JPH06302399A - Plasma generation and heating device - Google Patents

Abstract

PURPOSE:To always alleviate high-frequency power reflection for plasma load resistance by branching a part of an oscillator output circuit with a directional coupler for connection to a negative feedback electronic circuit, and then feeding back a signal to a high-frequency signal generator via the electronic circuit. CONSTITUTION:A twin stub tuner 14 with operating characteristics equivalent to a stub tuner having approximately 10 to 20 times of high-frequency wavelength is used in a high-frequency negative feedback control and matching circuit. The twin stub tuner 14 is a device equipped with another terminal section added to a stub tuner. Also, the stub tuner 14 is a long stub tuner equivalent to length 10 to 20 times of guide wavelength, and composed of a short stub tuner 14AS and a long stub tuner 14AL. Consequently, the stub tuner 14 operates as a stub tuner having high-frequency wavelength equivalent to 10 to 20 times, according to a decrease in the length of the tuner 14AS. As a result, high-frequency power reflection can be alleviated with frequency negative feedback control, even when plasma load resistance changes with the elapse of time.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a plasma generation / heating apparatus using an ion cyclotron high frequency, in which a frequency negative feedback control matching circuit is provided in an output circuit of a high frequency oscillator to constantly respond to a plasma load resistance which changes with time. The present invention relates to a plasma generation / heating device that is matched by frequency negative feedback control to minimize reflected power to an oscillator.

[0002]

2. Description of the Related Art A conventional technique will be described with reference to FIGS. 9, 10 and 11. Figure 9 shows the currently operating JET (Joint Eu
A cross-sectional view of a fusion experimental device called a ropean Torus) is shown. This is a type of plasma confinement device called a tokamak, which plays a leading role in the world's nuclear fusion research.
Research is done vigorously.

In FIG. 9, 1 is an internal poloidal magnetic field coil which is a primary winding, 2 is a vacuum container for confining plasma, 3 is an external poloidal magnetic field coil, 4 is a current transformer, 5 is a mechanical structure, 6 Indicates a toroidal field coil. FIG. 10 is a characteristic diagram in which various quantities are measured in a power reflectivity reduction experiment by position control of plasma in the JET device. FIG. 11 shows a conceptual diagram of the matching device of the experimental device. Figure
In 11, a high-frequency signal generator 7, a high-frequency oscillator 8, a directional coupler 9, 10 and 11 stub tuners, 12
Is an ion cyclotron heating antenna, and 13 is plasma. In the joint Europian torus (JET), the recent DT combustion (plasma produced by deuterium and tritium) experiments showed that the electric power injected into the plasma and the heat output generated by the fusion reaction were almost the same. Proved. In the JET ion cyclotron high-frequency heating experiment, a plasma heating of 22 MW for 10 seconds was successful, providing a phenomenon of physical interest. Among these, during the ion cyclotron high-frequency heating experiment, a transition occurred from the L mode having a short plasma confinement time to the H mode having a confinement time twice as long as that. However, due to this transition, the matching condition between the antenna placed in the device and the oscillator was broken, and the high frequency power reflection to the oscillator side increased. This is because the load resistance of plasma viewed from the antenna side has changed. In such a case, oscillation is stopped to protect the vacuum tube of the oscillator, but to avoid this, J
In ET, the current of the external poloidal magnetic field coil 3 is changed to bring the plasma 13 closer to the antenna 12 side (outer side) to return the plasma load resistance to the previous state and reduce the reflection of high frequency power. . The experimental data at this time are shown in FIG. In FIG. 10, a transition from the L mode to the H mode occurs during the high frequency heating of the ion cyclotron. By moving the plasma to the antenna side by about 2 cm as shown in Fig. 10, the load resistance of the antenna is always kept at 3Ω to prevent the high frequency power reflection from increasing. As can be seen from this FIG. 10, the plasma is moving with a time constant of 0.3 seconds. Here, the frequency is also changed, but this is to make the imaginary part of the impedance zero and does not affect the real part of the impedance.

Next, the operation of this device will be described.
In ion cyclotron high frequency plasma generation and heating,
The plasma load resistance of the antenna installed in the internal vacuum chamber of the plasma generation and confinement heating device is 4 to 5 at most with respect to the output impedance (for example, 50Ω) of the high frequency oscillator.
Ω, and a matching circuit is indispensable between the oscillator and the antenna. This matching circuit is composed of two stub tuners 10 and 11 whose ends are short-circuited as shown in FIG. Figure 11
In the figure, 7 is a high frequency signal generator, and 8 is a high frequency oscillator connected thereto. The high frequency oscillator 8 is connected to the antenna 12 via the directional coupler 9, the oscillator and the two stub tuners 10 and 11 provided on the antenna side. Reference numeral 13 is plasma, and 2 is a vacuum container surrounding the plasma. In a long-time plasma generation / heating experiment, the plasma load resistance fluctuates greatly due to changes in the density and temperature of the plasma 13 or scrape-off plasma 13, and the matching conditions are not satisfied, and the high frequency power reflection from the antenna 12 increases. In such a case, the output of the high frequency oscillator 8 must be stopped to protect the oscillation tube. Therefore, in order to stably generate and heat the plasma for a long time, it is essential to research and develop a matching circuit that can perform negative feedback control so that the output of the high frequency oscillator 8 does not stop. As shown in Figure 10,
Two stub tuners for changing plasma load resistance 1
The problem is solved in principle by moving 0 and 11 mechanically and finding a new matching point. Here, the stub tuner is
A tuner in which an inner conductor and an outer conductor of a coaxial tube are tangentially connected to electrically terminate.

