JP3085560B2 - Fusion device and its plasma control method and control device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a nuclear fusion device and a plasma control device thereof, and more particularly to a nuclear fusion device by reducing the amount of unnecessary high-energy escape electrons generated during plasma disruption by controlling a magnetic field. The present invention relates to a plasma control device and the like suitable for preventing damage to a plasma facing wall of a fusion device.

[0002]

2. Description of the Related Art In a nuclear fusion device, a dilute hydrogen gas is placed in a donut-shaped vacuum vessel, and the magnetic flux (flux generated by a current transformer magnetic field) interlinking with the vacuum vessel is changed, so as to rotate in a circular direction (toroidal direction). ) Is supplied with a current (plasma current) to bring the hydrogen gas into a plasma state. However, sometimes the plasma becomes unstable and the plasma current quickly increases (approximately 10
A phenomenon called disruption that disappears (during ms) occurs. At this time, the one-way voltage Vl in the toroidal direction along the plasma becomes a maximum of several hundred volts or more, and electrons in the plasma are accelerated by this voltage to generate runaway electrons circling at high speed in the toroidal direction. Such runaway electrons eventually collide with and damage the plasma facing wall in the vacuum vessel.

Heretofore, the mechanism of the generation of runaway electrons and the collision with the vacuum vessel wall has not been understood, and there has been no clear policy regarding the countermeasures. As a conventional technique related to the control associated with the disruption, there is one disclosed in Japanese Patent Publication No. 1-14555 (see FIG. 2).

In this prior art, in order to reduce an eddy current and an electromagnetic force generated in a structural material due to a high voltage at the time of extinction of a plasma current, a Rogowski coil 25, 26, the output of which is amplified through amplifiers 27 and 27, respectively, and then input to the differential amplifier 28 to generate a signal 30 proportional to the time change dIv / dt of the vacuum vessel current Iv. The comparator 29 outputs the signal 3
0 is compared with the limit value 31 of dIv / dt, and an alarm signal 33 is output based on the comparison result. After the signal 30 is integrated by the integrator 5, the signal 30 is compared with the limit value 32 of the vacuum vessel current Iv, and an alarm signal 33 is output based on the comparison result. After the alarm signal is detected, control is performed so that the eddy current flowing in the apparatus does not become excessive, that is, the vacuum vessel current Iv does not become excessive.

As described above, the conventional protection device at the time of disruption is a combination of a device for preventing an excessive electromagnetic force of a fusion device structural material with a plasma control device.

An apparatus having no countermeasures against such a disruption is disclosed in, for example, JP-A-63-210798.
As described in Japanese Patent Application Laid-Open Publication No. H10-107, the precursor is detected before the disruption occurs, and the plasma is stabilized while the discharge is stopped slowly.

[0007]

Problems to be Solved by the Invention
In the prior art described in Japanese Patent No. 98, the fusion device is slowly stopped by detecting a precursor of the disruption. However, it is intended to extend the time until the disruption and to stabilize the plasma during that time. Is what you do. However, with the current technology, it is unavoidable to completely avoid the disruption, and once the precursor of the disruption occurs, the time to the disruption can be extended, but the disruption itself must be avoided. You cannot wake it up slowly.

In the prior art described in Japanese Patent Publication No. 1-15555, measures against runaway electrons are not taken into consideration, and the soundness of the apparatus can be maintained against a mechanical load. No countermeasures are taken against damage to the vacuum vessel plasma facing surface. In order to consider this countermeasure, it is first necessary to consider the generation mechanism of runaway electrons.

FIG. 3 shows an example of the results of an experiment conducted by the present inventors regarding disruption in a small tokamak apparatus (Hitachi Tokamak HT-2). 5 shows a temporal change of a waveform of a plasma current Ip, a poloidal magnetic field Bp, and a vacuum vessel current Iv at the time of disruption. The plasma current Ip disappears in about 1 ms due to the disruption after time 19.4 ms. The resistance of one cycle Ωv of the vacuum vessel is about 14 mΩ, and the voltage of one cycle Vl is used during disruption.

[0010]

(Equation 1)

The change over time of Iv indicates that the one-cycle voltage is large at the time of disruption.

In the case of FIG. 3, it can be seen that the one-cycle voltage has increased to about 30V. Runaway electrons are generated by the increase in the one-cycle voltage. FIG. 4 shows the magnetic field configuration in the middle of the disruption obtained as a result of the magnetic field analysis for obtaining the equilibrium magnetic field configuration around the plasma using the measured magnetic field as an input.

