A method, computer-readable storage medium and system for suppressing the 2 / 1 neoclassical tearing mode in a tokamak

Abstract

A method, computer-readable storage medium and system for suppressing the 2 / 1 neoclassical tearing mode of a tokamak. The present invention obtains information related to the propagation, absorption and current drive of electron cyclotron (EC) waves through a ray tracing program, and obtains the peak value, full height width and radial position of the driving current peak under the EC wave Ohkawa mechanism dominant current drive (OKCD) on the 2 / 1 resonant magnetic surface. If the current profile of the OKCD is approximately Gaussian distribution, the obtained characteristic parameters are substituted into the modified Rutherford equation to calculate the suppression effect of OKCD on the 2 / 1 neoclassical tearing mode (NTM), and the EC wave emission parameters and the minimum EC wave power required for effectively suppressing the 2 / 1NTM are determined. The present invention is more likely to drive local non-inductive current to replace the missing bootstrap current on the 2 / 1 rational magnetic surface, thereby successfully and effectively suppressing the 2 / 1NTM. Compared with the previous solution of suppressing NTM using ECCD, the present invention has a better suppression effect on the 2 / 1 mode and a smaller EC wave frequency.

Description

Technical Field

[0001] The present invention relates to the technical field of magnetohydrodynamic instability control under discharge of a tokamak device, and in particular to a method for suppressing a 2 / 1 neoclassical tearing mode of a tokamak, a computer-readable storage medium and a system. Background Art

[0002] Neoclassical tearing modes (NTMs) are the most dangerous magnetohydrodynamic instabilities in the Tokamak magnetic confinement experiment, and usually occur on magnetic surfaces where the safety factor q of the Tokamak is a rational number (rational magnetic surfaces, or rational surfaces). The two neoclassical tearing modes generated at the rational surface positions of q = m / n = 3 / 2 (where m is the polar modulus and n is the toroidal modulus) and q = 2 / 1 are the most dangerous modes, and are called 3 / 2 mode and 2 / 1 mode respectively.

[0003] At present, the use of electron cyclotron wave current drive (ECCD, current drive dominated by the Fisch-Boozer mechanism) technology has achieved quite good results in experiments to suppress the 3 / 2 mode. However, for the 2 / 1 mode, since it is closer to the edge of the tokamak plasma, it is difficult to achieve effective suppression using the existing electron cyclotron wave current drive technology. Summary of the invention

[0004] One of the purposes of the present invention is to provide a new method for suppressing the 2 / 1 neoclassical tearing mode in a tokamak. The method deposits the power of the electron cyclotron wave on the low-field side of the tokamak device, and uses the Ohkawa mechanism dominant current drive (OKCD) to obtain a local non-inductive current on the 2 / 1 rational surface for suppressing the 2 / 1 NTM. Compared with depositing the wave power on the high-field side and using ECCD to generate a current on the 2 / 1 rational surface, this method makes it easier to drive the local non-inductive current to replace the missing bootstrap current on the 2 / 1 rational surface, thereby successfully and effectively suppressing the 2 / 1 NTM.

[0005] To achieve the above object, the method for suppressing the Tokamak 2 / 1 neoclassical tearing mode adopted by the present invention comprises the following steps:

[0006] S1. Determine the magnetic field B of the device based on the parameters of the large ring radius R0 and the small circle cross-section radius a of the tokamak device. T The size of the electron cyclotron wave and the wave parameters of the electron cyclotron wave are used to make the current driven by the Ohkawa mechanism the dominant current. By changing the emission angle in the ray tracing program, the peak value j of the driving current under the condition that the EC wave Ohkawa mechanism is dominant on the q=2 resonant magnetic surface is obtained. CD,max , drive current e -1 Full height width w dep and the radial position ρ where the peak value of the driving current is locatedec , and the peak position of the driving current and the 2 / 1 magnetic surface ρ 2 / 1 The offset size between

[0007] S2, EC wave parallel refractive index N calculated by ray tracing program || and the driving current density j CD Determine which mechanism is dominant in driving the current generated by the EC wave:

[0008] If N || *j CD >0, it is the OKCD driving current driven under the dominant Ohkawa mechanism, and step S3 is executed;

[0009] If N || *j CD <0, it is the ECCD driving current driven under the dominant Fisch-Boozer mechanism, and then returns to step S1;

