CN111383873A - A Novel Tunable Magnetic Focusing System for Ribbon Beam TWT - Google Patents

Abstract

The invention provides a novel adjustable magnetic focusing system suitable for a strip-shaped traveling wave tube, and belongs to the technical field of vacuum electronics. The novel adjustable magnetic focusing system comprises a periodic cusped magnetic field focusing system and a magnetic focusing system fixing device, and a By magnetic field is generated in a strip-shaped electron beam channel By loading staggered second permanent magnets in the Y direction of a first permanent magnet so as to offset the space charge force of the strip-shaped electron beam in the X direction; in addition, the invention provides a fixing device suitable for the novel adjustable magnetic focusing system, and in the fixing device for the magnetic focusing system, the staggered second permanent magnets have certain adjustable space in the X direction. Therefore, the novel adjustable magnetic focusing system has the advantages of miniaturization, low manufacturing cost, adjustability and the like.

Description

A Novel Tunable Magnetic Focusing System for Ribbon Beam TWT

technical field

The invention belongs to the technical field of vacuum electronics, and in particular relates to a magnetic focusing system of a band-shaped injection traveling wave tube suitable for millimeter wave and terahertz frequency bands.

Background technique

Ribbon electron beams have significant advantages such as large cross-sectional size, high DC power, and low space charge effect. Vacuum electronic devices in millimeter-wave and terahertz frequency bands using ribbon electron beams as electron sources have higher output power. Therefore, ribbon electron injection has received extensive attention in the field of millimeter-wave and terahertz vacuum electronic devices. The strip electron injection molding can be realized by a classic Pierce electron gun, which is transmitted under the focusing action of a uniform magnetic field or a periodically tangential magnetic field, thereby providing stable DC power for signal generation or amplification of vacuum electronic devices. Ribbon injection traveling wave tube is a new type of vacuum electronic device with the characteristics of high power, wide bandwidth, high efficiency and high gain. . With the increase of the operating frequency, such as 0.22THz, 0.34THz, etc., the size of the vacuum electronic device is reduced, and the required processing and assembly precision of the strip electron gun and magnetic focusing system is particularly high (micron order), which will This makes the formation and transmission of the ribbon-shaped electron beam more difficult.

In the millimeter-wave and terahertz frequency bands, there are few reports on the thermal measurement experiments of the band-shaped traveling wave tube. X.Shi et.al.,“Theoretical and experimental research on a novel small tunable PCM system instaggered double vane TWT,”IEEE Transactions on Electron Devices,vol.62,no.12,pp.4258-4264,Dec.2015. ) and the G-band strip traveling wave tube at the University of California, Davis (A. Baig et al., "Performance of a Nano-CNC machined220-GHz traveling wave tubeamplifier," IEEE Transactions on Electron Devices, vol.64 , no.5, pp.2390-2397, May2017.), the thermal test results have a power output of 100W. One of the reasons why it is difficult to develop the strip-beam TWT is that it is difficult to realize the electron optical system suitable for the strip-beam travel-wave tube. The electron optical system consists of an electron gun, a magnetic focusing system and a collector. The magnetic focusing system used in the traveling wave tube is generally a uniform magnetic field focusing system or a periodic permanent magnet focusing system. Its function is to use the focusing force provided by the magnetic field to balance the electron injection. space charge force, thereby achieving stable transport of banded electron beams. Therefore, the key to solving the band-shaped electron injection transport lies in the design of the magnetic focusing system. If a uniform permanent magnet is used to focus the band-shaped electron beam, the volume of the permanent magnet assembly forming a uniform magnetic field is larger than that of the permanent magnet used in the periodic magnetic field, which is not conducive to the miniaturization of the device. In addition, due to errors in the manufacture of the cathode assembly of the strip electron injection gun and the assembly of the gun, the injection waist position and laminar flow properties of the strip electron injector may change. Due to the change of the cross-sectional size of the strip electron injection, the injection current density changes, that is, the space charge force changes, and the required focusing magnetic field should be changed accordingly, that is, the magnetic focusing system should be adjustable. Therefore, a tunable magnetic focusing system for a strip electron injection traveling wave tube based on a permanent magnet to generate a periodically tangential magnetic field is studied, including the magnetic focusing system and the assembly design of the magnetic focusing system. The development of strip injection devices and the development of millimeter wave and terahertz radiation sources are of great significance.