The time at which the magnetic field analysis was performed is indicated by arrows a,
The time shown by b is 19.4 ms and 19.8 ms. The region indicated by the set of points is the region where the plasma current is present in the magnetic field analysis, and is the region where the plasma is present. FIG.
In the magnetic field configuration shown in (a), in the region inside the donut-shaped magnetic surface (the cross section of which is indicated by a + mark in FIG. 4A),
The lines of magnetic force do not come into contact with the vacuum vessel wall or the limiter, and the temperature of the electrons in the plasma existing in this region is high and is easily accelerated by the electric field. This is because the electrons move along the lines of magnetic force and move on the same magnetic surface, so that the electrons in this region do not collide with a plasma-facing structure such as a vacuum vessel or a limiter. Therefore, the fast runaway electrons are
This is generated in a region near the magnetic axis 30 (the central axis of the magnetic surface 40) in FIG.

On the other hand, in FIG. 4 (b), the magnetic axis has moved out of the vacuum vessel and is not present in the plasma, and there is no magnetic surface that does not come into contact with the structure (limiter, vacuum vessel, etc.). The state is shown. Therefore, runaway electrons are not generated. Therefore, it has been experimentally revealed that it is desirable to reduce the plasma current in the state of the magnetic surface as shown in FIG. 4B in order to reduce the damage caused by the escaped electrons during the disruption.

However, when the conventional control system is used, the above points are not taken into consideration, and the waveform tends to be disrupted as shown in FIG. In this disruption, after the plasma current starts to decay, control is performed to return the magnetic axis 30 to the center of the vacuum chamber by negative feedback control of the plasma current and the position and shape control system. It has a repeating waveform. During the increase and decrease of the plasma current, the magnetic field configuration alternates between the states shown in FIGS. 4A and 4B, and the high energy generated during the magnetic field configuration shown in FIG. It is repeated that the runaway electrons collide with the wall when moving to the magnetic field configuration of FIG. 4 (b). As a result, as shown in FIG.
Increases, and each time the runaway electrons collide with the wall, high-energy X-rays (HX) are emitted. During this time, the one-cycle voltage Vl and the plasma current Ip repeatedly increase and decrease. As a result, high-energy runaway electrons collide with the plasma facing surface many times, resulting in increased damage. In a fusion device, it is necessary to reduce this damage as much as possible for safe operation and maintenance of the device. In particular, in a large-scale fusion device, the round-trip voltage increases, so that measures to avoid damage due to runaway electrons are indispensable.

It is an object of the present invention to provide a nuclear fusion device with reduced damage caused by runaway electrons and a plasma control device thereof.

[0017]

The object of the present invention is to detect the occurrence of disruption in a fusion device having a plasma control device that controls a plasma current, a position, and a cross-sectional shape by adjusting a poloidal magnetic field. This is achieved by providing means for changing the plasma position or the magnetic axis position outside the vacuum vessel.

[0018]

According to the present invention, at the time of the disruption, the state is immediately shifted to the magnetic field configuration as shown in FIG. 4B, and the plasma current is attenuated. In other words, when the movement of the magnetic axis is detected and this movement becomes large and the decay of the plasma current cannot be avoided, or when the current decay due to the disruption is observed, the state shown in FIG. Magnetic field control is performed to shift to the magnetic field configuration and maintain this state.

For example, an operation as shown in FIG. 6 is performed by the control system. FIG. 6 shows a plasma current Ip, a plasma position X,
The waveform at the time of the disruption of the one-cycle voltage Vl and the high-energy X-ray HX is shown. At the plasma position X, the solid line is the movement of the plasma, while the broken line is the target value of the control system for controlling the plasma position. At the time of the arrow, the control system determines that it is inevitable that the plasma current disappears, as indicated by the dotted line, and moves the target value of the plasma position from the center of the vacuum vessel to the outside of the vacuum vessel. As a result, the disruption as shown in FIG. 5 in which runaway electrons are repeatedly generated is avoided.

[0020]

An embodiment of the present invention will be described below with reference to the drawings. A fusion device according to an embodiment of the present invention having a plasma control device that controls a plasma current, a position, and a cross-sectional shape by adjusting a poloidal magnetic field, a magnetic axis movement detector that detects movement of a magnetic axis, A plasma position and shape control system having a function of adjusting the poloidal magnetic field is provided. When the magnetic axis detector detects a magnetic axis movement exceeding a predetermined limit value, the magnetic axis detector outputs a command signal for changing a control target value to the plasma position and shape control system, and moves the magnetic axis to the plasma region in the vacuum chamber. It is controlled to shift to a position deviated from the position and maintain that position. As a result, it is possible to avoid a situation in which the magnetic axis is restored in the plasma and runaway electrons are repeatedly generated.

