RU2352017C1 - Traveling wave lamp with magnetic periodic focusing system - Google Patents

Abstract

FIELD: electrics.

SUBSTANCE: invention concerns electric vacuum ultra high frequency devices, particularly in O-type traveling wave lamp with magnetic periodic focusing system (MPFS). Lamp includes MPFS combined with resonance slow-down system and consisting of intermittent axially magnetised ring magnets, polar headpieces and ferromagnetic inserts. To achieve required harmonic component level in magnetic field with non-sinusoid distribution, at least a part of MPFS behind high frequency power input consists of adjoining cells, each including at least one unidirectional magnetisation magnet and three ferromagnetic inserts between polar headpieces. Magnets in each two neighbour cells have opposite magnetisation. Inserts are positioned with gaps against polar headpieces in hubs in the form of step rotation bodies and fixated by annular elements, and form inner cavities of high frequency resonators in slow-down system. Hubs and annular elements are made of non-magnetic material with high heat conductivity and comprise vacuum shell together with polar headpieces.

EFFECT: enhanced current permission of beam in high-performance traveling wave lamp in short-wave part of UHF range due to intense electron stream focusing in transit channel.

3 cl, 9 dwg

Description

The invention relates to microwave microwave devices, in particular to a traveling wave lamp (TWT) device used as generators, amplifiers, current switches, and other devices.

One of the requirements for powerful TWTs is to ensure their operation with a high level of electron flow through the collector. It is precisely the high level of beam passage through the passage channel that determines the value of the high-frequency output power, the efficiency, and also the reliability of the TWT operation.

A TWT design is widely known in practice, in which a magnetic periodic focusing system (MPFS) with axially magnetized ring magnets is used spatially combined with a retardation structure (ZS) like a chain of coupled resonators (Powerful Electrovacuum Devices) to focus an intense electron beam with an alternating sinusoidal magnetic field. Microwave, under the editorship of L. Klempitt, M .: Mir, 1974, p. 20). In this case, the period of MPFS is equal to the period of the AP. The disadvantage of this design is the impossibility of obtaining high levels of the focusing magnetic field necessary for transporting intense flux in the short-wave part of the microwave range, due to the small length of the magnets in the axial direction. In addition, the reliability of ensuring the vacuum density of ZS at the soldering sites during the development of TWT with a high gain is reduced due to the large number of soldered seams (at least equal to twice the number of cells of the resonators of the retarding system).

These drawbacks are deprived of the well-known TWT construction with MPFS (US patent No. 4399389, CL 315-3.5, 1983), in which the diaphragms of the RF cavities are made in the form of inserts of a special form of non-magnetic material placed between the pole pieces, as a result of which the MPPS period becomes twice the period of the ES and the size of the magnets becomes sufficient to provide the required magnitude of the focusing magnetic field. In this case, the risk of leakage of the TWT vacuum shell is reduced due to a half of the number of soldered joints.

However, the main drawback of the TWT with MPFS with an alternating magnetic field is the presence of alternating areas of stable and unstable focusing of the electron beam, characterized by the so-called magnetic field parameter α, the magnitude of which is directly proportional to the square of the product of the amplitude of the focusing magnetic field and its period and is inversely proportional to the value of the potential of the slowing system ( AP). For some values of the magnetic field parameter α, the amplitude of the flow pulsations can increase indefinitely as the beam moves along the axis of the passage channel and the beam’s current passage sharply deteriorates. In practice, focusing of the beam by a sinusoidal magnetic field in the first stability zone, for which the magnetic field parameter taking into account the space charge should be less than the critical value, is most widespread.

For the TWT of medium and high power of the short-wave part of the microwave range, the magnetic field amplitude necessary to obtain a beam of the required diameter often turns out to be so high that it cannot be realized for given design sizes of magnets, and an increase in the latter leads to a violation of requirement (1). Focusing in the second and subsequent zones of stable beam formation in a sinusoidal field is practically not used due to the large magnitude of the pulsations of the beam arising due to the insufficient steepness of the field growth at the boundaries of neighboring MPPS cells for large periods.

