion-resistant probe with an automatic regeneration function for the hot junction after corrosion. It can directly measure plasma particle and heat flux, and can quickly respond to changes in the surface temperature and heat flux of the divertor target plate. It can also operate normally under high-energy transient thermal pulse conditions.

[0028] The tungsten-rhenium thermoelectrode inside the thermocouple probe forms a hot junction through welding technology. This hot junction automatically renews itself after being eroded by plasma, ensuring the continuous and stable operation of the thermocouple. This allows the hot junction of the thermocouple to directly face the plasma for measurement, overcoming the slow response time of traditional thermocouples embedded in a target plate. In addition, the tungsten-rhenium thermoelectrode inside the thermocouple probe adopts a strip-shaped thin film structure and layered assembly technology, making the hot junction very small in volume and mass, and its heat capacity almost negligible, which can further reduce the response time of the thermocouple.

[0029] Preferably, the pyrolytic graphite shell 1 encapsulates the thermocouple probe 2 entirely within it. The front surface of the pyrolytic graphite shell 1 is flush with the measuring end surface of the thermocouple probe 2. The rear half of the pyrolytic graphite shell 1 is machined with external threads for internal thread connection with the tubular extension of the base 3. The pyrolytic graphite shell 1 is located in the cylindrical through hole between the tungsten copper string tubes 4. The front surface of the pyrolytic graphite shell 1 is flush with the surface of the divertor target plate.

[0030] Preferably, the base 3 is made of stainless steel and is located between the rear end of the divertor target plate and the box-shaped support structure 7. The outer contour of the base 3 consists of a cuboid base and a cylindrical extension. The base 3 has an inner cavity, and the top and bottom of the base 3 are respectively provided with inner cavity openings. The bottom of the base 3 is provided with a circular inner cavity opening. Two internally threaded blind holes are opened on both sides of the circular inner cavity opening at the bottom of the base 3 for screwing and connecting with screws 11. The top of the base 3 is provided with a tubular extension that communicates with the inner cavity of the base 3, and the tubular extension extends into the cylindrical through hole between the tungsten copper tubes 4. The lower end plane of the tubular extension is in close contact with the outer wall of the tungsten copper tubes 4 of the divertor target plate. The tubular extension at the top of the base 3 is machined with internal threads for threaded connection with the external threads of the rear half of the pyrolytic graphite shell 1.

[0031] Preferably, the fixed support plate 12 is made of stainless steel and is welded to the box-shaped support structure 7 at both ends. The fixed support plate 12 has three cylindrical through holes. The cylindrical through hole at the center of the fixed support plate 12 is used for the thermocouple lead 13 to pass through the inner cavity of the base 3. The cylindrical through holes on either side of the center are used for screws 11 to pass through the fixed support plate 12, spring washers 9, and nuts 10, and to be screwed into the blind holes of the inner threads at the bottom of the base 3, thus fixing the base 3 to the rear end of the divertor target plate. The base 3 is then fixed by tightening the nuts 10. A gap is left between the screws 11 and the fixed support plate 12 to allow for fine-tuning of the position of the screws 11 and the base 3 before tightening the nuts 10, so that the thermocouple probe 2 is positioned at the center of the through hole between the tungsten copper tubes 4.

[0032] Preferably, the lead wire 13 is led out through the bottom end face of the pyrolytic graphite shell 1, passes through the inner cavity of the base 3, and then exits from the circular inner cavity opening at the bottom of the base 3. The lead wire 13 is a C-type tungsten-rhenium thermocouple special compensation wire, consisting of positive and negative cores. The positive and negative poles are insulated with glass fiber and wrapped with stainless steel braided mesh to shield external interference signals.

[0033] Figure 1 , Figure 2 and Figure 3 The polar direction in the text refers to the direction along the axis of the active water cooling pipeline in the tungsten copper tube 4, while the circumferential direction refers to the direction perpendicular to the axis of the active water cooling pipeline in the tungsten copper tube 4 and parallel to the surface of the divertor target plate.

[0034] The surface thermocouple system of the present invention is applicable to the active water-cooled all-tungsten divertor of the magnetic confinement device. It can measure the temperature and heat flow on the surface of the divertor target plate, and provide experimental data for the study of the heat load on the surface of the divertor target plate.