SUMMARY OF THE INVENTION

Aiming at the problem that the band-shaped electron injection is difficult to transmit stably in the band-shaped traveling wave tube in the background art, the purpose of the present invention is to provide a novel tunable magnetic focusing system suitable for the band-shaped traveling wave tube. The invention is based on a permanent magnet generating a periodic tangential magnetic field and a designed fixing device for the magnetic focusing system, so that the magnetic focusing system has a certain adjustable range, so that the invention can be applied to the band-shaped electron beam tube to realize the stable transmission of the band-shaped electron beam.

For achieving the above object, technical scheme of the present invention is as follows:

A new type of tunable magnetic focusing system suitable for strip-shaped traveling wave tube, comprising a magnetic focusing system and a fixing device for the magnetic focusing system, characterized in that the magnetic focusing system includes n single-period magnet assemblies and a pair of pole pieces , the single-period magnet assembly consists of two sets of magnet units, the magnet units are symmetrically arranged, the set of magnet units includes two first permanent magnets and two second permanent magnets, the two first permanent magnets Arranged side by side, the first permanent magnets in the two groups of magnet units repel each other, and the two second permanent magnets are alternately adsorbed on the surfaces of the two first permanent magnets arranged side by side through magnetic attraction, and the surfaces are two groups of magnets the opposite surface of the mutually repelling surface of the first permanent magnet in the unit, the pole piece is arranged on the side of the first permanent magnet close to the electron gun;

The magnetic focusing system fixing device includes a first magnetic focusing system bracket, a second magnetic focusing system bracket, a magnetic focusing system bracket strip and a connecting plate; the first magnetic focusing system bracket and the second magnetic focusing system bracket are both L-shaped , the L-shaped first magnetic focusing system bracket and the second magnetic focusing system bracket have the same first side structure, and both are provided with through holes for placing the second permanent magnet in the magnetic focusing system; above the through holes is a circular The screw holes are matched with the circular screw holes on the magnetic focusing system bracket strip, and the single-period magnet assembly is fixed by the bracket strip; the connecting plate is located above the magnetic focusing system bracket strip, and a pair of circular screw holes are arranged on the connecting plate and a pair of U-shaped screw holes, wherein the circular screw holes are connected and fixed with the first magnetic focusing system bracket, and the U-shaped screw holes are connected and fixed with the second magnetic focusing system bracket; the second side surface of the first magnetic focusing system bracket A positioning block is provided, the two groups of magnet units are symmetrical about the positioning block, and the high-frequency structure is placed above the positioning block; the second side of the second focusing system bracket is fixedly connected to the first magnetic focusing system bracket through U-shaped screw holes the second side.

Further, the n is a positive integer.

Further, the U-shaped screw holes on the first side and the U-shaped screw holes on the second side of the second magnetic focusing system bracket are combined to adjust the distance between the two groups of magnet units in the magnetic focusing system.

Further, the height of the through hole is greater than the height of the second permanent magnet, which facilitates adjustment of the position of the second permanent magnet relative to the first permanent magnet.

Further, the vertical spacing between the staggered second permanent magnets is w, and when the value of w increases from small to large, the broad side of the band-shaped electron beam changes from over-focusing to under-focusing.

Further, the materials of the first permanent magnet and the second permanent magnet are both NdFeB; the material of the pole piece is pure iron; the material of the fixing device of the magnetic focusing system is non-magnetic metal.

Further, the non-magnetic metal is preferably aluminum.

To sum up, due to the adoption of the above-mentioned technical solutions, the beneficial effects of the present invention are:

1. The novel adjustable magnetic focusing system designed by the present invention is suitable for the strip-shaped injection traveling wave tube. By adsorbing the staggered second permanent magnets 1-2 in the Y direction of the first permanent magnet The electron injection channel generates By magnetic field to counteract the space charge force of the band-shaped electron injection in the X direction; and the loaded second permanent magnet 1-2 can be adjusted in the vertical X direction, that is, when the two second permanent magnets are staggered. When the spacing w between the magnets is larger, the generated By magnetic field is smaller, and vice versa.

2. The adjustable magnetic focusing system designed by the present invention has the advantages of miniaturization and low cost compared with other magnetic focusing systems in the form of uniform magnetic field. The development of terahertz radiation sources is of great significance.

Description of drawings

FIG. 1 is a schematic diagram of the overall structure of the magnetic focusing system of the present invention.

FIG. 2 is a schematic diagram of the fixing device of the magnetic focusing system of the present invention.

FIG. 3 is a schematic diagram of the magnetic focusing system of the present invention.

4 is a schematic diagram of the single-period structure and magnetization direction of the magnetic focusing system of the present invention;

Among them, (a) is the schematic diagram of the single-period structure of the magnetic focusing system (n=1); (b) is the Y-direction view of the single-period structure of the magnetic focusing system; (c) is the Z-direction view of the single-period structure of the magnetic focusing system; (d) It is a schematic diagram of the magnetization direction of the permanent magnet with a single-period structure of the magnetic focusing system.

