RU2528982C2 - Magnetron having triggering emitters at end shields of cathode assemblies - Google Patents

Abstract

FIELD: physics.

SUBSTANCE: invention relates to electronic engineering and is intended for use in high- and ultra high-power magnetrons in the centimetre, millimetre and sub-millimetre wavelength range. The result is achieved through structural division of the cathode assembly of the magnetron into two functional parts: the magnetron is triggered by electronic emission (thermionic or field) from end shields, and the operating mode of the magnetron is provided by a main secondary-emission cathode located in the electromagnetic field interaction space. The end shields are structurally made from a set of discs, one of which, which is the triggering emitter, is made of emission-active material (oxides or alloys). The triggering emitter is placed between two discs made of heat-resistant material, one of which shields the electron stream in the interaction space of the magnetron, and the second separates the triggering emitter from the main secondary-emission cathode, thereby preventing interaction of components contained therein. In a magnetron with instant triggering, the triggering emitter consists of a combination of field-emission cathodes and activators. The activators, made of active metals or compounds, are sources of activating substances which, when adsorbed on the surface of the field-emission cathodes, increase emission capacity thereof. The emission-active materials contain barium, calcium, yttrium, thorium and lanthanum oxides or alloys of platinum or palladium with barium or iridium with lanthanum or cerium, osmium with lanthanum etc.

EFFECT: high stability of exciting a magnetron, reliability and longevity of said magnetron.

3 cl, 10 dwg

Description

The invention relates to electronic equipment and can be used in microwave devices of the M-type, in particular in magnetrons of the centimeter, millimeter and submillimeter wavelength ranges.

The main problem that arises when creating magnetrons of this class is to ensure the stability and durability of the cathode nodes under conditions of intense electron and ion bombardment, the effect of which leads to overheating of the emitters, to a change in their composition and structure, and, consequently, to a change in emission properties. These changes affect the stability of magnetrons, lead to a change in the frequency of the generated oscillations, to a drop in output power and electronic efficiency, to a decrease in durability.

The solution to these problems is especially important when developing high-power short-wavelength magnetrons. In a number of cases, it is also necessary to solve the problem of quickly starting the magnetron into the generation mode. This is achieved by modernizing the design of the cathode assembly and using highly efficient emission materials as part of the cathodes.

A fast-turn magnetron is known [1], which consists of an anode (4), a metal core (5) coaxially placed inside it with a secondary emission cathode from iridium or platinum (1), an end shield (2) and an auxiliary electron removed from the interaction space guns (6) with low thermal inertia (figure 1).

The electron gun forms and directs the electron flow into the annular space between the anode and cathode, thereby initiating the excitation of electromagnetic waves.

The main disadvantages of this magnetron are the following:

- in magnetrons of the millimeter and submillimeter wavelength ranges due to the small overall dimensions and extremely high mounting density in most cases, the placement of an auxiliary electron gun is not possible;

- the design of the magnetron is significantly complicated due to the need to introduce at least two additional vacuum inlets to power the electron gun;

- the use of an electron gun in the magnetron design leads to a deterioration in the tactical and technical characteristics of the transceiver equipment due to the need to use a special power source in its composition to heat the thermionic cathode of the gun. In addition, an additional power source causes an increase in the overall dimensions and weight of the equipment;

- only a small fraction of the electron flux from the gun is involved in the initiation of magnetron generation (most of the electron flux, deposited on the end surface of the anode and the inoperative surface of other magnetron elements, causes spurious emission);

- to achieve a short magnetron readiness time, the cathode of the electron gun must be constantly maintained in the operating mode, i.e. must be heated to a certain temperature. This, along with additional energy consumption, leads to a decrease in the life of the electron gun and a decrease in the electric strength of the device due to evaporation of evaporation products from the thermionic cathode on the surface of parts.

Known magnetron used in domestic microwave ovens [2], the cathode assembly of which is schematically depicted in figure 2.

