A Tokamak Boronization Process

Abstract

The present invention provides a tokamak boronization process, comprising: coating a layer of initial boron film on the first wall of a fusion device, when the measured current boron film thickness is a preset percentage of the initial boron film thickness, debugging a specific, stable and repeatable plasma configuration in the fusion device, and after plasma cleaning the boron film deposited on the first wall, starting to inject boron powder into the fusion device under preset process conditions through a boron powder injection device connected to the fusion device, so as to achieve the deposition of a boron film on a preset position of the fusion device. The present invention can effectively extend the life of the boron film, improve the quality of the boron film, alleviate the problem of unevenness of the boron film after bombardment, further improve the boron film's ability to suppress the adsorption of impurities, and provide more reliable wall conditions for the plasma discharge operation of the fusion device.

Description

Technical Field

[0001] The present invention relates to the technical field of controlled nuclear fusion devices, and in particular to a tokamak boronization process. Background Art

[0002] Tokamak is a toroidal container that uses magnetic confinement to achieve controlled nuclear fusion. The center of the tokamak is a toroidal vacuum chamber with a coil wrapped around the outside. When the power is turned on, a huge spiral magnetic field will be generated inside the tokamak, heating the plasma inside to a very high temperature to achieve the purpose of nuclear fusion. Impurity suppression and particle recycling are important research directions for high parameters and steady-state operation of tokamak reactors. In the physical experiments of tokamak nuclear fusion devices, plasma impurities mainly come from the interaction between the plasma and the first wall. The presence of impurities will cause a large amount of radiation energy loss, affecting the energy balance of the plasma, causing the plasma to cool, or even extinguish the plasma. Boriding technology has been used in major devices around the world as a wall treatment method to suppress high-Z impurities such as metals and carbon and oxygen. The widely used glow boriding technology uses boron hydride compounds such as B2H6, B 10 H 14 Or organic boron compounds such as B(CH3)3 are used as boron sources to deposit a boron film with a thickness of about 30-60nm on the first wall of the fusion device by plasma vapor deposition. However, after a certain number of discharges, the film layer tends to be corroded or saturated; in addition, after the boron film is bombarded by plasma, there is a problem of uneven damage to the boron film, especially under the condition of the limiter plasma configuration, the film layer on the central column limiter is seriously damaged after dozens of plasma bombardments. Through long-term monitoring and calculation and measurement, it is known that the consumption rate of the boron film on the central column limiter is about 0.15-0.25nm / gun, while at this time, most of the boron films on the surrounding inner walls are still relatively intact. As the plasma discharge continues, the difference in the thickness of the boron film on the inner wall of the chamber will continue to increase. Therefore, it is necessary to occupy the discharge test machine of the fusion device to perform additional boronization treatment on the inner wall of the chamber. In addition, with the continuous increase of subsequent plasma current, more stringent requirements are also put forward for the wall conditions of the fusion device. Summary of the invention

[0003] In view of this, the present invention proposes a tokamak boronization process, aiming to solve the problem that the boron film deposited on the first wall of the existing tokamak has a short life and is unevenly damaged after being attacked by plasma.

[0004] The first aspect of the present invention provides a tokamak boronization process, comprising the following steps:

[0005] Step 1, depositing an initial boron film on the first wall of the fusion device, ensuring that the initial boron film reaches a preset thickness so that the plasma discharge can operate stably;

[0006] Step 2, real-time detection of the thickness of the boron film deposited on the first wall, when the current boron film thickness is a preset percentage of the initial boron film thickness, a preset plasma configuration is debugged in the fusion device, and boron powder is injected into the fusion device under preset process conditions by the boron powder injection device, thereby achieving the deposition of a boron film on a preset position of the fusion device. Further, in the above-mentioned tokamak boronization process, in step 1, a mixed gas of hydrogen and diborane is dissociated under the action of glow plasma, and an initial boron film with a thickness of 30-50nm is deposited on the first wall of the fusion device by plasma vapor deposition.

[0007] Furthermore, in the above-mentioned tokamak boronization process, in the step 2, when the thickness of the current boron film is 50-60% of the thickness of the initial boron film, boron powder is injected into the fusion device.

[0008] Furthermore, in the above-mentioned tokamak boronization process, in said step 1 and in said step 2, the purity of the boron powder is greater than 99.9%, and the particle size of the boron powder is 50-100 μm.

[0009] Furthermore, in the above-mentioned tokamak boronization process, in step 1 and step 2, before injecting the boron powder into the fusion device, the boron powder is stored in a vacuum environment at 950-1100°C for a period of time to remove residual volatile impurities and moisture in the boron powder.