[0005]

In the conventional matching circuit using the stub tuners 10 and 11, two stub tuners 10 are provided in order to reduce the high frequency power reflection with respect to the time fluctuation of the plasma load resistance as described above. , 11 must be moved during heating of the high power high frequency oscillator 8. However, there are some problems to be solved. The problems to be solved by the invention are summarized as follows.

(1) Terminal part of stub tuner In the heating state of the movable number MW, 1 is installed at the terminal part of the stub tuner.
A high-frequency current of about kA is flowing, and it is dangerous to move this end part. (2) Controllable matching circuit that responds at high speed It is important to respond quickly to changes in the plasma state with time and to constantly reduce power reflection and reduce the burden on the high-frequency oscillator. Therefore, a mechanically operated system has a drawback that the response time is long. (3) High-frequency power loss in the matching device Since a large standing wave is generated in the matching device, the high-frequency power loss in the stub tuner cannot be ignored. Therefore, a matching device with low loss is desired.

The present invention has been made in order to solve the above problems, and by providing a high-speed frequency negative feedback control matching circuit without moving the terminating portion of the stub tuner, a time fluctuation of about 1 ms can be achieved. The purpose is to constantly reduce high frequency power reflection to the plasma load resistance. The present invention further invents a twin stub tuner which is designed to minimize the high frequency power loss in the matching device.

[0008]

The present invention is connected to an ion cyclotron heating antenna via a high frequency signal generator, a high frequency oscillator connected thereto, a directional coupler connected to the output side thereof, and a stub tuner. In the plasma generation and heating device using the ion cyclotron high frequency, a part of the output of the oscillator is branched by the directional coupler to connect a negative feedback electronic circuit, and the high frequency is generated via the negative feedback electronic circuit. It is configured to feed back to the signal generator, and by this, it is configured to always match the time-varying plasma load resistance by negative frequency feedback control and reduce the reflected power to the oscillator as much as possible. It is in the plasma generation and heating device.

[0009]

The high-speed negative feedback control matching circuit according to the present invention uses a twin stub tuner having operating characteristics equivalent to those of a stub tuner having a high frequency wavelength of about 10 to 20 times.

Twin stub tuners are devices in which a conventional stub tuner is equipped with another termination. This twin stub tuner is a long stub tuner that is equivalent to a length of 10 to 20 times the guide wavelength, and the stub tuner is characterized in that it is composed of a short stub tuner and a long stub tuner.

[0011]

【Example】

Example 1 The operating characteristics of the twin stub tuner will be described with reference to FIG. In FIG. 1, 14 is a twin stub tuner, 14A
S is a short stub tuner, 14 AL is a long stub tuner, 15 is a cross-branch coaxial tube, 16 is a coaxial tube, and 17 is a movable terminal end. The twin stub tuner 14 is composed of a short stub tuner 14AS (0.1 wavelength or less) and a long stub tuner 14AL (0.4 to 0.5 wavelength). By combining the lengths of these two stub tuners 14 AS and 14 AL, the synthetic length (Ar) and the effective length (A _eff ) when acting as a conventional stub tuner are given by the following chemical formulas. Where AS, AL, Ar and A
All the values such as _eff are values standardized at high frequency wavelengths.

[0012]

[Equation 1]

[0013]

[Equation 2]

In FIG. 2, the calculation result of the equation (1) is given as a composite value of the short stub tuner 14AS and the long stub tuner 14AL. FIG. 2A shows a three-dimensional display, and shows the combined length (Ar) at which the twin stub tuner 14 acts as a conventional stub tuner by its height. Further, FIG. 2B shows the contour lines of Ar in FIG. As can be seen in FIGS. 2 (A) and 2 (B), the shorter the stub tuner of 14 AS, the shorter the A
The contour lines of r are dense. This shows that the synthetic length (Ar) can be largely changed by slightly changing 14AL while keeping 14AS constant. In order to express this quantitatively, when the frequency is slightly changed, how long the twin stub tuner 14 effectively corresponds to the long stub tuner 14AL is calculated by using the equation (2). Shown in. Similar to FIG. 2, FIG. 3A shows a three-dimensional display, and shows how A _eff changes depending on the values of 14AS and 14AL of the twin stub tuner. As shown in FIG. 3A, it can be seen that the shorter the stub tuner 14AS is from 0.01 to 0.01, the more the stub tuner has a high-frequency wavelength corresponding to 10 to 20 times.

