EP0393485A1 - Quasi-optical gyrotron - Google Patents

Abstract

A quasi-optical gyrotron for generating electromagnetic radiation in the form of mm-waves has a plurality of high power resonators (6, 7). The resonators (6, 7) each comprise two mirrors (12a, 12b and 12c, 12d respectively) located on a resonator longitudinal axis (10, 11) aligned at right angles to the electron beam axis (1). In this case, the electron beam axis (1) is provided by the path of the electrons which are forced into gyration by a static magnetic field. The resonator longitudinal axes (10, 11) are located essentially in a common plane, at right angles to the electron beam axis (1), and enclose an angle alpha , which is greater than zero. <IMAGE>

Description

Technical field

The invention relates to a quasi-optical gyrotron for generating electromagnetic radiation in the form of mm waves, in which electrons traveling on an electron beam axis are forced to gyrate by a static magnetic field aligned parallel to the electron beam axis and in a resonator of high power, which on a first longitudinal axis of the resonator aligned perpendicular to the electron beam axis, excite an electromagnetic alternating field of high power, so that electromagnetic radiation in the form of mm waves is coupled out at the mirrors.

State of the art

• 1. Da der Resonator nicht koaxial sondern senkrecht zur Elektronenstrahlachse liegt, kann er unabhängig vom "Klystronteil" dimensioniert werden. Insbesondere kann die Strahlungsbelastung von Resonatorspiegel und HF-Fenster durch Vergrössern des Durchmessers herabgesetzt werden.
• 2. Die im Resonator vorhandene Energie kann über zwei Ausgänge ausgekoppelt werden.

A quasi-optical gyrotron of the type mentioned at the outset is, for example, from the patent CH-664045 or from the article "The gyrotron, key component for high-power microwave transmitters", HG Mathews, Minh Quang Tran, Brown Boveri Review 6-1987, pp. 303-307. This gyrotron has the advantage over a conventional cylindrical gyrotron that it can generate a multiple of power. The reasons for this include the following facts:

• 1. Since the resonator is not coaxial but perpendicular to the electron beam axis, it can be dimensioned independently of the "klystron part". In particular, the radiation load on the resonator mirror and RF window can be reduced by increasing the diameter.
• 2. The energy present in the resonator can be coupled out via two outputs.

In principle, it is desirable that the gyrotron has the greatest possible efficiency. In the documents cited above, it is therefore proposed to arrange a control resonator in front of the power resonator. The control resonator packages ("prebunching") the electrons so that they arrive in the subsequent power resonator with a suitable phase position.

In addition to improving the efficiency, the effective output of the radiation emitted is of particular interest. It can be seen that the development of high-performance gyrotron (P> 500 kW continuous wave) has its limits in the load capacity of the windows, through which the radiation generated in the resonator is coupled out of the evacuated tube. Even with optimal transparency, these windows would have to heat up so much in the desired performance range that they would break within a very short time.

It is known that the load limit can be pushed out if the window is made up of two spaced panes, between which a liquid circulates and thus creates areal cooling. However, such a measure is far from sufficient when it comes to achieving radiation outputs in the MW range.

An important aspect of gyrotrons is the large but inevitable expenditure on auxiliary systems (superconducting coils, vacuum system, energy supply). Of course, this should be can be kept as small as possible and be used well at the same time. This is the case, for example, if a system can be used for different purposes.

Presentation of the invention

The object of the invention is to design a gyrotron of the type mentioned at the outset in such a way that, on the one hand, the highest radiation powers can be generated, but on the other hand the outlay on equipment can be kept to a minimum.

According to the invention, the solution is that at least one further resonator of high power is provided, which at least one further resonator also comprises two further mirrors lying on a further longitudinal axis of the resonator, the further longitudinal axis of the resonator likewise lying perpendicular to the electron beam axis and being oriented such that the first and further longitudinal axis of the resonator are rotated relative to one another by a given angle greater than zero.