[0010] Furthermore, in the above-mentioned tokamak boronization process, in the step 3, under the adjusted plasma configuration, the plasma current is maintained at 110 kA for more than 3 s during the discharge plateau period, and the thermal electron temperature of the edge plasma is greater than 30 eV.

[0011] Furthermore, in the above-mentioned tokamak boronization process, in the step 3, the process conditions for injecting boron powder into the fusion device are: the injection rate of boron powder is 2-12 mg / s; multiple boron powder injection operations are performed continuously, and the duration of each boron powder injection is 1.3-3.3s.

[0012] Furthermore, in the above-mentioned tokamak boronization process, in the step 3, the injection rate of the boron powder is 8-10 mg / s; and the duration of each injection of the boron powder is 1.5-2.5 s.

[0013] Furthermore, in the above-mentioned tokamak boronization process, in the step 3, before injecting boron powder into the fusion device, the boron film deposited on the first wall is plasma cleaned.

[0014] The tokamak boronization process provided by the present invention first plates an initial boron film on the first wall of the fusion device, and monitors the thickness change of the initial boron film in real time under the condition of stable plasma discharge operation. When the current boron film thickness is a preset percentage of the initial boron film thickness, boron powder is injected into the fusion device under preset process conditions to deposit a uniform and dense boron film at a preset position of the fusion device. The service life of the boron film is effectively extended, the quality of the boron film is improved, the problem of unevenness of the boron film after bombardment is alleviated, and the ability of the boron film to suppress the adsorption of impurities is further improved, thereby providing more reliable wall conditions for the plasma discharge operation of the fusion device. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 A schematic diagram of a process flow of a Tokamak boronization process provided in an embodiment of the present invention;

[0016] FIG. 2( a ) is a picture of a boron film formed on the inner wall of a fusion device chamber after glow boriding in an embodiment of the present invention;

[0017] FIG2( b ) is a picture showing uneven damage to the initial boron film after several plasma bombardments in an embodiment of the present invention;

[0018] FIG3( a ) is a plasma current curve when a relatively large boron powder injection rate is used in an embodiment of the present invention;

[0019] FIG3( b ) is a plasma current curve when a relatively low boron powder injection rate is used in an embodiment of the present invention;

[0020] FIG4( a ) is a picture of the boron powder shining and ablating after entering the plasma in an embodiment of the present invention;

[0021] FIG4( b ) is a picture of the boron powder ionized and filling the vacuum chamber of the fusion device under the action of a magnetic field in an embodiment of the present invention;

[0022] Figure 5 This is a curve diagram showing the evolution of the radiation intensity of oxygen impurities before and after the injection of boron powder in an embodiment of the present invention;

[0023] Figure 6 This is a curve diagram showing the evolution of radiation intensity of metal impurities before and after boron powder injection in an embodiment of the present invention;

[0024] Figure 7 This is a picture of the coating film deposited on the central column and the central column limiter after five consecutive boron powder injections in an embodiment of the present invention;

[0025] FIG8( a ) is a graph showing the evolution of the radiation intensity of carbon impurities in an initial boron film formed only after glow boriding under 236 plasma discharge bombardments in an embodiment of the present invention;

[0026] FIG8( b ) is a graph showing the evolution of the radiation intensity of carbon impurities in a boron film formed after glow boriding and then implanting boron powder using an appropriate process under 328 plasma discharge bombardments in an embodiment of the present invention. DETAILED DESCRIPTION

[0027] The following is a preferred embodiment of the present invention. It should be noted that a person skilled in the art may make several improvements and modifications without departing from the principles of the present invention. These improvements and modifications are also considered to be within the scope of protection of the present invention.

[0028] See also Figure 1 The present invention proposes a Tokamak boronization process, comprising the following steps:

[0029] Step S1, depositing an initial boron film of a preset thickness on a first wall of a fusion device so that plasma discharge can operate stably.

[0030] Specifically, the preset thickness of the initial boron film is 30 to 50 nm. A mixed gas of hydrogen and diborane is dissociated under the action of glow plasma, and a boron film with a thickness of 30-50 nm is deposited on the first wall of the fusion device by plasma vapor deposition. Preferably, in the mixed gas of hydrogen and diborane, the volume concentration of diborane is 1%-5%. This mixing ratio makes the surface structure of the boron film formed by glow boration smooth, high density, no loose structure of the film layer and good bonding force of the boron film. In practice, a mixed gas of diborane and hydrogen is used as a boron source for glow boration for 3 hours to form a boron film in the chamber of the fusion device. By installing a quartz crystal film thickness tester system on the fusion device, the thickness of the boron film at a specific position in the fusion vacuum chamber is measured online in real time, and the thickness evolution data of the boron film and the loss rate of the boron film by plasma discharge are obtained by monitoring and calculation.

