JPH01320495A - Method and device for induction heating of nuclear fusion device - Google Patents

Abstract

PURPOSE:To approximate the heat generation distribution of a vacuum vessel to a desired distribution by determining the currents of the sets of respective poloidal coils in such a manner that the currents of plural sets of the poloidal coils attain the distribution nearest the target heat generation distribution. CONSTITUTION:Ohmic heating coils 3a-3e are successively connected in the same manner as in the prior art and are connected to one power source 5a for induction heating. The other poloidal coils 4a-4h are also connected as one set to another power source 5b for induction heating. The eddy current density distribution and heat generation distribution above the vacuum vessel in case of using only the power source 5b are so distributed that the much eddy current flows on the outer side and the heat generation density is highly distributed at the center thereof. The heat generation densities superposed according to the current ratios of the poloidal coils 3a-3e and 4a-4h are attained when two sets of the coils 3a-3e and 4a-4h are simultaneously energized by using the power sources 5a and 5b. The heat generation distribution of the vacuum vessel 1 is approximated to a desired distribution in this way.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a torus-type nuclear fusion device, and particularly to an induction heating method and device suitable for heating a vacuum vessel.

[Conventional technology]

Conventionally, in nuclear fusion devices, in order to keep the vacuum chamber that confines the plasma clean and obtain a high degree of vacuum, the vacuum chamber is
It is necessary to heat (baking) to about 0'C to 400C. There are roughly two types of methods for heating a vacuum container. One method is to directly attach a heating element such as a heater to the outside of the vacuum container, and this method is already used in many devices, but in addition to the need to secure space for installing the heater, the However, large-scale equipment has the disadvantage that it requires a large number of heaters and large-scale auxiliary equipment for heating them with electricity. Another method for heating a vacuum container is the induction heating method, which uses Joule heat generated by energizing an ohmic heating coil (hereinafter referred to as an OH coil) to generate and maintain plasma current to generate an induced current in the vacuum container. For example, Fusion Technology 1986, Vol. 1, pages 347 to 352 (Fusion Technology 19
86. Vol.

pp347-352. Pergamon Press
) is discussed in Compared to the above-mentioned method using a heater, this method is characterized in that it only requires the use of an existing OH coil to generate heat in the vacuum container, and requires less incidental equipment. Hereinafter, this conventional induction heating method for a vacuum container will be explained in detail with reference to FIGS. 2 and 3.

FIG. 2 is a poloidal cross-sectional view of a nuclear fusion device for explaining a conventional induction heating method for a vacuum vessel. In the figure, 1 is a vacuum vessel, 2 is a toroidal coil, 3 and 4 are poloidal coils, and 5 is an induction heating power source. Three of the poloidal coils are installed specifically for the purpose of generating and maintaining plasma current, and are called OH coils. The OH coil usually has a plurality of coils connected to the current as a set, such as 3a to 3e. On the other hand, the poloidal coil 4 is installed to control the position and shape of the plasma, and although it is not shown in this figure, like the OH coil 3, it is a set of multiple coils connected to the power source. In some cases, individual coils are connected to a single power source. In the device with this configuration, when the current of the OH coil 3 is changed, the vacuum vessel 1
When fuel gas is supplied into the toroidal coil 2 and the toroidal coil 2 is energized, plasma is generated along the magnetic field created by the toroidal coil, and a plasma current flows based on the principle of electromagnetic induction. However, when there is no fuel gas in the vacuum vessel or when the toroidal coil 2 is not energized, eddy currents occur in the vacuum vessel.

The prior art induction heating method for vacuum containers utilizes the latter phenomenon. FIG. 3 shows waveforms of induction heating according to the prior art. In this figure, when the current in the OH coil 3 is changed sinusoidally at 50Hz as shown in Fig. 3(a), an eddy current flows on the vacuum vessel as shown in Fig. 3(b), and as a result, Joule heat is generated. As a result, heat as shown in FIG. 3(c) is generated.

[Problem to be solved by the invention]

The above-mentioned conventional technology has the advantage that the vacuum container can be heated without requiring the installation of a heater or the like.

There was a problem in that the vacuum container could not be heated uniformly.

This is because the eddy current flowing on the vacuum vessel is concentrated inside the torus due to current changes in the OH coil.

FIG. 4 is a schematic diagram for explaining this, in which the eddy current density distribution is represented using a circle 6 whose radius is proportional to the eddy current density on a poloidal cross-sectional view of the vacuum vessel 1.

