A magnetic focusing system for a terahertz strip-line traveling wave tube

Abstract

The application provides a magnetic focusing system for a terahertz strip beam row wave tube, and belongs to the technical field of vacuum electron devices. The system is characterized in that a plurality of parallel long strip magnets are arranged at intervals on a main magnet, and the interval between the long strip magnets is simultaneously adjusted through a synchronous knob, so that a suitable magnetic field is generated in a slow wave structure channel to focus the strip beam and prevent the strip beam from diverging and being intercepted by the inner wall of the channel. Meanwhile, the main magnet and the long strip magnet are arranged at intervals to eliminate most of the unnecessary B x components near the center of the electron beam channel, so that the magnetic field generated by the magnet can better focus the strip beam and effectively improve the flow rate of the strip beam.

Description

Technical Field

[0001] This invention belongs to the field of vacuum electronic device technology, specifically relating to a magnetic focusing system for a terahertz ribbon injection traveling wave tube. Background Technology

[0002] Terahertz waves are electromagnetic waves with frequencies between microwaves and light waves. Compared to microwaves, they have shorter wavelengths, and compared to light waves, they exhibit less attenuation during atmospheric transmission. Terahertz science and technology have received increasing attention in recent years. Traveling wave tubes (TWTs), as one of the most promising terahertz radiation sources, are in high demand in radar, communications, medicine, and materials analysis due to their high power, high gain, and high efficiency. However, the development of traditional circular-beam TWTs into the terahertz band has encountered bottlenecks. As the frequency increases, the device size gradually decreases, and circular beams cannot transmit large currents in narrow channels, leading to a decline in device performance. Using strip beams with approximately rectangular or elliptical beam cross-sections is one important means to solve this problem. Compared to traditional circular beams, strip beams have advantages such as a larger interaction area and greater current capacity. Therefore, in-depth research on terahertz strip-beam TWTs is particularly important.

[0003] When the electron beam generated by the electron gun undergoes beam-wave interaction in a slow-wave structure, an external magnetic field is required to focus the beam and prevent it from diverging and being intercepted by the inner wall of the channel. The device that applies the external magnetic field is called a magnetic focusing system. Stable propagation of the electron beam has always been a major challenge in the development of electron beam devices. Traditional uniform magnetic field focusing is difficult to suppress the "Diocotron" instability of the electron beam, and its large structural size is also detrimental to the miniaturization of terahertz devices. In contrast, periodic magnetic field focusing is a better approach. Periodic magnetic focusing systems are now widely used in vacuum electronic devices, and various focusing structures have emerged, such as periodic tangential magnetic fields (PCM), wobble magnetic fields (Wiggler), and periodic permanent magnet magnetic fields (PPM). For the electron beam to propagate stably in a periodic permanent magnet focusing magnetic field, the voltage of the electron beam must be tens of kilovolts or even higher, which is difficult to achieve in many systems. In 1993, inspired by the Wiggler magnetic field and the PPM structure, Booske et al. first proposed the concept of PCM and the closed PCM structure (JHBooske et al., “Stability and Confinement of Nonrelativistic Sheet Electron Beams with Periodic Cusped Magnetic Focusing,” Journal of Applied Physics, vol. 73, no. 9, pp. 4140-4155, 1993.). Subsequently, Booske et al. proposed the offset PCM structure by opening the sides of the closed PCM structure and placing the residual magnet off-center (JHBooske et al., “Periodic Magnetic Focusing of Sheet Electron Beams”, Physics of Plasmas, vol. 1, no. 5, pp. 1714-1720, 1994.). This structure can not only overcome the “Diocotron” instability to a certain extent, but also effectively suppress the problem of lateral divergence of the electron beam. Subsequently, many researchers conducted extensive theoretical and experimental studies based on the periodic shear magnetic field.