[0031] Step S2, detecting the thickness of the boron film deposited on the first wall in real time, and when the current boron film thickness is a preset percentage of the initial boron film thickness, debugging a preset plasma configuration in the fusion device, and injecting boron powder into the fusion device under preset process conditions through a boron powder injection device connected to the fusion device, thereby achieving the deposition of a boron film on a preset position of the fusion device.

[0032] Specifically, when the thickness of the current boron film is 50-60% of the thickness of the initial boron film, boron powder is injected into the fusion device.

[0033] Before injecting the boron powder into the fusion device, the boron powder is stored in a vacuum environment at 950-1100°C for a period of time to remove the residual volatile impurities and moisture in the boron powder. For example, the powder is stored in a vacuum environment at a high temperature of 1000°C for 4 hours to further prevent the boron powder from carrying impurities and moisture. Furthermore, ensure that the boron powder is stored and transported in a dry inert gas atmosphere.

[0034] In this embodiment, before injecting boron powder into the fusion device, a boron powder injection device needs to be installed on the top of the fusion device. After pre-treating the boron powder injection device, the boron powder injection device is connected to the vacuum chamber of the fusion device.

[0035] Specifically, a boron powder injection device is installed at the flange on the top of the fusion device. After the boron powder injection device is installed on the top of the fusion device, the gate valve on the fusion device is closed first to temporarily isolate the fusion device and the boron powder injection device. After the pretreatment of the boron powder injection device is completed, the gate valve is opened to connect the two by vacuum, thereby minimizing the impact on the vacuum degree of the fusion device. Among them:

[0036] The pretreatment of the boron powder injection device includes: vacuuming the boron powder injection device once, leaking once, baking once, filling powder and sealing, vacuuming twice, leaking twice, and baking twice. In this process, the first baking is preferably baked at 90-110°C for 24-48 hours, such as baking at 100°C for 24 hours; the second baking is preferably baked at 90-110°C for 1-3 hours, such as baking at 100°C for 2 hours.

[0037] Since the boron powder injection device is baked after being loaded with boron powder, water molecules escaping from the wall of the boron powder injection device during the baking process will enter the boron powder, causing it to absorb moisture and stick together, resulting in poor powder fluidity. Therefore, in this embodiment, the boron powder injection device is baked before being loaded with boron powder.

[0038] In specific implementation, after the boron powder injection device is connected to the fusion device by vacuum, the background pressure of the boron powder injection device needs to be pumped down to 10 -6 Pa level, in order to reduce the impact of the vacuum degree of the boron powder injection device on the fusion vacuum degree.

[0039] In this embodiment, after 60-100 conventional plasma discharge experiments, the average thickness of the boron film measured by a quartz microcrystal film thickness meter is about 20nm, and the film thickness is about 60% of the thickness of the initial boron film. The plasma configuration can be selected according to the actual situation, such as the limiter plasma configuration and the deviator plasma configuration. The debugged plasma configuration needs to remain stable and repeatable. For example, under the condition of the limiter plasma configuration, effective coating on the limiter can be preferentially achieved. It can be seen that by injecting boron powder, the boron powder can be preferentially deposited on the part corresponding to the specific plasma configuration in the fusion device.

[0040] In this embodiment, in order to ensure that the boron powder can be fully ablated and ionized after being injected into the plasma, under the adjusted plasma configuration, the plasma current (IP) is maintained at 110kA for more than 3s during the discharge plateau period, and the thermal electron temperature of the edge plasma is greater than 30eV. In this step, the purity of the boron powder is greater than 99.9% to avoid the introduction of new impurities during the boron powder injection process. The particle size of the boron powder is 50-100μm, which is easy to achieve sufficient ablation and dissociation under the discharge conditions of the fusion device.

[0041] In addition, in step 2, before injecting boron powder into the fusion device, the boron film deposited on the first wall is plasma cleaned. For example, 5-10 shots of plasma are used to plasma clean the boron film deposited on the first wall, and the initial boron film deposited on the inner wall of the fusion device is activated while cleaning the wall of the fusion device.

[0042] In this embodiment, it is necessary to first conduct offline experimental debugging on the powder injection device to ensure the repeatability and controllability of the powder injection, and control the powder injection rate to be less than 12 mg / s to avoid excessive boron powder injection rate that may cause plasma discharge rupture.

[0043] In this step, the process conditions for injecting boron powder into the fusion device are: the injection rate of boron powder is 2-12 mg / s; multiple boron powder injection operations are performed continuously, and the duration of each boron powder injection is 1.3-3.3 s.

