JP2728296B2 - Plasma current driver - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a device for exciting a current in a plasma of a fusion device, and more particularly to a plasma current suitable for a tokamak device which is a torus-shaped magnetic field confinement fusion device. It relates to a driving device.

[Prior art] Conventionally, in a torus-type fusion device, especially a tokamak-type fusion device, a DC plasma current for confining plasma in the device is generated by electromagnetic induction by a current transformer. In principle, it must be operated intermittently, so that there is a problem that the economical efficiency of the fusion reactor cannot be improved, and the life of the device is shortened due to repeated stress based on the intermittent operation. As a means for solving this problem, there is a method of giving a unidirectional momentum to electrons in plasma by using a high frequency to excite the flow of electrons, that is, a current. This method can obtain a steady-state current in principle, and is relieved of the problem due to the intermittent operation of the tokamak device. This method is generally called high-frequency current driving.

In the high-frequency current drive, research on a method using a lower-hybrid wave has been most advanced, and there is a track record of maintaining a plasma current of 2 MA for several seconds. Lower-Hybrid wave is several hundred MHz
It is an electrostatic wave in the plasma existing in the frequency range from to several GHz and gives momentum to the electrons in the plasma by a wave absorption mechanism called Landau attenuation. In order to impart one-directional momentum to electrons, it is necessary to propagate a Lower-Hybrid wave in one direction, that is, to make it a traveling wave. Therefore, a launcher 2 in which a plurality of rectangular waveguide antennas 1 are arranged as shown in FIG. 6 is used. This launcher is connected to a torus vacuum vessel. This launcher has the same function as a phased array antenna to enhance radiation directivity in the field of communications, and utilizes the wave interference phenomenon by simultaneously radiating high-frequency waves with slightly different phases from multiple waveguide antennas. To selectively excite only waves in a specific direction.

Conventionally, for example, a device as shown in FIG. 7 has been used as this kind of current driving device. In FIG. 7, 3
Is a low power (hundreds of watts) reference oscillator, 4a to 4g are 3db (decibel) distributors that divide high frequency power into two, 5a to 5h are variable phase shifters that adjust the high frequency phase of each system, and 6a to 6h are A high-frequency amplifier for amplifying the high-frequency power to the power required for driving the high-frequency current (several hundreds of kW to several tens of watts, depending on the scale of the fusion device), 2 is a launcher described in FIG. ... 1h is each rectangular waveguide antenna 1 in FIG.
It shows. Reference oscillator 3 and high frequency amplifier 6a ~
As 6h, a klystron can be used in the case of a lower-hybrid wave. In the current driver shown in FIG. 7, the phase of the high frequency wave incident on the rectangular waveguide antennas 1a to 1h constituting the launcher 2 is adjusted with reference to the output phase of the reference oscillator 3. Related devices of this type include, for example, the research report JAERI-M8 of the Japan Atomic Energy Research Institute.
The apparatus described on page 2, page 10 and page 11 of 7-061 (1987) may be mentioned. In this device, the high-frequency amplifier 6a shown in FIG.
Although the output of ~ 6h is further finely divided, the principle of adjusting the phase of the high frequency wave incident on each rectangular waveguide with reference to the reference oscillator is the same.

[Problem to be Solved by the Invention] The above-mentioned prior art is characterized in that the direction of the high frequency radiated from the launcher can be freely changed by the variable phase shifter, but many devices are arranged near the fusion device. Therefore, there is a problem that the system becomes complicated. In addition, 5 to 10 GHz required for large-scale equipment at the fusion reactor level
High frequency amplifiers have low power conversion efficiency
Only 10 kW of power can be obtained, so more than 1000 high-frequency amplifiers are required to obtain the high-frequency output of 50 to 100 MW required for large-scale fusion reactor-level equipment, which is a huge There are problems such as high cost and low reliability of the device.

In order to improve the economy and reliability of the current driving device, a method of using a large power oscillator having high power conversion efficiency and providing a power distributor and a phase shifter on the output side of the large power oscillator can be considered. In this method, the reference oscillator 3 has a large output and the high-frequency amplifiers 6a to 6h are removed in FIG. 7 for explaining a conventional plasma current driving device. However, if multiple such systems are installed in order to obtain the required power of 50 to 100 MW for large fusion devices, the radiated phase will not be uniform because the high-frequency phase of each system will naturally change every moment and the phases will not be aligned. There is a problem that the high frequencies cancel each other out and cannot effectively drive the plasma current.