[0010] S3. Compare the calculated OKCD distribution with the Gaussian distribution fitted according to the distribution characteristic parameters to verify whether the OKCD driving current distribution is similar to the Gaussian distribution. The expression for Gaussian fitting according to the calculated characteristic parameters is shown in formula (1):

[0011]

[0012] If the OKCD driving current distribution calculated by the ray tracing program is close to the Gaussian distribution, then step S4 is executed, otherwise, the process returns to step S1;

[0013] S4, substituting each characteristic parameter of the OKCD driving current obtained in step 1 into the modified Rutherford equation to calculate the suppression effect of OKCD on the 2 / 1 mode, and determining the EC wave emission parameters and the minimum EC wave power required to effectively suppress the 2 / 1 mode;

[0014] The modified Rutherford equation is:

[0015]

[0016] In the above formula, r s Δ′ o is the linear stabilizing term of the balancing current, r s δΔ′ o is the equilibrium current stabilization term caused by the external driving current, r s Δ′ BS is the disturbance term caused by the loss of bootstrap current leading to the increase of the width of the magnetic island in the neoclassical tearing mode, r s Δ′ CD The external localized drive current replaces the stabilizing term of the missing bootstrap current, r sΔ′ H is the stabilizing term caused by the electron cyclotron wave heating effect;

[0017] S5. According to the EC wave emission parameters for effectively suppressing the 2 / 1 mode and the required minimum EC wave power obtained in step S4, the EC wave emission parameters and EC wave power values ​​of the Tokamak device are adjusted accordingly.

[0018] Further, in step S4, the linear stabilizing term r of the balancing current s Δ′ o =-m=2; Balance current stability term r caused by external drive current s δΔ′ o The specific expressions of are shown in equations (3)-(5):

[0019]

[0020]

[0021] F(x)=1-2.92x+2.02x 2 -0.40x 3 (5);

[0022] Where x = x dep / w dep , x dep =r dep -r s , r dep =ρ ec ·a,r s =ρ m / n a, k are the elongation ratios of the tokamak device, D mod is the modulation duty cycle of the current drive, μ0 is the vacuum permeability, L q is the characteristic length of the equilibrium gradient, B θ is the magnitude of the poloidal magnetic field;

[0023] The perturbation term r of the growth of the width of the magnetic island in the neoclassical tearing mode due to the absence of the bootstrap current s Δ′ BS The expressions of are shown in equations (6)-(7):

[0024]

[0025]

[0026] Among them, W marg is the critical magnetic island width. When the width of the magnetic island reaches this width, the growth rate of the magnetic island is the largest. BS is the bootstrap current, T e is the electron temperature, T iis the ion temperature, n e is the electron density; except for equation (7), j BS It can also be calculated by the Sauter model;

[0027] The external localized driving current replaces the stabilizing term r of the missing bootstrap current s Δ′ CD The expressions of are shown in equations (8)-(16):

[0028]

[0029] F CD =N CD (w * )G CD (w * , x dep )M CD (w * , D mod ) (9);

[0030]

[0031]

[0032]

[0033]

[0034]

[0035]

[0036]

[0037] The stabilizing term r caused by the electron cyclotron wave heating effect s Δ′ H The expressions of are shown in (17)-(23):

[0038]

[0039]

[0040] F H =N H (w * )G H (w * , x dep )M H (w * , D mod ) (19);

[0041]

[0042]

[0043] g(w * )=0.00035w *4 -0.008w 3 +0.07w *2 +0.02w * +0.5 (22);

[0044]

[0045] Among them, j s =j || -j BS , j s is the balance current, ⊥ is the vertical thermal diffusivity, k B is the Boltzmann constant, P tot is the injected wave power.

[0046] In addition, in step S1, the wave power is deposited on the low-field side, and the diffusion area of ​​the electron cyclotron wave in the velocity space is just below the capture / passing boundary. At this time, the contribution of the current driven by the Ohkawa mechanism to the total current is much greater than that of the Fish-Boozer mechanism, making the current driven by the Ohkawa mechanism the dominant current.

