JPS6097291A - Stabilizer for plasma - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Application of the Invention] The present invention relates to a control device for preventing new phenomena such as a plasma current generated during a tokamak-type nuclear fusion device [17+], or a plasma current [IIL].

[Background of the invention]

In tokamak-type fusion devices, a plasma current disruption phenomenon called major disruption may occur. When this phenomenon occurs, all of the heat and electromagnetic energy possessed by the plasma is released outside the plasma, which may lead to damage to surrounding coils, vacuum vessel walls, etc. Therefore, there is a need to prevent this phenomenon.

Conventionally, as a means to prevent such a plasma current interruption phenomenon, a helical coil is arranged around the plasma, and when a precursor phenomenon of the interruption phenomenon occurs, a current is passed through the helical coil. Techniques have been proposed to prevent this new phenomenon. (For example, Nuclear
(Fusion 198020/9) However, this conventional technique had the drawback that the structure of the nuclear fusion device was complicated because the helical coil was arranged around the vacuum vessel.

As another conventional technology, an electron cyclodrore wave heating device is installed to locally concentrate the part of the plasma where the precursor phenomenon occurs when a precursor phenomenon occurs. A technique has been proposed to prevent the cutoff phenomenon by heating. (For example, Nuclear
Fusion 198222/272) This method is
Although it does not require a complicated furnace structure, it is an indirect method of suppressing the precursor phenomenon by heating the plasma and locally changing the plasma current distribution at the edge of the precursor phenomenon region. , especially plasma is IKey
Large-scale nuclear fusion devices that reach such high temperatures have the disadvantage that the prevention effect is not sufficiently effective.

[Purpose of the invention]

SUMMARY OF THE INVENTION An object of the present invention is to provide an apparatus that works effectively even in high-temperature plasma and prevents plasma current cutoff phenomena without complicating the furnace structure.

[Summary of the invention]

In order to achieve the above object, the present invention uses an oscillator in the low mixed wave band WLIT and forcibly drives the plasma current at a constant frequency, thereby suppressing the precursor phenomenon and preventing the cutoff phenomenon.

That is, the present invention detects all precursory phenomena in plasma,
The high frequency oscillation is forced into the plasma to drive the VC6 current in the plasma, and the driving part of the VC6 current in the plasma is most effective in suppressing the precursory phenomenon. The phase and amplitude of the plasma are adjusted to prevent the plasma flow from being cut off.

The present invention has been made based on the findings described below.

The plasma II flow cutoff phenomenon occurs due to abrasive MHD (magnetohydrodynamic) instability.

This instability is a so-called m=2 tearing mode. This instability is relatively mild, forming a magnetic island as shown in Fig. 1, and τ = η
It grows with a time constant of about /lto/1°, where η is plasma resistivity and μ is vacuum permeability. (In a large device, it is about τ~IS.) The growth force of this instability is determined by the shape of the current distribution around the magnetic island, and the shape of the current distribution is determined by the initial discharge conditions of the plasma and the current distribution in the plasma during discharge. The decision is made by a complex intertwining of factors such as engineering, labor, baranos, etc.

Note that FIG. 1 depicts isomagnetic surfaces on a longitudinal section of plasma, and the term "magnetic island" refers to a portion where the isomagnetic surfaces are island-shaped. An equimagnetic surface is 1(p=ψ×PφfB
p refers to a surface where the magnetic flux function ψ defined by a voidal magnetic field and Pφ a unit vector in the torus direction is constant. Furthermore, on this magnetic surface, the plasma temperature Te and current density J have a property of being constant values.

When this magnetic island increases due to the above-mentioned growth force and exceeds a certain limit value, the plasma confinement ability is lost, leading to a phenomenon in which the plasma current is suddenly cut off.

The equation describing the dynamic characteristics of the magnetic high medium W during this period is given by the following equation.

Here, η: plasma resistivity on the magnetic island boundary [Ωnl]Jn'
The plasma current is [A]. Δ' (w) in the first term on the right side is a quantity given by λ-, and the current distribution around the magnetic island Jfr
It is a quantity determined by l. Plasma originally has...:
The force that causes the entire magnetic island to grow due to the current distribution, and the force that reduces the magnetic island when controlling the peripheral current distribution by electron cyclotron wave heating as described in the prior art section, is expressed by this first term Δ' (W). Ru.

Here, r: plasma secondary radial direction It [m] rS: magnetic island center position Cm).

On the other hand, the second term on the right-hand side corresponds to the force that suppresses the growth of the magnetic tail by driving the entire current on the magnetic tail using high frequency. J r, iψ) represents the increment of the drive current from the value in the magnetic island field, and is given by the following equation.

Here, Jrf(r) is the r-direction distribution of the drive current.

J'rf(ψ) is the average of Jrf(ri) on the magnetic surface. Here, V and ψ have a relationship of ψ=V·ψ.

The value of Δ′(W) in the first term of the first equation is usually Δ′(W)~0,
J r+ / J o
When it is set to ~30%, the second term becomes about 5, and has a stronger influence on the rate of change of the magnetic island by about one order of magnitude than the first term.

Note that Equation [11, (2), +3) is based on the basic equations of electromagnetic fluids, such as Anopère's law (μ. (
Pressure=η(J-'Jrf)).

In this case, the high-frequency drive current JrfCr) is generated under the condition that a high frequency in the temperature range hybrid wave frequency band is externally applied and forms a traveling wave in the toroidal direction with a phase velocity η, = C/lower. It is expressed by the following formula.

n. Plasma density [n'I-8] '1゛. The plasma temperature is (e, vl n7, 1) The lower limit of the upper limit of the refractive index in the toroidal direction of the high frequency is n//''//I + n//2)/2.The slow depth re of the cylindrical frequency bullet is , given by .