The essence of the invention is that for a given, maximum load on a window, the total output that can be decoupled is increased by ingeniously multiplying the window area available for decoupling. Since the energy of the electron beam can be multiplied without major technical problems, another alternating field of the same strength can also be built up in each of the largely independent power resonators. Depending on the number of power resonators, the total stored energy and the number of RF windows available for decoupling are multiplied.

The improvement according to the invention is achieved with the previously known window technology and is essentially based on the special construction of the quasi-optical gyrotron.

Another advantage of the invention is that the entire system can be used better, since the quasi-optical gyrotron with its modular structure can be expanded in its area of application by installing resonators with different frequencies. This is important, for example, in production engineering applications.

It should be noted that the resonators according to the invention fulfill a completely different task than the known control resonators responsible for prebunching the electrons. In contrast to the so-called prebunching resonators, the power resonators according to the invention do not increase the efficiency of the gyrotron, but rather its overall radiation power and flexibility

There are a number of advantageous embodiments for the invention. The main ones are:
- Gyrotron with two mirror resonators which are slightly rotated with respect to each other with their axes and which operate at the same or closely adjacent frequency;
- Gyrotron with resonators, which vibrate optionally or simultaneously on different harmonic frequencies;
Gyrotron, in which the resonators lie essentially in the same plane;
The resonators preferably have at least one tiltable mirror, so that each resonator can be deactivated by slightly tilting the resonator mirror in order to increase the efficiency of the remaining active resonators.

Further embodiments result from the dependent patent claims.

Brief description of the drawing

• Fig. 1 einen Längsschnitt durch ein erfindungsgemässes quasi-optisches Gyrotron; und
• Fig. 2 einen Querschnitt durch den Resonatorteil des Gyrotrons.

The invention will be explained in more detail below on the basis of exemplary embodiments in conjunction with the drawing. Show it:

• 1 shows a longitudinal section through a quasi-optical gyrotron according to the invention; and
• Fig. 2 shows a cross section through the resonator part of the gyrotron.

The reference symbols used in the drawing and their meaning are summarized in the list of designations. In principle, the same parts are provided with the same reference symbols.

Ways of Carrying Out the Invention

1 shows the essential part of a quasi-optical gyrotron according to the invention in longitudinal section. Along an electron beam axis 1, electrons e⁻ (from left to right in FIG. 1) run on a helical path first through a control resonator (prebuncher) 2 - represented by two mirrors 3a, 3b - and a drift zone 4 - covered by a magnetic shielding body 5 - Before in a first and a second resonator 6 respectively. 7 occur. The electrons e⁻ are generated and accelerated by an electron gun (not shown in FIG. 1).

Two superconducting coils 8a, 8b, each in a container 9a, respectively. 9b, generate a static one, aligned parallel to the electron beam axis 1 Magnetic field through which the electrons e⁻ are forced to gyrate with a corresponding cyclotron frequency. The coils 8a and 8b are arranged on the electron beam axis at a distance corresponding to their radius (so-called Helmholtz arrangement). The whole is housed in an evacuated vessel (not shown in FIG. 1).

In practice, the two coils 8a, 8b are supported against one another by a supporting structure which is provided with bores for the resonators 6, 7 in the gap between the coils 8a, 8b.

With the exception of the resonators, the parts described so far do not essentially differ from the prior art, as e.g. emerges from the above-cited patent CH-664045. In this respect, a detailed explanation can therefore be dispensed with. In contrast, the arrangement of power resonators described below is new.

According to a preferred embodiment, two resonators 6 and 7 of high power are arranged between the two coils 8a and 8b. Each of the two resonators 6, 7 comprises two mirrors 12a, 12b, respectively. 12c, 12d, which are located opposite each other on a longitudinal axis 10, 11 of the respective resonator 6, 7. Both longitudinal resonator axes 10, 11 are perpendicular to the electron beam axis 1. In addition, they lie essentially in a common plane.

FIG. 2 shows a cross section through the resonator block along the line shown in FIG. 1. 2, the electron beam axis is perpendicular to the plane of the drawing, so that the electrons e⁻ run towards the viewer.