[0044] Preferably, the injection rate of the boron powder is 8-10 mg / s; each injection of the boron powder lasts for 1.5-2.5 s; more preferably, the injection rate of the boron powder is 10 mg / s; each injection of the boron powder lasts for 2 s. The number of boron powder injections may preferably be 5-8 times.

[0045] In this embodiment, the following may also be included: Step 3, evaluating the effect of the boronization process by high-speed camera observation, visible spectrum monitoring, plasma parameter analysis, boron film morphology observation, and boron film thickness measurement using a quartz crystal film thickness tester.

[0046] Specifically, a high-speed camera is used to observe the movement trajectory of boron ions that are ablated and glowed under the action of plasma after boron powder is injected, a crystal film thickness meter is used to monitor and measure the thickness of the boron film, the boron ionization spectrum is determined using the visible spectrum, the impurity intensity in the vacuum chamber is quantified using the visible spectrum, the coating condition of the fusion device is observed with the naked eye, and the boronization effect is comprehensively analyzed in combination with the plasma discharge parameters.

[0047] From the above, it can be seen that the tokamak boronization process provided by the present invention first coats a layer of initial boron film on the first wall of the fusion device, and monitors the thickness change of the initial boron film in real time under the condition of stable plasma discharge operation. When the current boron film thickness is a preset percentage of the initial boron film thickness, boron powder is injected into the fusion device under preset process conditions to deposit a uniform and dense boron film on a preset position of the fusion device, which can effectively extend the life of the boron film, improve the quality of the boron film, alleviate the problem of unevenness of the boron film after bombardment, further improve the boron film's ability to suppress the adsorption of impurities, and provide more reliable wall conditions for the plasma discharge operation of the fusion device.

[0048] The present invention is described in detail below with a specific embodiment:

[0049] A boron powder injection device is installed on the top of the spherical tokamak fusion device through a flange. The device is pre-treated by vacuuming and baking, and then loaded with boron powder with a particle size of 70 microns. Glow boronization is first carried out on the fusion device, using a mixed gas of diborane and hydrogen as a boron source for 3 hours. The initial boron film formed in the chamber of the fusion device is shown in Figure 2(a), and the thickness of the boron film is about 30nm.

[0050] After 60-100 high-intensity plasma discharge experiments, the average thickness of the boron film was measured by a quartz microcrystal film thickness meter to be about 20nm, and the film thickness was about 60% of the initial thickness. Statistical calculations showed that the loss rate of the boron film was about 0.15nm / discharge, and the boron film was unevenly damaged after being bombarded by plasma, especially in the limiter plasma configuration. The film layer on the central column limiter was severely damaged after dozens of plasma bombardments, as shown in Figure 2(b).

[0051] After the stable limiter plasma configuration is formed through debugging, the deposited boron film is cleaned by 5-10 shots of plasma discharge to prepare for the injection of boron powder. The results of the preliminary experiments show that the injection rate of boron powder>15mg / s is prone to cause plasma discharge rupture, resulting in the collapse of the plasma current curve, as shown in Figure 3(a); the injection rate of boron powder at 5-8mg / s can effectively improve the plasma discharge quality, as shown in Figure 3(b), so the preferred boron powder injection parameters are shown in Table 1, the injection rate of boron powder is 8-10mg / s, combined with Figure 3(b), the injection of boron powder begins at 1.3s of plasma discharge, and enters the upper scraping layer of plasma after about 0.45s of free fall (the plasma scraping layer is the boundary plasma outside the outermost closed magnetic surface of the tokamak magnetic field, and is the main plasma layer for the interaction between the plasma and the wall material), and is ablated and ionized in the plasma discharge platform period of about 1.75s. The duration of a single injection is 2s. Under this condition, a single injection of boron powder can be achieved on the surface of the central column of the fusion device (15m 2 ) deposited a boron film with a thickness of 0.3 nm, which is greater than the consumption rate of a single plasma bombardment (0.15-0.25 nm / time). In this embodiment, five consecutive boron powder injection experiments were carried out under this parameter condition.

[0052] Table 1 Boron powder injection parameters

[0053]

[0054] It should be noted that the gun number in Table 1 refers to the number of the fusion device discharge. For example, the number 12063 represents the 12063 plasma discharge since the fusion device was built. In this embodiment, the numbers 12063 and 12069 represent that the discharge of the gun does not involve the operation of injecting boron powder, and the discharge of the guns 12064, 12065, 12066, 12067 and 12068 all involve the operation of injecting boron powder.