[0047] Further, in step S1, under the given device magnetic field configuration and plasma temperature density and other profile conditions, a ray tracing program is used to determine the cyclotron angular frequency Ω of the magnetic field lines of electrons around the geometric center of the device. ce0 and EC wave angular frequency ω ec The ratio of lΩ ce0 / ω ec range and emission angle range, so that the OKCD peak current position is located on the 2 / 1 rational surface or close to the rational surface, where ω ec =2πf ec , f ec is the EC wave frequency, Ω ce0 =q e B T / m e is the cyclotron angular frequency of electrons around magnetic field lines, q e and m e are the electron charge and electron rest mass, B T is the magnetic field size at the center of the tokamak, l is the harmonic number of the EC wave, for the fundamental frequency ordinary mode EC wave, l = 1, and for the double frequency extraordinary mode EC wave, l = 2.

[0048] Specifically, in step S1, the emission angle includes a circumferential emission angle α and a poloidal emission angle β. The circumferential emission angle range of the effective OKCD near the 2 / 1 magnetic surface is: |180°-α|=15°~25°, and the poloidal emission angle β is determined by the position of the EC wave cold plasma resonance layer, the radial position of the 2 / 1 magnetic surface and the initial emission position of the EC wave; in the ray tracing program, the circumferential emission angle α is the angle between the projection of the wave vector of the electron cyclotron wave on the mid-plane and the large radius vector R of the tokamak device, and the poloidal emission angle β is the angle between the projection of the wave vector in the tokamak polo plane and the plane where Z is equal to a constant.

[0049] In step S4, the EC wave modulates the duty cycle D mod The setting range is between [0.4,0.6].

[0050] In one embodiment of the present invention, in step S1, the tokamak device is a medium-sized tokamak device with a small aspect ratio, and its aspect ratio R0 / a is in the range of [2.6, 2.9].

[0051] In one embodiment of the present invention, in step S1, the electron cyclotron wave Ohkawa mechanism dominates the frequency of the driving current lΩ ce0 / ω ec Set to 1.25±0.1 and emit from the mid-plane window.

[0052] In addition, the present invention also relates to a computer-readable storage medium storing a computer program, which is used to execute the above-mentioned method for suppressing the neoclassical tearing mode of Tokamak 2 / 1 when the computer program is run.

[0053] Furthermore, the present invention also relates to a system for suppressing a 2 / 1 neoclassical tearing mode of a Tokamak, comprising a data acquisition module, a data analysis module and an execution module, wherein the data analysis module communicates with the data acquisition module and the execution module;

[0054] The data acquisition module is used to obtain the parameters of the large ring radius R0 and the small circle cross-section radius a of the tokamak device. The data analysis module executes steps S1-S4 in the above method according to the parameters of the large ring radius R0 and the small circle cross-section radius a of the tokamak device obtained by the data acquisition module. The execution module adjusts the EC wave emission parameters and EC wave power values ​​of the tokamak device accordingly according to the EC wave emission parameters for effectively suppressing the 2 / 1 mode and the required minimum EC wave power calculated by the data analysis module.

[0055] The present invention uses the electron cyclotron wave Ohkawa mechanism as the dominant mechanism of current drive and fully suppresses the reverse current generated by the Fisch-Boozer mechanism, which can drive the local non-inductive current in the area with a normalized radius greater than 0.5, replacing the missing bootstrap current on the 2 / 1 rational magnetic surface, thereby effectively suppressing the 2 / 1NTM. Compared with the previous scheme of suppressing the new classical tearing mode of the tokamak by using electron cyclotron wave current drive (ECCD, current drive dominated by the EC wave Fisch-Boozer mechanism), this method has a better suppression effect on the 2 / 1 mode, requires a smaller frequency of EC waves, and can reduce the q when the tokamak device is discharged. 95 The value of (q 95 It is the safety factor value corresponding to 95% normalized flux position), which is particularly suitable for suppressing 2 / 1NTM in small-diameter tokamak devices, and can provide a new solution for the effective control of 2 / 1 neoclassical tearing mode in small-diameter tokamak devices at home and abroad (such as HL-2M device, JT-60SA device, etc.). BRIEF DESCRIPTION OF THE DRAWINGS

[0056] Figure 1 It is a flow chart of the method for suppressing the Tokamak 2 / 1 neoclassical tearing mode in the embodiment;

[0057] Figure 2 Schematic diagram of the low field side and 2 / 1 magnetic surface of the Tokamak device in the embodiment;

[0058] Figure 3 Two physical mechanism diagrams of electron cyclotron wave current drive in the embodiments;