To increase the area of stable focusing of the electron beam, MPPS is used with a non-sinusoidal distribution of the magnetic field, which is ensured by introducing higher harmonic components. So, for the distribution of the magnetic field with the first and third harmonics, the optimal value of the third harmonic is half the amplitude of the first harmonic (see Danovich I.A. Analysis of focusing and stability of intense electron beams in periodic magnetic fields / Izv. Vuzov. Ser. Radiophysics, 1966 , vol. 9, issue 2, p. 351-361).

In the patent of Russia No. 2091898, class. H01J 25/42, published on September 27, 1997, describes the construction of the TWT with MPPS, in which a non-sinusoidal magnetic field distribution with certain values of the first, third, and fifth harmonic components of the magnetic field is implemented to increase the effective focusing value of the magnetic field while maintaining beam focus stability . However, the pole tips of the MPPS in this TWT design are placed outside the vacuum shell, which does not allow us to obtain the required amplitude values and the structure of the magnetic field distribution for focusing the intense flux in the short-wave part of the microwave range.

The closest prototype of the present invention is the construction of the TWT with a magnetic periodic focusing system (MPFS), consisting of alternating axially magnetized ring magnets, pole pieces with hubs of ferromagnetic material, spatially aligned with capacitive bushings of resonators, diaphragms made of non-magnetic material between capacitive bushings pole lugs (US No. 3334339, Cl. 315-3.5, 1967), in which the required magnetic field is achieved by increasing con- cern magnets in the axial direction and thereby increase MPFS period compared with the period of AP twice. The spatial compatibility of the MPFS design with the CS is achieved by alternating the pole pieces inside the vacuum shell with the copper diaphragms forming the RF resonator. In addition, in this design, one or two ring elements made of ferromagnetic material are mounted between the pole tips of the MPFS, mounted on thin-walled copper disks of the diaphragm of the RF resonator. Due to this, a non-sinusoidal distribution of the axial component of the magnetic field induction with significant positive values of the third or third and fifth harmonics is created.

The disadvantage of this design is that when switching to the short-wave part of the microwave range, the elements of the LC become miniature and the operability of the design becomes problematic. So, for TWT operation in the three-centimeter wavelength range at an accelerating voltage level of less than 20,000 V, the ring sleeve of ferromagnetic material has the following typical dimensions: thickness 0.25-0.5 mm, inner diameter of the sleeve 2.0-3.0 mm, length bushings in the axial direction of 3-4 mm. The thickness of the thin-walled copper disk is ~ 0.8-1.2 mm. The amplitude of the magnetic field required for focusing an intense beam can be ~ 0.3 T. With such dimensions, the material of the capacitive ring bushings is saturated and the required magnetic field distribution is not provided. In addition, the coaxial fastening of the ferromagnetic ring sleeve on a thin-walled copper disk becomes non-technological and difficult to implement, provided that small tolerances for deviations in the size of the RF resonators are provided, due to the electrodynamic characteristics of the slow-wave system. Placing a large number (up to several dozens) of ferromagnetic annular sleeves located in the ZS, with their axes skewed relative to each other, leads to a decrease in the actual cross section of the passage channel, as well as to the appearance of transverse components of the magnetic field. The worsening conditions of electron beam transport leads to a decrease in the fraction of the beam current passing through the span channel of the ZS, as well as to a decrease in the output power and efficiency of the device and thermal overload of the ZS.

The task to which the invention is directed is to increase the power and efficiency of TWT with MPPS.

The technical result of the use of the invention is to improve the current flow of intense electron flux through the passage channel of a powerful TWT of the short-wave part of the microwave range by reducing ripple of the beam boundary in static and dynamic modes of operation.

