RU2796977C1 - Magnetic focusing system - Google Patents

Abstract

FIELD: vacuum microwave devices.

SUBSTANCE: invention relates to magnetic periodic focusing systems (MPFS). The magnetic focusing system comprises a periodic system in the form of a row of annular magnets with annular pole pieces following each other with reverse polarity. In the end wall of the magnetic screen located on the side of the electron gun, there is a central hole and an additional hole in which an annular radially magnetized magnet is installed perpendicular to the system axis, having a polarity opposite to the first axially magnetized magnet located between the pole piece and the end wall of the magnetic screen. The pole pieces are connected by ring elements in the form of stepped bodies of revolution made of non-magnetic material. The cylindrical wall of the magnetic screen completely covers the area of the electron gun.

EFFECT: increased output power and efficiency of the microwave device, decreased thermal load of the slow-wave system (SWS) by improving the current flow of the electron flow through the span channel.

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Description

The invention relates to vacuum microwave devices, in particular to magnetic periodic focusing systems (MPFS).

A known design of a magnetic focusing system for microwave devices, consisting of a gun magnet containing ring magnets with axial and radial magnetization, and located behind it MPFS [invention "Magnetic focusing system", H01J23/08, copyright certificate No. 656129, priority 13.04.1977 ]. The presence of a cannon magnet in the design makes it possible to raise the amplitude of the magnetic field in the area of the cathode of the device up to 1400÷1800 gauss, which ultimately leads to a decrease in the noise factor of the device.

However, such a system has significant weight, dimensions, and stray fields. In addition, the unshielded cathode region adds to the difficulty in setting up and operating the microwave device.

Known MPFS, in which an additional axially magnetized magnet is installed between the magnetic screen on the side of the electron gun and the first magnet [invention "Magnetic periodic focusing system", H01J23/08, copyright certificate No. 337846, priority 11/18/1969]. The design of the output area is similar to the input one. In the indicated MPFS, the value of the first and last maxima of the magnetic induction can be controlled by changing the dimensions of the axially magnetized rings, as well as their magnetization.

The disadvantage of this MPFS is that these additional magnets do not affect the nature of the distribution and the amplitude of the magnetic field in the cathode region.

Closest to the proposed magnetic focusing system is MPFS containing a magnetic rectifier installed in the Central hole of the end wall of the magnetic screen from the side of the electron gun coaxially with the MPFS (prototype) [patent for invention No. 2074448 "Magnetic focusing system of the O-type microwave device", H01J23/087, priority 20.0.1994]. The presence of a magnetic rectifier makes it possible to reduce the transverse component of the magnetic field in the region of the cathode and the input part of the MPFS. Accordingly, the thermal load on the electrodynamic system of the microwave device decreases.

The disadvantage of this design is that the rectifier is actually placed under the first MPFS magnet. This causes an increase in the transverse and longitudinal dimensions of the first magnet, which accordingly leads to an increase in the weight and size parameters of the entire MPFS. In addition, the rectifier affects the distribution of the axial transverse component of the magnetic field without changing its amplitude in the cathode region.

The technical result of the invention is to increase the output power and efficiency of the microwave device as a whole, as well as to reduce the thermal load on the slow-wave system (SS) by improving the current flow of the electron flow through the passage channel.

The technical result is achieved by the fact that the magnetic focusing system contains a periodic system in the form of a series of successive ring magnets with reverse polarity with annular pole pieces, a magnetic screen located on the side of the electron gun, with a central hole in its end wall and an additional hole in in which an annular radially magnetized magnet is installed perpendicular to the axis of the system, having a polarity opposite to the first axially magnetized magnet located between the pole piece and the end wall of the magnetic screen, and

Bp ≥ Bm,

where Bp is the value of the radial magnetization of the ring magnet,

Bm is the value of the axial magnetization of the first magnet;

the pole pieces are connected by ring elements in the form of stepped bodies of revolution made of non-magnetic material, while the cylindrical wall of the magnetic screen completely covers the area of the electron gun.