The detection of the movement of the magnetic axis includes, for example, a method using a magnetic detector and a method using a radiation intensity distribution of low energy X-rays. Among the methods using a magnetic detector, FIG.
As shown in Fig. 3, there is a method for obtaining the equilibrium magnetic field of the entire plasma region using data from a large number of magnetic detectors. However, a method for obtaining the equilibrium magnetic field more easily can be devised from the experimental results shown in Fig. 3.

FIG. 7 shows the moving direction 20 of the plasma 2, the vacuum vessel 1, and the arrangement of the magnetic detectors (the inner magnetic detector 3 and the outer magnetic detector 4). In such a system, the time change of the magnetic field detected at the time of the disruption is shown as a measured value inside and outside Bp in the center graph of FIG. Since the plasma moves toward the vacuum vessel wall, a toroidal current in the same direction as the plasma current strongly flows through the vacuum vessel wall in the plasma movement direction at the end of the disruption. Therefore, when the plasma is stable, the vacuum vessel 1
As a result, the plasma current existing at the center of the magnetic field moves to the vacuum vessel wall in the moving direction, the direction of the poloidal magnetic field near the inner magnetic detector 3 is reversed, and the sign of the output BpIN is also reversed. By detecting the sign of BpIN, it can be immediately detected that the magnetic axis has moved.

As shown in the example of FIG. 3, the outputs (BpIN, BpOUT) of the outer and inner magnetic detectors are initially BpIN> BpOUT, but after the magnetic axis has moved due to the disruption. Since BpOUT> BpIN, the output Bp of the outer magnetic detector
By comparing the size of IN and the inner magnetic detector BpOUT,
Magnetic axis movement can be detected. If there is an internal structure inside the vacuum vessel and a current can flow through the structure in the toroidal direction, BpIN and BpOUT will be measured near the structure.

On the other hand, the low-energy X-rays SX are strongly emitted at a place where the plasma pressure is large, and the plasma pressure is detected by utilizing the property of being maximized near the magnetic axis of the plasma. The magnetic axis can be detected by arranging many SX detectors with directivity in different directions and comparing the outputs to find the position where the maximum output can be obtained. If the movement of the magnetic axis position exceeds a preset limit value, it can be determined that the magnetic axis has moved. Further, when the magnetic axis moves and reaches the vacuum vessel wall, emission of the SX from the magnetic axis disappears, which can be used as the magnetic axis movement detecting means.

According to the plasma position / shape control system having the above-described magnetic axis movement detecting means and capable of changing the control reference signal, the generation of high-energy runaway electrons can be reduced. As a result, damage to the plasma facing surface in the vacuum vessel can be reduced.

Hereinafter, embodiments of the present invention will be specifically described.
FIG. 1 is a block diagram of a plasma control device of a nuclear fusion device according to one embodiment of the present invention. Unlike conventional control systems,
In the plasma control apparatus of the present embodiment, a magnetic axis movement detector 8 is provided. The output of the magnetic axis movement detector 8 is input to a reference signal generator 9 for position / shape control. Further, as the magnetic axis movement detector, an inner magnetic detector 3 and an outer magnetic detector 4 are arranged in pairs with respect to the vacuum vessel wall.

Outputs of the two magnetic detectors 3 and 4 are input to a position shape calculator 7 after passing through integrators 5 and 5. The position and shape calculator 7 calculates a plasma current Ip and a plasma surface position which are control parameters of the plasma. These control parameter signals 16, which are the calculation results, are output to the control arithmetic unit 10, where they are compared with a reference signal 18,
The comparison result is the command value 1 to the poloidal magnetic field coil power supply 11
7 is output.

Since it is not possible to know in advance which direction the plasma moves during the disruption, the magnetic detectors 3 and 4 paired on the inside and outside are arranged at various positions on the poloidal section. The position and shape calculator 7 used in the present embodiment detects the plasma position and outputs the signals BpIN and BpOUT of the magnetic detector pair BpIN and BpOUT arranged in a direction extending the deviation of the plasma from the reference position.
Is output to the magnetic axis movement detector. Therefore, the magnetic detector pair data in the moving direction is obtained from several magnetic detector pairs.
Data 14 is selected and output. The magnetic axis movement detector 8 receives the data 14 of the pair of magnetic detectors in the moving direction and detects that the magnetic axis has moved to the vicinity of the vacuum vessel wall based on the magnitude relationship and the sign. That is,

[0029]

(Equation 2)

Or

[0031]

(Equation 3)

If so, it is determined that the magnetic axis has moved.
The result of this determination is input to the reference signal generator 9 for position and shape control together with the information on the moving direction. In response to this signal, the reference signal generator 9 operates the reference signal so that the movement of the plasma is further increased and the magnetic axis moves out of the vacuum vessel. As a result, the poloidal magnetic field coil power supply does not recreate the magnetic axis of the plasma in the plasma, and does not repeatedly generate runaway electrons.