The problem is solved in such a way that in the TWT with a magnetic periodic focusing system (MPFS), consisting of axially magnetized ring magnets and pole pieces made of ferromagnetic material, spatially aligned with a resonator retardation system (ZS), at least part of the MPFS located after input RF energy, consists of adjacent to each other cells, each of which contains at least one magnet with unidirectional axial magnetization and three ferromagnetic inserts, ras laid with a gap between the pole pieces and between each other in bushings made of non-magnetic material, and secured by ring elements made of non-magnetic material, and the magnetization of the magnets in adjacent cells of the MPPS has the opposite direction. In addition, the bushings in the TWT with MPPS are made in the form of stepped bodies of revolution, consisting of at least two cylindrical parts, and together with the placed and fixed ring elements and inserts, the internal cavities of the RF RF resonators are formed, so that the ratio of the MPFS period to the period of the LC equals four. In addition, non-magnetic bushings and ring elements are made of a material with high thermal conductivity, for example, copper, and form a vacuum tight connection together with pole tips.

Figure 1 schematically shows the TWT of the claimed design. Figure 2-3 presents options for various designs of cells MPS. Figures 4-5 show the beam contour (1) with a current I = 4.0 A, ES potential U = 24000 V in a magnetic field (2) for an ordinary TWT with MPPS with an amplitude Bo = 0.246 T, and a period of MPFS L = 21.0 mm ( the magnetic field parameter α = 0.31), with a period of AP L L _ЗС = 10.5 mm with a length of capacitive bushings ЗС and pole pieces l _W = 3.5 mm (Fig. 4), and a beam contour (3) for TWT with MPPS of the claimed design in experiment the realized magnetic field (4) with an amplitude Bo = 0.246 T, a period of MPFS L = 42 mm (magnetic field parameter α = 1.24) with a period of LC L _ZS = 10.5 mm (Fig. 5). Figures 6 and 7 show the dependences of the amplitude of the pulsation of the beam δ (1) in the region of the passage channel with the optimal radius of the beam in MPPS R _in (2) on the value of the magnetic field parameter α up to the “no transmission” zone (3) in a conventional TWT with MPPS (Fig.6) and TWT with MPPS of the claimed design (Fig.7). On Fig, 9 presents the experimental values of the current at the ES (1) from the magnetic field parameter α (2) for the usual TWT (Fig. 8) and for the TWT with MPPS of the claimed design (Fig. 9).

TWT contains an electron gun 1, which forms an intense electron beam, MPFS, located after the input of RF energy 2 and consisting of alternating ring magnets 3, pole tips 4, inserts of ferromagnetic material 5, as well as bushings 6 and ring elements 7 made of non-magnetic material. The annular axially magnetized magnets 3 together with three inserts of a ferromagnetic material 5 located with a gap, which are fixed in the bushings 6 by ring elements 7, are joined between the pole pieces 4 and form an MPFS cell. In each MPPS cell, the magnets have the same direction of magnetization, and the magnetization of the magnets in adjacent adjacent MPFS cells has the opposite direction. The bushings of non-magnetic material 6, in which the ferromagnetic inserts 5 are mounted with a gap, fixed by non-magnetic ring elements 7, are made in the form of stepped bodies of revolution, consisting of at least two cylindrical parts, and together with the inserts form the internal cavities of the RF RF resonators. In this case, the ratio of the period of MPPS to the period of AP is four. Non-magnetic bushings 6 and ring elements 7 are made of a material with high thermal conductivity, for example, copper, and form a vacuum tight connection together with pole tips 4.

The location of the ferromagnetic inserts fixed in the bushings by ring elements of non-magnetic material in the cells of the MPFS, in accordance with the proposed design of the TWT with MPFS provides the necessary distribution of the longitudinal component of the magnetic induction along the axis of the device, focusing of the intense electron beam with small ripples (figure 5) in a wide range changes in TWT parameters with MPFS (Fig. 9) and the required electrodynamic characteristics of the ES.

A comparative analysis of the experimental and calculated results (Figs. 4-7) shows that the proposed TWT design with MPPS provides significantly lower amplitudes of pulsations of the electron beam in the span channel compared to the amplitudes of the pulsations of the beam in a conventional TWT with MPPS. The experimental results of measurements of current subsidence at the ES, shown in Fig.8-9, show that the passage of the beam through the span channel ZS for TWT of the claimed design is significantly higher compared to the passage of the beam in the span channel of a conventional TWT.