An additional hole in the end wall of the magnetic screen serves as a pole for a radially magnetized magnet, which is necessary to increase the axial symmetry of the field in this area. The arrangement of the radially magnetized magnet in the magnetic screen makes it possible to reduce the weight and size parameters of the magnetic system.

An annular radially magnetized magnet serves to increase the induction of the magnetic field created by an annular magnet with axial magnetization located between the pole tip and the end wall of the magnetic screen in the region of the electron gun of the microwave device. The use of a ring magnet with radial magnetization makes it possible to "deform" the symmetric bell-shaped curve of the magnetic field distribution on the axis of the system and shift the minimum point of the magnetic field induction to the left.

The direction of magnetization is chosen so that their fields add up in the region of the electron gun. In order for an axially magnetized ring magnet not to demagnetize a radially magnetized magnet, their magnetizations should be taken from the condition: Bp ≥ Вm.

A new positive feature of the design is an increase in the efficiency of tuning the microwave device for maximum current transmission due to the possibility of placing pole pieces without distortions, which together with ring elements made of non-magnetic material with high thermal conductivity form a vacuum-tight connection. The choice of dimensions and material of the ring elements also makes it possible to reduce the effect of transverse magnetic fields associated with the inhomogeneity of the magnetization of the magnets in the azimuthal direction.

The cylindrical wall of the magnetic shield serves to shield stray fields from ring magnets with axial magnetization in the region of the electron gun.

The presence of a magnetic field in the region of the electron gun makes it possible to significantly increase the current flow of the electron beam, especially tubular electron beams. This, in turn, increases the output power and efficiency of the microwave device, reduces the thermal load on the AP.

Thus, the use of an additional magnet in the MPFS design in accordance with the proposed claims makes it possible to provide a magnetic field in the cathode region of 30 gauss and above.

The invention is illustrated by drawings. Figure 1 shows a longitudinal section of the proposed magnetic focusing system, where:

ring magnets 1,

pole pieces 2,

magnetic shield 3,

electron gun 4,

end wall of the magnetic screen 5,

ring radially magnetized magnet 6,

the first annular axially magnetized magnet 7,

ring element 8,

cylindrical wall of the magnetic shield 9,

electronic flow 10.

Figure 2 presents a graph of the distribution of the magnetic field on the axis of the system.

The operation of the proposed magnetic focusing system for a microwave device, containing ring magnets 1 and pole pieces 2 and a magnetic screen of the electron gun 3, in the end wall of which there is an annular radially magnetized magnet 6, is as follows.

Pole pieces 2 and ring elements 8 form a single outer screen of the SL, which allows to significantly reduce its transverse size, and thereby increase the magnetic field induction on the axis of the system to improve the current flow of the electron flow 10.

The electron gun 4 forms an intense electron flow 10 by the electric field of the compression gun and the magnetic field monotonically increasing from the cathode Vk, then the focusing by the periodic field of the MPFS occurs and the flow passes through the passage channel to the collector of the microwave device.

The distribution of the longitudinal component of the magnetic field along the SL is determined by the magnetization of the ring magnets 1. To ensure the required magnetic field in the area of the electron gun 4, it is necessary to exclude the influence of the ring magnets 1. This is achieved by completely shielding the area of the electron gun 4 due to the cylindrical wall of the magnetic screen 9.

The magnitude of the magnetic field induction in the region of the electron gun 4 is determined by ring magnets 6 and 7, subject to the condition Bp ≥ Bm. Moreover, the additional magnet 6 and the ring magnet 7 have such a polarity that the addition of magnetic fields is ensured.

Heat removal from the pole pieces 2 is carried out by a ring element 8 with high thermal conductivity, for example, made of copper. Otherwise, increasing the radial size of the pole pieces 2 and going beyond the outer radius of the magnets 1 will lead to an increase in the leakage flux of magnetic induction and to an undesirable decrease in the magnitude of the magnetic field on the axis of the focusing system. Magnets 1, to which the copper ring element 8 adjoins, protect them from possible overheating, as well as a reversible decrease in the magnetic field in the system with an increase in the temperature of the magnets.