Therefore, the object of the present invention is: It is an object of the present invention to provide an economical and highly reliable plasma current driving device capable of effectively driving a plasma current by using a plurality of large power oscillators capable of obtaining a large output per unit by controlling an oscillation frequency.

[Means for Solving the Problems] In order to achieve the above object, the present invention divides a launcher including a large number of rectangular waveguide antennas into a plurality of groups, and uses a single high-power high-frequency oscillator for each group. The generated high frequency power is split and incident. Further, the present invention is characterized in that the oscillation frequency of each high-power high-frequency oscillator is controlled and adjusted so that the frequencies slightly differ between groups.

[Operation] With the high-frequency transmission line, the power divider, and the fixed phase shifter according to the present invention, when one of a plurality of high-frequency oscillators is operated alone, a wave in a specific direction is selectively emitted. In the present invention, the frequency control device solves the problem of a decrease in efficiency that occurs because a phase is not aligned when a plurality of large power oscillators having high power conversion efficiency are used in a conventional plasma current driving device. This will be described below.

Now, divide the launcher into two groups, the angular frequency ω ₁ from the first _group, the angular frequency ω ₂ from the second group
It is assumed that the lower-hybrid wave is excited in the plasma.
At this time, the synthesized high-frequency electric field is expressed as follows: E = E ₁ exp (iω ₁ t) + E ₂ exp (iω ₂ t) = E ₁ exp (iω ₁ t) + E ₂ exp (iω ₁ t + φ) (1) However, φ = (ω ₁ −ω ₂ ) t. That is, two types of Lower-H with slightly different frequencies
The interaction of the ybrid waves is such that the phase difference φ is the frequency difference Δω = (ω
₁ −ω ₂ ) Lower-Hybrid at high frequency that fluctuates with time
It is equivalent to exciting the wave. As explained below,
The frequency difference Δω has an optimum value for efficiently driving the plasma current.

First, when Δω is too large, one of the frequencies
Since the lower-hybrid wave cannot be excited due to deviation from the frequency of the r-hybrid wave, one of the high-frequency powers is not useful for current driving. Therefore, there is an upper limit for the optimum value of Δω.

When Δω is small, the equation (1) is given by E = exp (iω ₀ t) × [(E ₁ + E ₂ ) cos (Δωt / 2) + i (E ₁ −E ₂ ) sin (Δωt / 2)] .. (2) where ω ₀ (ω ₁ + ω ₂ ) / 2, and the amplitude of the synthesized high frequency fluctuates at a frequency of Δω / 2. The current excited in the plasma is determined by the balance between the ability to impart unidirectional momentum to the electrons by the high frequency and the ability to uniform the velocity distribution due to the collision process between the electrons. Therefore, the collision frequency of electrons (usually several hundred
If the frequency of the high-frequency amplitude fluctuation is higher than (kHz), the fluctuation of the high-frequency amplitude is averaged in the process of collision between electrons, and an effect similar to the absence of the amplitude fluctuation is obtained. However, when the frequency of the amplitude fluctuation is lower than the collision frequency of the electrons, the electrons sense the intensity of the high frequency at each time and a current proportional to the intensity flows, so that a steady plasma current cannot be maintained. Therefore, there is a lower limit for the optimum value of Δω.

The optimum frequency difference Δω for the plasma current drive depends on the plasma parameters, the size of the nuclear fusion device, and the like, but is 1 to 10 MHz for a large device. The frequency control device according to the present invention maintains the frequency difference between the oscillators at an optimum value for driving the plasma current.