FIG. 8 shows an embodiment in which the movement of the magnetic axis position is detected from the soft X-ray radiation intensity distribution. The control of the plasma current / position / shape in the normal state is performed by magnetic field data, and a plasma position / shape calculator 7 exists. In the present embodiment, it is assumed that the magnetic axis moves up and down, and the soft X-ray detector array 22 is arranged on the side having the larger main radius. The individual detectors of the soft X-ray detector array observe only a specific portion of the plasma as indicated by the dotted line by the slit 24, and the entire array is like a pinhole camera.
Since soft X-rays have high radiation intensity near the magnetic axis, the magnetic axis exists in the direction of the line of sight of a detector that detects soft X-rays having high radiation intensity. Therefore, the soft X-ray radiation intensity distribution calculator 19 calculates the magnetic axis position from the radiation intensity distribution and outputs the magnetic axis position to the magnetic axis movement detector 8. A limit value is set in advance for the movement of the magnetic axis. When the limit value is exceeded, a magnetic axis movement signal 15 for notifying the reference signal generator 9 of the plasma current / position / shape that the magnetic axis movement has been detected is output. Output. In response to this result, the changed reference signal 18 is output to the control arithmetic unit 10, and the command current / voltage value 17 obtained as a result of the operation in accordance with the changed reference signal is output.
Is output to the power supply, and the coil current is adjusted. As a result, as shown in FIG. 5, the plasma current does not attenuate due to the disruption in which runaway electrons are repeatedly generated, and damage to the plasma facing wall due to runaway electrons can be reduced.

Conventionally, there have been many fusion devices in which the vacuum vessel wall is directly opposed to the plasma. However, as a future fusion device, there is a fusion device in which a structure is arranged in a vacuum vessel. FIG. 9 shows this example, in which a shell for stabilizing the plasma position is provided near the plasma in the vacuum vessel.
In such a fusion device, if the magnetic detector is arranged as shown in FIG. 1, the movement of the magnetic axis of the plasma cannot be measured with high accuracy. In this case, the stabilization of the plasma, which is arranged closer to the plasma, is performed. The magnetic field around the stabilizing shell 34 or the return current conductor 35 through which the return current flows and the current of the stabilizing shell itself are measured. In the example of FIG. 9, a shell magnetic detector 36 corresponding to the inner detector 3 and the outer magnetic detector 4 of FIG. 7 is disposed around the stabilizing shell 34. By using such a magnetic detector pair, it is possible to configure a device that functions similarly to the plasma control device of FIG. 1 even when a structure exists inside the vacuum vessel.

[0035]

According to the present invention, it is possible to reduce the generation of runaway electrons generated in the plasma current decay process at the time of disruption generated in the fusion device, and the runaway electrons collide with the plasma facing surface in the vacuum vessel. Damage can be reduced. As a result, there is an effect that the nuclear fusion device can be operated more stably.

[Brief description of the drawings]

FIG. 1 is a block diagram of a plasma control device according to one embodiment of the present invention.

FIG. 2 is a block diagram of a conventional plasma control device.

FIG. 3 is a graph showing the results of a disruption experiment on which the present invention is based with respect to a plasma current, a poloidal magnetic field, and a vacuum vessel current.

FIG. 4 is a diagram showing an example of a magnetic field configuration at the time of plasma current decay accompanying the disruption in FIGS. 3 (a) and 3 (b).

FIG. 5 is a diagram showing a waveform at the time of current decay due to disruption by a conventional control system and a generation state of runaway electrons.

FIG. 6 is a graph showing a waveform example at the time of disruption when the control system of the present invention is used.

FIG. 7 is a diagram showing an example of the arrangement of magnetic detectors used in the present embodiment.

FIG. 8 is a diagram showing an embodiment in which a detector for a magnetic axis using soft X-rays is used.