The longitudinal resonator axes 10 and 11 intersect with the electron beam axis 1 and are at an angle to one another α rotated greater than zero. The angle α is therefore the angle between a first plane spanned by the first longitudinal axis 10 of the resonator and the electron beam axis 1, and a second plane spanned by the second longitudinal axis 11 of the resonator and the electron beam axis 1.

The resonators 6, 7 are accommodated in an evacuated vessel 13 which is provided with four windows 14a, 14b, 14c, 14d which are transparent for mm waves. The desired electromagnetic radiation can exit through each of these windows 14a, 14b, 14c, 14d.

The electrons entering the resonators 6, 7 with a precisely defined cyclotron frequency and phase position simultaneously excite an alternating electromagnetic field in both resonators. According to a preferred embodiment, the alternating fields vibrate at the same frequency, which is typically greater than 100 GHz. This means that the mirrors 12a, 12b, 12c, 12d are essentially all the same and have the same distance from one another in pairs.

Each mirror is fixed by a holder suitably attached to the vessel 13. Since the alternating field vibrating in the resonator is coupled out at the edge of the mirror, the holder and the rear of the mirror must also be designed so that the electromagnetic radiation can emerge as freely as possible through the window behind the mirror.

According to a preferred embodiment, at least one of the two mirrors 12a and 12b, respectively. 12c and 12d of the resonators 6 and 7 are movable relative to the corresponding longitudinal axis of the resonator.

In the example according to FIG. 2, these are all mirrors. With a suitably designed bracket, for example, the Mirrors 12a and 12b respectively. 12c and 12d (and thus in particular also their mirror surfaces) with respect to the respective longitudinal axis 10 of the resonator. 11 tilt and move. In this way, the mirrors of a resonator can be adjusted to one another and to the resonance frequency. Furthermore, the quality Q₁ of the resonator 6 can be reduced or. be adjusted.

If an alternating field is excited at the same time in both resonators 6, 7, it cannot be expected a priori that the two alternating fields will also oscillate to the same extent. In practice it is therefore necessary that e.g. by slightly tilting the mirrors 12a and 12b, the two qualities Q₁ and Q₂ of the two resonators 6 and 7 can be adapted to one another, so that an equally strong, maximum radiation can be emitted via all four windows 14a, 14b, 14c, 14d. In this case, the total radiation emitted is also maximum for a given maximum load on a window.

An important aspect of the invention is the angle α at which the two longitudinal resonator axes 10 and 11 intersect. Its size has a significant influence on the efficiency of the gyrotron. This will now be explained in more detail.

In a quasi-optical gyrotron with only one resonator of high power, the cyclotron frequency of the electrons, the resonance frequency of the resonator and the phase position of the electrons entering the resonator must be coordinated. In particular, the phase position of the gyrating electrons is suitably prepared in the control resonator 2 and in the subsequent drift zone 4 (“prebunching”), so that the electrons interact optimally with the alternating electromagnetic field oscillating in the resonator. This guarantees optimal efficiency.

An important factor in this optimal setting is the correct adjustment to the direction of the longitudinal axis of the resonator. However, this is now a problem when there are two non-coinciding longitudinal resonator axes, as is the case with the invention. According to a preferred embodiment, this problem is solved in such a way that the angle α is kept as small as possible. If an alternating field is now to be excited in both resonators 6 and 7 at the same time, the phase position of the electrons is adjusted such that they are optimal for the bisector (the smaller of the two angles α and 180 ° -α) between the two longitudinal axes 10 and 11 of the resonator is. In this way, the electrons excite both alternating fields to approximately the same extent. A largely uniform distribution of the energy between the two resonators 6 and 7 can be achieved by additionally tilting the mirror in the manner described above.

An arrangement with a minimal angle α is shown in FIG. It is determined on the one hand by the distance between the two mirrors 12a and 12b, respectively. 12c and 12d of a resonator 6 respectively. 7, on the other hand by the diameter of the adjacent mirrors 12a and 12c, respectively. 12b and 12d and the space required for coupling out the electromagnetic radiation between the wall of the vessel 13 and the edge of the respective mirror.