Here, a Plasma minor radius [m] R Plasma main radius [m] PLH high frequency total power [W] Prf High frequency power density absorbed by plasma CWm-
”:] is.

Now, in order to realize an effective control method 1 to reduce the size of the magnetic island by utilizing the properties related to the behavior of the magnetic island described above, Jr defined by the equation (3) is If it is necessary to devise ways to obtain a large value, it is necessary to solve the following three points.

Since Te is included in the exp term as shown in equation (4), Jrl shows a sharp peak shape that reaches its maximum value at r = re.However, (3)
According to the formula, the average operation on the magnetic surface becomes Jrl, so Jrl is smaller than the peak value of Jrf(r). Therefore, J'rf ( Qk diamagnetic rotation speed ωoVc is synchronized and rotated so that high frequency waves are oscillated only when the center of the magnetic island approaches the antenna.This causes the drive on the boundary of the magnetic island in the second term of equation (3) to occur. The current Jrf (ψ1) can be made smaller, and as a result, dy will have four peaks of rF.) Therefore, a device was devised to make the arrival position re of the 11 waves coincide with the central bow of the magnetic island. This is the first (
This is possible by changing the Jt opening refraction index n// in the toroidal direction using the 5-inch formula. In other words, when nN total increases (decreases), Frf(n total increases (decreases) and PL
Under constant H, r. decreases (increases).

Finally, if you try to draw a magnetic island using the formula (3),
Generally, information regarding the position r of the center of the magnetic island is required. However, as a measuring means that has good heat on the fire time PTt side and @roughness, it is possible to use magnetic high-temperature W using an electromagnetic globe.
Currently, only information on the subject can be obtained. Therefore,
Let us consider a method that allows the optimum current drive position r0 to be determined using only information regarding W. Section (1), (3)
As is clear from the formula, the reducing force of the magnetic island is r, = r,
Since it has the property of decreasing monotonically from the maximum, r, accordingly, the point at which the high frequency is large should coincide with the optimal drive position r. To search for ntt for which 17 is the maximum, use the idea of nonlinear programming (steepest descent method) or modify “n’!: according to (7).Here, (dw/dt ) refers to measurement data.

[Embodiments of the invention]

The present invention will be explained below with reference to Examples. FIG. 2 is a diagram showing the configuration of the present invention. Usui's Ki Globe 3 installed near the plasma 1 detects the time rate of change B of the boroidal magnetic field Bθ.
Detect θ. This iθ is a sine wave with a diamagnetic rotation frequency ωD. Since the square of this amplitude is proportional to the width W of the magnetic island 2, it is converted into a magnetic high-medium signal W through a detector 4, passed through a differentiator 5, and outputs the time rate of change W of W. is input to the switch circuit 6, and according to equation (7), 1:l//
The time rate of change of the refractive index n// is calculated as = -K sign (weak/ntt). ntt is further input to the integrator 7, divided by n//time, and ntt(!- is calculated. n〃 is input to the converter 8, and the phase ψ is output. The conversion formula is ψ L 2π λn // Here], : Width of one length of 2M wave antenna [mlλ: Vacuum wavelength [m] The output ψ is input to the phase shifters 9a to 9dK.

On the other hand, the output signal Bθ of the magnetic globe 3 misses the grid bias circuit 12 and is directly transmitted to the oscillator 11a-1ld+
Normally, it is input to a klystronon grid with an oscillation frequency of 100 MHz to I GHz, and the oscillator output Ea E
Amplitude modulation is performed on the dVC at a diamagnetic rotation frequency of ~100 KHz. Oscillator output Ea-Ea is output from phase shifter 9a-9.
d and undergo phase shifts of 0, ψ, 2ψ, and 3ψ, respectively. The output from the phase shifter is a grill-type antenna 10a.
10dfWaveG_ide), where the toroidal direction refractive index n//? have 1
1 emits magnetic waves.

Due to this electromagnetic wave, a high-frequency driving current as shown in equation (42) flows in the plasma, and the magnetic island shrinks according to the dynamic characteristics of equation (1).

In this example, a case has been described in which four antennas are used in parallel, but the same applies generally to a case in which n antennas are used in parallel. Further, the processing from the detector 4 to the converter 8 or a part thereof can be realized by a control # calculator.

〔Effect of the invention〕

As explained above, according to the present invention, it is only necessary to install a high-frequency antenna on the fusion drum-shaped main body, that is, without complicating the reactor structure, and by adopting a method of directly driving current at high frequency. Therefore, it is possible to operate sufficiently effectively even with a large m device VCB that confines high-temperature plasma. This makes it possible to prevent the plasma current cut-off phenomenon, and therefore, in a nuclear fusion device using this, it is expected that the beta value will be improved and the construction cost of the nuclear fusion device will be reduced.

[Brief explanation of the drawing]

Figure 1 is an explanatory diagram depicting the plane of incidence on the longitudinal section of the plasma, and Figure 2 is a fijIg diagram of one embodiment of the present invention.

Claims (1)

[Claims] ■, by electromagnetic probes installed around the plasma,
a means for detecting an oscillating boloidal magnetic field and estimating the width of a magnetic island generated in the plasma from the detection result; a means for oscillating a high frequency wave in a frequency band corresponding to a low-frequency hybrid wave of the plasma; It has a hand B2 that shifts the phase of the oscillating cylinder frequency according to the high temperature, and a grill-type antenna that radiates the phase-shifted high frequency wave into the plasma as a traveling wave in the torus direction. This is a plasma stabilizing device characterized by preventing the J- and new phenomena of the plasma current.