[0059] Figure 4 A schematic diagram of the definition of the emission angle in the ray tracing program in the embodiment;

[0060] Figure 5 Schematic diagram of the large radius and small radius of the Tokamak in the embodiment;

[0061] Figure 6 M in the embodiment CD With the modulation duty cycle D mod Schematic diagram of the changes;

[0062] Figure 7 Schematic diagram of the result of 105 GHz OKCD suppressing 2 / 1 neoclassical tearing mode in the embodiment;

[0063] Figure 8 This is a schematic diagram of the result of 140 GHz ECCD suppressing the 2 / 1 neoclassical tearing mode in the embodiment. DETAILED DESCRIPTION

[0064] In order to help those skilled in the art better understand the improvements of the present invention relative to the prior art, the present invention is further described below in conjunction with the accompanying drawings and embodiments.

[0065] Figure 1 The process of suppressing the Tokamak 2 / 1 neoclassical tearing mode in this embodiment is shown. As shown in the figure, it specifically includes the following steps:

[0066] The first step is to determine the magnetic field B of the device based on the parameters of the large ring radius R0 and the small circle cross-section radius a of the tokamak device. T The size of the electron cyclotron wave and the wave parameters of the electron cyclotron wave are used to make the current driven by the Ohkawa mechanism the dominant current. By changing the emission angle in the ray tracing program, the peak value j of the driving current under the condition that the EC wave Ohkawa mechanism is dominant on the q=2 resonant magnetic surface is obtained. CD,max , drive current e -1 Full height width w dep and the radial position ρ where the peak value of the driving current is located ec , and the peak position of the driving current and the 2 / 1 magnetic surface ρ 2 / 1 The offset size between .

[0067] The second step is to calculate the parallel refractive index N of the EC wave according to the ray tracing program. || and the driving current density j CD Determine which mechanism is dominant in the current generated by the EC wave: If N || *j CD <0, it is the current driven by the dominant Fisch-Boozer mechanism, which is called ECCD. Under this condition, return to the first step and reset the emission angle in the ray tracing program; if N || *j CD >0, indicating that the current generated by the EC wave is driven by the dominant Ohkawa mechanism, which is called OKCD. In this case, proceed to the next step.

[0068] In the third step, the calculated OKCD distribution is compared with the Gaussian distribution fitted according to the characteristic parameters of the distribution to verify whether the OKCD driving current distribution is similar to the Gaussian distribution. The expression for Gaussian fitting according to the calculated characteristic parameters is shown in formula (1):

[0069]

[0070] If the OKCD driving current distribution calculated by the ray tracing program is close to the Gaussian distribution, the next step is executed, otherwise, the first step is returned.

[0071] The fourth step is to substitute the characteristic parameters of the OKCD driving current obtained in the first step into the modified Rutherford equation to calculate the suppression effect of OKCD on the 2 / 1 mode, and determine the EC wave emission parameters and the minimum EC wave power required to effectively suppress the 2 / 1 mode. The modified Rutherford equation is:

[0072]

[0073] In the above formula, r s Δ′ o is the linear stabilizing term of the balancing current, r s δΔ′ o is the equilibrium current stabilization term caused by the external driving current, r s Δ′ BS is the disturbance term caused by the loss of bootstrap current leading to the increase of the width of the magnetic island in the neoclassical tearing mode, r s Δ′ CD The external localized drive current replaces the stabilizing term of the missing bootstrap current, r s Δ′ H is the stabilizing term caused by the electron cyclotron wave heating effect.

[0074] It should be understood by those skilled in the art that for the neoclassical tearing mode with m=2 / n=1, the linear stabilizing term r of the equilibrium current is s Δ′ o =-m = 2; and the equilibrium current stabilization term r caused by the external drive current s δΔ′ o The specific expressions of are shown in equations (3)-(5):

[0075]

[0076]

[0077] F(x)=1-2.92x+2.02x 2 -0.40x 3 (5);

[0078] Where x = x dep / w dep , x dep =r dep -r s , r dep =ρ ec ·a,r s =ρ m / n a, k are the elongation ratios of the tokamak device, D mod is the modulation duty cycle of the current drive, μ0 is the vacuum permeability, L q is the characteristic length of the equilibrium gradient, B θ is the magnitude of the poloidal magnetic field;

[0079] The perturbation term r of the growth of the width of the magnetic island in the neoclassical tearing mode due to the absence of the bootstrap current s Δ′ BS The expressions of are shown in equations (6)-(7):

[0080]

[0081]

[0082] Among them, W marg is the critical magnetic island width. When the width of the magnetic island reaches this width, the growth rate of the magnetic island is the largest. BS is the bootstrap current, T e is the electron temperature, T i is the ion temperature, n e is the electron density. In addition to equation (7), j BS It can also be calculated using the Sauter model.