[0004] In experiments, the magnitude of the current and the cross-sectional dimensions of the ribbon-shaped beam can differ from simulation results due to various factors. This causes changes in the beam current density, i.e., a change in the space charge force. Consequently, the required focusing magnetic field should be adjusted accordingly, meaning the magnetic focusing system should be adjustable. Patent CN111383873B discloses a novel adjustable magnetic focusing system suitable for ribbon-shaped traveling wave tubes. This system adjusts the focusing magnetic field provided by the magnetic focusing system by adjusting the relative position of the second permanent magnet on the first permanent magnet. However, this method requires manual adjustment of each second permanent magnet individually, which is cumbersome. Furthermore, it is difficult to ensure that the adjusted second permanent magnets are at the same height, which may prevent the system from generating the expected focusing magnetic field.

[0005] In summary, a novel easily adjustable PCM magnetic focusing system has been developed, which simplifies the adjustment steps in experiments and enables precise control of the magnetic field in the electron beam channel, resulting in high flow rate of the strip beam during transmission in the channel, which is of great significance. Summary of the Invention

[0006] To address the problems raised in the background art, the present invention aims to provide a magnetic focusing system for a terahertz strip-beam traveling wave tube. This system generates a suitable magnetic field in the slow-wave structure channel by arranging a group of parallel elongated magnets at a certain distance on the main magnet, and simultaneously adjusting the spacing between the elongated magnets using a synchronization knob. This magnetic field is used to focus the strip-beam and prevent it from diverging and being intercepted by the channel's inner wall. Simultaneously, the spacing between the main magnet and the elongated magnets helps to eliminate most of the unwanted B-wave radiation near the center of the electron beam channel. x The component allows the magnetic field generated by the magnet to be better focused on the strip jet, effectively improving the flow rate of the strip jet.

[0007] To achieve the above objectives, the technical solution of the present invention is as follows:

[0008] A magnetic focusing system for a terahertz strip injection traveling wave tube includes two pole shoes, a main magnet, two sets of long strip magnets, an L-shaped support, a flat plate support, a pressure bar, and a long strip magnet adjustment device.

[0009] The main magnet includes two magnetic groups, each magnetic group having a pole piece on one vertical side, and the pole piece being located on the side of the main magnet closer to the electron gun; the two magnetic groups are used to transmit electron beams.

[0010] The flat plate bracket and the L-shaped bracket are fixedly arranged to form a rectangle, with the horizontal arm of the L-shaped bracket located within the rectangle. A boss is set at the center of the horizontal arm of the L-shaped bracket, and magnetic assemblies of the main magnet are placed on both sides of the boss. A pressure strip is set on the top of the magnetic assemblies to fix the main magnet in the vertical direction and prevent the main magnet from being misaligned or sliding out. The flat plate bracket and the L-shaped bracket together fix the main magnet in the horizontal direction.

[0011] Both the vertical arm of the L-shaped support and the outer surface of the flat plate support are fixedly equipped with a bar magnet adjustment device and a set of bar magnets. Each set of bar magnets consists of two parallel bar magnets, with their length directions parallel to the electron beam transmission direction. The bar magnet adjustment device is used to adjust the vertical spacing between the two bar magnets and ensure that the two bar magnets are always symmetrical about the central axis of the electron beam channel, thereby generating a B-type focusing effect on the wide side of the strip-shaped beam. y Quantity.

[0012] Furthermore, the elongated magnet adjustment device includes a baffle, a synchronization knob, a fixed slider, and a synchronization knob fixing seat;

[0013] The baffle includes two sets of baffle strips. A set of baffle strips is fixedly installed parallel to each other on both sides of the vertical arm of the L-shaped bracket and both sides of the flat plate bracket. Vertical slides are opened at corresponding positions of the baffle strips and the bracket. The synchronization knob fixing seat is fixedly installed at the center of the vertical arm of the L-shaped bracket and the flat plate bracket, and a synchronization knob is installed on it. A slide is set vertically at the center of the two brackets. Two slides are symmetrically arranged on the synchronization knob. A slider is fixed at the center and two ends of each bar magnet. The slider at the center is set in the slide of the synchronization knob, and the slider at the end is set in the slide of the baffle strip. By rotating the synchronization knob, the two bar magnets are moved away from or closer to each other in the vertical direction, thereby adjusting the distance between the two bar magnets in the vertical direction.

