RU2430493C1 - Multipolar magnetic plasma trap - Google Patents

Abstract

FIELD: physics. ^ SUBSTANCE: proposed trap comprises three myxines spaced apart in parallel planes to form triangle in cross section, each vertex of the latter makes center of relevant myxene. Note here that one of myxenes is located between other myxenes. Besides, it comprises pushers. Every myxene and pusher represents current-conducting coil made up of closed ring. Geometrical centers of closed rings are located on common axis. First two identical-diameter pushers located on side of smaller-diameter myxene and between said myxene and other myxenes and feature diameter smaller than that of other myxenes, while two other identical-diameter pushers are located on outer side of larger-diameter myxenes and between them. ^ EFFECT: optimised plasma shape and density in maximum magnetic fields. ^ 7 dwg, 1 tbl

Description

The invention relates to the field of plasma physics, in particular, to the design of a trimix-type magnetic galathea trap designed to hold a plasma volume enclosed in a torus by a magnetic field around three coils.

The methods of quasistationary magnetic confinement of high-temperature thermonuclear plasma in closed traps of the tokamak and stellarator type are well known and used in experiments (L. Artsimovich, “Controlled Thermonuclear Reactions”, M., “Nauka”, 1963). At present, the fusion power comparable to the power of plasma production has been obtained on the JET and JT-60U tokamaks. Thus, the possibility of creating a controlled thermonuclear reactor based on confinement of a thermonuclear plasma in a closed magnetic trap has been practically proved.

An important characteristic that determines the parameters of a fusion reactor with magnetic confinement is the parameter β, defined as the ratio of the plasma pressure (the product of the plasma density and temperature) to the pressure of the confining magnetic field (squared magnetic field modulus). Since the power of the thermonuclear reaction is directly determined only by the plasma pressure, then, naturally, we must strive for values of the parameter β close to unity, when the holding capacity of the created magnetic field is fully used. Unfortunately, the tokamak and stellarator systems, which have a magnetic field that is almost uniform along the magnetic axis, work stably only at small values of the parameter β ~ 0.05. Such small values of the parameter β are in good agreement with the predictions of the modern theory of magnetic confinement.

A significant advance in the development of this topic was the method of confinement of thermonuclear plasma in a closed trap, described in SU No. 1062795 (publ. 23.12.83). In this method, sections of a homogeneous axially symmetric magnetic field with cylindrical magnetic surfaces were connected by closing curved sections with circular sections of magnetic surfaces, the configuration of which was selected so that within each curved section the condition

where s is the arc length of the magnetic axis of the trailing section, measured from its middle;

L is the length of this section;

k (s) is the curvature of the axis;

B (s) is the magnetic field strength on the axis;

C (s) is the current rotation angle of the magnetic field lines.

Condition (1) ensured the internal closure of the secondary plasma currents and their non-exit into homogeneous axially symmetric sections, which made it possible to make the homogeneous sections sufficiently long and to obtain plasma with a high value of the parameter β on them.

In the description of the known method for holding plasma in a closed trap, a variant of the closing magnetic element in the form of three sections of a toroidal uniform field rotated by 120 ° is given. Minor technological changes made to this system are described in SU No. 1508288 (publ. 15.05.89).

Theoretical studies show that in the known method, you can also use rectilinear axially symmetric sections with an inhomogeneous magnetic field and curved locking elements with an elliptical cross section. Moreover, condition (1) is generalized and takes on a rather complicated form (V. M. Glagolev, B. B. Kadomtsev et al. In Proceedings of the 10th European Conference on Controlled Fusion and Plasma Physics, Moscow, 1981, v. 1, E-8)

where exp (η) is the ratio of the axes of the elliptical magnetic surface;

δ (s) is the angle of the main normal to the axis and the minor axis of the ellipse;

- кручение оси.

- torsion of the axis.

However, the known method, as predicted by some theoretical calculations, allows you to create a trap with holding properties worse than in stellarators and tokamaks. This was, apparently, one of the main reasons for which so far not a single large experiment with such a trap has been carried out. The reason for poor retention in such a system is associated with the presence of the so-called “super-banana” drift trajectories of hot charged plasma particles. These trajectories are characterized by very large radial deviations of charged plasma particles from magnetic surfaces, which should cause a rapid loss of plasma on the trap wall. The appearance of "super-banana" trajectories is a consequence of the three-dimensionality of the magnetic configuration of the trap and violation of the topography of the level lines of the magnetic field modulus on the magnetic surfaces of the trap.