[0083] The external localized driving current replaces the stabilizing term r of the missing bootstrap current s Δ′ CD The expressions of are shown in equations (8)-(16):

[0084]

[0085] F CD =N CD (w * )G CD (w * , x dep )M CD (W * , D mod ) (9);

[0086]

[0087]

[0088]

[0089]

[0090]

[0091]

[0092]

[0093] The stabilizing term r caused by the electron cyclotron wave heating effect s Δ′H The expressions of are shown in (17)-(23):

[0094]

[0095]

[0096] F H =N H (w * )G H (w * , x dep )M H (w * , D mod ) (19);

[0097]

[0098]

[0099] g(w * )=0.00035w *4 -0.008w 3 +0.07w *2 +0.02w * +0.5 (22);

[0100]

[0101] Among them, j s＝ j ||- j BS , j s is the balance current, ⊥ is the vertical thermal diffusivity, k B is the Boltzmann constant, P tot is the injected wave power.

[0102] Finally, according to the EC wave emission parameters and the required minimum EC wave power for effectively suppressing the 2 / 1 neoclassical tearing mode calculated above, the EC wave emission parameters and EC wave power values ​​of the tokamak device are adjusted accordingly.

[0103] The following is an example of a medium-sized tokamak device with a small ring-diameter ratio (such as the HL-2M tokamak device) Figure 1 The effectiveness of the method shown in the figure, wherein the aspect ratio R0 / a of the HL-2M type tokamak device used to verify the effectiveness of the above method in this embodiment is 2.7, and the magnetic field B of the device is T = 2.25 T. Schematic diagram of the low field side and 2 / 1 magnetic surface of the tokamak device can be found in Figure 2 , Figure 3Two physical mechanisms of electron cyclotron wave current drive are shown, Figure 5 Schematic diagram of the large radius and small radius of the Tokamak.

[0104] In the first step, the size of the device magnetic field and the wave parameters of the electron cyclotron wave are appropriately selected: the device magnetic field B T =2.25T, the wave frequency is set to f ec =105GHz, select the unusual second harmonic mode, whose harmonic number l=2, and the wave is emitted from the mid-plane window on the low field side, so that the diffusion area of ​​the electron cyclotron wave in the velocity space is just below the capture / pass boundary. Under this condition, the contribution of the current driven by the Ohkawa mechanism to the total current will be much greater than that of the Fish-Boozer mechanism, becoming the dominant current driving mechanism. By changing the emission angle in the ray tracing program, the peak value j of the driving current under the condition that the Ohkawa mechanism of EC wave is dominant on the q=2 resonant magnetic surface is obtained. CD,max , drive current e -1 Full height width w dep and the radial position ρ where the peak value of the driving current is located ec , so we can also get the driving current peak position and 2 / 1 magnetic surface ρ 2 / 1 The offset between them can be determined by using a ray tracing program under the given device magnetic field configuration and plasma temperature density and other profile conditions to determine the cyclotron angular frequency Ω of the magnetic field lines of electrons around the geometric center of the device. ce0 and EC wave angular frequency ω ec Ratio (lΩ ce0 / ω ec ) range and emission angle range, so that the OKCD peak current position is located on the 2 / 1 magnetic surface or very close to the magnetic surface, where ω ec =2πf ec , f ec is the EC wave frequency, Ω ce0 =q e B T / m e is the cyclotron angular frequency of electrons around magnetic field lines, q e and m e are the electron charge and electron rest mass, B T is the magnetic field at the center of the tokamak, under effective OKCD, lΩ ce0 / ω ec The value of is about 1.25. l is the harmonic number of the EC wave. For the EC wave of the fundamental frequency ordinary mode (O1-mode), l = 1, and for the EC wave of the double frequency extraordinary mode (X2-mode), l = 2. The aforementioned emission angle includes the circumferential emission angle α and the polar emission angle β, see Figure 4As shown, in the ray tracing program, the toroidal emission angle α is the angle between the projection of the wave vector of the electron cyclotron wave on the mid-plane and the large radius vector R of the tokamak device, and the poloidal emission angle β is the angle between the projection of the wave vector in the tokamak poloidal plane and the plane where Z is equal to a constant. The toroidal emission angle range of the effective OKCD near the 2 / 1 magnetic surface is: |180°-α|=15°~25°, and the poloidal emission angle β is determined by the position of the EC wave cold plasma resonance layer, the radial position of the 2 / 1 magnetic surface and the initial emission position of the EC wave. In the curvilinear coordinate system, the general ray tracing program can use the geometric optics approximation to simulate the propagation and absorption of radio frequency waves in the plasma, and calculate the current generated by the non-inductive current drive of the radio frequency wave.