FIG. 5 is a distribution diagram of the axial magnetic induction intensity of the magnetic focusing system along the Z axis obtained by the simulation calculation in Embodiment 1 of the present invention.

6 is the narrow-side transmission track (Y-Z section) of the band-shaped electron injection under the action of the magnetic focusing system in the first embodiment of the present invention.

FIG. 7 is the broad-side transmission track (X-Z section) of the band-shaped electron injection under the action of the magnetic focusing system in Example 1 of the present invention.

FIG. 8 is a distribution diagram of the axial magnetic induction intensity of the magnetic focusing system along the Z axis obtained by the simulation calculation in Embodiment 2 of the present invention.

FIG. 9 is the narrow-side transmission track (Y-Z section) of the band-shaped electron injection under the action of the magnetic focusing system in Embodiment 2 of the present invention.

FIG. 10 is the broadside transmission track (X-Z section) of the band-shaped electron injection under the action of the magnetic focusing system in Example 2 of the present invention.

In the figure, the magnetic focusing system 1 includes: a first permanent magnet 1-1, a second permanent magnet 1-2 and a pole piece 1-3; the first magnetic focusing system bracket 2 includes: a rectangular through hole 2-1 and a rectangular positioning block 2 -2; the second magnetic focusing system bracket 3 includes: a rectangular through hole 3-1, a first U-shaped screw hole 3-2 and a first circular screw hole 3-3; the magnetic focusing system bracket bar 4 includes a second circular Screw holes 4-1; the connecting plate 5 includes: a third circular screw hole 5-1 and a second U-shaped screw hole 5-2.

Detailed ways

In order to make the objectives, technical solutions and advantages of the present invention clearer, the present invention will be further described in detail below with reference to the embodiments and accompanying drawings.

This embodiment takes the G-band band-shaped electron beam tube electron optical system as an example to illustrate that the novel tunable magnetic focusing system in the present invention can be used to realize the stable transmission of the band-shaped electron beam. The strip electron injection gun in the present invention has been described in Chinese invention patent CN201910870119.7: the injection waist size of the strip electron injector is about 0.4mm×0.1mm, and the injection current and cathode emission current density are respectively 130mA and 26A/cm ² , the compression ratio is 12.5:1, and the injection current density at the injection waist is 325A/cm ² .

Example 1

A schematic diagram of the overall structure of a new type of tunable magnetic focusing system suitable for strip-shaped TWT , which provides a focusing magnetic force for balancing the space charge force of the banded electron beams, so that the banded electron beams can be transported stably.

FIG. 2 is a schematic diagram of a magnetic focusing system fixing device of the present invention. The magnetic focusing system fixing device includes a first magnetic focusing system bracket 2 , a second magnetic focusing system bracket 3 , a magnetic focusing system bracket bar 4 and a connecting plate 5 .

The first magnetic focusing system bracket 2 and the second magnetic focusing system bracket 3 are both L-shaped and arranged side by side. The first side structure of the L-shaped first magnetic focusing system bracket 2 and the second magnetic focusing system bracket 3 The same, two upper and lower rows of staggered through holes 2-1 and 3-1 are symmetrically arranged for placing the staggered second permanent magnets 1-2 in the magnetic focusing system; a first circular screw hole 3 is arranged above the through holes -3, the magnetic focusing system support bar 4 is provided with a second circular screw hole 4-1, the circular screw hole provided on the side of the first magnetic focusing system support The circular screw hole 4-1 is used to fix the single-period magnet assembly to prevent the double row of the first permanent magnet 1-1 from moving in the vertical direction (X direction) of the first side surface; the connecting plate is located at 5 in the magnetic focusing system Above the bracket bar 4, a pair of third circular screw holes 5-1 and a pair of second U-shaped screw holes 5-2 are provided on the connecting plate 5, wherein the third circular screw hole 5-1 is connected to the first magnetic focus The system bracket 2 is connected and fixed, and the second U-shaped screw hole 5-2 is connected and fixed with the second focusing system bracket 3; the second side of the first magnetic focusing system bracket 2 is provided with a positioning block 2-2 for positioning the tape For the positioning of the traveling wave tube in the X direction, the two sets of magnet units are symmetrical about the positioning block; the second side of the second focusing system bracket 3 is fixedly connected to the first magnetic focusing system bracket 2 through the first U-shaped screw hole 3-2 The second side of the magnetic focusing system; the first U-shaped screw hole 3-2 and the second U-shaped screw hole 5-2 are used to adjust the distance d of the double-row permanent magnets 1-1 of the magnetic focusing system. The closer the distance, the greater the axial magnetic field. powerful.