The following numerical example should serve as a guide for the angle α. With a mirror spacing of 800 mm and a mirror diameter of 65 mm, an inner diameter of the vessel (bore) of approximately 145 mm is required. For design-mechanical reasons (flange connections), a minimum angle α in the order of 30 ° can be achieved.

The angle α can of course also be reduced by increasing the mirror spacing. Because of the axial Larger mirrors and windows are then required in the direction of the diverging alternating field, which means that more power can also be extracted. These technical advantages must be weighed from case to case against the economic disadvantages of the larger space requirement and the higher manufacturing costs.

What has been said so far for the case of resonators of the same frequency also applies mutatis mutandis to the variants with different frequencies explained below.

A first variant is that e.g. the resonator 7 oscillates at a frequency which differs only slightly from that of the resonator 6 in percentage terms. The corresponding frequency shift is e.g. achieved so that the mirror spacing of one of the two almost identical resonators 6, 7 is shifted by a maximum of half a wavelength of the excited alternating field.

How large the frequency difference is in number depends essentially on the free spectral range of the resonator. If the two mirrors 12a, 12b of the resonator 6 are at a distance of e.g. 400 mm and the alternating electromagnetic field has a wavelength of 1 mm, there is space for 800 half wavelengths between the mirrors. The relative free spectral range is thus about 1/800 i.e. approx. 0.1% of the resonance frequency.

A possible area of application for gyrotron with only slightly different mm waves is the heating of a plasma in the case of nuclear fusion. In particular, closely adjacent regions of the plasma can be heated in this way.

A second variant provides a resonator 7 with a frequency which is in a harmonic relationship to that of the resonator 6. So an alternating field resonates a frequency which is several times that of the other alternating field. The ratio is preferably 2: 1.

So far it has always been assumed that the two resonators 6 and 7 are in operation simultaneously. However, a quasi-optical gyrotron according to the invention can also be operated with only one of the two resonators. This will be particularly advantageous if the two resonators have different frequencies, each of which is tailored to a specific application. A wide range of applications can be covered with extremely little additional effort. The existing auxiliary equipment will be better used.

If only one of the two resonators is in operation, the other is shut down by tilting one of its mirrors. In addition, the phase position of the electrons is optimally matched to the running resonator. This guarantees optimal efficiency.

In this case, the angle α is generally not subject to any restriction. In particular, the two longitudinal resonator axes 10 and 11 can be easily aligned perpendicular to each other (α = 90 °), which is extremely advantageous in terms of operation.

• 1. Grundsätzlich müssen alle Leistungsresonatoren zwischen den beiden Spulen in Helmholtz-Anordnung Platz finden.
• 2. Jeder Resonator 6, 7 muss einen gewissen Abstand zu den Behältern 9a, 9b wahren, damit das im Prinzip seitlich nicht begrenzte Wechselfeld nicht zu stark gestört wird.
• 3. Wenn die Resonatorlängsachsen um einen geeigneten Abstand verschoben werden, kann erreicht werden, dass die Elektronen für beide Resonatoren die richtige Phasenlage haben.

The longitudinal resonator axes 10, 11 either lie in the same plane (which is perpendicular to the electron beam axis) or are slightly displaced in the direction of the electron beam axis. How the geometric arrangement should be in the specific case depends on various factors. The following points are of importance:

• 1. Basically, all power resonators must be placed between the two coils in a Helmholtz arrangement.
• 2. Each resonator 6, 7 must maintain a certain distance from the containers 9a, 9b so that the alternating field, which in principle is not laterally limited, is not disturbed too much.
• 3. If the longitudinal axis of the resonator is shifted by a suitable distance, it can be achieved that the electrons have the correct phase position for both resonators.

Due to the limited width of the gap between the coils, the longitudinal axis of the resonator will lie essentially in a common plane.

In the exemplary embodiments explained with reference to the figures, only quasi-optical gyrotrons with two power resonators have always been shown. However, it is clear that, according to the invention, gyrotrons with three or even more power resonators can be implemented.

In the exemplary embodiment explained with reference to the figures, electromagnetic radiation is coupled out for each mirror. However, this is not essential for the invention. In certain applications, it may be desirable to couple out power in one or more resonators with only one mirror. In this case, an RF window is only arranged behind one of the two mirrors.