Since the heat generation density due to current is proportional to the square of the current density when the resistances are equal, the area of circle 6 in FIG. 4 represents the heat generation density, and it can be seen that heat is generated intensively inside the torus. In order to investigate the eddy current density distribution and the heat generation density distribution in more detail, we take and expand the coordinate Q that starts from the outer equatorial plane of the torus and circles counterclockwise on the poloidal cross section of the vacuum vessel, as shown in Figure 5. , FIG. 6, and
It will look like Figure 7. In these figures, the horizontal axis is the coordinate Q, and A, B, C, D, and E on the horizontal axis are A in FIG.

They correspond to B, C, D, and E, respectively. As can be seen from FIG. 6, the eddy current density has a large peak at the equatorial plane C inside the torus, and as a result, as shown in FIG. 7, the heat generation density differs greatly between the inside and outside of the torus.

If the heat generation distribution is uneven in this way, a large temperature difference will occur on the vacuum container, and thermal stress will occur. In order to avoid this problem, in a known example, an air flow path is provided along the vacuum container at the same time as induction heating is performed using an ○H coil.
The temperature of the vacuum chamber is made uniform by circulating compressed air. However, this method requires additional equipment for the compressed air @ ring, and like the method using a heater, it is necessary to secure space for installation in a vacuum container.

The problem was that it was expensive.

An object of the present invention is to provide an inexpensive induction heating method for a nuclear fusion device that uniformizes the distribution of heat generated by induction heating and requires almost no additional equipment for varying the temperature distribution of a vacuum vessel.

[Means to solve the problem]

The above purpose is to simultaneously energize other poloidal coils 4 in addition to the OH coil 3 when performing induction heating of a vacuum container, so that the eddy current distribution on the vacuum container generated by the currents of these multiple sets of poloidal coils is This is achieved by determining the current for each poloidal coil set so that it is closest to the target heat generation distribution, taking advantage of the fact that the current distribution differs depending on the set of poloidal coils.

[Effect]

When a particular set of poloidal coils is energized and the current changes over time, the magnetic flux interlinking the vacuum vessel always changes, causing eddy currents to flow on the vacuum vessel. The eddy current distribution on the vacuum vessel at this time is uniquely determined by the positional relationship between the poloidal coil set and the vacuum vessel. Therefore, the eddy current distribution on the vacuum vessel when a plurality of poloidal coil sets are energized at the same time is determined by the superposition of the eddy current distributions created by the respective poloidal coil sets. This means that when multiple sets of poloidal coils are used to determine the eddy current distribution on the vacuum vessel, there is a degree of freedom corresponding to the number of sets of poloidal coils. - While it is impossible to change the heat generation distribution in the conventional technology that uses only one set of poloidal coils, in the present invention that uses multiple sets of poloidal coils, the heat generation distribution in the vacuum vessel can be changed by changing the current ratio of each set of poloidal coils. It is possible to get closer to the target distribution.

〔Example〕

An embodiment of the present invention will be described below with reference to FIG. In this figure, the OH coils 3a to 3e are connected in sequence and connected to one induction heating power source 5a, as in the prior art. On the other hand, other poloidal coils 4a, 4b, 4d,
4e, 4g, and 4h are also combined into a separate induction heating power source 5.
connected to b. In this case, the set of poloidal coils 4 connected to the power source 5b are connected to generate a vertical magnetic field for controlling the horizontal position of the plasma. In a nuclear fusion device having such a configuration, when only the power source 5a is used, the eddy current density distribution and heat generation density distribution on the vacuum vessel are as shown in FIGS. 6 and 7, respectively, as in the prior art.
It will look like the figure. Next, the eddy current density distribution on the vacuum vessel when only the power source 5b is used, and the 1 heat generation density distribution are the 8th
It becomes as shown in Fig. 9. In these figures, the horizontal axis is the length q when rotating counterclockwise on the poloidal cross section of the vacuum vessel from the outer equatorial plane of the torus, as shown in FIG. It can be seen from FIGS. 8 and 9 that when a vertical magnetic field is applied using the power source 5b, many eddy currents flow outside the torus and the heat generation density is highest there. The eddy current density distribution and heat generation density distribution on the vacuum vessel when the two sets of poloidal coils 3 and 4 are energized using the power supplies 5a and 5b are shown in FIGS. 6 and 8, and FIGS. 7 and 9, respectively. is obtained by superimposing two sets of poloidal coils according to the current ratio. Curve 101 in FIG. A curve 111 in FIG. 11 represents the eddy current distribution on the vacuum vessel obtained by energizing the two sets of poloidal coils in this manner.

