JPH0447279B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a plasma position control device in a tokamak type nuclear fusion device.

A tokamak-type nuclear fusion device generates plasma by passing an electric current through a diluted gas in a vacuum container.

For this reason, a magnetic field B→ is applied from the outside, and the Lorentzka (I→
The plasma position can be controlled by applying p×B→). However, if the plasma position control is incomplete, the plasma moves within the vacuum chamber and eventually interacts with the walls of the vacuum chamber, limiters, etc., causing impurities to flow into the plasma and cooling the plasma.

In order to stabilize the plasma position, feedback plasma position control is performed in which the plasma position is detected in real time and the externally applied magnetic field (poloidal magnetic field) is adjusted in real time based on the detection result.

FIG. 1 shows the configuration of such a conventional plasma position control device, and shows the case of plasma horizontal position (large radius) control as plasma position control.

In the figure, 1 is a position detector, 2 is a position calculator, 3 is a control signal generator, 4 is a current control circuit, and 5
1 is a control coil current, 6 is a control coil, 7 is a plasma, 8 is a vacuum vessel, 9 is a limiter, 10 is a poloidal coil, 11 is a toroidal coil, 12 is a center column, 13 is a support frame, and 14 is a coil support.

In such a configuration, plasma 7 is generated in a limited area by limiter 9 in vacuum vessel 8. The position of the plasma 7 is in the vacuum container 8,
It is detected by a pair of position detectors 1 arranged in the horizontal plane of symmetry of the tokamak device. In the position calculation section 2,
A signal proportional to the plasma horizontal position is generated based on the position signal detected by the position detector 1, and is sent to the control signal generator 3. In this control signal generating section 3,
Calculations corresponding to control operations such as proportional integration and differentiation are performed to generate a control signal proportional to the target value of the control coil current 5 to be passed through the control coil 6 and sent to the current control circuit 4.

The current control circuit 4 causes a current 5 to flow through the control coil 6 based on this control signal, stabilizes the position of the plasma 7, and creates a magnetic field in the plasma region that stops the plasma 7 at a fixed position.

FIG. 2 shows the configuration of a position detector and a position calculation section of a conventional feedback position control system.

In the figure, 15 is a loop provided in the vacuum vessel 8 in a poloidal direction, 16 is a magnetic probe, 17 is the edge of the plasma, and 18 to 21
is an integrator, 22 and 23 are coefficient units, 24 and 25 are adders, and 26 is a subtracter. Other signs are 1st
They correspond to the same reference numerals in the figure.

The plasma position detection method shown in FIG. 2 will be explained below.

When the position of the plasma 7 is inappropriate, it interacts with the limiter 9, the wall of the vacuum vessel 8, etc. in FIG.
It is mainly around the plasma 7 and at the edge 17. Therefore, the edge 17 of this plasma 7, for example,
In the case of a circular shape as shown in the figure, it is desirable that it be concentric with the limiter 9. By the way, the edge 1 of plasma 7
7 is on the equal magnetic flux plane (φ=constant). Here, the magnetic flux φ is the magnetic flux contained in a circle created when a certain point on a poloidal cross section (a tight cross section of the doughnut-shaped vacuum vessel 8 as shown in Fig. 1) is made to go around in the toroidal direction. . Moreover, the lines of magnetic force run on the plane of equal magnetic flux. Therefore, if the tip of the limiter 9 defined by the surface facing the plasma 7, that is, the magnetic flux φl at the position closest to the plasma 7, is constant on the poloidal cross section, the outer edge 17 of the plasma 7 will form a concentric circle with the limiter 9. This will not cause any violent interaction with the limiter 9 or the like. The position detection method shown in Fig. 2 calculates the value Δφl of the magnetic flux at the tip of the limiter 9 provided on the inside and outside (hereinafter simply referred to as inside and outside) with the plasma 7 in between with respect to the center of the donut-shaped vacuum container. In particular, it is a method for determining the plasma position. The magnetic flux φ can be obtained by directly integrating the output voltage Vl of the loop 15 as shown in the following equation (1). In other words, it is expressed by the following equation.

φ=∫Vl dt (1) However, if the one-turn loop 15 is placed at the limiter tip, it will be damaged by the plasma 7, so the one-turn loop 15 is placed at a position farther from the plasma 7 than the limiter tip. Therefore, one round loop 15
Therefore, the following relational expression (2) holds true between the magnetic flux φo measured at the position Ro and the magnetic flux φl measured at the limiter position (position Rl) by the magnetic probe 16.

