EP0770264B1 - Magnetic system for gyrotrons - Google Patents

Description

The invention relates to a magnet system for gyrotrons for production the axial magnetic direct field between the emitter and collector area.

The purpose of the invention is that the operation is complex powered gyrotron magnet system, be it conventional or superconducting electromagnets, thanks to a maintenance-free Permanent magnet system to replace without constructive Conversion measures on the gyrotron tube itself would be necessary.

Gyrotrons are sources for the generation of high microwave powers at high frequencies, such as those used to heat fusion plasmas are needed. Typical orders of magnitude are 1 MW output power and frequencies in the range of 100 GHz.

The basic structure and description of a gyrotron shows Meinke-Gundlach in "Taschenbuch der Hochfrequenztechnik" (Springer Verlag Berlin Heidelberg New York Tokyo 1986) on pages M82 - M85. Leave Gyrotron Oscillators yourself in the vacuum tube and the guide field without any special effort Disassemble the generating magnet system. Especially High-performance gyrotrons are used as additional heating for fusion plasmas provided (see pages S17 and S18).

So far there are only theoretical works on mastery of electron beam instabilities in gyrotrons. In Int. Journ. of Infrared and Millimeter Waves, Vol. 14, No. 4, 1993 is an article by A. N. Kuftin et al. under the title: "Theory of Helical Electron Beams in Gyrotrons" published. Permanent magnet systems for guiding helical electron beams are considered. The permanent magnet system exists from a central, axially polarized permanent magnet and at its two end faces, in opposite directions, radially polarized permanent magnets (Fig. 10 therein). With this System finds one in the electron beam area of the gyrotron strong magnetic field reversal of the axial field and a sharp increase of the field on the edge instead of.

All electrons should have the same starting conditions, allowed the sharp rise in the field in the area of the emitter above furthermore only the use of effectively narrow emitter rings. Emitter ring and magnetic field must be adjusted exactly.

The field reversal at the collector places restrictions on the design of the collector, especially in the case of preloaded collectors after itself.

Technically speaking, gyrotrons currently have an electrical one Efficiency of 50% reached (operation in the first Harmonics of the cyclotron frequency). Another increase it is not so urgent at least at the moment. Indeed are gyrotrons for industrial use such. B. Surface coatings and ceramic sintering interesting, see above that the question of higher efficiency and associated with it also the question of lower cooling capacity required and lower Material expenditure gets economic importance.

Parameters of such gyrotrons are relatively lower frequencies (e.g. 30 GHz) at low powers (e.g. 10 kW). Size Losses of efficiency arise in the one serving as an interaction space Gyrotron resonator, the largest cooling effort arises on Collector, the second largest cooling effort is created with normal conductive Magnet working gyrotrons in the magnet. The Losses in the magnet can be reduced by using permanent magnets decrease drastically.

The invention has for its object the previously used supra- or normal conducting magnets through permanent magnet arrangements to replace the - unlike previously designed Permanent magnet arrangements - neither additional scientific or require construction work in the gyrotron tube nor the use of constructive developments Previously available gyrotrons (such as equipment with prestressed Restrict collectors) or make them impossible. In addition are said to be electron beam reflections and electron beam instabilities be avoided in the gyrotron.

The object is achieved by the characterizing Features of claim 1 solved. A central, radial polarized, one brought to the collector area (13), axially polarized ring magnet (15) and one on the opposite End face of the central ring magnet (14) ring magnet arrangement blocking the outbreak of the field (15) generate the desired magnetic field profile in the electron beam area basically. Due to the required field course (Claim 4, for example), the geometry of the permanent magnets (14, 15) determined with computer help. A strong one, however so only meaningless field reversal only takes place outside of Electron beam area in extension of the emitter (9) instead. A second reversal in the prior art of magnet systems of the magnetic field is avoided or in its amplitude meaningless. The mechanical tension of the magnet system is a technically known solution.

Subclaim 2 characterizes the simplest, namely symmetrical, but also a more material-intensive construction the permanent magnet system (7).

Claim 3 indicates a material-saving, asymmetrical Structure of the permanent system 7, with which one has a strong Magnetic field reversal generated outside the electron beam range, but which has no influence.

With a simple, axially polarized permanent magnet in the Emitter area can be the axial emitter constant field, which is considerable is weaker than the axial resonator constant field (Claim 5).

For field correction and flux concentration, there are power operated Solenoids and soft iron assemblies still in use (claims 6 and 7). Other known correction options on the axial DC magnetic fields can be achieved with sliding solenoids will.

In the following the device is to be explained and explained in more detail will. For this purpose, six figures are included in the drawing will.

Show it:

Figure 1 shows the basic structure of a gyrotron with the invention Device for generating the static magnetic field.

Figure 2 shows the basic desired dependence of the magnetic Leading field along the gyrotron axis.