The circular screw holes and U-shaped screw holes are suitable for M2 screws, as shown in the figure; among them, the groove at the connection between the first side and the second side of the first magnetic focusing system bracket, the two magnetic focusing systems The steps on the first side of the bracket close to the through holes are all limitations of the processing technology and have nothing to do with the realization effect of the technical solution.

3 is a schematic diagram of the magnetic focusing system of the present invention, the magnetic focusing system includes four single-period magnet assemblies and a pair of pole pieces 1-3, the single-period magnet assemblies are composed of two sets of magnet units, and the magnet units are symmetrically arranged , the magnet unit includes two first permanent magnets 1-1 and two second permanent magnets 1-2, the first permanent magnet 1-1 and the second permanent magnet 1-2 are magnetized respectively; the pole piece 1- 3 is arranged on the side of the first permanent magnet 1-1 close to the electron gun; the magnetic focusing system can be applied to the G-band band injection traveling wave tube with medium power output.

FIG. 4 is a schematic diagram of the single-period structure and magnetization direction of the magnetic focusing system of the present invention. 4(a) is a schematic structural diagram of a pair of magnet units in the magnetic focusing system of the present invention, the magnet units include two first permanent magnets 1-1 and two second permanent magnets 1-2, and the second permanent magnet 1-2 It is staggered and adsorbed on the surface of the first permanent magnet 1-1XOY; Fig. 4(b) is a Y-direction view of the single-period structure of the magnetic focusing system of the present invention; Fig. 4(c) is a Z-direction view of the single-period structure of the magnetic focusing system of the present invention; Fig. 4 (d) is a schematic diagram of the magnetization direction of the permanent magnet with a single-cycle structure of the magnetic focusing system of the present invention, the arrow points to the N-pole representing the magnetic steel, and the staggered second permanent magnets 1-2 loaded in a single cycle and the first permanent magnet at the corresponding loading position The magnetization directions of one permanent magnet 1-1 are the same.

In this embodiment, the structural parameters are set as follows: a=16mm, b=2.4mm, c=1.5mm, d=2.4mm, e=4mm, h=4.8mm, w=5mm. In this embodiment, both the first permanent magnet 1-1 and the second permanent magnet 1-2 are made of sintered NdFeB (Sintered NdFeB) magnetic material. Compared with the samarium cobalt permanent magnet material, NdFeB has a higher magnetic energy product And coercivity, better mechanical properties, more conducive to the realization of millimeter-wave and terahertz band magnetic focusing system.

In order to illustrate that the focusing magnetic force provided by the adjustable magnetic focusing system of the present invention can better balance the space charge force of the above-mentioned band-shaped electron injection, a joint simulation of the band-shaped electron gun and the new adjustable magnetic focusing system is carried out. The three-dimensional electromagnetic simulation software is used to simulate and calculate, and the following results are obtained:

When the period n of the magnetic focusing system is 4, the magnetic focusing system of the present invention is suitable for the G-band band injection traveling wave tube with medium gain and medium output power. In this case, the first permanent magnets 1-1 and the staggered second permanent magnets 1-2 are located in the range of Z=9.3mm˜28.5mm. As shown in Figure 5, the distribution diagram of the axial magnetic induction intensity Bz along the Z axis at the center position of the magnetic focusing system with a length of 4 cycles is obtained by the simulation calculation of the present invention. The period of Bz is 4.8mm, and the absolute value is about 0.35T at the maximum . In addition, the cross-sectional views of the transport trajectories of the strip electron beam on the YZ plane (narrow side) and the XZ plane (broad side) are shown in Figures 6 and 7, respectively. changes, which indicates that the banded electron injection was not intercepted by the tube body during the transport process.

Example 2

When the period n of the magnetic focusing system is 18, the magnetic focusing system of the present invention is suitable for the G-band band-shaped TWT with high gain and high output power. In this case, the first permanent magnet 1-1 and the staggered No. The two permanent magnets 1-2 are located in the range of Z=9.3mm˜95.7mm. As shown in Figure 8, the distribution diagram of the axial magnetic induction intensity Bz along the Z axis at the center position of the magnetic focusing system with a length of 18 periods is obtained by the simulation calculation of the present invention. The period of Bz is 4.8mm, and the absolute value is about 0.35T at the maximum. . In addition, the cross-sectional views of the transport trajectories of the banded electron beams on the YZ plane (narrow side) and the XZ plane (broadside) are shown in Figures 9 and 10, respectively. It can be seen from the figures that the banded electron beams are longer than 90mm Under the transmission distance of , the fluctuation amplitudes of electron beams in the broadside and narrowside directions are very small, which indicates that the periodic magnetic field generated by the designed magnetic focusing system is sufficient for the focusing of the electron beams on the narrowside. Therefore, the novel tunable magnetic focusing system can be used for stable transport of ribbon electron beams.