φl=φo+∂φ/∂R｜Ro(Rl−Ro) …(2) Here, R: position in the main radial direction By the way, the R dependence of the magnetic flux φl is determined by the magnetic field Bv and the following
The relationship is as shown in equation (3).

∂φ/∂R|Ro=2πRo Bv (3) Therefore, the magnetic flux φl can be measured using the following equation (4).

φl=φo+2πRo BvΔl …(4) Here, Δl=Rl−Ro In Fig. 2, the magnetic probe 16 and the loop 15
The outputs are integrated by integrators 19, 20 and 18, 21 to become signals Bv and φo, respectively. Bv
The signal is obtained by the coefficient multipliers 22 and 23 using equation (4), the second on the right side.
By calculating the sum of this signal and the φo signal, the magnetic fluxes φl _io and φl _put inside and outside the limiter tip position are determined. After this, the difference between the inner and outer magnetic fluxes is determined and used as a signal Δφl. This signal Δφl is linearly related to the center position ΔRp of the circle of the plasma outer edge 17, as shown in FIG.
ΔRp on the horizontal axis in FIG. 3 indicates the horizontal shift between the center of the circle of the plasma outer edge 17 and the center of the limiter circle. Further, in FIG. 3, the plasma 7 has a main radius Rp of 3.5 m and a small radius ^a p of 0.7 m, and the limiter tip positions are set to main radii R=2.8 m (inner side) and 4.2 m (outer side). Therefore, using FIG. 3, the output signal Δφl in FIG. 2 becomes the plasma position displacement ΔRp
It can be converted into , and is used in the feedback plasma position control system shown in FIG.

Conventionally, a control system using the plasma position detection method as described above is used, and in that case, the detector 15,
16 was often placed inside the vacuum container 8. However, in large-scale nuclear fusion devices, in order to deal with the complexity of the device, the difficulty of repair, and the reduction in reliability due to damage caused by plasma 7, the detectors 15 and 16 are placed in vacuum containers as shown in FIG. It is becoming necessary to place it outside of 8. But in this case,
In the position detection method shown in FIG. 2, eddy currents flowing through the vacuum vessel 8 (generated by magnetic field fluctuations due to changes in coil current, plasma current, and plasma position) cause errors in position measurement. In other words, the magnetic flux including eddy current is expressed by the following equation (5).

φl′e＝φoe＋2πRoBveΔl …(5) Here, φl′e: Magnetic flux estimated value from the measured value including eddy current at the limiter tip φoe: Magnetic flux measured value including eddy current at the one-round loop position Bve: Magnetic probe position However, as shown in FIG. 5, there is a singular point 27 where the magnetic flux direction due to eddy currents, that is, the magnetic flux gradient changes rapidly between the outer and inner walls of the vacuum vessel 8. Exists on the wall of. This means that a singular point exists between the detector provided outside the vacuum container and the limiter tip provided inside the vacuum container. In the method of detecting the plasma position by detecting the magnetic flux gradient from the plasma center as shown in equation (3), when estimating the magnetic flux gradient inside the vacuum vessel from the magnetic flux gradient outside the vacuum vessel, it is difficult to estimate the magnetic flux gradient at the singular point due to eddy currents. Rapid gradient changes will give magnitude errors to plasma position measurements.

Note that 28 indicates lines of magnetic force.

In other words, in the conventional position detection method of the plasma position control system, when the detector is placed outside the vacuum vessel in a large fusion device or fusion reactor,
The disadvantage was that the error in position measurement was large. In addition, even in small-sized experimental equipment, it is desirable to have a plasma position control device in which the detector is placed outside the vacuum chamber for ease of maintenance, but this poses the above-mentioned problems.

The purpose of the present invention is to detect the plasma position accurately and with less time delay even when the detector is placed outside the vacuum vessel, thereby weakening the interaction between the plasma and the vacuum vessel and preventing the generation of high-temperature plasma. An object of the present invention is to provide a plasma position control device that prevents damage to the wall of a vacuum vessel.

In order to achieve the above object, the present invention includes a detection means for detecting the position of the plasma outside a vacuum vessel in which plasma is generated, and a plasma position for controlling the plasma position based on a detected value by the detection means. In the control device, a correction means is provided for obtaining a measurement error of the plasma position based on an eddy current value of the wall of the vacuum vessel, and the detected value of the plasma position is corrected based on the measurement error obtained by the correction means. It is something.