The magnetron contains an anode (4), a heater (3) coaxially placed inside it with an emission sleeve (1), and end screens (2). The operation of the cathode is based on the fact that the heater, on which the emission sleeve is mounted, performs two functions. Firstly, it provides heating of the emission sleeve to the required operating temperature, and secondly, being in the flow of the active substance evaporating from the emission sleeve, it forms a starting electron flow and thereby ensures the magnetron is quickly put into operation.

However, despite the originality of the solution, this design does not provide the necessary form-stability of the cathode assembly in the operation modes of powerful and heavy-duty magnetrons, which are more rigid in comparison with the operation mode of domestic microwave ovens.

Known magnetron with non-initial (instant) start [3 ... 5], consisting of an anode (4) and a cathode assembly coaxially placed inside it, the design of which is schematically depicted in figure 3.

The cathode assembly includes a core (5) made of a refractory metal or alloy, a heater (3), end screens (2) and a combination of field-emission cathodes (7) with secondary emission emitters (1). Auto-electron cathodes in the form of washers made of tantalum foil ~ 4 μm thick are placed between secondary-emission, in particular, pressed palladium-barium emitters. When a pulse voltage is applied to the anode, the field emission current initiates the operation of the magnetron. Palladium - barium emitters that act as activators of field-emission cathodes, are at the same time secondary-emission cathodes that support the generation of microwave oscillations during the life of the devices. (The heater is used for degassing and activating the cathode in the process of pumping the magnetron, and thereafter it is no longer needed.) The disadvantage of this design of the cathodes is the inability to use them in powerful and heavy-duty magnetrons due to the rapid destruction (burning out) of the cathodes under the influence of ion and reverse electron bombardments .

Known magnetron [6] (prototype), consisting of an anode (4) and a cathode coaxially placed inside it (figure 4).

The cathode assembly contains a cathode core (5) made of a refractory metal or alloy, a heater (3), end screens (2) and a thermo-secondary emission cathode (1), mounted on the cathode core. The heater is placed either inside the core directly below the cathode or outside the cathode (wound onto the core of the cathode using heat-resistant insulating materials). In the centimeter wavelength range, magnetrons with a similar design of the cathode assembly have quite satisfactory lifetimes, but upon transition to the region of shorter wavelengths, a sharp deterioration of the parameters of the devices occurs. This is due to the fact that in the short-wavelength region of wavelengths, due to a decrease in the effective surface of the cathodes and an increase in the concentration of the electric field in the interaction space of the magnetrons, the loads on the cathode sharply increase. This leads to a rapid failure of the cathode and, accordingly, the magnetron as a whole. The service life of such magnetrons can be increased by selecting cathode material that is more resistant to the effects of reverse electron bombardment.

So, for example, the life of a magnetron with a power of P ~ 4 kW and a frequency of f ~ 150 GHz (a magnetron with a 2 mm wavelength range) is:

- no more than 2 ... 3 dozens of hours with a metal-porous tungsten-aluminate cathode;

- about 250 hours with a metal-alloy iridium-lanthanum cathode.

Thus, from the foregoing, it follows that with an increase in power and a transition to the generation of ultrashort electromagnetic oscillations, the stability, reliability, and service life of a magnetron mainly depend on both the design of the cathode assembly and the properties of the cathode material.

The main disadvantages of the design of the magnetron, taken as a prototype, are the following.

1. In high-power and super-power short-wavelength magnetrons under the influence of ion and reverse electron bombardments, which cause cathodes to overheat even when the heat is completely off, the emission parameters rapidly degrade due to intense evaporation of the emissive active component from the surface of the emitters.

2. To increase the durability of the above magnetrons in recent years, various types of high-temperature cathodes with an operating temperature range of 1400 ... 1600 ° C have been used. However, the use of such cathodes was not widespread in the creation of small-sized, but powerful magnetrons due to the excessively high operating temperature, leading to overheating of the design of the devices.

