JPH01186600A - Faraday shield for high frequency heating device - Google Patents

Abstract

PURPOSE:To improve heating efficiency by forming a pipe with a high melting point material, coating the good conductive substance having a low electricity ratio resistance on the pipe surface, and moreover coating the substance having low atomic number on the surface of the side directly facing a plasma. CONSTITUTION:The good conductive substance 2 such as copper, etc., having a low electricity ratio resistance is coated with the thickness of a skin depth degree for a high frequency on the surface of a pipe 1 having a circular cross section and composed of a high melting point material having a thickness of 3mm or more such as inconel 625, etc. Moreover a substance 3 having a low atomic number such as TiC, etc., is coated on the surface of the coated part mentioned above. The coating thickness of the low atomic number substance 3 is made thicker at the side facing a plasma and thinner at the reverse side, and the maximum thickness is 20mum degree. And a cooling medium such as water or nitrogen gas, etc., is made to flow within the pipe 1. This enables the lowering of heating efficiency to be restrained with the mixture of a substance having a high atomic number into a plasma prevented.

Description

[Detailed Description of the Invention] [Objective of the Invention] (Industrial Application Field) The present invention is particularly applicable to the ion cyclotron frequency band (hereinafter abbreviated as ICRF) in the radio frequency heating method fjjt for additionally heating the plasma of a nuclear fusion device, for example. ) This relates to an improvement of the 7 Alladay shield used in high frequency heating equipment.

(Prior art) Conventionally, methods for heating the plasma of, for example, nuclear fusion devices include Joule heating, which heats the plasma by passing an electric current through it, as well as neutral particle injection heating and high-frequency heating as second-stage heating methods. There are laws etc. The high-frequency heating method is a method of increasing the temperature of the plasma by absorbing high-frequency electromagnetic energy into the plasma, and there are various methods available depending on the frequency used.
One of them is ICRF' high frequency heating device.

FIG. 4 shows the schematic configuration of Tonohaji's ICRF high frequency heating device. As shown in the figure, this device consists of a high-frequency oscillator 4 that generates and amplifies a high-power high-frequency wave of 100 MHz @, a coaxial tube 6 that transmits the high-frequency output generated by this high-frequency oscillator 4, and this coaxial The coupling system 8 is connected to the tube 6 and corresponds to an antenna that emits the high frequency output to the plasma 7 of the fusion device.

On the other hand, the coupling system 8 includes a T-shaped waveguide system and a Loog antenna system from the viewpoint of compatibility with the tokamak device main body 5, but the loop antenna system will be explained here.

This Roog antenna type coupling system 8 consists of 7 lanterns 9. is directly connected to the tokamak device main body 5. Further, a loop antenna conductor 10 is attached to the tip of the coaxial tube 6, and a 7-array shield 11 is attached to the plasma 7 side of the loop antenna conductor 10. This 7Araday shield 1 protects the loop antenna conductor 10 from collision with plasma particles, allows the magnetic field formed by the high Ml wave current flowing through the loop antenna conductor 10 to pass to the outside, and electrostatically protects the loop antenna conductor 10 from collisions with plasma particles. It plays the role of shielding the conductor 10 from the outside world. - On the other hand, since the tokamak device main body 2 is in a high vacuum, the space between the outer conduit 61 and the inner conduit 6b of the coaxial tube 3 is vacuum-sealed with a 7-round through 12.

Generally, in plasma heating using high frequency, it is necessary to bring the antenna conductor 10 as close to the plasma 7 as possible and to be able to apply as much power as possible to one loop antenna conductor 10 in order to perform efficient heating. By the way, as research on nuclear fusion has progressed recently, plasma 7 has become higher in temperature and density, and high-frequency heating equipment cannot operate at large capacity for long periods of time. Another problem arises: atoms and molecules on the surface scraped off by plasma particles enter the plasma 7, resulting in a decrease in heating efficiency due to lowering the plasma temperature.

Therefore, in order to deal with this heat load problem, the conventional 7
As shown in a perspective view in FIG. 5, the Allade Shield 1 is provided with a jacket 14 on the side surface of the antenna cushioning 13 in order to remove the high heat load, and is further equipped with a jacket 14 and a large number of pipes f1'5. is connected so that the cooling medium is passed through the pi fzs for cooling.