So, in the TWT with MPPS of the proposed design and with the parameters of the electron flux corresponding to the most commonly used parameters of the magnetic field 0.2 <α <0.35, the amplitude of the pulsations of the beam in the region of the passage channel is almost three times less than in the TWT with the usual MPFS (Fig. 6 -7). When the magnetic field parameter changes within 0.4 <α <0.55, the beam focusing in a conventional TWT with MPPS sharply worsens (Figs. 6, 8), and the relative magnitude of the beam pulsations in the TWT with MPPS of the proposed design does not exceed 10% even at α = 3.0 (Fig.7, 9).

The profile of the ferromagnetic inserts, the gaps between the inserts and the pole pieces, as well as the magnetization of the magnets in the MPFS cells are determined on the basis of a calculation or experiment from the condition of ensuring the required ratios between the higher harmonics of the magnetic field for given electrodynamic characteristics of the TWTs.

A new positive feature of the design is an increase in the efficiency of tuning the TWT to maximum current flow due to the possibility of placing pole pieces, ferromagnetic inserts, bushings and ring elements of non-magnetic material without distortions. The choice of sizes and material of the inserts, as well as their placement in accordance with the proposed claims, allows to reduce the influence of transverse magnetic fields associated with the heterogeneity of the magnetization of the magnets in the azimuthal direction.

Upon transition to the short-wavelength part of the microwave range, inserts of ferromagnetic material remain coarse-grained, can be placed between the pole pieces with the required accuracy and provide the magnetic field distribution with higher harmonic components necessary for focusing the intense flux.

In addition, the number of brazed joints required to create a vacuum shell in the TWT with MPPS of the claimed design does not increase compared to the conventional TWT design.

The practical manufacture of bushings and ring elements of non-magnetic material, as well as inserts of ferromagnetic material in the proposed design does not require numerous technological operations and is performed on standard metalworking equipment, which facilitates industrial applicability.

Analysis of the designs of analogues and the prototype of the claimed device shows that the signs associated with the specification of the number of inserts of ferromagnetic material, their fastening between the tips and each other with ring elements of non-magnetic material in the bushings of non-magnetic material with high thermal conductivity, as well as signs associated with the relationship between the period of MPPS and the period of LC, the resulting positive effect of increasing current flow in the TWT due to a decrease in the amplitude of the pulsations of the beam are unknown.

The use of the TWT design with MPFS in accordance with the proposed claims made it possible to reduce the beam current loss and to reduce the thermal load on the retarding system in static and dynamic modes of operation at elevated levels of the effective focusing magnetic field, as well as at reduced accelerating potentials.

Thus, the proposed TWT design has the following advantages:

improved current flow in O-type devices in a static mode of operation, due to a decrease in the magnitude of the pulsations of the beam;

decrease in dynamic defocus due to the ability to increase the value of the effective focusing magnetic field.

Claims (3)

1. A traveling wave lamp containing an electron gun, high-frequency energy input, a magnetic periodic focusing system consisting of axially magnetized ring magnets and pole pieces made of ferromagnetic material spatially aligned with high-frequency resonators of the retardation system, characterized in that at least the part of the magnetic periodic focusing system located after the input of high-frequency energy consists of adjacent cells, each of which contains not at least one magnet with magnetization unidirectional in the axial direction, bushings in the form of a stepped body of revolution of at least two cylindrical parts of non-magnetic material, in which three ferromagnetic inserts are arranged with ring elements of non-magnetic material, located with a gap between the pole pieces and between each other moreover, the magnetization of the magnets in neighboring cells has the opposite direction, and the bushes form, together with the ring elements and ferromagnetic inserts, internal Lost high-frequency resonators delay system. 2. The traveling wave lamp according to claim 1, characterized in that the ratio of the period of the magnetic periodic focusing system to the period of the slowing system is four. 3. The traveling wave lamp according to claim 1 or 2, characterized in that the bushings and ring elements are made of a material with high thermal conductivity, for example, copper and form a vacuum tight connection together with the pole pieces.

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