[0105] In addition, in the fourth step, in general, the EC wave modulation duty cycle D mod Set the range to [0.3,1.0], D mod = 1.0 corresponds to continuous EC wave injection into the plasma, Figure 6 Shows M CD With the modulation duty cycle D mod Here, D mod The setting range is between [0.4, 0.6]. Compared with the continuous injection condition, the suppression effect on the m=2 / n=1 neoclassical tearing mode is the best. At the same time, it should be pointed out that although the bootstrap current calculation model of equation (7) in the fourth step is relatively simple, it is accurate enough. Of course, in addition to equation (7), j BS It can also be calculated using the Sauter model, which is more accurate but more complex. The model takes into account the impact of the collision rate and is more consistent with the actual value.

[0106] Figure 7 and Figure 8 The results of suppressing the m=2 / n=1 neoclassical tearing mode by 105GHz OKCD and 140GHz ECCD on a small-diameter tokamak are shown respectively. TIt is set to 2.25T and the ring diameter ratio is 2.7. As can be seen from the figure, this embodiment successfully suppresses 2 / 1NTM in a small ring diameter ratio tokamak device by using the local current dominated by the electron cyclotron wave Ohkawa mechanism. This method is better than the previous technology using electron cyclotron wave current drive (ECCD, current drive dominated by the EC wave Fisch-Boozer mechanism) because under the same plasma equilibrium, this method requires the least power to completely suppress 2 / 1NTM, and it also requires a smaller frequency of EC waves. Therefore, the above method is particularly suitable for suppressing 2 / 1NTM in a small ring diameter ratio tokamak device, and can provide a new solution for the effective control of 2 / 1NTM in small ring diameter ratio tokamak devices at home and abroad (such as the HL-2M device, JT-60SA device, etc.).

[0107] It should be pointed out that the process of determining the EC wave emission parameters and the minimum EC wave power required for effectively suppressing the 2 / 1 mode in this embodiment can also be implemented with the help of a computer. For example, according to the algorithm logic for determining the EC wave emission parameters and the minimum EC wave power required for effectively suppressing the 2 / 1 mode in the embodiment, a corresponding computer program is written and encapsulated in a computer-readable storage medium. In this way, the above process of determining the EC wave emission parameters and the minimum EC wave power required for effectively suppressing the 2 / 1 mode can be executed by running the computer program. Of course, a system for suppressing the 2 / 1 mode of a tokamak can also be constructed based on existing computer technology. The system should include a data acquisition module, an execution module, and a data analysis module that communicates with the above two. The data analysis module obtains the parameters of the large ring radius R0 and the small circle cross-section radius a of the tokamak device through the data acquisition module (the data acquisition module can be a data input device) and executes the calculation process of determining the EC wave emission parameters and the minimum EC wave power required for effectively suppressing the 2 / 1 mode in the embodiment (based on the corresponding calculation program implementation), and the execution module adjusts the EC wave emission parameters and EC wave power values ​​of the tokamak device according to the calculation results of the data analysis module.

[0108] The above embodiments are preferred implementation schemes of the present invention. In addition, the present invention may also be implemented in other ways. Any obvious replacement without departing from the concept of the present technical solution is within the protection scope of the present invention.

[0109] In order to make it easier for ordinary technicians in the field to understand the improvements of the present invention over the prior art, some drawings and descriptions of the present invention have been simplified, and for the sake of clarity, some other elements are omitted in this application document. Ordinary technicians in the field should realize that these omitted elements may also constitute the content of the present invention.