FIG. 9 is a diagram showing an example of a magnetic detector arrangement when a structure exists in a vacuum vessel.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Vacuum container, 2 ... Plasma, 3 ... Inner magnetic detector, 4
... Outside magnetic detector, 5 ... Integrator, 6 ... Output signal of magnetic detector, 7 ... Plasma position shape calculator, 8 ... Magnetic axis movement detector, 9 ... Reference signal generator, 10 ... Control arithmetic unit, 11
... Coil power supply, 12 ... Coil supply current, 13 ... Poloid magnetic field coil, 14 ... Magnet detector pair data in plasma movement direction, 15 ... Magnetic axis movement signal, 16 ... Control parameter signal, 17 ... Coil current voltage Command value, 18: Reference value of control parameter, 19: Soft X-ray radiation intensity distribution calculator, 20
... plasma moving direction, 21 ... vacuum vessel wall in plasma moving direction, 22 ... soft X-ray detector array, 23 ... line of sight of soft X-ray detector, 24 ... slit, 25 ... inner logo key coil, 26 ... outer logo key Coil, 27 ... Amplifier, 28
... operating amplifier, 29 ... comparator, 30 ... magnetic axis, 31 ... limit value of vacuum vessel current change, 32 ... limit value of vacuum vessel current, 33 ... alarm signal, 34 ... stabilization shell, 35 ... reflux current conductor, 36 ... Shell magnetic detector.

────────────────────────────────────────────────── ─── Continuation of front page (56) References JP-A-4-258789 (JP, A) JP-A-4-169894 (JP, A) JP-A-58-123493 (JP, A) JP-A-57-123 176697 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) G21B 1/00 H05H 1/00

Claims (10)

(57) [Claims] 1. A fusion apparatus for controlling a plasma current, a position, and a cross-sectional shape by adjusting a poloidal magnetic field, a magnetic axis movement detector for detecting a magnetic axis movement at the time of disruption, and a magnetic axis movement detector for detecting the magnetic axis movement. A nuclear fusion device, comprising: a reference signal generator for changing a reference signal for controlling a position of a magnetic axis when detected and shifting the magnetic axis to outside the vacuum vessel. 2. The nuclear fusion device according to claim 1, wherein the magnetic axis movement detector includes a pair of magnetic detectors on the plasma side and the anti-plasma side with respect to the vacuum vessel wall or the plasma facing wall. apparatus. 3. A fusion device for controlling a plasma current, a position, and a cross-sectional shape by adjusting a poloidal magnetic field, a calculator for calculating a plasma position and a cross-sectional shape from magnetic data, and a vacuum vessel wall or a plasma facing side. Detector group with multiple magnetic detector pairs arranged on the plasma side and anti-plasma side with respect to the wall, and plasma position / cross-sectional shape calculation with the function of selecting and outputting signals of the magnetic detector pairs in the direction of plasma movement Nuclear fusion device characterized by comprising a vessel. 4. A fusion device for controlling a plasma current, a position, and a cross-sectional shape by adjusting a poloidal magnetic field. When a movement of a magnetic axis due to a disruption is detected, a reference signal for control is changed to change a magnetic axis position. Nuclear fusion device provided with a reference signal generator having a function of transferring a laser beam out of a plasma region. 5. The nuclear fusion device according to claim 1, wherein a soft X-ray detector array is provided as the magnetic axis movement detector. 6. A fusion device that controls a plasma current, a position, and a cross-sectional shape by adjusting a poloidal magnetic field, detects a disruption, and outputs a reference signal of a plasma position or a magnetic axis position outside a plasma region. A fusion device comprising a reference signal generator for changing. 7. A fusion device that controls a plasma current, a position, and a cross-sectional shape by adjusting a poloidal magnetic field, when detecting a movement of a magnetic axis during a disruption.
A plasma control method comprising: changing a reference signal for controlling a position of a magnetic axis to shift the magnetic axis to outside the vacuum vessel. 8. A fusion device for controlling a plasma current, a position, and a cross-sectional shape by adjusting a poloidal magnetic field, forcibly moving a magnetic axis out of a vacuum vessel or a plasma region when a sign of disruption is detected. A plasma control method characterized by causing the plasma to extinguish by shifting to (c). 9. A plasma controller for a fusion device for controlling a plasma current, a position, and a cross-sectional shape by adjusting a poloidal magnetic field, means for detecting a magnetic axis movement at the time of disruption, and detecting the magnetic axis movement. Means for changing a reference signal for controlling the position of the magnetic axis when detected, and shifting the magnetic axis to outside the vacuum vessel. 10. A plasma controller for a fusion device for controlling a plasma current, a position, and a cross-sectional shape by adjusting a poloidal magnetic field, a means for detecting a sign of disruption, and forcing when the sign is detected. Means for causing the magnetic axis to move outside the vacuum vessel or outside the plasma region to extinguish the plasma.