[0055] As shown in FIG4(a), the high-speed camera can be used to observe that the boron powder is completely melted and glows after entering the plasma. As shown in FIG4(b), the boron powder is completely ionized and rotates under the action of the magnetic field to fill the entire vacuum chamber.

[0056] Combination Figure 5 and Figure 6 By comparing the oxygen and metal impurity data of the #12063 plasma discharge experiment before boron powder injection (the last plasma discharge before boron powder injection in this embodiment) and the #12069 plasma discharge experiment after boron powder injection (the first plasma discharge after boron powder injection in this embodiment), it can be seen that boron powder injection can effectively reduce the radiation intensity of impurities.

[0057] Combination Figure 7 , observing the vacuum chamber, it was found that the coating was successfully achieved on the center column limiter.

[0058] From the statistical data of carbon impurity radiation intensity in Figure 8(a), it can be seen that after only glow boriding, the radiation intensity of carbon impurities began to increase after about 240 plasma discharges. From Figure 8(b), it can be seen that after the comprehensive boriding process combining glow boriding and boron powder injection, the radiation intensity of carbon impurities began to increase after about 330 high-intensity plasma discharges.

[0059] It can be seen from the above results that the boronization process of the present invention can effectively prolong the life of the boron film, improve the quality of the boron film, further suppress the impurity radiation intensity of the fusion vacuum chamber, alleviate the uneven problem of the boron film after bombardment, and provide better wall conditions for plasma discharge operation.

[0060] In summary, the tokamak boronization process provided by the present invention supplements and upgrades the existing boronization process, establishes a processing cycle of the boronization process based on the statistical results of the boron film loss rate evaluation and the impurity radiation intensity, and adopts real-time boron powder boronization as a supplement to the glow boronization technology, which can effectively extend the life of the boron film, improve the quality of the boron film, alleviate the problem of unevenness of the boron film after bombardment, and further enhance the boron film's ability to suppress the adsorption of impurities, providing better wall conditions for the plasma discharge operation of the fusion device.

[0061] The above-mentioned embodiments only express several implementation methods of the present invention, and the description thereof is relatively specific and detailed, but it cannot be understood as limiting the scope of the patent of the present invention. It should be pointed out that, for ordinary technicians in this field, several variations and improvements can be made without departing from the concept of the present invention, which all belong to the protection scope of the present invention. Therefore, the protection scope of the patent of the present invention shall be subject to the attached claims.

Claims

1. A tokamak boronization process, characterized in that: The following steps are involved: Step 1, depositing an initial boron film of a preset thickness on a first wall of the fusion device so that the plasma discharge can operate stably; Step 2, detecting the thickness of the boron film deposited on the first wall in real time, and when the current boron film thickness is a preset percentage of the initial boron film thickness, debugging a preset plasma configuration in the fusion device, and injecting boron powder into the fusion device under preset process conditions through a boron powder injection device connected to the fusion device, thereby achieving the deposition of a boron film on a preset position of the fusion device; the particle size of the boron powder is 50-100 μm; The process conditions for injecting boron powder into the fusion device are: the injection rate of boron powder is 2-12 mg / s; The boron powder injection operation is performed multiple times continuously, and the duration of each boron powder injection is 1.3-3.3s.

2. The Tokamak boronization process according to claim 1, characterized in that: In the step 1, a mixed gas of hydrogen and diborane is dissociated under the action of glow plasma, and an initial boron film with a thickness of 30-50 nm is deposited on the first wall of the fusion device by plasma vapor deposition.

3. The Tokamak boronization process according to claim 1, characterized in that: In step 2, when the thickness of the current boron film is 50-60% of the thickness of the initial boron film, boron powder is injected into the fusion device.

4. The Tokamak boronization process according to claim 1, characterized in that: In step 2, the purity of the boron powder is greater than 99.9%.

5. The Tokamak boronization process according to claim 1, characterized in that: In the step 2, before injecting the boron powder into the fusion device, the boron powder is stored in a vacuum environment at 950-1100° C. for a period of time to remove residual volatile impurities and moisture in the boron powder.

6. The Tokamak boronization process according to claim 1, characterized in that: In the step 2, under the preset plasma configuration obtained by debugging, the plasma current is maintained at 110 kA for more than 3 seconds during the discharge plateau period, and the hot electron temperature of the edge plasma is greater than 30 eV.

7. The Tokamak boronization process according to claim 1, characterized in that: In step 2, the injection rate of the boron powder is 8-10 mg / s; and the duration of each injection of the boron powder is 1.5-2.5 s.

8. The Tokamak boronization process according to claim 1, characterized in that: In the step 2, before injecting boron powder into the fusion device, the boron film deposited on the first wall is plasma cleaned.

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