Embodiment An embodiment of the present invention will be described below with reference to FIG. FIG. 1 is a diagram showing a configuration of a plasma current driving device according to one embodiment of the present invention, together with a partial top view of a tokamak fusion device. This plasma driving device is divided into groups a, b, c, and d having the same configuration, and each group has a subscript a, b, c, or d indicating the group to which the group belongs.
Will be added. In FIG. 1, a frequency control device 30 includes directional couplers 8a to 8d for extracting a part of the output of the high-frequency oscillators 9a to 9d, frequency control power supplies 20a to 20d for adjusting the high-frequency oscillators 9a to 9d, It is configured by a controller 21 that measures a high frequency and supplies a control signal to the frequency control power supply according to a difference from a set frequency. First
In the figure, reference numerals 9a to 9d denote high frequency oscillators, which generate a high frequency having a frequency optimal for driving the plasma current according to the output of the frequency control device 30. High frequency power is high frequency transmission line 7a ~ 7d
Through the multi-junction launchers 100a, 100b, 100c, and 100d. The Multi-Ju
The nction launcher is mounted on the wall 11 of the vacuum vessel of the tokamak fusion device. The arrow 14 in FIG. 1 indicates the toroidal direction of the tokamak fusion device.

Here, the structure of the Multi-Junction launcher 100a will be described with reference to FIG. Other Multi-J
The structure of the unction launchers 100b, 100c, 100d is the same. The Multi-Junction launcher 100a separates a large rectangular waveguide in which a plurality of rectangular waveguide antennas 1 arranged in the direction of the toroidal magnetic field of the tokamak fusion device are grouped as a group by an E-plane splitting plate 44a, Fixed phase shifter 1
According to 5a, the height of the inner wall is changed in a part of the waveguide. The E-plane splitting plate 44a distributes the incident high frequency 19 into two, and corresponds to the power divider described in claim 1 of the claims. The fixed phase shifter 15a changes the phase speed at which the high frequency propagates according to the height of the waveguide inner wall,
That is, it adjusts the high-frequency phase, and corresponds to the fixed phase shifter described in claim 1.

In the above plasma current driving device, the phase adjustment in the group is performed by the fixed phase shifter 15a or the like in the rectangular waveguide, and the frequency difference Δω between the groups is adjusted by the frequency control device 30 between the upper limit value and the lower limit value. Maintain the optimal value.

FIG. 3 shows a plasma 10 using the apparatus of the embodiment of FIG.
FIG. 3 is a diagram showing a power spectrum radiated to the radiator. The horizontal axis is the refractive index in the toroidal direction 14. This amount corresponds to the traveling direction of the radiated high frequency. The vertical axis represents the high-frequency power density (power spectrum) radiated in each direction.
In FIG. 3, a narrow spectrum indicated by 40a is a spectrum when one high-frequency oscillator operates alone. When all the high-frequency oscillators 9a to 9d operate at the same time, the power spectrum fluctuates with time at a speed sufficiently higher than the collision frequency of electrons, such as 40a, 40b, 40c, and the plasma 40a, 40b, 40
I feel a spectrum like an envelope which overlaps a narrow spectrum like c, and the current is excited in the plasma.
According to this embodiment, it is possible to provide an economical device that efficiently drives a plasma current with a simple configuration such as a high-frequency oscillator, a high-frequency transmission line, a frequency control device, and a multi-junction launcher.

FIG. 4 shows a second embodiment. In this embodiment, the group a,
The configuration is divided into b, c, and d. FIG. 4 shows only an example of a part constituting the group a in FIG. 4 for simplification of the drawing. The configuration is the same for other groups. In this embodiment, the launchers (2a, 2b, 2c, 2d) of each group have the same structure as in FIG. This embodiment is different from the first embodiment in that the power distribution function is 3d.
The b distributor 40a and the U-link (for changing the length of the waveguide) 18a perform the phase adjustment function. That is, the portion including the launcher 2a, the 3db distributor 40a, and the U link 18a performs the same function as the launcher 100a having the E-plane partitioning plate 44a and the fixed phase shifter 15a in the first embodiment. This embodiment has a disadvantage in that the number of constituent devices increases as compared with the first embodiment. However, by adjusting the U-link, the high-frequency phase difference between adjacent waveguide antennas can be adjusted. Since the direction can be adjusted, there is an effect that the plasma current distribution and the like can be finely controlled.