3. To ensure moderate temperatures that allow the use of effective cathodes in magnetrons with an operating temperature of no higher than 1200 ° C, refractory metals and special alloys with high thermal conductivity are used in the design of cathode assemblies, providing intensive heat removal from thermo-secondary emission cathodes. Further stabilization of the temperature regime at the cathode nodes is ensured by cooling the design of the magnetrons with special devices and devices with a cooling liquid (liquid cooling of magnetrons), which significantly complicate the design of the transceiver equipment.

4. At the same time, excessive heat removal from the cathode assembly can lead to a decrease in temperature to a level at which the value of the emission current from the thermo-secondary-emission cathode may be insufficient to start the magnetron in the generation mode. Therefore, when designing magnetrons, it is often envisaged that they can be switched on in forced mode, when a 2-, 3-fold supply voltage of the glow is supplied to the cathode assembly heater for a short time, which significantly reduces the resource of the heaters.

Thus, in high-power and super-powerful magnetrons of the centimeter, millimeter, and submillimeter wavelength ranges, the use of standard designs of the cathode assembly does not significantly improve the operational and tactical and technical characteristics of the devices.

The problem to which the invention is directed, is the creation of powerful and super-powerful magnetrons of the specified wavelength range with a cathode assembly that provides high reliability and stability of operational parameters.

This is achieved as follows.

1. The cathode assembly is structurally divided into two functional parts, each of which has a very specific role: the triggering emitters (one or more) initiate generation, and the secondary-emission cathode ensures the magnetron is operational throughout the entire life of the device.

2. The most effective location for triggering emitters is the end screens. This is due to the following factors:

- end screens are outside the magnetron interaction space, and therefore the level of bombardment of their surface by reverse electrons is incommensurably small compared to the intensity of the bombardment of the surface of the main cathode;

- the concentration of the electric field near the surface of the end screens is significantly higher than that of the surface of the main cathode.

Figure 5 shows a picture of the distribution of the electric field in the space of interaction of the magnetron. As can be seen from the above picture of the field distribution, near the surface of the end screens, the electric field has a fairly high concentration level (a bright halo around the screens indicates a high concentration of the electric field).

Therefore, by placing these or other electron sources on them, it is possible to obtain electron flows sufficient to initiate the start of the magnetron in the generation mode.

Subject of invention

The magnetron of the centimeter, millimeter, and submillimeter wavelength ranges (Fig. 6) consists of an anode (4), a cathode core of a refractory metal or alloy (5) coaxially placed inside it, a heater (3), and a main secondary emission cathode (1) and end screens (2) that act as trigger emitters.

The essence of the invention is as follows.

Trigger emitters (9), made of compounds with high emission activity, are placed on one or both end screens located outside the space of interaction of electromagnetic fields in the magnetron, due to which the emitting surface is practically not subjected to reverse electron bombardment.

An external washer (10) made of molybdenum, hafnium, zirconium or another refractory metal or alloy with a high work function provides shielding of the electron beam in the space of interaction of electromagnetic fields in the magnetron. The inner washer (8), made of refractory metal, for example tungsten or molybdenum, separates the main secondary-emission cathode from the starting emitter and thereby interferes with the processes of interaction of the components included in their composition.

The main secondary emission cathode, made of emission-active compounds or metals with stable secondary emission properties and resistant to ion and reverse electron bombardments, for example, iridium, platinum, osmium, rhenium or various intermetallic alloys: iridium with lanthanum, iridium with cerium , osmium with lanthanum, rhodium with barium, etc., provides high reliability and durability of the magnetron. Below are various structural and technological solutions according to the invention.