Further research shows that when the value of w increases from small to large, the By generated by the staggered second permanent magnets in the band-shaped electron injection area will change from large to small, and the broad side of the band-shaped electron injection will change from over-focusing to under-focusing. The invention can change the magnetic field By required for the broadside focusing of the band-shaped electron beamer by adjusting the spacing w of the staggered second permanent magnets. It is worth noting that, in the simulation calculation of the present invention, the transmission distance of the band-shaped electron injection in the magnetic field area is greater than 86mm, and the band-shaped electron injection does not collapse or diverge violently during the transmission process, and the current passing at the position of Z=95.7mm Consistent with the emission current, it shows that the focusing magnetic force provided by the magnetic focusing system can better offset the space charge force of the band electron beam itself, thereby avoiding the divergence of the band electron beam, which indicates that the designed new tunable magnetic focusing system The ability to focus the band electron beam well is of great value for the development of high-gain, high-power millimeter-wave and terahertz band-beam traveling wave tubes.

The above descriptions are only specific embodiments of the present invention, and any feature disclosed in this specification, unless otherwise stated, can be replaced by other equivalent or alternative features with similar purposes; all the disclosed features, or All steps in a method or process, except mutually exclusive features and/or steps, may be combined in any way.

Claims (7)

1. A novel adjustable magnetic focusing system suitable for a strip traveling wave tube comprises a magnetic focusing system and a magnetic focusing system fixing device, and is characterized in that the magnetic focusing system comprises n single-period magnet assemblies and a pair of pole shoes, the single-period magnet assemblies comprise two groups of symmetrically arranged and mutually exclusive magnet units, each magnet unit comprises two first permanent magnets arranged side by side and two second permanent magnets attached to the surfaces of the first permanent magnets in a staggered mode, and the pole shoes are arranged on one sides, close to an electron gun, of the first permanent magnets;

the magnetic focusing system fixing device comprises a first magnetic focusing system bracket, a second magnetic focusing system bracket, a magnetic focusing system bracket strip and a connecting plate; the first magnetic focusing system bracket and the second magnetic focusing system bracket are both L-shaped, and the first magnetic focusing system bracket and the second magnetic focusing system bracket have the same side surface structure and are provided with through holes for placing a second permanent magnet in the magnetic focusing system; a magnetic focusing system bracket strip is fixedly arranged above the through hole and is matched with the magnetic focusing system bracket to fix the monocycle magnet assembly; the connecting plate is positioned above the magnetic focusing system support strip and is used for fixedly connecting the first magnetic focusing system support and the second magnetic focusing system support; the bottom surface of the first magnetic focusing system bracket is provided with a positioning block, a high-frequency structure is placed above the positioning block, and the two groups of magnet units are symmetrical relative to the positioning block; the bottom surface of the second magnetic focusing system bracket is fixedly connected with the bottom surface of the first magnetic focusing system bracket.

2. The novel adjustable magnetic focusing system for ribbon traveling wave tube according to claim 1, wherein n is a positive integer.

3. The novel adjustable magnetic focusing system for ribbon traveling wave tubes according to claim 1, wherein the distance between the two sets of magnet units in the magnetic focusing system is adjusted by adjusting the distance between the bottom surface of the second magnetic focusing system support and the bottom surface of the first magnetic focusing system support.

4. The novel adjustable magnetic focusing system for ribbon traveling wave tube according to claim 1, wherein the height of the through hole is larger than the height of the second permanent magnet for adjusting the position of the second permanent magnet relative to the first permanent magnet.

5. The novel adjustable magnetic focusing system for the ribbon traveling-wave tube according to claim 1, wherein the vertical distance between the second permanent magnets arranged in a staggered manner is w, and when the value of w is changed from small to large, the wide side of the ribbon electron beam is focused from over-focusing to under-focusing.

6. The novel adjustable magnetic focusing system for the ribbon traveling wave tube according to claim 1, wherein the first permanent magnet and the second permanent magnet are made of neodymium iron boron; the pole shoe is made of pure iron; the magnetic focusing system fixing device is made of non-magnetic metal.

7. The novel adjustable magnetic focusing system for ribbon traveling wave tube according to claim 6, wherein the non-magnetic metal is preferably aluminum.

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