Figure 3a and 3b and 4a and 4b the basic structure of the Device according to the invention for generating the static magnetic field and the field along the axis.

In the gyrotron, Fig. 1, the electrons propagate as a hollow beam on helical tracks - guided by a static magnetic field - From the cathode 1 to the resonator (11) and leave it as a "used" beam to the collector (13), where the the resulting heat must be dissipated.

The radius of the hollow electron beam R is determined by the magnetic guide field B through the relationship B * R 2nd = const (see Gyrotron Oscillators, Their Principles and Practice, edited by CJ Edgcombe, Taylor & Francis, 1993; especially Chapter 5 by B. Piosczyk). With a predetermined speed ratio α and magnetic field in the resonator 11 and a selectable (triode) or fixed (diode) compression ratio (ratio of the hollow beam radii), the axial magnetic field at the emitter 9 is also fixed. In the case of electrons propagating on helical orbits, the ratio of the transverse to the axial velocity component becomes α = v ┴ / v ∥ through the equation v ┴ 2nd / B = const fixed. If the transverse speed reaches the total speed, the electron beam is reflected (magnetic mirror).

The static magnetic field not only serves to guide the electron beam, but also places according to the equation ω c = e * B / m the cyclotron frequency of the electrons in the resonator 11 fixed. m is the relativistic mass of the electrons with the elementary charge e, B is the magnetic flux density. The frequency ω generated by the gyrotron is included ω = n * ω c n is an integer and is called the order of the cyclotron harmonic. In the case of gyrotrons which generate microwave power at 30 GHz, the required magnetic field in the first harmonic is approximately 1.1 T in the second harmonic approximately 0.55 T. The field sought along the gyrotron axis (8) can be seen in FIG. 2.

Generation of the magnetic field with superconductors is required a high expenditure on equipment and a constant operation Helium or nitrogen requirement. Generation of the magnetic field with normal conducting magnets requires high connection and Cooling capacity. The energy consumption of the magnets is opposite not to neglect the generated power.

A generation of the magnetic field with permanent magnets brought fundamental problems with the arrangements examined so far with yourself. In principle, these arrangements consist of one middle, axially polarized and two radially polarized Magnets (see Fig. 10 from Kuftin, Int. J. of Infrared and Millimeter waves). The disadvantages of such systems are zero crossings on the axis and unused fields (worse Efficiency), as well as steep waste at the edges. The steep Waste on the edges have the disadvantage for the emitter side that the adjustment gyrotron magnet is critical and the effective one Emitter width is restricted. The zero crossing has to Consequence that with an increasingly negative magnetic field along the axis the electron beam can be reflected (magnetic Mirror). This makes the design of the collector more difficult. The use of prestressed collectors for energy recovery becomes practically impossible.

Prestressed collectors are necessary to increase the efficiency. The ratio of the energy taken from the electrons to the original energy is the electrical efficiency η _ei . The overall efficiency can now be increased by letting the beam strike a prestressed collector, whereby part of the energy of the beam used is recovered with the efficiency η _c . The overall efficiency of a gyrotron with a biased collector is: η = η el / [1 - η c (1 - η el )] The use of prestressed collectors is practically impossible or drastically complicated by a reversal of the sign of the axial magnetic guide field along the electron beam path.

Laminar cathodes should also be used on the cathode side to be able to and to keep adjustment problems low - in the area the cathode (1) the axial magnetic field locally constant be, see Figure 2.

Figure 1 shows the basic schematic structure of a gyrotron. In a nutshell, the essentials about the gyrotron in Meinke Gundlach, "Taschenbuch der HF-Technik, M 82 ff., read up.

Figure 2 shows, as already mentioned, the course of the desired axial magnetic constant field in the gyrotron areas: Emitter (9), compression area (10), resonator (11), decompression area (12) and Collector (13). The wavy course of the magnetic flux density is more or less provoked depending on the interpretation (see DE 42 36 149 A1), namely through the structure of the inner surface on the permanent magnets (15, 14, 15). The field strength about 5 - 25% of the axial constant field is in the emitter region in the resonator area.

Figure 3a shows a symmetrical arrangement of the permanent magnet system 7. It is therefore only the right half as a computer printout shown, since it is the one relevant for the gyrotron Magnetic field line course shows. The radially polarized middle one Magnet 14, better the drawn axial half is over Brackets, which are not shown, with the right, axially polarized magnet (15), over the common conical surfaces in touch. There is none or only one in the gyrotron area easily compensable zero crossing of the field lines instead. Of the entire river runs rotationally symmetrical to the z-axis.

The course of the constant field depending on the z-axis, 3b shows part of the gyrotron axis 8. This The flux density curve is point symmetrical to the axis origin and there also has only one zero crossing (stagnation point) Field reversal. Thus, the radially polarized ones shown in Fig. 3a are Permanent magnet half and the right of it subsequent axially polarized permanent magnet (15) basically suitable a magnetic DC field without zero crossing to generate in the gyrotron area. Only the weaker is missing DC field for the emitter area. The not hinted at The left half essentially serves to erupt the Prevent field.