[0035] The parts of this invention not described in detail are well-known in the art. Although illustrative specific embodiments of the invention have been described above to help those skilled in the art understand the invention, it should be understood that the invention is not limited to the scope of the specific embodiments. For those skilled in the art, various changes are obvious as long as they are within the spirit and scope of the invention as defined and determined by the appended claims, and all inventions utilizing the concept of this invention are protected.

Claims

1. A surface thermocouple system suitable for an active water-cooled all-tungsten divertor in a magnetically confined device, characterized in that, The system includes a box-shaped support structure and a thermocouple assembly. The box-shaped support structure secures the tungsten-copper tubes supporting the divertor. The thermocouple assembly includes a thermocouple probe, a pyrolytic graphite shell, a base, a fixing support plate, screws, nuts, spring washers, and leads. The thermocouple probe is entirely encapsulated within the pyrolytic graphite shell, with the measuring end surface of the probe flush with the front end surface of the pyrolytic graphite shell. The leads extend from the bottom end face of the pyrolytic graphite shell. The base is located below the cylindrical through-hole between adjacent tungsten-copper tubes. After the thermocouple probe, pyrolytic graphite shell, and base are assembled, they are inserted through the rear end of the cylindrical through hole between the tungsten copper tubes and screwed in. The screw passes through the fixed support plate, spring washer, and nut and is screwed in. The base is fixed to the fixed support plate by tightening the nut. The two ends of the fixed support plate are welded to the box-shaped support structure. The thermocouple probes of multiple thermocouple assemblies are distributed along the surface of the divertor target plate with the poles of the surface thermocouple system facing upwards. The front end surface of the pyrolytic graphite shell is flush with the surface of the divertor target plate.

2. The surface thermocouple system for an active water-cooled all-tungsten divertor in a magnetically confined device according to claim 1, characterized in that, The divertor target plate is composed of multiple sets of parallel tungsten copper tubes, with gaps between adjacent tungsten copper tubes and cylindrical through holes.

3. The surface thermocouple system for an active water-cooled all-tungsten divertor in a magnetically confined device according to claim 1, characterized in that, The rear half of the pyrolytic graphite shell is machined with external threads for connection with the internal threads of the tubular extension of the base.

4. The surface thermocouple system for an active water-cooled all-tungsten divertor in a magnetically confined device according to claim 1, characterized in that, The thermocouple probe is a type C tungsten-rhenium thermocouple.

5. The surface thermocouple system for an active water-cooled all-tungsten divertor in a magnetically confined device according to claim 1, characterized in that, The base is made of stainless steel.

6. The surface thermocouple system for an active water-cooled all-tungsten divertor in a magnetically confined device according to claim 1, characterized in that, The base consists of a cuboid base and a cylindrical extension. The base has an inner cavity, with openings at the top and bottom of the base.

7. The surface thermocouple system for an active water-cooled all-tungsten divertor in a magnetically confined device according to claim 6, characterized in that, The base has a circular inner cavity opening at its bottom, and two internally threaded blind holes are opened on both sides of the circular inner cavity opening at the bottom of the base for screwing in with screws; the top of the base has a tubular extension that communicates with the inner cavity of the base, and the tubular extension extends into the cylindrical through hole between adjacent tungsten copper tubes, with the lower end plane of the tubular extension closely attached to the outer wall of the tungsten copper tube.

8. The surface thermocouple system for an active water-cooled all-tungsten divertor in a magnetically confined device according to claim 1, characterized in that, The fixed support plate is made of stainless steel and has three cylindrical through holes machined on it.

9. The surface thermocouple system for an active water-cooled all-tungsten divertor in a magnetically confined device according to claim 6, characterized in that, The lead wire is led out through the bottom end face of the pyrolytic graphite shell, passes through the inner cavity of the base, and exits from the circular inner cavity opening at the bottom of the base.

10. The surface thermocouple system for an active water-cooled all-tungsten divertor in a magnetically confined device according to claim 4, characterized in that, The lead wire is a compensating wire for a type C tungsten-rhenium thermocouple. The positive and negative terminals are insulated with glass fiber and wrapped with a stainless steel braided mesh to shield external interference signals.

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