A more advanced trap, adopted as a prototype, adopted the well-known magnetic trap galatea "Trimix" with three mixins, described in g. “Plasma Physics”, 2006, Volume 32, No. 3, pp. 195–206, article “Injection of Plasma into the Galatea“ Trimix ”, authors A. I. Morozov, A. I. Bugrova, A. M. Bishaev, M. V. Kozintseva, A.S. Lipatov, V.I. Vasiliev and V. M. Strunnikov.

The concept of galactic magnetic traps as candidates for the role of a plasma confinement system in a thermonuclear reactor suggests that in these traps with current-carrying conductors washed by plasma (“mixins”) (Braginsky SI, Kadomtsev BB) Plasma Physics and Problem controlled thermonuclear reactions ", under the editorship of M. A. Leontovich, vol. 3. M., publishing house of the Academy of Sciences of the USSR, 1958, p. 300; Kerst DW, Ohkawa T." Nuovo Cimento ", 1961. V.22, p.784; Peregood BP, Lehnert B. "Nucl. Instrum. Methods", 1981, v.180, p.357; Yoshikawa S. "Nucl. Fusion", 1973, v.13, p.433; Prager SK " Nucl. Instrum. Methods ", 1983, v.207, p. 187; Zhukov V.V., Morozov A.I., Schepkin G.Ya." Letters to JETP ", 1969, vol. 9 p. 24), the value β ₀ (β ₀ = 2µ _o Pmax / B ² max, where Pmax and Bmax are the maximum plasma pressure and the maximum field in the reactor) can reach values of the order of unity, and the transfers can be classical. Today's tokamaks and stellators do not meet the specified requirements.

The study of toroidal multipole galatas (quadrupole and octupole) confirms the feasibility of these qualities, including the classical nature of the transfers. However, the studied types of traps (the equilibrium in them was calculated on the basis of the Grad-Shafanov equation) (Morozov AI, Savelyev VV "Advances in Physical Sciences", 1998, vol. 168, No. 11, p. 1153) have a significant drawback : the distance between the separatrix and the mixin surface δ _{sm is} small, which, of course, limits the plasma retention time. Of course, this drawback is unprincipled and can simply be overcome by a proportional increase in all sizes of the trap. But at the initial stage of research, with the limited size of the available vacuum chambers, this drawback forces us to look for new variants of multipole galatas, where, with the usual size of the trap, the value of δ _sm would be significant. The search led to the Trimiks configuration proposed by A. I. Morozov (A. Morozov, A. I. Bugrova, AM Bishaev “XXX Zvenigorod Conference on Plasma Physics and TCB”, February 24-28, 2003, abstract. ., p. 70), which is presented in figures 1 and 2.

Figure 1 shows the magnetic configuration of the Trimix galatas in the absence of plasma. This configuration is formed by five coaxial coils 1-5. The coils of solenoid 5 are closest to the axis. Further along the radius are the windings of three mixins 1, 2 and 4, one of which 1 is “internal”, and the other two 2 and 4 are “external”. A “pusher” 3 is placed between the “external” mixins, which weakens the electrodynamic interaction of the mixins. The coils were attached by holders to the support frame. The holders were made of a stainless steel tube with a diameter of 10 mm, on which tubes of quartz with a diameter of 15 mm were worn.

Figure 1 shows the line BO along which (in the direction of myxine 2) the injection of plasma clots was carried out. The positions of the probes (points C and D along the BO line), with which the directional velocity of the bunch in the trap were measured, are also shown there. The dashed line marks the separatrix. The distribution of the normal component of the magnetic field induction along the line OB is shown in figure 2.

An analysis of the results of studying the plasma volume in such a trap showed the following. When a trap is filled with plasma using plasma clots, a toroidal plasma volume is formed in the trap volume. The BO line is the most optimal direction of injection, since the clot, when approaching the trap, overcomes the front magnetic barrier, penetrates into the region of zero magnetic field and is completely braked and thermalized at the rear magnetic barrier, in which the magnetic field is 3-4 times higher than in front.