Claims

1. A method for suppressing the 2 / 1 neoclassical tearing mode of a tokamak, characterized in that: The following steps are involved: S1. Determine the magnetic field B of the device based on the parameters of the large ring radius R0 and the small circle cross-section radius a of the tokamak device. T The size of the electron cyclotron wave and the wave parameters of the electron cyclotron wave are used to make the current driven by the Ohkawa mechanism the dominant current. By changing the emission angle in the ray tracing program, the peak value j of the driving current under the condition that the EC wave Ohkawa mechanism is dominant on the q=2 resonant magnetic surface is obtained. CD，max , drive current e -1 Full height width w dep and the radial position ρ where the peak value of the driving current is located ec , and the peak position of the driving current and the 2 / 1 magnetic surface ρ 2 / 1 The offset size between S2, EC wave parallel refractive index N calculated by ray tracing program || and the driving current density j CD Determine which mechanism is dominant in driving the current generated by the EC wave: If N || *j CD >0, it is the OKCD driving current driven by the dominant Ohkawa mechanism, and then step S3 is executed; If N || *j CD <0, it is the ECCD driving current driven under the dominant Fisch-Boozer mechanism, and then returns to step S1; S3. Compare the calculated OKCD distribution with the Gaussian distribution fitted according to the distribution characteristic parameters to verify whether the OKCD driving current distribution is similar to the Gaussian distribution. The expression for Gaussian fitting according to the calculated characteristic parameters is shown in formula (1): If the OKCD driving current distribution calculated by the ray tracing program is close to the Gaussian distribution, then step S4 is executed, otherwise, the process returns to step S1; S4, substituting each characteristic parameter of the OKCD driving current obtained in step 1 into the modified Rutherford equation to calculate the suppression effect of OKCD on the 2 / 1 mode, and determining the EC wave emission parameters and the minimum EC wave power required to effectively suppress the 2 / 1 mode; The modified Rutherford equation is: In the above formula, r s Δ′ o is the linear stabilizing term of the balancing current, r s δΔ′ o is the equilibrium current stabilization term caused by the external driving current, r s Δ′ BS is the disturbance term caused by the loss of bootstrap current leading to the increase of the width of the magnetic island in the neoclassical tearing mode, r s Δ′ CD The external localized drive current replaces the stabilizing term of the missing bootstrap current, r s Δ′ H is the stabilizing term caused by the electron cyclotron wave heating effect; S5. According to the EC wave emission parameters for effectively suppressing the 2 / 1 mode and the required minimum EC wave power obtained in step S4, the EC wave emission parameters and EC wave power values ​​of the Tokamak device are adjusted accordingly.

2. The method for suppressing the 2 / 1 neoclassical tearing mode of a tokamak according to claim 1, characterized in that: In step S4, the linear stabilizing term r of the balancing current s Δ′ o =-m=2; Balance current stability term r caused by external drive current s δΔ o The specific expressions of are shown in equations (3)-(5): F(x)=1-2.92x+2.02x 2 -0.40x 3 (5); Where x = x dep / w dep , x dep =r dep -r s , r dep =ρ ec ·a,r s =ρ m / n a, k are the elongation ratios of the tokamak device, D mod is the modulation duty cycle of the current drive, μ0 is the vacuum permeability, L q is the characteristic length of the equilibrium gradient, B θ is the magnitude of the poloidal magnetic field; The perturbation term r of the growth of the width of the magnetic island in the neoclassical tearing mode due to the absence of the bootstrap current s Δ′ BS The expressions of are shown in equations (6)-(7): Among them, W marg is the critical magnetic island width. When the width of the magnetic island reaches this width, the growth rate of the magnetic island is the largest. BS is the bootstrap current, T e is the electron temperature, T i is the ion temperature, n e is the electron density. In addition to equation (7), j BS It can also be calculated by the Sauter model; The external localized driving current replaces the stabilizing term r of the missing bootstrap current s Δ′ CD The expressions of are shown in equations (8)-(16): F CD =N CD (w * )G CD (w * ,x dep )M CD (w * ,D mod ) (9); The stabilizing term r caused by the electron cyclotron wave heating effect s Δ′ H The expressions of are shown in (17)-(23): F H =N H (w * )G H (w * ,x dep )M H (w * ,D mod ) (19); g(w * )=0.00035w *4 -0.008w *3 +0.07w *2 +0.02w * +0.5 (22); Among them, j s =j || -j BS , j s is the equilibrium current, χ⊥ is the vertical thermal diffusivity, k B is the Boltzmann constant, P tot is the injected wave power.