The proposed technical solution makes it possible to eliminate the detuning of the MPFS with increasing temperature.

Example. The magnetic focusing system contains a periodic system made in the form of a number of ring magnets 1, following each other with reverse polarity, and separated by annular pole pieces 2, a magnetic screen 3 and a ring magnet 6. All magnets are made of samarium-cobalt alloy, pole pieces 2 and magnetic screen 3 - made of Armco steel.

The ring magnets 1 have an inner diameter of 8 mm, an outer diameter of 14 mm and a length of 3 mm. Ring magnet 6 size: inner diameter 15mm, outer diameter 21mm, length 1.2mm. The magnetization values of ring magnets 6 and 7 are Bp = Bm = 0.7 T.

Pole pieces 2 are made in the form of stepped bodies of revolution, consisting of at least two cylindrical parts with dimensions: inner diameter D0 = 5.5 mm, outer diameter D1 = 7 mm, length L1 = 2.6 mm and inner diameter D1 = 7 mm, outer diameter D2 = 11 mm, length L2 = 1.2 mm. Pole pieces 2 have a permanent connection with copper ring elements 7, made in the form of stepped bodies of revolution from two cylindrical parts with dimensions: inner diameter D0 = 5.5 mm, outer diameter D1 = 7 mm, length L3 = 1.66 mm, and inner diameter D1 = 7 mm, outer diameter D3 = 8 mm, length L4 = 3.06 mm.

The end wall 5 of the magnetic shield 3 has an inner diameter of 5.5 mm, an outer diameter of 26 mm, and a length of 1.2 mm. Cylindrical wall 8 magnetic shield 3 size: inner diameter 23 mm, outer diameter 26 mm, length 26.04 mm.

The level of the magnetic focusing field in the area of the electron gun 4 is determined by the parameters of the ring magnets 6 and 7, and in the regular part of the system by the parameters of the ring magnets 1. Analysis of the graph shown in Fig. 2 shows that if ring magnet 6 is installed in the design of the magnetic system of the microwave device, the level of the magnetic field in the region of electron gun 4 is Vk = 60 G, and in the absence of ring magnet 6, the magnetic field in the region of electron gun 4 is close to zero. The values of the magnetizations of the ring magnets 6 and 7, as well as their geometrical parameters, are selected in each specific case, based on the requirements for achieving the minimum level of the magnetic field in the region of the electron gun 4.

Figure 2 shows a graph of the distribution of the longitudinal component of the magnetic focusing field B, T along the axis of the device, where: the position of the electron gun corresponds to Z=0 mm, the level of the magnetic field at the cathode Vk: solid line - in the presence of an annular radially magnetized magnet 6, dash-dotted line - without him.

The use of the proposed design of the magnetic system in a microwave device makes it possible to reduce the beam current loss and reduce the thermal load on the SWS, providing increased levels of the effective focusing magnetic field on the system axis and in the region of the electron gun.

Thus, the microwave device with the proposed design of the magnetic system has the following advantages: increased output power and efficiency, improved operational parameters.

Claims (5)

A magnetic focusing system containing a magnetic periodic system in the form of a series of successive ring magnets with reverse polarity with ring pole pieces, a magnetic screen located on the side of the electron gun, with a central hole in its end wall, characterized in that in the end wall of the magnetic The screen additionally has a hole in which an annular radially magnetized magnet is installed perpendicular to the axis of the system, having a polarity opposite to the first axially magnetized magnet located between the pole piece and the end wall of the magnetic screen, and Bp ≥ Bm, where Bp is the value of the radial magnetization of the ring magnet, Bm is the value of the axial magnetization of the first magnet, the pole pieces are connected by ring elements in the form of stepped bodies of revolution made of non-magnetic material, while the cylindrical wall of the magnetic screen completely covers the area of the electron gun.

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