In other words, the error is corrected using the eddy current in the vacuum vessel wall obtained in real time using a circuit equation related to eddy current for a signal proportional to the plasma position obtained using a detector such as a magnetic probe or a one-round loop. This is what I did.

First, the principle of the present invention will be explained.

The magnetic flux measurement error ∂φl′ due to the eddy current in equation (5) is given by the following equation (6) by subtracting φle from the true value of the magnetic flux.

Δφl′=φle−φl′e =φle−(φoe+2πRoBveΔl)…(6) Since each term on the right side of this equation is all proportional to the magnitude of the eddy current, find the eddy current value and depend on the current distribution. By multiplying the coefficients, the right side of equation (6) can be found.

That is, the following equation (7) is obtained.

Δφl'=KeIe...(7) Here, Ke: Coefficient dependent on eddy current distribution Ie: Eddy current value However, the flow path of this eddy current is not constant, and the coefficient
Ke is also not constant. The reason is that eddy currents
It is a superposition of several eigenmodes, such as a double-polar eddy current mode that generates a uniform vertical magnetic field, and a quadrupole eddy current mode that generates a quadrupole magnetic field, and the eddy current of each mode has a time constant between the modes. This is because they are different. This situation can be expressed as the following equation (8).

Ie(t)= 〓 ^m Cm(t)Jm …(8) Here, Jm: Unit current of the m-th mode Cm: Intensity coefficient of the m-th mode Considering each mode, in each mode, the current The distribution is constant. Since the flow path of the eddy current changes as the intensity of each mode changes relatively, equation (7) can be expressed as the following equation (9).

Δφl′= 〓 ^m Kem Cm(t)Jm …(9) Here, Kem: Correction coefficient for magnetic flux measurement error for eddy current in the m-th mode In addition, in equation (9), the correction coefficient Kem is a constant value,
Further, CmJm corresponds to the eddy current value Im of the m-th mode.

Next, a method for obtaining this eddy current value Im will be explained.

In each eigenmode, the current distribution does not change over time, so each mode can be considered to be a passive coil, and the circuit equation shown in equation (10) below is established.

dIm/dt=1/Lm(−ΣMmjdIj/dt−∂Mpm/
∂RpIpdRp/dt) − Rm/LmIm…(10) Lm: Self-inductance of m-th mode eddy current Mmj: Mutual inductance between m-th mode eddy current and j-th coil or plasma Rm: m-th mode Resistance value of eddy current flow path ∂Mpm/∂Rp: Plasma position dependence of mutual inductance of m-th mode eddy current and plasma Ip: Plasma current Ij: Coil current and plasma current Rp: Plasma horizontal position (10 ), the circuit constants Lm, Mmj, and Rm can be determined by calculation or experimentally, so if the current Ij of each coil out of the current Ij is determined using a shunt resistor or Rogowski coil, ( The eddy current value of each mode is determined by equation 10),
The magnetic flux measurement error can be corrected using equation (9).

Regarding the eddy current modes to be considered, the most important is the double-polar eddy current mode that generates a perpendicular magnetic field as shown in Figure 5 for circular plasma, and the quadrupole eddy current mode in the quadrupole magnetic field mode is considered. This will improve accuracy. This is because the magnetic field created by the coil that interacts with the vacuum vessel is only in these two modes near the vacuum vessel.

Compared to circular plasma, it is important to consider quadrupolar eddy currents in vertical inertia circular plasma, and
When performing vertical position control to suppress vertical position instability, it is also necessary to consider the eddy current mode that generates the horizontal magnetic field.

FIG. 6 shows the configuration of an embodiment of the plasma position control device according to the present invention, in which 30 is a correction section;
1 to 37 are coefficient units, 38 is an integrator, 39 to 43 are adders, 44 is a subtracter, and 45 is a differentiator. Other numerals correspond to the same numerals as those of the conventional apparatus shown in FIGS. 1 and 2. Also. The subscript el of the coefficient written in the block of the correction section 30 corresponds to m in equation (10).

The plasma position is one loop 15 as before.
The position calculation unit 2 calculates the magnetic flux at the inner and outer limiter tip positions measured by the magnetic probes 16 and 16.

The correction unit 30 is a part added according to the present invention, and this part includes the coefficient units 31 to 37 and the integrator 3.
8. It is composed of adders 39 to 43, etc., and has the function of calculating the above-mentioned equations (9) and (10).