(Problem to be Solved by the Invention) However, there is a limit to the cooling flow path area and the coolant flow rate due to the mechanical strength of the pipe 15, etc., so there is a limit to the heat load that can be cooled. When atoms and molecules on the surface that have been scraped off by the plasma particles invade f-) zuma, the energy of the plasma 7 is lost in proportion to the square of the atomic number.

Generally, substances used as structural materials are metals with large atomic numbers. However, if this oak metal is used in a place that directly faces the plasma 2, such as in the 7Araday shield 11, there is a risk that the plasma 7 will be cooled for the reasons mentioned above, reducing the heating efficiency of the high-frequency heating device. be.

The present invention has been made to solve the above-mentioned problem, and its purpose is to provide a highly reliable high-frequency heating device that can withstand high heat loads, reduce high-frequency loss, and increase heating efficiency. 7 Alladay Shield.

[Structure of the invention]

(Means for Solving the Problems) In order to achieve the above object, the present invention transmits high frequency output generated by a high frequency wave oscillator through a coaxial tube, and an antenna attached to the tip of the coaxial tube. A high-frequency heating device in the ion cyclotron frequency band that emits energy into the plasma through the antenna.It is made up of multiple pipes connected and is installed on the plasma side of the antenna to shield the electric field formed by the high-frequency current flowing through the antenna. In a Faraday shield, the pipe is made of a high melting point material,
In addition, a highly conductive material with low electrical resistivity is coated on the surface of the No. 4 Ig, and a low atomic number material is coated on at least the surface directly facing the plasma.

(Accordingly, in the present invention, even when the ICRF and llilli frequency heating devices operate at a large capacity for a long time,
The gJL loss at the high part can be suppressed to a low level, and the risk of melting, breakage, etc. is reduced even under high heat loads, and it is possible to further improve heating efficiency.

(Example) Hereinafter, an example of the present invention will be described with reference to the drawings.

FIG. 1 is a sectional view showing an example of the configuration of a Faraday shield for an ICRF high-frequency heating device according to the present invention. The Faraday shield according to this embodiment has three
■ On the surface of Pi f1, which has a circular cross section and is made of a high melting point material such as Inconel 625, which has a wall thickness of more than The surface is further coated with a low atomic number substance such as Tic. Here, the coating thickness of the low atomic number substance 3 is thicker on the side facing the plasma and thinner on the opposite side, so that the coating thickness is at most 20
The thickness is about μm. Further, a cooling medium such as water or nitrogen gas is allowed to flow inside the pipe fl.

In the 7Araday shield h with such a configuration, current due to high frequency flows only on the surface.If the thickness is δ, the specific resistance of the material is ρ, the angular frequency is ω, and the magnetic permeability is μ, then
The thickness δ is given by the following formula.

δ=meter f7τ7 For example, when using copper for a frequency of 1×10 Hz, δ is about 20 tim. Inconel 6 on pi f1
25 and copper is used as the conductive material 2, the high frequency loss differs by more than 5 times with and without the coating, and the thermal load due to the high frequency loss is reduced by the coating. In addition, when the surface of the conductive material 2 is coated with the low atomic number material 3, the high frequency loss increases by the specific resistance of the low atomic number material 3, but the thickness of the coating is set to be less than or equal to the low atomic number material δ. In particular, the increase in high frequency loss can be reduced. In this case, the electrical resistivity of the conductive substance 2 is ρ, the coating thickness is dl, and the specific resistance of the low atomic number substance 3 is ρ,
If the coating thickness is DOS and the skin depth for high frequencies of the low atomic number material 3 is δ, then the ratio of high frequency loss when the low atomic number material 3 is coated and when it is not is given by the following equation.

2h However, [,=[t9 δ Here, ρe and ρme' are functions of temperature, so K is also a function of temperature, but copper is used as the good conductive material 2, and low atomic number material 3 When Tic t- is used as a material and the thickness of the coating is 20 mm, K becomes about 2 at a temperature of 100°C. Compared to the high frequency loss of the material using Inconel 625 for pipe 1, copper and Tic
The high frequency loss is reduced to about one-third by covering the tomomonite.

