JPS6116034B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a plasma control device in a plasma generator for nuclear fusion.

Conventionally, in small devices, the plasma discharge time was short, on the order of tens of milliseconds, so it was difficult to feedback control the various amounts of plasma.However, recently, large devices have been made, and plasma The discharge time has also become longer, ranging from hundreds of milliseconds to several seconds.
Therefore, in such a device, the plasma current value,
There is an opportunity for feedback control to maintain the position and shape at target values. However, even in such a device, when starting up the plasma current, there are large changes in the plasma current and each magnetic field coil current, and the starting up is done in a short time of about several tens of milliseconds, so it is difficult to control the various quantities of the plasma. It is difficult to control feedback. Therefore, a method has been considered in which the current in each coil is caused to flow according to a pre-program set in advance during start-up, and the plasma is feedback-controlled after the time period (flat top) during which the plasma current is maintained after the start-up is completed. ing. However, this method has problems with control during the transition from startup to flat top. This point will be explained with reference to the drawings.

FIG. 1 is a diagram for explaining the shape of a fusion plasma generator, in which a plasma current I is passed in an annular manner as shown in FIG. 1a. In reality, a toroidal magnetic field coil that creates a magnetic field to confine the plasma current in a ring is wound around the plasma current ring, and a vacuum device is provided to keep the area where the plasma current flows in a vacuum. However, it is omitted in the figure. Although only one poloidal magnetic field coil 2 is shown in the figure, it consists of a current transformer coil for flowing a plasma current and various control magnetic field coils for creating a magnetic field for holding the plasma at a predetermined position.

In the cross-sectional view shown in FIG. 1B, it is assumed that the plasma current is flowing in the direction shown. Due to its current and plasma pressure, the plasma current ring
In general, there is a force that tries to spread outward. This force must be counteracted by an inwardly directed force to keep the plasma in place. For this purpose, a vertical magnetic field coil (a type of poloidal magnetic field coil)
2a are arranged as shown, and a current is applied as shown. This coil current creates a vertical magnetic field as shown by the arrow in the figure. The electromagnetic force caused by this magnetic field and plasma current becomes an inward force. By adjusting the vertical field coil current so that both forces are equal, the plasma can be kept in place.

Next, the operating method of this apparatus will be explained with reference to FIGS. 2 and 3. In FIG. 2, 1a is the plasma self-inductance, 1b is the plasma resistance, and the plasma ring is represented in terms of a current circuit. 2
b is a current transformer coil for flowing plasma current;
The plasma 1a, the vertical magnetic field coil 2a, and the current transformer coil 2b are electromagnetically coupled. A circuit for flowing plasma current is connected to the current transformer coil 2b. This circuit consists of a resistor 3, changeover switches 4, 4', a direct current disconnector 5, and a thyristor converter 6.

In FIG. 3, a shows the plasma current, and b shows the current transformer coil current. Before time t ₁ in FIG. 3, the DC circuit and disconnector 5 are closed, the changeover switches 4 and 4' are connected to the a side, and the thyristor conversion device is controlled (the control device is not shown). The current in the current transformer coil 2b is kept at a predetermined value. When the DC disconnector 5 is opened at time _t1 , the current in the current transformer coil 2b flows through the resistor 3 and generates a high voltage between the terminals, so that a discharge occurs in the plasma ring and a plasma current begins to flow. Furthermore, the plasma current increases due to the change in the current in the current transformer coil 2b. From time _t2 , the plasma current maintenance period (flat top) begins. Since the current in the plasma tends to decrease due to its own loss, it is necessary to slowly change the current in the current transformer coil 2b. For this purpose, the changeover switches 4 and 4' are set to the b side, and the thyristor conversion device 6 is reconnected to allow the required current to flow. Perform the stop operation from time _t3 .

In such an operation, the current in the vertical magnetic field coil 2a must be raised approximately in proportion to the plasma current between t ₁ and t ₂ (at startup), as shown in FIG. 3c. In addition, in the flat top, the plasma is reheated (performed by a heating device not shown).
As the plasma pressure increases due to such reasons, it is necessary to slightly increase the current of the vertical magnetic field coil 2a correspondingly. In reality, the position of the plasma is detected and the coil current is changed using feedback control. On the other hand, at the time of startup mentioned above, the current changes very quickly, so if the actual position is detected and feedback control is performed, the positional deviation will become large due to the time delay of the control circuit, etc. Therefore, pre-programming is performed to calculate in advance a value that can maintain the plasma in a predetermined position as the current or voltage of the vertical magnetic field coil 2a, and to control the thyristor conversion device 7 of the coil power supply so as to provide such current or voltage. There is control. This method will be explained with reference to FIG. 2. A thyristor conversion device 7 is connected to the vertical magnetic field coil 2a. The control circuit includes a control loop that makes the current measured by the current detector 8 equal to the current set value i _vp (it can also be a loop that controls the coil voltage), and a control loop that makes the current measured by the current detector 8 equal to the current set value A control loop is provided that makes the position equal to the set value X ₀ . 11 and 13 are control calculation circuits, 14
15 is a signal switching circuit, 15 is a pulse phase shifter 16, which is a central control device, and a preprogramming control loop a that operates the signal switching circuit 14 according to a command from the central control device 16, and controls the current before time _t2 .
After time _t2 , feedback control loop b for controlling the position is selected.