FIG. 5 is a view showing a third embodiment in which an isolator 32a and a stub tuner 31a are added to the first embodiment. For simplicity of illustration, FIG. 5 shows only the group a, but the configuration and operation are the same for the other groups b, c, and d. The stub tuner 31a has the effect of achieving load matching between the high-frequency oscillator 9a and the launcher 100a and radiating more high-frequency power from the launcher. In the conventional plasma current driving device shown in FIG.
The stub tuner could not be installed on the transmission line because of the problem of disturbing the high-frequency phase. In the third embodiment of the present invention, since the phase is adjusted by the launcher after the stub tuner 31a, there is no such problem as in the conventional plasma current driving device. Therefore, with the stub tuner,
There is an effect that high-frequency power generated by the high-frequency oscillator can be efficiently radiated. Further, the isolator 32a has a function of absorbing a reflected wave generated by an accident such as an arc in the launcher 100a or the stub tuner 31, and has an effect of preventing the high-frequency oscillator 9a from being destroyed by a large amount of reflected waves.

The embodiment shown in FIG. 4 can be provided with an isolator and a stub tuner.

In the first embodiment, if means for externally changing the height or length of the fixed phase shifter 15 in the multi-junction launcher is attached, the radiated power spectrum is finely adjusted for controlling the plasma current distribution and the like. be able to.

[Effects of the Invention] According to the present invention, the plasma current can be efficiently driven even when a plurality of high-output high-frequency oscillators whose phases of generated high-frequency change momentarily change in parallel, so that high-power high-frequency is required. It is possible to provide an economical and highly reliable plasma current driving device suitable for a large-scale fusion device.

[Brief description of the drawings]

FIG. 1 is a diagram showing a first embodiment of the present invention together with a partial top view of a tokamak-type fusion device, and FIG. 2 is a diagram showing Mu in FIG.
FIG. 3 is a perspective view showing the lti-junction launcher partially cut away, and FIG. 3 is a view for explaining a power spectrum radiated by the device of the first embodiment. FIG. 4 is a view showing the second embodiment, FIG. 5 is a view showing the embodiment of FIG. 3, FIG. 6 is a perspective view showing a plasma current drive launcher partially cut away, and FIG. FIG. 9 is a diagram illustrating a conventional plasma current driving device. DESCRIPTION OF SYMBOLS 1 ... Rectangular waveguide antenna 2 ... Launcher, 7 ... High frequency transmission line 8 ... Directional coupler, 9 ... High frequency oscillator 10 ... Tokamak plasma 11 ... Vacuum container wall, 14 ... Toroidal direction 15: fixed phase shifter, 18: U-link 20: frequency control power supply 21: controller, 30: frequency control device 31: stub tuner 32: isolator, 44: E-plane partition 100 Multi-Junction launcher

Claims (7)

(57) [Claims] 1. A plasma current driving device for exciting a plasma current in a fusion device for confining plasma by a magnetic field, wherein a plurality of rectangular waveguide antennas are arranged in a direction of a toroidal magnetic field generated by the fusion device. The divided launcher is divided into a plurality of groups with a plurality of adjacent rectangular waveguide antennas as one group, and a high-power high-frequency oscillator, a high-frequency transmission line, and power for each rectangular waveguide antenna are provided for each group. A distributor and a fixed phase shifter are provided so that each group alone can selectively radiate a high frequency in a predetermined direction in the fusion device, and the oscillation frequency of each high power high frequency oscillator is slightly different between the groups. A plasma current driving device comprising a frequency control device for adjusting the frequency in a similar manner. 2. The plasma current driving device according to claim 1, wherein the oscillation frequency of each high-power high-frequency oscillator is adjusted to differ by several MHz between groups. 3. The launcher is a multi-junction (Mult
3. The plasma current driving device according to claim 1, wherein the plasma current driving device is a launcher, and includes a power distributor and a fixed phase shifter. 4. The plasma current driving device according to claim 1, wherein the power divider is a 3 dB divider, the fixed phaser is a U-bent, and is externally provided in the launcher. 5. A frequency control device comprising: a part for extracting a part of an output of a high-frequency oscillator for frequency measurement; a current for adjusting an oscillation frequency; and a command value corresponding to a difference signal between the measured frequency and a set frequency. 5. The plasma current driving device according to claim 1, further comprising a portion for supplying a power supply for adjusting the oscillation frequency. 6. The plasma current driving device according to claim 1, wherein a stub tuner is provided in a high-frequency transmission line between the high-power high-frequency oscillator and the power distributor. 7. The plasma current driving device according to claim 1, wherein an isolator is provided in a high-frequency transmission line between the high-power high-frequency oscillator and the power divider.