Figure 6 shows a schematic representation of a magnetron with a cathode assembly, in which the triggering emitters are placed on both end screens. In this node, the function of the screens is performed by the external washers (10), and the emitters (9) of a conical shape, located between the external and internal washers, are the sources of electrons that initiate the start of the magnetron in the generation mode. After turning on the filament and reaching the appropriate temperature inherent for a given emitter material, the electrons emitted from its surface, rushing towards the anode along the electric field lines, form an electron flux that initiates the start of the magnetron in the generation mode. On fragment A of FIG. 6, the following dimensions are indicated:

d ₁ ; d ₄ - the diameters of the outer and inner washers of the screens;

d ₂ ; d ₃ - diameters of the bases of the starting emitter having a conical surface;

d ₅ is the diameter of the secondary emission cathode;

h is the thickness of the starting thermionic emitter. Diameters are selected as follows:

d ₄ ≤d ₁ ; d ₂ ≤ d ₁ ; d ₃ ≤d ₂ ; d4≤d ₃ ≤d ₄

The angle φ is determined from the ratio:

tgφ = (d ₂ -d ₃ ) / 2h; where 0 <φ <Arctan (d ₂ -d ₃ ) / 2h;

If φ <0, then along with an increase in the parasitic current to the anode-resonator system and pole tips, the electron beam will be redistributed, as a result of which the fraction of electrons initiating the start of the magnetron in the generation mode will decrease.

If φ> Arctan (d ₂ -d ₃ ) / 2h, a step is formed between the thermionic and secondary-emission cathodes, which can lead to a deterioration of the magnetron parameters.

The configuration of a thermionic emitter depending on the angle φ can be very diverse.

If φ = 0 (special case), the thermionic emitter takes the form of a cylinder, shown in Fig.7 (fragment A).

Dimensions d ₁ ; d ₂ ; d ₃ and h are selected so that the ratio is satisfied: (d ₂ -d ₁ ) / 2h = 0 ... 1 .; d ₁ ≤ d ₂ ; d ₃ ≤d ₁ .

If (d ₂ -d ₁ ) / 2h <0, the parasitic current at the anode and pole tips will increase.

If (d ₂ -d ₁ ) / 2h> 1, the emission current from the cathode due to shielding by the washers may be insufficient to initiate magnetron generation.

In the design of the cathode assembly of Fig. 8 (fragment A), the triggering emitter is made with a toroidal annular belt of radius r made from the material of the triggering emitter or other material with high emissivity. The value of radius r is selected experimentally for each specific magnetron. If r≥h / 2, the emitter surface takes the form of a barrel.

As mentioned earlier, one of the most important parameters determining the tactical and technical characteristics of microwave equipment is the readiness of the magnetrons.

Figures 9 and 10 show the designs of magnetrons with firing auto-electronic cathodes on the end screens, which provide instant (non-incandescent) starting of powerful and super-powerful magnetrons in the generation mode with a standby time of no more than 0.5 sec.

In the proposed magnetron design, the end screens of the cathode assemblies consist of a combination of one or several field-effect cathodes (7) and activators (11) placed between washers made of refractory metal, one of which actually serves as a screen.

Autoelectronic cathodes (AEC) with a thickness of several microns to several tens of microns are made of tantalum or special alloys of refractory metals, for example tantalum with tungsten, tantalum with zirconium, tungsten with rhenium, tantalum with rhenium, etc.

As activators, various chemical compounds or alloys containing rare earth or alkali metals are used.

Gaskets (11) made of foil several tens of microns thick from tungsten, an alloy of tungsten with rhenium, molybdenum with rhenium, etc., separate the AEC from the activator and thereby prevent the interaction of the components that make up them.

Various metals and compounds with high secondary emission properties and resistant to reverse electron bombardment are used as secondary emission (primary) cathodes.

In particular, Fig. 9 shows, by way of example, the design of a magnetron with triggering emitters consisting of a combination of a single field-effect cathode and two activators having a conical surface. It should be noted that the number of field-emission cathodes and activators can vary depending on the thickness of the end screen h and the value of the field emission current rating sufficient to initiate the generation of a particular type of magnetron.