Dynamic clot pressure in front of the front magnetic barrier:

ρV ² = n · m _p · V ² ≈ 8.3 · 10 ² Pa,

where m _p is the mass of the proton, while the magnetic pressure calculated from the maximum value of the magnetic field in the front barrier B = B _max = 2.2 · 10 ² T,

B ² / (2µ ₀ ) = 1.9 · 10 ² Pa.

Thus, the dynamic pressure of the bunch is noticeably higher than the magnetic pressure, and the plasma should easily enter the trap. However, when a plasma bunch passes into a trap, it displaces the magnetic field of the trap from its volume. Therefore, the energy of the bunch decreases by an amount proportional to the volume of the displaced magnetic field. Since in the Trimix trap the magnetic field weakly decreases outside the trap (the field has a noticeable value at a distance of 70 cm from the trap (see Fig. 2)), the energy that the bunch spends to displace this field can be a significant amount of initial energy of the bunch.

Therefore, obtaining a plasma with a high density and unclear boundaries inside the trap requires the use of a plasma gun for injection of plasma clumps along the BO line with sufficiently high energy indices (the energy of the injected bunch should be higher than the energy of the magnetic barrier in the weakest part of the magnetic barrier).

Thus, plasma capture is effective, but it should be borne in mind that part of the energy of the plasma bunch is lost when passing the front magnetic barrier.

The plasma that has entered the trap (the azimuth Θ = 0 ° is assigned to the entrance region) spreads along the azimuth symmetrically in two directions: clockwise (Θ <0) and counterclockwise until the antidirectional plasma flows merge into the torus.

Thus, in the design of the Trimix trap, it was found that the plasma boundary coincides with the magnetic surface lying near the Okawa surface; plasma occupies a volume of about 100 liters. Plasma concentration has a maximum not at the zero of the magnetic field, but on a magnetic surface lying closer to the center of the trap than the Okawa surface (Fig. 3, where 1 is Okawa A, γ is the line bounding the plasma). All this is consistent with classical ideas about transport processes in a trap. Studies were also conducted of the plasma retention time in the trap under various modes of its filling. The plasma retention time in the trap decreases with increasing plasma density and increases with increasing magnetic field faster than according to the linear law. The retention time can reach 1 ms.

However, the issue of the economics of the setup in terms of creating both plasma clumps and a confining magnetic field remains a serious obstacle to obtaining a well-held high-density plasma volume.

The present invention is aimed at achieving a technical result for optimizing the shape of the plasma volume and its density in the zone of action of the largest magnetic fields around the mixins and making it possible to form a section of a reduced magnetic field in the magnetic shell of the mixins to enter the plasma bunch into the trap. The achieved result is aimed at obtaining the following advantages:

- providing injection of plasma clots in the most convenient and advantageous directions (from the point of view of overcoming the plasma magnetic barrier at the entrance and subsequent retention inside the trap);

- providing the ability to enter microwave power into the plasma volume;

- facilitation of optical measurements and visual observations.

The indicated technical result is achieved in that in a multipole magnetic trap for a plasma containing three mixins, each of which is a current-carrying coil winding made in the form of a closed ring, and which are located in parallel planes at a distance from each other with the formation of a triangle in cross section, each vertex of which is the center of the cross section of the corresponding mixin, with one of the mixins located between the other mixins, as well as pushers, each of which represents a current-carrying coil winding made in the form of a closed ring, with the mixins and pushers remotely located relative to each other, and the geometric centers of the closed rings placed on a common axis, the first two pushers of the same diameter are placed on the side of the mixin of smaller diameter and between this mixin and other mixins and made with a diameter smaller than the diameter of the other mixins, and the other two pushers of the same diameter are placed on the outside of the mixins of larger diameter and between them.

These features are significant and are interconnected with the formation of a stable set of essential features sufficient to obtain the desired technical result.

The present invention is illustrated by a specific example of execution, which, however, is not the only possible, but clearly demonstrates the possibility of achieving the desired technical result.

Figure 1 shows the magnetic configuration of the trap-galatea "Trimix", a prototype;

figure 2 - distribution of the normal component of the induction of the magnetic field along the injection line IN, the origin corresponds to the center of the myxine 2. A, B and γ are the points of intersection of the injection line with the border of Okawa A, the border of Okawa B and the boundary of plasma γ, respectively, prototype;

figure 3 - the boundary γ of the distribution of plasma in the trap of the prototype;

4 is a design of a plasma trap according to the invention;

figure 5 - arrangement of coils and the configuration of the magnetic field in the trap according to the invention;

Fig.6 - distribution of the magnetic field in the trap of Fig.4;

Fig.7 - distribution of the normal component Bn of the magnetic field of the trap along the injection line.