Example 2 A study was conducted on a system in which the frequency of the high-frequency oscillator was slightly changed with respect to the fluctuation of the plasma load and the matching was performed again. The principle conceptual diagram of the experimental apparatus is shown in FIG. This matching device uses a two stub tuner system. 8 times longer stub tuner on oscillator side and antenna side
10A1 and a short stub tuner 11A3 with a wavelength of 0.1 wavelength or less were used. These intervals are set to 1/4 wavelength. The length of the stub tuner 10A1 on the oscillator side is normalized by wavelength, A1 = 7.5-α (α <1), and the stub tuner 11A3 on the antenna side has A3 = 0.0602. FIG. 5 shows the experimental results. In FIG. 5, the matching condition of zero power reflectance is satisfied when the load resistance is 2.2 Ω at the frequency of 42.5 MHz. Here, if the load resistance is 5.6 Ω, the power reflectivity increases to 8%. Here, the reflectance decreases as the frequency is lowered from 42.5 MHz, and the power reflectance becomes almost zero at 42.2 MHz. Therefore, the frequency fluctuation rate is 0.7%
Thus, the power reflectivity can be made zero for load resistance fluctuation rates of 2.2 Ω to 5.6 Ω.

The same experiment was conducted with several kinds of load resistors. The results are shown in FIGS. 6 (A) and 6 (B). When the load resistance is 2.2 Ω, the matching condition of zero power reflectance is satisfied. When changing from no plasma load (estimated to be vacuum load) to 5.6 Ω, the reflectance increases to 8% without load resistance and 6.5% (white circle) at 5.6 Ω. At this time, if the frequency with which the reflection is minimized is selected for each plasma load, the reflectance can be reduced to 1% or less with respect to a wide range variation of the plasma load as shown by a black circle. Improvement rate in this case (reflectance with frequency control /
FIG. 6B shows the reflectance when there is no frequency control, a black circle) and the frequency change rate (df / f, a white circle) required to achieve it.
Shown in. Thus, for values larger than the load resistance initially set, it is possible to reduce the reflectance of high frequency power to 0.2% or less. This shows that the principle experiment of the frequency negative feedback control system with respect to the time change of the plasma load resistance was completed.

Third Embodiment In the second embodiment, the principle experiment of the frequency negative feedback control system with respect to the change of the high frequency resistance was conducted by using the stub tuner 10 having a frequency of 8 times the high frequency. Since an 8 times stub tuner has a large high frequency power loss and low plasma generation / heating efficiency, a twin stub tuner 14 is used instead of the 8 times stub tuner 10 as shown in FIG. FIG. 7 shows a conceptual diagram of the high-speed negative feedback control matching system developed by the present invention.

In FIG. 7, 19 is a high frequency signal generator, and 20
Is a high-frequency amplifier connected to this, and 21 is a directional coupler connected to this amplifier. In the present invention, the directional coupler 21 is connected to the antenna 18 via the twin tuners 14AS, 14AL and the stub tuner 11A3. A part of the output of the directional coupler 21 is branched to control the negative feedback. The reflected power input 23 is detected by the detector 22 of the electronic circuit 29, and the differential amplifier 26A, 26B, 27A, 27B, 28A, 28 is detected.
The output of B is input to the frequency modulator of the high frequency generator 19. Using this device, a simulated experiment of a high-speed negative feedback control matching circuit that always minimizes the reflectance of high-frequency power with a time constant of millisecond (ms) was conducted. Therefore, a high-frequency load resistor 31 that changes at high speed was manufactured using a pin diode. The load resistance can be changed within the range of 1 to 7 Ω by externally voltage-controlling this. The experimental results are shown in FIG. The configuration of the twin stub tuners 14AS and 14AL used here has a length AS of 14AS = 0.025 and a length AL of 14AL = 0.465. In FIG. 8A, the high frequency incident power (FP), the high frequency load resistance (RP), and the power reflectivity (REP) are shown from the top.
The high frequency incident power is almost constant. High frequency load resistance (R
P) changes to 2 to 6Ω with a time constant of 3 ms. Matching is set so that the reflected power factor becomes zero when the high frequency load resistance (RP) is 2Ω. When the high frequency load resistance becomes 6Ω, the power reflectivity (REP) becomes 10%. At this time, the frequency negative feedback control is not performed. On the other hand, FIG. 8B shows the result when the frequency negative feedback control is performed. The high frequency load resistance (RP) changes by 2 to 6Ω as in the case of FIG. Power reflectivity (REP) at this time
Is 0.2% at maximum, and the frequency fluctuation is ± 0.05 MHz correspondingly. The frequency used here is 4
Since it is 2.5 MHz, the frequency change rate is ± 0.12%.