3. The method for suppressing the 2 / 1 neoclassical tearing mode of a tokamak according to claim 1, characterized in that: In step S1, the wave power is deposited on the low field side, and the diffusion area of ​​the electron cyclotron wave in the velocity space is just below the capture / passing boundary. At this time, the contribution of the current driven by the Ohkawa mechanism to the total current is much greater than that of the Fish-Boozer mechanism, making the current driven by the Ohkawa mechanism the dominant current.

4. The method for suppressing the 2 / 1 neoclassical tearing mode of a tokamak according to claim 1, characterized in that: In step S1, under the given device magnetic field configuration and plasma temperature density and other profile conditions, a ray tracing program is used to determine the cyclotron angular frequency Ω of the magnetic field lines of electrons around the geometric center of the device. ce0 and EC wave angular frequency ω ec The ratio of lΩ ce0 / ω ec range and emission angle range, so that the OKCD peak current position is located on the 2 / 1 rational surface or close to the rational surface, where ω ec =2πf ec , f ec is the EC wave frequency, Ω ce0 =q e B T / m e is the cyclotron angular frequency of electrons around magnetic field lines, q e and m e are the electron charge and electron rest mass, B T is the magnetic field size at the center of the tokamak, l is the harmonic number of the EC wave, for the fundamental frequency ordinary mode EC wave, l = 1, and for the double frequency extraordinary mode EC wave, l = 2.

5. The method for suppressing the 2 / 1 neoclassical tearing mode of a tokamak according to claim 1, characterized in that: In step S1, the emission angle includes a circumferential emission angle α and a poloidal emission angle β. The circumferential emission angle range of the effective OKCD near the 2 / 1 magnetic surface is: |180°-α|=15°~25°, and the poloidal emission angle β is determined by the position of the EC wave cold plasma resonance layer, the radial position of the 2 / 1 magnetic surface and the initial emission position of the EC wave; in the ray tracing program, the circumferential emission angle α is the angle between the projection of the wave vector of the electron cyclotron wave on the mid-plane and the large radius vector R of the tokamak device, and the poloidal emission angle β is the angle between the projection of the wave vector in the tokamak polo plane and the plane where Z is equal to a constant.

6. The method for suppressing the 2 / 1 neoclassical tearing mode of a tokamak as claimed in claim 2, characterized in that: In step S4, the EC wave modulation duty ratio D mod The setting range is between [0.4, 0.6].

7. The method for suppressing the 2 / 1 neoclassical tearing mode of a tokamak according to claim 1, characterized in that: In step S1, the tokamak device is a medium-sized tokamak device with a small aspect ratio, and its aspect ratio R0 / a ranges from [2.6, 2.9].

8. The method for suppressing the 2 / 1 neoclassical tearing mode of a tokamak as claimed in claim 4, characterized in that: In step S1, the frequency of the electron cyclotron wave Ohkawa mechanism driving the current is lΩ ce0 / ω ec Set to 1.25±0.1 and emit from the mid-plane window.

9. A computer-readable storage medium, characterized in that: A computer program is stored, and when the computer program is run, it is used to execute the method for suppressing the 2 / 1 neoclassical tearing mode of a tokamak as described in any one of claims 1 to 8.

10. A system for suppressing the 2 / 1 neoclassical tearing mode of a tokamak, characterized in that: It includes a data acquisition module, a data analysis module and an execution module, wherein the data analysis module communicates with the data acquisition module and the execution module; The data acquisition module is used to obtain the parameters of the large ring radius R0 and the small circle cross-section radius a of the tokamak device. The data analysis module executes steps S1-S4 in claims 1-8 according to the parameters of the large ring radius R0 and the small circle cross-section radius a of the tokamak device obtained by the data acquisition module. The execution module adjusts the EC wave emission parameters and the EC wave power value of the tokamak device accordingly according to the EC wave emission parameters and the required minimum EC wave power for effectively suppressing the 2 / 1 mode calculated by the data analysis module.

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