According to the present invention, there is considered the construction of a trimix-type magnetic galathea trap designed to hold a plasma volume enclosed in a torus by a magnetic field around three coils.

The new design of the magnetic trap for plasma according to the invention pursues the following objectives:

- providing injection of plasma clots in the most convenient and advantageous directions (from the point of view of overcoming the plasma magnetic barrier at the entrance and subsequent retention inside the trap);

- providing the ability to enter microwave power into the plasma volume;

- facilitation of optical measurements and visual observations.

The calculations of the configuration of the magnetic field of the trap for various options for the mutual arrangement of the coils were performed using the FEMME program.

The criteria for selecting the desired configuration were as follows:

- the current density in the coils should not exceed the current density in the coils of the prototype (130 MA / m ² );

- the axial forces between the mixins must be equal to zero (this requirement is due to the fact that the mixins are located inside the plasma volume, and the holders of these coils must be thin);

- the magnetic field along the injection line should fall sharply to zero outside the trap coils (in other words, the field should be concentrated in the volume occupied by the trap coils);

- the location of the magnetic coils of the trap should be convenient for introducing into the trap plasma clots and microwave power and such that it allows to study the plasma parameters in the trap using optical methods.

Figure 4 shows the design of a plasma trap according to the invention.

A multipole magnetic plasma trap contains three mixins 1, 2 and 4, which are located in parallel planes A, B and C at a distance from each other with the formation of a triangle in cross section, each vertex of which is the center of the cross section of the corresponding mixin, while one of the mixins 1 located between the other mixins 2 and 4. To attenuate the electrodynamic interaction of adjacent mixins, pushers 3, 6, 7 and 8. Each mixin and each pusher is a current-carrying coil winding, made in the form of a closed ring. The geometric centers of the closed rings are located on the common axis 9. The first two pushers 6 and 7 of the same diameter are placed on the side of the mixin 1 of smaller diameter and between this mixin 1 and other mixins 2 and 4, are made with a diameter smaller than the diameter of other mixins 2 and 4, and are located in the plane of these other mixins. Two other pushers 3 and 8 of the same diameter are placed on the outside of the mixins 2 and 4 of a larger diameter and between them.

The coils of mixins and pushers are attached by holders 10 (supports made of non-magnetic material) to the supporting frame 11, which is also made of non-magnetic material. For ease of assembly, the trap is made of two halves, which are assembled held on two parts of the bed, interconnected by screeds 12. The holders allow spatial orientation of the mixins and pushers relative to each other, leaving the structure itself transparent for the possibility of using a research tool and choosing the place for introducing plasma clots .

Thus, the multipole magnetic plasma trap according to the present invention consists of 7 magnetic coils: three mixins (coils for pos. 1, 2 and 4) and 4 pushers (coils for pos. 3, 6, 7 and 8). The cross section of all the coils is a circle with a diameter of 2 cm. The diameters of the coils (in the center of the section) were chosen as follows: the diameter of the pusher coils 6 and 7 is 460 mm, the diameter of the mixin coil 1 is 400 mm, the diameter of the mixin coils 2 and 4 is 700 mm, the diameter of the pusher coils 3 and 8 is 900 mm. The distance along the Z axis between the coils-pushers 6 and 7 is 220 mm, between the coils-mixins 2 and 4 - also 220 mm, between the coils-pushers 3 and 8 - 120 mm.

The nominal parameters of the magnetic coils are summarized in the table.

Coil number one 2 3 four 6 7 8 Current density, MA / m ² 119,366 95,493 -56.25 95,493 -39,536 -39,536 -56.25 Strength along the Z axis, N 0 0 -1.3010 ³ 0 8.34 · 10 ² -8.3410 ² 1.30 · 10 ³

The “-” sign in the “Current Density” column indicates that the currents in the mixins and pushers are directed in different directions, and in the “Z-axis” column the minus sign indicates that the force is directed in the direction opposite to the OZ axis. The table shows that the forces acting on the mixins along the Z axis vanish. At the same time, the attractive forces between the pushers are quite significant. However, these coils are outside the plasma volume and the forces indicated in the table can be perceived (transmitted) to the massive pusher holder.