Dimensions d ₁ ; d ₂ ; d ₃ ; d ₄ ; d ₅ and h (fragment A) are selected by analogy with a variant of the node of Fig.6.

d ₄ ≤d ₁ ; d ₃ ≤d ₂ ; d ₅ ≤d ₃ ≤d ₄ ;

The angle of inclination φ between the generatrix of the conical surface and the axis is determined from the relation:

tgφ = (d ₁ -d ₃ ) / 2h; where 0 <φ <Arctan (d ₂ -d ₃ ) / 2h;

If φ <0, then along with an increase in the parasitic current on the anode-resonator system and pole tips, the electron beam will be redistributed, as a result of which the fraction of electrons initiating the start of the magnetron to the generation mode will decrease.

If φ> Arctan (d ₂ -d ₃ ) / 2h, a step is formed between the activator and the secondary-emission cathodes, which can lead to a deterioration of the magnetron parameters.

In the case where φ = 0 (special case), the cathode design takes the form shown in Fig. 10, with activators having a cylindrical surface. It should be noted that for this design of the triggering emitter, the number of autoelectronic cathodes with activators can vary depending on the thickness of the end screen h and the magnitude of the nominal field emission current sufficient to initiate the generation of a specific type of magnetron.

The geometric dimensions of this cathode correspond to the conditions:

(d ₃ -d ₁ ) / 2h = 0 ... 1; d ₁ <d ₃ ; 0 <(d ₂ -d ₁ ) ≤0.4 mm; 0≤φ≤90 °.

If (d ₂ -d ₁ ) <0 - field emitters are shielded by activators. If 0.4 mm <(d ₂ -d ₁ ) - there is a high probability of destruction of the edge of the field emitter due to overheating due to ion bombardment and the flow of field emission current through it.

Results Achieved

Unlike the prototype in the magnetron, which is the subject of the invention, the cathode assembly is structurally divided into two functional parts, each of which has a very specific role: the triggering emitter initiates generation, and the secondary-emission cathode ensures the operability of the magnetrons throughout the entire service life.

Thanks to this separation, high reliability and stability of the operational parameters of high-power and super-power magnetrons of the short-wave range of wavelengths are achieved.

Practical implementation of the invention

1. End screens consist of two washers, one of which screens the electron beam in the magnetron interaction space, and the triggering emitters placed between them are made of material with a low work function with a conical, barrel-shaped or cylindrical surface.

2. As starting emitters, providing an instant start-up of the magnetron in the generation mode, various combinations of field-effect cathodes and activators are used.

3. As a secondary-emission (main) cathode, materials and compounds with stable secondary-emission properties and resistant to reverse electron bombardment are used.

The service life of high-power and heavy-duty magnetrons of the centimeter, millimeter and submillimeter wavelength ranges with the proposed design of the cathode assembly, which is the subject of the invention, is significantly longer than that of magnetrons with a standard design of the nodes.

Example 1

To study the processes of starting up into the generation mode at a low cathode temperature, magnetrons of a 2-mm wavelength range with a power of P ~ 4.5 kW were manufactured and investigated.

Trigger cathodes, corresponding to the design of FIG. 6, were made of a tungsten porous matrix impregnated with barium-calcium aluminate, with the following dimensions: h = 0.4 mm, d ₂ = 2.5 mm, d ₃ = 2.3 mm, angle φ = Arctg (d ₂ -d ₃ ) / 2h≈15 °.

The secondary emission cathode, made of an intermetallic compound of iridium with lanthanum, had dimensions: d ₅ = 2.05 mm; h = 2.25 mm.

The generation of this magnetron was initiated at a temperature of the triggering emitter T ~ 950 ° C.

The start-up temperature of the magnetron generation mode with the standard design of the thermo-secondary-emission iridium-lanthanum cathode was more than 1250 ° C, which is about 300 ° C higher than that of the magnetron claimed in the invention.