[0019]

【The invention's effect】

(1) A twin stub tuner was invented as a substitute for a stub tuner having 10 to 20 times the high frequency wavelength. (2) In the two stub tuner matching circuit system, if a stub tuner with a wavelength of about 8 times is used on the oscillator side, high frequency power reflection is reduced by negative frequency feedback control even if the load resistance of plasma changes with time. Has the effect of (3) By applying the twin stub tuner to the frequency negative feedback control matching circuit, it is possible to reduce the frequency change rate and reduce the load on the oscillator. Even if the load resistance is changed at high speed, it responds with a time constant of about ms, and has the effect of reducing the power reflectivity to 0.2% or less over a wide range of load resistance.

[Brief description of drawings]

FIG. 1 is a conceptual diagram showing details of the structure of a twin stub tuner for carrying out Embodiment 1 of the present invention.

FIG. 2 is a diagram showing Embodiment 1 of the present invention, and is a characteristic diagram showing an operating state in which a twin stub tuner acts as a conventional stub tuner.

FIG. 3 is a characteristic diagram showing how long an operation characteristic of a twin stub tuner corresponds to a long stub tuner in the first embodiment of the present invention.

FIG. 4 is a conceptual diagram of a matching device for performing a principle experiment of frequency negative feedback control in a second embodiment of the present invention.

FIG. 5 shows that in Embodiment 2 of the present invention, when a stub tuner having a wavelength of about 8 times longer is used, the power reflectivity can be made zero again by a slight change in frequency with respect to a change in load resistance. It is a characteristic view to show.

FIG. 6 is a characteristic diagram showing a minimum reflectance value by frequency adjustment for various load resistances and a frequency change rate at that time in Example 2 of the present invention.

FIG. 7 is a conceptual diagram of an experimental apparatus of Example 3 of the present invention, and is a circuit diagram of a matching system using a twin stub tuner for performing high-speed negative feedback control.

FIG. 8 (A) is a characteristic diagram showing a result of power reflectivity in the third embodiment of the present invention in the absence of frequency negative feedback control. FIG. 8B is a characteristic diagram showing the result of the power reflectivity in the case where the frequency negative feedback control is provided in the third embodiment of the present invention.

FIG. 9 is a joint europian torus (JE
T) is a schematic view of an apparatus.

FIG. 10 is a joint Europian torus (J
FIG. 6 is a characteristic diagram showing the result of a power reflectivity reduction experiment by controlling the position of plasma in the (ET) device.

FIG. 11 is a circuit diagram of a matching device using a conventional two-stub tuner.

[Explanation of symbols]

 1 Internal poloidal magnetic field coil which is a primary winding 2 Vacuum container 3 External poloidal magnetic field coil 4 Current transformer 5 Mechanical structure 6 Toroidal magnetic field coil 7 High frequency signal generator 8 High frequency oscillator 9 Directional coupler 10 Oscillator side stub tuner 11 Antenna side stub tuner 12 Antenna 13 Plasma 14 Twin stub tuner 14AS Short stub tuner 14AL Long stub tuner 15 Cross-branch coaxial tube 16 Coaxial tube 17 Movable terminal 18 Antenna 19 High frequency signal generator 20 High frequency amplifier 21 Directional coupler 22 Detector 23 Reflected power input 24 Positive offset power supply terminal 25 Negative offset power supply terminal 26A, 26B, 27A, 27B, 28A, 28B Differential amplifier 29 Negative feedback control electronic circuit 30 Low frequency signal generator 31 High frequency resistance (pin diode)

Claims (3)

[Claims] 1. A high frequency signal generator, a high frequency oscillator connected to the high frequency signal generator, and a directional coupler connected to the output side thereof.
In a plasma generation and heating device using an ion cyclotron radio frequency connected to an ion cyclotron heating antenna via a stub tuner, a part of the output of the oscillator is branched by the directional coupler and a negative feedback electronic circuit is connected. Then, it is configured to feed back to the high-frequency signal generator through the negative feedback electronic circuit, whereby the plasma load resistance that changes with time is always matched by the frequency negative feedback control, and the reflected power to the oscillator is adjusted. A plasma generation / heating device characterized by being configured to reduce as much as possible. 2. The plasma generation / heating apparatus according to claim 1, wherein the matching circuit adopts a two-stub tuner system, and a twin stub tuner is incorporated on the oscillator side. 3. The twin stub tuner has a tube wavelength of
The plasma generation / heating apparatus according to claim 1, wherein the plasma generation / heating apparatus is configured to operate as a stub tuner having a length equal to 10 to 20 times.