This shows an example of heat generation density distribution. As described above, according to this embodiment, it is possible to make the heat generation distribution of the vacuum vessel more uniform during induction heating of the vacuum vessel compared to the conventional technology, and it is possible to make the heat generation distribution of the vacuum vessel more uniform during induction heating of the vacuum vessel than with the conventional technology. The burden on equipment can be greatly reduced.

FIG. 12 is a flowchart of a method for determining the current to be passed through a plurality of sets of poloidal coils, which is another embodiment of the present invention. The heat generation distribution necessary to make the temperature distribution of the vacuum container uniform is generally determined by the shape of the vacuum container, the heat radiation distribution, etc. In this example, first, in step 121, such a target heat generation distribution xo is determined.Next, in step 122, the result when a unit current is applied individually to all the independent poloidal coil sets (N sets) is determined. Vacuum vessel heat generation distribution xk, = 1 to N is calculated or determined by experiment. In 123, matrix P with all Xk as columns, P: () CIX2... xk... XN
). A vector whose elements are this P and the current flowing through the poloidal coils from the first set to the Nth set ■1 to IN
(T is transposed), the heat generation distribution of the vacuum container realized by N sets of poloidal coils is expressed as x = P I . In 124, the weighted sum of squares between X in the above equation and the target heat generation distribution xo, (x-xo)"W(x-xo) = (PI-xo)"W(PI-xo)W: the weight matrix is The current flowing through each set of poloidal coils is determined by the least squares method so as to minimize the current. As described above, according to this embodiment, when performing induction heating of a vacuum container using a plurality of poloidal coil sets, it is possible to determine the current value of each poloidal coil set so as to be closest to the target heat generation distribution. can.

FIG. 13 is a poloidal cross-sectional view of a nuclear fusion device according to another embodiment of the present invention. This figure is equivalent to FIG. 1 showing the first embodiment of the present invention, but the grouping of the poloidal coils 4 and the method of connection to the power source are different. The following table shows how the poloidal coils are grouped and connected to the power supply in this embodiment.

Of the five power supplies above, excluding 5a which is the OH coil <5c
, 5d, 5e, and 5f are shown in FIGS. 14 and 15, respectively.

In these figures, the horizontal axis is the length Q when rotating counterclockwise on the poloidal cross section of the vacuum vessel from the outer equatorial plane of the torus as shown in FIG. Furthermore, the correspondence between the curve numbers and power supplies in these figures is as shown in the table below.

From these figures, it can be seen that the eddy current distribution on the vacuum vessel and the position on the vacuum vessel poloidal cross section where the heat generation distribution is maximum differ depending on each power source, and it is easy to obtain an arbitrary heat generation density distribution by combining them. In order to make the heat generation density distribution on the poloidal cross section of the vacuum vessel as close to uniform as possible using the heat generation density distribution shown in FIG. The eddy current density distribution on the vacuum vessel when the current is determined is shown by the curve 102 in FIG. 10, and the heat generation density distribution is shown by the curve 112 in FIG. 11. This embodiment has the effect that a heat generation distribution closer to the target heat generation distribution can be obtained compared to the first embodiment which uses only two power sources.

In this example, even if the arrangement of the poloidal coils is the same, there is no need to limit the method of combining them and the method of connecting them to the power source, and the more power sources used, the closer the heat generation distribution to the target will be. It has the characteristic that it is easy to obtain the distribution.

FIG. 16 shows a poloidal cross-sectional view of a nuclear fusion device according to another embodiment of the present invention. The configuration of the device in this figure, the arrangement of the poloidal coils 3 and 4, their combination, and the wiring method are the same as in FIG. 13, which is the third embodiment of the present invention, but only the configuration of the power source is different.

That is, in this embodiment, the power source is only 5g, and one power source is connected to a set of four poloidal coils via resistors 7a to 7d. According to this embodiment, the resistor 7
By adjusting the resistance values of a to 7d, the ratio of current in each poloidal coil pair connected to it can be changed, and a single power supply can achieve the same effect as the third embodiment using four separate power supplies. can be mentioned.