On the other hand, when plasma particles enter a substance, atoms and molecules are repelled from the surface, enter the plasma, and become charged particles. These charged particles release energy in the glazma to the outside by bremsstrahlung radiation. The rate at which this bremsstrahlung radiation occurs is proportional to the square of the atomic number. for example,
The ratio of atomic numbers between Tic and iron is about 3, and the rate at which bremsstrahlung radiation occurs is about 1/8 smaller in TlC0. Therefore, Tic also has a smaller rate of cooling the plasma.

As mentioned above, in the 7 Alladay shield according to this embodiment, by suspending the pie f) made of a high melting point material with a wall thickness of 3 m or more, it is possible to cool the shield and increase its mechanical strength at high temperatures. In addition, by coating the surface of the pipe 1 with a material 2 with good electrical conductivity, the heat load due to high frequency loss is reduced, and at least on the side directly facing the plasma, a material 20 with good electrical conductivity is coated from the surface of the material 20 with good electrical conductivity. By coating the material 3 with a low atomic number, it is possible to prevent a material with a high atomic number from entering the plasma, thereby suppressing a decrease in heating efficiency.

Therefore, even when the ICfLF high-frequency heating device operates at a large capacity for a long time, it is possible to keep the high-frequency loss low, and there is also a risk of melting or breaking even under high heat loads. Heating efficiency can be increased.

In the above embodiment, a circular cross-section was used as the i4 if, but the invention is not limited to this. For example, a via "1" with a non-circular cross-section as shown in FIG. In addition, by using the pipe 1 having an elliptical cross section as shown in Fig. 3, the rigidity against bending in the long axis direction of the cross section can be increased. It is possible.

In addition, the present invention can be modified and implemented in various ways without changing the gist thereof.

〔Effect of the invention〕

As explained above, according to the present invention, the pipe is formed of a high melting point material, the surface of the pipe is coated with a highly conductive material having low electrical resistivity, and furthermore, at least the surface directly facing the plasma is 7 Alladay shield for high frequency heating equipment is extremely reliable because it coats low atomic number materials, can withstand high heat loads, reduce high frequency losses and increase KjII effectiveness. Can be provided.

[Brief explanation of the drawing]

FIG. 1 is a sectional view showing one embodiment of the present invention, FIGS. 2 and 3 are sectional views showing other embodiments of the invention, and FIG. 4 is an I
FIG. 5 is a block diagram schematically showing a CRF high-frequency heating device, and a perspective view showing a conventional 7 Allade shield. 1... High melting point material pipe, 2... Good conductive substance, 3
...Low atomic number substance, 4...High frequency oscillator, 6...
・Coaxial tube, 2... Goo yxma, 8... Coupling system, 10
...Loop antenna conductor, 11°°/7 Alladay shield, 13...Antenna casing, 14...Jacket, 15...Faraday shield pipe. Applicant: Takehiko Suzue, Patent Attorney Figure 1 Figure 3 ■ Figure 4 Figure 1 Q5 Leap 1, Case Description Japanese Patent Application No. 63-005133 2, Title of Invention Faraday Shield 3 for High Frequency Heating Device, Amendment Patent applicant (409) Japan Atomic Energy Research Institute (and 1 other person) 4. Agent UBE Building 7, 3-7-2 Kasumigaseki, Chiyoda-ku, Tokyo.
On page 10, line 4 of the specification of contents of correction, rTic is about 1/8 smaller. " is corrected to "Tic is about 8 minutes of iron."

Claims (1)

[Claims] An ion cyclotron frequency band high-frequency heating device that transmits high-frequency output generated by a high-frequency oscillator through a coaxial tube and emits it into plasma via an antenna attached to the tip of the coaxial tube. In the Faraday shield, which is formed by connecting two pipes and is installed on the plasma side of the antenna to shield the electric field formed by the high frequency current flowing through the antenna, the pipe is formed of a high melting point material, and the A Faraday shield for a high frequency heating device, characterized in that the surface of the pipe is coated with a good conductive material having low electrical resistivity, and further, at least the surface directly facing the plasma is coated with a low atomic number material. .