If mm-waves are spoken of in the present description, this should in no way be interpreted as restrictive. This simply means a wavelength range, which typically comprises wavelengths of approximately 1 mm and is definitely one to two decades wide.

It should be noted that the control resonator 2 in FIG. 1 is not part of the invention. It can also be omitted if the resulting "prebunching" is not desired.

In conclusion, it can be said that the invention creates a quasi-optical gyrotron which, on the one hand, can achieve a great overall performance and, on the other hand, has a wide range of applications with minimal expenditure on equipment.

Claims (10)

1. Quasi-optical gyrotron for generating electromagnetic radiation in the form of mm waves, in which a) electrons running on an electron beam axis (1) are forced to gyrate by a static magnetic field aligned parallel to the electron beam axis (1) and b) in a resonator (6) of high power, which comprises two mirrors (12a, 12b) lying on a first longitudinal axis of the resonator (11) oriented perpendicular to the electron beam axis (1), excite an electromagnetic alternating field of high power, so that the mirrors (12a , 12b) electromagnetic radiation is coupled out in the form of mm waves,
characterized in that c) at least one further resonator (7) of high power is provided, which at least one further resonator (7) also comprises two further mirrors (12c, 12d) lying on a further resonator longitudinal axis (11), the further resonator longitudinal axis (11) likewise is perpendicular to the electron beam axis (1) and is oriented such that the first and further longitudinal axis (11) of the resonator are rotated relative to each other by a given angle (α) greater than zero. 2. Quasi-optical gyrotron according to claim 1, characterized in that the first and the at least one further resonator longitudinal axis (10) lie essentially in a common plane oriented perpendicular to the electron beam axis. 3. Quasi-optical gyrotron according to claim 1, characterized in that a) the longitudinal axis of the resonator (10, 11) of the first and the at least one further resonator (6, 7) enclose a minimum possible angle (α) due to the diameter of the mirrors (12a, 12b, 12c, 12d) and b) that the mirrors (12a, 12b, 12c, 12d) of the first and the at least one further resonator (6, 7) are adjusted in such a way that an electromagnetic alternating field is excited in the resonators at the same time and for all mirrors (12a, 12b , 12c, 12d) electromagnetic radiation is coupled out in the form of mm waves. 4. A quasi-optical gyrotron according to claim 1, characterized in that each resonator (6, 7) has at least one mirror (12a, 12c) movable with respect to the longitudinal axis of the resonator (10, 11) for setting a quality factor and a resonance frequency of the resonator (6 , 7). 5. Quasi-optical gyrotron according to claim 1, characterized in that the resonators (6, 7) are designed such that the alternating fields excited therein oscillate at frequencies which are in a harmonic relationship to one another. 6. Quasi-optical gyrotron according to claim 1, characterized in that the resonators (6, 7) are designed such that the alternating fields excited therein vibrate at frequencies which differ only slightly in percentage terms. 7. Quasi-optical gyrotron according to claim 4, characterized in that the movable mirrors (12a, 12c) are set relative to the respective longitudinal axis of the resonator in such a way that an alternating electromagnetic field can only be excited in one resonator (6, 7). 8. Quasi-optical gyrotron according to claim 3, characterized in that a) exactly one further resonator (7) is provided and that b) the angle (α) between the longitudinal axes of the resonator is approximately 30 °. 9. Quasi-optical gyrotron according to claim 2, characterized in that a) the resonators (6, 7) of high power between two coaxially aligned to the electron beam axis (1) coils (8a, 8b) are arranged in a Helmholtz arrangement for generating the static magnetic field and that b) to increase the efficiency of the gyrotron, a control resonator (2) is arranged so that the electrons first pass through the control resonator (2) and a drift zone (4) before they enter the resonators (6, 7). 10. Quasi-optical gyrotron according to claim 8 and 9, characterized in that the phase position of the electrons is adjusted so that it is optimal with respect to an bisector of the longitudinal axis of the resonator (10, 11).

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