FIG. 17 shows a final embodiment of the invention. In this figure, 8 is a measuring device (for example, a thermocouple) for measuring the temperature distribution or heat generation distribution on the vacuum container, and 9 is a coil current measuring device. In this example, the target value y for the signal y(t) from the measuring instruments arranged on the vacuum container is
o(t) and the difference between these signals δy”y−yo
Based on this, the coil current target value calculating section 171 calculates the current target value Io for each poloidal coil set. This I
.

and the coil current value actually measured by the measuring device 9 to find the difference δ = 0, and the coil power supply voltage calculation unit 172 calculates the power supply connected to each poloidal coil set so that δ becomes 0. It is designed to determine the voltage ■ such as 5h and 51. In this way, in this embodiment, for example, '1
If 0 is set as the target value of the temperature distribution at each measurement point on the vacuum vessel, the coil current and voltage can be feedback-controlled so that not only the temperature distribution but also its time change coincides with the target value.

〔Effect of the invention〕

According to the present invention, the heat generation distribution of the vacuum container can be brought close to the desired distribution only by induction heating due to current changes in the poloidal coil, and the additional equipment required for heating the vacuum container can be greatly reduced. .

[Brief explanation of the drawing]

FIG. 1 is a boloidal sectional view of a fusion device according to an embodiment of the present invention, FIG. 2 is a boloidal sectional view of a conventional fusion device, and FIG. 3 is a waveform diagram during induction heating of a vacuum vessel according to the prior art. Figure 4 is a diagram of eddy current density distribution in a vacuum vessel of the prior art, Figure 5 is a diagram showing coordinates on the poloidal cross section of the vacuum vessel, and Figure 6 is a diagram showing coordinates on the poloidal cross section of the vacuum vessel.
The figure is a diagram of eddy current density distribution on a vacuum vessel of the prior art, Figure 7 is a heat generation distribution diagram of a vacuum vessel of the prior art, Figure 8 is a diagram of eddy current distribution on a vacuum vessel explaining Figure 1, and Figure 9 is a diagram of eddy current density distribution on a vacuum vessel of the prior art. 10 is a heat generation density distribution diagram of the vacuum container, FIG. 10 is an eddy current density distribution diagram on the vacuum container according to the second and third embodiments of the present invention, and FIG.
The figure is also a vacuum vessel heat generation density distribution diagram, Figure 12 is a flowchart showing how to determine the current of a set of poloidal coils, which is the second embodiment of the present invention, and Figure 13 is the core, which is the third embodiment of the present invention. A boloidal cross-sectional view of the fusion device, FIG. 14 is an eddy current density distribution diagram on a vacuum vessel explaining the third embodiment of the present invention, FIG. 15 is a heat generation density distribution diagram of the vacuum vessel, and FIG. 16 is a diagram of the present invention. FIG. 17 is a poloidal coil current feedback control system diagram showing a fifth embodiment of the present invention. 1... Vacuum container, 2... Toroidal coil, 3...
・Poloidal coil (○H coil), 4... Poloidal coil, 5... Induction heating power source, 7... Resistor,
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Claims (1)

[Claims] 1. In a torus-type nuclear fusion device including a vacuum vessel for generating plasma and a plurality of sets of poloidal coils installed to surround the vacuum vessel, the An induction heating method for a nuclear fusion device in which the vacuum vessel is heated by independently energizing multiple sets of poloidal coils. 2. In a torus-type nuclear fusion device that includes a vacuum vessel for confining plasma and a plurality of sets of poloidal coils installed to surround the vacuum vessel, the heat distribution of the vacuum vessel is determined by a plurality of power sources connected to the An induction heating method for a nuclear fusion device, characterized in that the induction heating method is determined using the plurality of sets of the poloidal coils. 3. In a torus-type nuclear fusion device including a vacuum vessel for generating plasma and a plurality of sets of poloidal coils installed to surround the vacuum vessel, energizing the plurality of sets of poloidal coils at a specific ratio. An induction heating method for a nuclear fusion device, characterized by: 4. An induction heating device for a nuclear fusion device, characterized in that current values of a plurality of sets of poloidal coils are determined so that the least square sum of differences between a target value and an actual value of heat generation distribution in a vacuum vessel is minimized. 5. A nuclear fusion device characterized in that measuring instruments are distributed and arranged on a vacuum vessel, and the currents of a plurality of sets of poloidal coils are controlled so that the difference between the signal from the measuring instruments and a target value is minimized. induction heating device. 6. The induction heating device for a nuclear fusion device according to claim 5, wherein the measuring device is a thermocouple.