SU1612967A1 - Antenna device for excitation of slow waves in plasma contained in magnetic trap - Google Patents

Abstract

The invention relates to antenna devices for driving electromotive waves in a plasma toroidal trap type tokamak, stellarizer. The purpose of the invention is to simplify the design of known antenna devices by reducing the number of waveguide leads from the vacuum chamber. The device consists of a high-frequency power source 1, which through waveguide path 2 is connected to one of the ends of the powering waveguide 3, whose axis is parallel to the trap magnetic field power line. The walls of the powering waveguide are wide, formed by a system of waveguide emitters 4. whose open ends are facing the plasma surface 5. The wide walls of the waveguide emitters are perpendicular to the direction of the magnetic field lines. The electromagnetic wave in the powering waveguide is excited at the connection point of waveguide path 2 and propagates to its opposite end. An electromagnetic field with an electric component parallel to the magnetic power line, m 1 silt, is excited on the wide wall of the powering waveguide by the formed waveguide emitter system. LO

Description

The invention relates to antenna devices for exciting electromagnetic waves in a plasma and can be used in experiments on plasma high-frequency heating and maintaining a steady-state current in tokamaks and stellarators. including thermo nuclear reactor parameters.

The aim of the invention is to simplify the design of the antenna device for exciting slow waves in the plasma of a magnetic trap.

The drawing shows the scheme of the antenna of the orgo device.

The high frequency source 1 is connected via waveguide path 2 to one of the ends of the feeding rectangular waveguide 3.

The axis of the impinging waveguide 3 is parallel to the magnetic field H magnetic field trap lines. The wall of the powering waveguide 3 is wide, formed by a system of waveguide emitters 4, the open ends of which face the plasma surface 5. The wall of the waveguide emitters is perpendicular to the direction of the magnetic field lines.

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The device works as follows.

An electromagnetic wave from a waveguide 3 is excited in a megaparticle of 2 m p wavelength; it propagates to the opposite end of the feeding waveguide 3 with a phase velocity

 w, where Nil is the wave slowdown value; C is the speed of light in, Phase wave velocity Vф should be less than the speed of light, i.e. NH 1. This condition is necessary in order for one to | | | | | Sobliding such a propagating wave in a waveguide (conventionally

the absence of radiation, when there is no plasma), and to be able to excite slow waves in the plasma, which can then be absorbed by the electrons

5 plasma due to the Cherenkov effect. For example, for the purpose of maintaining a stationary current in a tokamak reactor using the absorption of slow waves, it is necessary that V 0 3-0 7

10 c (Nii 1,3 + 3).

An analysis of the electrodynamic characteristics of such a system shows that for given dimensions of the feeding waveguide and d and b (see dash.), Frequency o), the value of NH should be equal to the height h of the system of waveguide emitters:

For example, at d -10 (f 5 GHz), b 5 cm, d 1 cm, it follows from the formula that the deceleration value Nn 1.5 is provided at h 2.5 cm.

The above formula is valid if the distance between the adjacent waveguides. As the size increases, the wave in the waveguide will be complex, which corresponds to the superposition of the waves traveling in different directions along the axis of the main waveguide. Therefore, for | In order that only waves running in one direction along the axis of an axial waveguide exist, it is necessary to at least ensure the condition Д Д {| / 2.

Thus, in the absence of plasma, the traveling electromagnetic wave with C, which can be absorbed only due to ohmic losses in the waveguide machines, will propagate along the powering waveguide 3. In this case, an electric field 3. formed by a waveguide system facing the plasma 5, will be excited by an electromagnetic field having a waveguide 3. Having an polarization required for exciting a slow polarization in the plasma, namely: an electric field parallel to the magnetic power lines of the traps.

Therefore, in the presence of plasma, if its concentration is not very small near /

the waveguide, 20 electromagnetic (slow) waves will be excited in the plasma, carrying away the high frequency energy of the plasma. In this case, the wave propagating along the feeding waveguide 3 becomes damped, i.e. its intensity will decrease as it propagates in the feeding waveguide 3 due to radiation into the plasma. Therefore, if the length of the powering waveguide I is chosen greater than

25

thirty

wavelength of attenuation due to radiation into the plasma t, to the other end of the energizing

waveguide, the opposite connection point. In the H source, the electromagnetic wave will not reach, and, therefore, there will be no reflected in the system

35 waves running to the HF source. This will also result in the absence of slow waves in the plasma propagating in different directions along the magnetic field lines, which ensures the generation of a stationary current in the plasma with maximum efficiency.

Since the size of the feeding waveguide is limited by the requirement that the width is L C / t (otherwise

45 becomes multimode), the power introduced through a separate such waveguide will be limited according to the conditions of providing electrical strength, for example, at f GHz and the maximum electric voltage jpM4ecKoro the field in the waveguide is E "10 kV / cm

wavelength of attenuation due to radiation into the plasma t, to the other end of the energizing

The maximum power introduced into the plasma will be MW. Therefore, to introduce higher levels of RF power into the plasma (20–80 MW in the tokamak reactor), it is possible to use a system of such devices located close to each other. The advantages of the invention consist in a significant simplification of the system due to the reduction in the number of waveguides that need to be removed from the vacuum chamber with vacuum electrical isolation. In addition, in the proposed system there are no such additional elements as phase shifters, with the help of which a traveling field is provided on the aperture of the antenna.

The advantage is also the weakening of the effect of changes in plasma parameters near the antenna on its operation. Changing the parameters of the plasma, for example its density, in the proposed device will only lead to a change in the attenuation length of the wave in the powering waveguide. Therefore, if the length of the powering waveguide is longer than the maximum possible attenuation length, then there will always be no reflected waves from the end of the powering waveguide, which ensures

system performance even when plasma parameters change.

Claims (1)

Claims Antenna device for exciting a slow-wave plasma in a magnetic trap, including a system of rectangular waveguide emitters connected to a high-frequency power source, the open ends of which face the plasma surface, in order to simplify it, it is additionally introduced the powering rectangular waveguide, a system of waveguide emitters is formed by segments of the waveguides, the open ends of which are on one side facing the inside of the powering rectangular in the waveguide, forming its wide wall, with the axis of the feeding waveguide parallel to the trap magnetic field power lines, the distance between adjacent waveguides of the waveguide emitter system is less than half the length of the slow electromagnetic wave, while the feeding waveguide is connected at one end to a high-frequency power source, and its length is greater than the attenuation length of a slow electromagnetic wave in it.