Inputs to the correction unit 30 are the time rate of change I〓j of each coil and plasma current, and the rate of change R〓p of the plasma position. The current value can be obtained by differentiating the output of the Rogowski coil and the output of the shunt resistor.

The coefficient units 31 to 33 correspond to MmjdIj/dt on the right side of equation (10). A corresponding signal is generated, and the coefficient multiplier 34 calculates ∂Mpm/∂RpIpdRp/dt Create a signal corresponding to .

Next, the adders 39 to 41 calculate the sum of these sums, and thereby the first term on the right side of equation (10) is calculated. Next, the adder 42 subtracts the second term on the right side of equation (10) to create a signal proportional to the rate of change of the eddy current. The integrator 38 integrates this signal to obtain the eddy current Im. The coefficient unit 35 creates the second term on the right side of equation (10), and the coefficient unit 36 performs an operation of multiplying by the correction coefficient Kem of equation (9). Further, the coefficient multiplier 37 is provided depending on the number of types of eddy currents to be considered, and has the same function as the coefficient multiplier 36.

The adder 43 performs an operation of summing the right side of equation (9), and outputs the measurement error Δφl'. Further, the subtracter 44 subtracts the measurement error Δφl' obtained by the correction section 30 from the value Δφl obtained by the position calculation section 2 to obtain the plasma position Rp. The differentiator 45 calculates the rate of change Rp of the plasma position and inputs it to the correction unit 30.

The effect of this correction section 30 will be explained with reference to FIG.

Assuming that the main radius of the plasma is 3.5 m and the minor radius is 0.7 m, the outer diameter of the minor radius of the vacuum vessel is 1.0 m, and the wall thickness of the vacuum vessel is 0.06 m, the double-pole mode eddy current shown in Figure 5 is The time constant Lm/Rm is approximately 100ms.

In Figure 7, the plasma position curve 50 shifts from Ro to Rd in a ramp-like manner due to rapid heating of the plasma, and at this time, a detector is placed outside the vacuum vessel using the conventional detection method. In this case, the plasma position has a time constant of 100ms, as shown by curve 51.
measured with a certain degree of lag. However, the correction unit 30 outputs a signal such as the curve 52, corrects the time delay of the curve 51, and outputs a signal proportional to the actual position of the plasma as the curve 50.

FIG. 8 shows that the plasma current is as shown by curve 63.
It shows temporal changes in plasma current and plasma position when changing at a rate of 10 ⁷ A/S.

At this time, assuming that the plasma position does not change,
In the conventional method, a measurement error of about 0.035 m, that is, about 5% of the plasma small radius is given as shown by curve 61, but in the present invention, the correction section generates an output as shown in curve 62, so that a measurement error as shown in curve 60 is generated. It is possible to find the correct plasma position.

Note that the correction section 30 may be configured with a computer and the correction may be performed using its software, or the correction section 30 may be realized with an analog circuit.

As described above, according to the present invention, even when the detector is placed outside the vacuum vessel, errors in plasma position measurement due to vacuum vessel eddy currents can be corrected and the plasma position can be detected accurately. By controlling the plasma position based on the detection results,
The plasma position is stabilized, the interaction between the vacuum vessel wall and the plasma is reduced, and it is possible to prevent the inflow of impurities, increase in plasma temperature, and damage to the vacuum vessel wall.

[Brief explanation of drawings]

Figure 1 is a configuration diagram of a conventional plasma position control device, Figure 2 is a configuration diagram of the plasma position detection section in Figure 1, and Figure 3 is a diagram showing the relationship between the magnetic flux difference at the limiter position and the plasma position. , FIG. 4 is a diagram showing the detector placed outside the vacuum vessel, FIG. 5 is a diagram showing an example of magnetic field lines due to wall current of the vacuum vessel, and FIG. 6 is a configuration of an embodiment of the plasma position control device according to the present invention. figure,
FIG. 7 is a diagram showing the effect of the present invention when the plasma position changes, and FIG. 8 is a diagram showing the effect of the present invention when the plasma current changes. 1...Position detector, 2...Position calculation section, 7...
Plasma, 30...correction section.

Claims (1)

[Scope of Claims] 1. A plasma position control device comprising a detection means for detecting the position of the plasma outside a vacuum vessel in which plasma is generated, and controlling the plasma position based on a detected value by the detection means, A correction means for determining a measurement error of the plasma position based on an eddy current value of the wall of the vacuum container is provided, and the detected value of the plasma position is corrected based on the measurement error determined by the correction means. Plasma position control device.