An example of the movement of the plasma horizontal position X under such control is shown in FIG. 3d.

The solid line in the figure is the plasma horizontal position X, and the dashed line is the target value X ₀ (X ₀ =0). At startup, as mentioned above, the coil current is controlled to a predetermined value without directly controlling the plasma horizontal position Therefore, it is inevitable that a certain degree of deviation will occur in the plasma horizontal position X. In such a state, when switching from a state where _a deviation X ₁ occurs at time t ₁ to feedback control of the plasma horizontal position Shoot. Such a state is not desirable from the viewpoint of plasma control. In other words, since the plasma is electromagnetically coupled to other coils and containers, oscillating currents may flow through these as well, and the plasma itself may become unstable.

An object of the present invention is to provide a fusion plasma device having a control device capable of stably controlling plasma.

The present invention stably controls plasma by smoothing the control switching from start-up to flat top.

An embodiment of the invention is shown in FIG. In the figure,
Components that are the same as those in FIG. 2 are given the same reference numerals, and their explanations will be omitted. 17 is a signal switching circuit, and 18 is a first-order delay circuit. The operations other than the position control circuit in FIG. 4 are the same as in FIG. 2. In FIG. 4, at the time of rising, the signal switching circuit 17 selects the signal b, and the signal switching circuit 14 selects the signal a. At time t ₂ ,
The signal switching circuit 17 is activated by a command from the central controller 16.
14 switches the selection signal from b to a, and from a to b. That is, the signal switching circuit 17 takes in the actual position X instead of the position control target value X ₀ at the time of rising. However, since the position control loop is not selected by the signal switching circuit 14, it is not related to actual control. When the signal is switched by the signal switching circuit 17 at time t ₂ , the target value changes from X ₁ to X ₀ in Fig. 3.
The value changes. Therefore, if the first-order delay circuit 18 is added, the output of 18 will be as shown by the dashed-dotted line in Figure 3e.
Changes smoothly from X ₁ to X ₀ . That is, the target value of the position control changes smoothly at a rate of change within a range such that the plasma position X does not overshoot as described above. On the other hand, after time _t2 , the signal switching circuit 14
operates, b is selected, and the position control loop operates, so the actual position X changes as shown by the solid line in FIG. 3e. As described above, according to this embodiment, even when the control mode is switched, the plasma position is maintained at a predetermined position while changing smoothly, so that the plasma position can be stably controlled.

Further, although a thyristor conversion device is shown as an example of the coil power source, other controllable DC power sources such as transistors may be used.

As described above, according to the present invention, plasma can be stably controlled even if the control mode is switched.

[Brief explanation of the drawing]

Figure 1 is a diagram for explaining a nuclear fusion device, where a is a schematic perspective view, b is a sectional view, Figure 2 is a circuit diagram showing a conventional example, and Figure 3 shows the operation of Figures 2 and 4. FIG. 4 is a circuit diagram showing an embodiment of the present invention. 1a... Plasma inductance, 2a... Vertical magnetic field coil, 2b... Current transformer coil, 7... Thyristor converter, 8... Current detector, 9... Position detector, 14
... Signal switching circuit, 17... Signal switching circuit, 18... First-order delay circuit.

Claims (1)

[Claims] 1 A plasma ring, at least one poloidal magnetic field coil for controlling the position of the plasma, a power source for controlling the current or voltage of the coil, and a control device for controlling the power source, and the control device has the above-mentioned In a device that is provided with a preprogramming control loop that controls the current or voltage of the coil and a feedback control loop that controls the position of the plasma, and is controlled by selectively switching between the two in time, the preprogramming control loop When switching to the feedback control loop, the input is switched from the actual plasma position X to the plasma position control target value X ₀ , so that the plasma position control target value X ₀ does not exceed a predetermined rate of change. A fusion plasma device characterized in that the feedback control loop is provided with a first-order delay circuit that causes smooth changes.