An analysis of studies of the pattern of the distribution of the magnetic field and plasma in the trap with this design of the plasma trap showed the following.

Figure 5 shows the location of the coils in the trap, as well as the configuration of the magnetic field in it, found as a result of calculations and studies to optimize the magnetic field of the trap. In this drawing, OZ is the axis of the magnetic coils (that is, the cross section of the magnetic coils of the trap by the ZOR plane is shown in the drawing). The thin lines in this drawing give the configuration of the magnetic lines of force in this section.

6 also shows the distribution of the magnetic field modulus in the trap according to the invention. From this drawing it can be seen that the magnetic field in the region between the coils drops to zero. This region is surrounded on all sides by a magnetic crust, and the minimum magnetic field in the crust is ~ 0.1 T. In the same drawing, an injection line RO is shown in this section of the trap. It should be noted that for the chosen configuration of the magnetic coils, it is possible to inject in any direction Θ in the plane Z = 0, where Θ is the azimuthal coordinate. In this plane, you can enter microwave power and optical measurements.

Fig. 7 shows the distribution of the normal component Bn of the magnetic field of the trap along the injection line, i.e. along the coordinate R. The distance along the abscissa in the graph is measured from the surface of the mixin 1. From Fig. 7 it is seen that when moving away from the mixin 1, the field decreases rapidly, at a distance of ~ 8.5 cm from it passes through a minimum [Bn] ~ 0.017 T, and then, without changing sign, again increases in absolute value and at a distance of 19.5 cm from the myxine 1 it increases to the barrier value [Bn] ~ 0.095 T. Then a further decrease in the field magnitude occurs (up to a zero value at a distance of 26.8 cm from the myxin), and after passing through zero, a maximum of 0.016 T is reached again at a distance of 31 cm from the myxin. With a further increase in the distance, the field value gradually decreases to zero. Thus, the region with a strong magnetic field, which must be overcome by a bunch in front of the front magnetic barrier, has a length of ~ 7 cm. In the prototype, this region had a length of 30 cm.

The total energy of the magnetic field generated by the trap was calculated using the software at the nominal parameters indicated in the table (the current in each coil of the trap wire is 1500 A). The magnetic field energy turned out to be ~ 2.14 kJ. The magnetic flux through the R – O plane was also calculated for these parameters. According to these data, the inductance of the trap coil system connected in series is 1.9 mH.

Thus, it became possible to form a portion of the magnetic field in the direction of RO (Fig. 6), in which the barrier field is concentrated in a narrow region of ~ 7 cm and substantially weakened outside it, which allows the passage of plasma clumps from the plasma duct, eliminating the exit of plasma through this barrier zone.

Analysis of the results of the study of the plasma volume in the new trap showed that the torus-shaped plasma volume inside the trap has a higher density than the plasma volume in the trap according to the prototype. The magnetic barrier is formed in the region of high magnetic field induction, but in the zone between the pushers 3 and 6, a section is formed whose magnetic field is much lower than the magnetic barrier in other areas, which makes it possible to use a plasma gun for injection of plasma clots along the RO line with high energy indicators.

The use of four pushers with a certain spatial orientation with respect to the mixins provides correction of the magnetic field barrier of the trap, forming a barrier as the boundary of the plasma torus, which allows to increase the plasma density in the trap and to eliminate blurring of the boundary, as is the case in the prototype.

Claims (1)

A multipole magnetic plasma trap containing three mixins, each of which is a current-carrying coil winding made in the form of a closed ring, and which are located in parallel planes at a distance from each other with the formation of a triangle in cross section, each vertex of which is the center of the cross section of the corresponding mixin , while one of the mixins is located between other mixins, as well as pushers, each of which is a current-carrying coil winding made in the form of a lock a long ring, the mixins and pushers are remotely located relative to each other, and the geometric centers of the closed rings are placed on a common axis, characterized in that the first two pushers of the same diameter are placed on the side of the myxine with a smaller diameter and between this myxine and other mixins are made with a diameter smaller the diameter of other mixins, and are located in the plane of these other mixins, and the other two pushers of the same diameter are placed on the outside of the mixins of larger diameter and between them.

Images