The permanent magnet system (7) in Figure 4a meets the requirements of the constant field in the gyrotron, with it in particular Magnetic material saved. It consists of the central, radially polarized, ring-shaped permanent magnets (14). On the right (collector side) in the figure, the axially closes polarized, ring-shaped permanent magnet (15). Left closes the magnetic arrangement blocking the outbreak of the field on. This geometric shape of the enables the required field structure in the gyrotron area. The low DC field in the emitter zone is due to the overlay of the small annular, axially polarized permanent magnet fully achieved with a rectangular longitudinal section.

The course according to strength and sign, depending on the location, shows Figure 4b. There is far behind the emitter 9, on the left the strong, concentrated, inevitable field reversal. The gyrotron areas Emitter (9), compression area (10), resonator (11), decompression area (12) and collector (13) are indicated. Now exists the constant magnetic field in the emitter area, the high one DC field in the resonator (11) and that going back to almost zero DC field in the collector area (13).

The field is thus more complete through the borehole of the Magnet system forced. A sign reversal of the axial Magnetic field is not found in the gyrotron area or only of minor importance Strength instead and only once. In order to can the electron beam from the emitter (9) to the collector (13) be stably managed.

The field is thus more complete through the borehole of the Magnet system forced. A sign reversal of the axial Magnetic field is not found in the gyrotron area or only of minor importance Strength instead and only once. In order to the electron beam can be stable from the emitter to the collector be performed.

By fine structuring on the inner surface (claim 4) In the middle of the resonator, a constant or a predetermined one wavy magnetic field generated. Spatially (locally) constant Fields can be located in the area of the emitter (9) (see Fig. 4a) and in the area of the collector (13) by additionally axially polarized Reach magnets. Zero crossings of weak fields can be suppressed in this way.

By combining with weak electromagnets one can Readjust the magnetic field or achieve further material savings to reach. Another way to tune are radially and / or axially displaceable magnets.

Reference list

1

cathode

3rd

Acceleration anode

5

Decoupling line

7

Permanent magnet system

8th

Gyrotron axis

9

Emitter

10th

Compression range

11

Resonator

12th

Decompression area

13

collector

14

Central ring magnet

15

Axially polarized ring magnet

16

Field lines

17th

Vacuum vessel

Claims (7)

1. Magnetic system for gyrotrons, which comprises a permanent magnet system (7), for producing the steady axial magnetic field, by which electrons, emerging from the emitter (9), are guided, characterised in that
   the permanent magnet system (7) comprises a central, radially polarised annular magnet (14), an axially polarised annular magnet (15), which attaches to collector (13) in the direction of its end face, and an annular magnet arrangement which attaches to the other end face, said annular magnet arrangement being a partial system which blocks the flow of the magnetic field,
   the partial magnets of the permanent system (7) are in direct contact with their faces which lie opposite one another,
   a constant or variably rippled magnetic field is produced by the geometry of the annular magnets (15, 14, 15) and their mutual mechanical tension in the region of the resonator (11), and no magnetic field reversal or, at most, an easily compensatable axial magnetic field reversal enters the collector (13) and emitter region, and the field reversal of the steady axial magnetic field is effected in the extension of the emitter region externally of the region of the electron trajectories.
2. Magnetic system for producing the steady axial magnetic field for gyrotrons according to claim 1, characterised in that the permanent magnet system (7) is symmetrical, with an axis perpendicular to the system axis.
3. Magnetic system for producing the steady axial magnetic field for gyrotrons according to claim 1, characterised in that the permanent magnet system (7) is constructed asymmetrically and produces a powerful magnetic field reversal in the extended emitter region externally of the electron beam source.
4. Magnetic system for producing the steady axial magnetic field for gyrotrons according to claims 2 and 3, characterised in that the axially polarised annular magnet (15), extending towards the collector (13), has a structured internal surface, whereby the steady magnetic field course in the resonator region is given a prescribed fine structure.
5. Magnetic system for producing the steady axial magnetic field for gyrotrons according to claim 4, characterised in that an axially polarised, annular permanent magnet is situated in the region of the emitter (9), and the steady magnetic field, which is weaker in the emitter region but is locally constant, is achieved with said permanent magnet by superimposition.
6. Magnetic system for producing the steady axial magnetic field for gyrotrons according to claim 5, characterised in that, to correct the axial magnetic field strength, at least one current-operated solenoid is combined with the permanent magnet system (7).
7. Magnetic system for producing the steady axial magnetic field for gyrotrons according to claim 5, characterised in that, to correct the axial magnetic field course and to guide the flow in the gyrotron region, soft iron configurations are tensioned with the permanent magnet system (7).

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