SU1621186A1 - Aerial device for exciting slow waves in plasma in magnetic trap - Google Patents

Abstract

The invention relates to antenna devices for exciting electromagnetic waves in a plasma and can be used to generate and heat a plasma. The goal of the isetret is to increase the efficiency of the excitation of slow kinetic waves in the plasma of magnetic traps. The device consists of an electrically conductive screen 1 and a retarding comb-type structure made in the form of a system of mutually parallel conductors 3 located in a plane parallel to the plasma boundary between the electrically conductive screen 1 and the plasma boundary perpendicular to the magnetic field. The conductors 3 are connected to the electrically conductive screen 1 by jumpers 4, the distance between which is less than half the wavelength. Jumpers 4 adjacent conductors 3 are offset,. one relative to another at a distance equal to half the distance by the jumpers 4 of one conductor 3. In the gap between the conductors 3 and the plasma boundary, surface slow electromagnetic waves are driven by a slit or loop type exciter traveling along the direction of the magnetic field. Due to this, at the plasma boundary, slow kinetic waves, propagating deep into the plasma, are excited. 2 Il. R yut

Description

figure 1

The invention relates to antenna devices for exciting electromagnetic waves in a plasma and can be used to produce and heat a plasma9 to maintain a stationary current in closed magnetic traps, including in a nuclear reactor, as well as for diagnostic purposes, such as receiving radiation from plasma,

The aim of the invention is to increase the efficiency of excitation of slow kinetic waves in a plasma.

Fig. 1 shows the proposed antenna device in Fig. 2 - the same view from the plasma side (arrows show currents in conductors that can lead to parasitic excitation of a fast wave),,

And the area between the screen 1, which may be the wall of the vacuum chamber

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Antenna device works blowing

Through the use of pathogens (not shown) in the retarding structure formed by the system of conductors 3 and jumpers 4, and in the vacuum gap between the conductors 3 and the plasma, the surface slow electromagnetic wave MV (E) is excited. It spreads along the retarding structure in the direction of the magnetic field of the BO and, due to the connection at the plasma boundary between MB (E) and MB (K), excites 5 MB (K), which carries energy deep into the plasma. Through the use of a system of conductors 3 connected to screen 1 with a jumper 4 with hd, the slowing down of the surface MV (E) is significantly greater than one, which leads to an increase in the coupling of the surface MV (E) with MB (K) and a decrease in the attenuation length.

the magnetic trap boundary of plasma 2 is a system of flat mutually parallel conductors Zr oriented, perpendicular to the magnetic field BQ. by the jumpers of one conductor (in chess order), the distance d between the conductors 3 and the plasma boundary 2 is chosen less than the height h of the jumpers 4. For the antenna device (Fig. 1), it is intended for the excitation of slow kinetic waves MB (K) in the current of a poppy with the following parameters

of plasma plasma 4

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T „e B0 4Tl; ne

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3 / SOS 1, 95; the working gas is deuterium, where n, J and n „are the density of ions and electrons; T (and Te are the temperature of ions and electrons; 03 is the circular frequency of the generator; G3C; is the ion cyclotron frequency j BQ is the constant magnetic field, the optimal dimensions are the following; h 10 cm and d 1 cm, and the distance 1 1 m between the adjacent bridges 4 of one conductor 3 are chosen significantly larger than the cross section (diameter) of the jumpers 4E but less than half the wavelength A. For these values of the magnetic field B 2Ts / (0 5 m (s is the speed of light in vacuum). The distance between the conductors 3 S 3 cm

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It is necessary that the distance between the bars does not exceed half the wavelength. Otherwise, it is possible to excite higher modes of the surface MV (E), which propagate along the magnetic field with a phase velocity greater than the speed of light. The excitation of such modes is unacceptable, since their attenuation length due to radiation into the plasma becomes extremely large. Because of the discrete type of bridges 4 in the conductors 3, currents I ,, flowing perpendicular to the magnetic field B0 (Fig. 2) appear. Such currents can excite a parasitic fast wave in the plasma, which can carry a significant fraction of the RF power supplied to the antenna. In order to suppress this undesirable effect, the jumpers 4 of the adjacent conductors 3 are shifted one relative to another by a distance equal to half the distance between the jumpers 4 of the conductor 3 (Fig. 2). In this case, the currents in the adjacent conductors 3 flow in opposite directions. Therefore, the spectrum of the long wave numbers of the fast waves excited in the plasma lies in the region of very high decelerations and the propagation of the fast wave in the plasma becomes impossible

When using the proposed antenna device, the total ohmic loss of RF energy in the elements of the antenna device is significantly reduced, and consequently, K11D of RF energy input into the plasma increases. This allows

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to simplify the cooling system of the antenna, and also makes it possible to use stainless steel or graphite as the antenna materials, which are most acceptable from the point of view of reducing the influx of heavy impurities into the plasma, but have low electrical conductivity.

Claims (1)

Invention Formula An antenna device for exciting slow-waves in a plasma trapped in a magnetic trap, containing a retarding structure connected to an RF generator and an electrically conductive screen characterized in which, in order to increase the efficiency of the excitation of slow kinetic waves in a plasma, slowing down the structure made in the form of mutually parallel conductors located in a plane parallel to the plasma boundary in the magnetic trap between the plasma boundary and the screen so that each wire is perpendicular to the direction of the magnetic field in the trap and connected to the screen by electrically conducting jumpers, the distance between which is less half the length of the electromagnetic wave, with the jumpers of adjacent conductors being offset one relative to another by a distance equal to half the distance between the jumpers of the conductor, Fig-g