Example 2

To study the process of instantly starting a magnetron into the generation mode, magnetrons of a 2 mm wavelength range with a power of P ~ 4.5 kW were manufactured. The cathode assemblies corresponded to the design shown in FIG. 10. Each of the triggering emitters placed on both end screens consisted of a combination of three AEC made of tantalum foil ~ 4 μm thick and four palladium-barium activators 0.1 mm thick, the height of the protruding part of the AEC was 0.08-0.09 mm with a diameter of AEC 2.5 mm. A metal-alloyed iridium-lanthanum cathode (d ₃ = 2.05 mm, _emitter h = 2.25 mm) was used as the secondary-emission main cathode.

The generation of this magnetron was initiated at a cathode temperature T _cat ~ 20 ° C. The time for the magnetron to enter full generation mode was 0.3 ... 0.4 s after applying the anode voltage.

The service life of a magnetron of a 2 mm wavelength range with triggering emitters on the end screens was more than 2000 hours, which is more than 8 times longer than the life of a similar device (prototype) with a thermo-secondary-emission metal-alloy iridium-lanthanum cathode.

Information sources

1. US patent No. 3896332 (priority 04.06.1973). The applicant is Valve Co.

2. Abstract for the degree of Ph.D. Polivnikova O.V. Research and development of effective magnetron cathodes based on the principle of transfer of an active substance from an independent source to an emitting surface through a vacuum.

3. Kopylov M.F., Bondarenko B.V., Makhov V.I., Nazarov V.A. Magnetron. RF patent No. 2007777, priority dated April 15, 1992

4. Pipko Yu.A., Semenov L.A., Galaktionova I.A., Eremeeva G.A., Esaulov N.P., Ilyin V.N., Margolis L.M. Magnetron with a non-cathode cathode. RF patent №2019877, priority of 04.17.1991

5. Li I.L., Dubois B.Ch., Kashirina N.V., Komissarchik S.V., Lifanov N.D., Zybin M.N. Magnetron with a non-cathode cathode. RF patent No. 2380784, priority of 10.24.2008

6. The magnetron of the centimeter range, trans. from English under the editorship of S.A. Zusmanovsky, ed. "Soviet Radio", M., 1951, pp. 134-138.

BRIEF DESCRIPTION OF THE DRAWINGS

1. The main thermo-secondary-emission (secondary-emission) cathode.

2. The end screen.

3. Heater.

4. The anode.

5. The cathode core.

6. Auxiliary electron gun.

7. Autoelectronic cathode.

8. The inner washer.

9. Trigger emitter.

10. The outer washer.

11. Activator auto-electronic cathodes.

12. Gasket.

Claims (3)

1. The magnetron of the centimeter, millimeter and submillimeter wavelength ranges, consisting of an anode and a cathode assembly coaxially placed inside it, including a heater, end screens and a secondary emission cathode located in the space of interaction of electromagnetic fields, characterized in that to increase the reliability of operational parameters and magnetron service life, the initiation of generation is provided by triggering emission-active emitters located on end screens outside space magnetron interaction, and the operating mode of the device is supported by the main cathode made of iridium, platinum, osmium, rhenium, gold, tungsten, tantalum or an intermetallic compound of iridium with cerium, iridium with lanthanum, platinum with barium, rhenium with thorium, osmium with thorium, osmium with lanthanum, rhodium with barium, which have stable secondary emission properties and are resistant to ion and reverse electron bombardments. 2. The magnetron according to claim 1, characterized in that the triggering emitters containing emission-active materials (oxides or alloys) and structurally made with a cylindrical, conical or barrel-shaped surface are placed between two washers made of refractory metal, one of which screens the electron beam in the interaction space of the magnetron, and the second separates the main secondary-emission cathode from the triggering emitter and thereby interferes with the processes of interaction of the components included in their composition. 3. The magnetron according to claims 1, 2, characterized in that in order to ensure the magnetron is instantly started in the generation mode, the triggering emitters are structurally made of alternating autoelectronic cathodes and activators having a cylindrical, conical or barrel-shaped surface, the evaporation products from which are continuously adsorbed on the surface autoelectronic cathodes, cause stable and stable autoelectronic emission throughout the life of the magnetron.

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