[0014] Furthermore, the magnetic focusing system also includes a support block, which is disposed above the pressure strip and fixedly connected to the flat plate support and the L-shaped support, so that the vertical arms of the flat plate support and the L-shaped support remain parallel.

[0015] Furthermore, the magnetic focusing system can be fixed using a screw and screw hole combination.

[0016] Furthermore, the elongated magnet is separated from the main magnet by a support wall, thereby eliminating most of the unwanted B-type magnets near the center of the electron beam channel. x Magnetic field components; if the support wall is too thin, the support strength will be insufficient; if the support wall is too thick, the B generated by the long bar magnet in the injection channel will be insufficient. y Too small.

[0017] Furthermore, the main magnet uses neodymium iron boron (N48SH) rare-earth permanent magnet material, while the long strip magnet uses neodymium iron boron (N35SH) rare-earth permanent magnet material with a smaller maximum magnetic energy product; the support is preferably made of antiferromagnetic material to prevent it from affecting the magnetic field generated by the magnetic block; the pole shoes are made of DT8A pure iron material to shield the magnetic field in the electron gun.

[0018] Furthermore, the main magnet's constituent magnetic assembly consists of several rectangular magnets attracting each other, each rectangular magnet having a length of m. 1l The height is m 1h Width is m 1t The length of the bar magnet is m 2l The height is m 2h Width is m 2t The distance between the two rows of main magnets is d, and the pole shoe width is l. p Two elongated magnets on one side are symmetrical about the center and are spaced apart by dx. The distance between the elongated magnets and the main magnet is h. The length, width, and height of the main magnet are determined by the required longitudinal periodic magnetic field B. z The peak value and its period are determined; the size of the bar magnet is based on the required B. y The size of the component is determined.

[0019] Furthermore, the length direction of the magnetic assembly is the same as the transmission direction of the electron beam.

[0020] The present invention also provides an application of the above-mentioned magnetic focusing system, the specific process of which is as follows: a slow wave structure is placed between two rows of magnetic groups. The slow wave structure is provided with four ports, two of which are the input and output ports of the signal to be amplified, and the other two are the input and output ports of the electron beam.

[0021] By rotating the synchronization knob, the vertical spacing of the long magnets is adjusted, thereby generating a suitable magnetic field in the slow-wave structure channel to focus the electron beam and prevent it from diverging. During the transmission of the electron beam, beam-wave interaction occurs to amplify the signal.

[0022] The working principle of this invention is as follows:

[0023] A strip-shaped beam can only propagate stably and undergo beam-wave interaction under the influence of a suitable external magnetic field. In the system of this invention, the main magnet primarily generates a periodic B-wave that focuses the narrow edge of the strip-shaped beam. z The magnetic field component, while the long bar magnet mainly produces an approximate constant B that has a focusing effect on the wide side of the strip. y Components. To effectively focus the narrow edge of the banded injection, the longitudinal periodic magnetic field B... z The peak value should be greater than the Brillouin magnetic field. Once the injection current, injection voltage, and injection waist size of the strip are determined, the period B... z The peak value of the component can be initially determined by the Brillouin magnetic field, and this banded jet generally corresponds to an optimal B. y The portion size should not be too large or too small. B yThe position of the bar magnets is extremely sensitive. Manually moving the bar magnets makes it difficult to ensure symmetry about the center on one side, potentially significantly reducing the flow rate of the strip injection. Therefore, this invention designs a bar magnet adjustment device. By rotating a synchronization knob, the vertical spacing between the two bar magnets is precisely and synchronously changed, thereby altering B. y The weight distribution avoids the asymmetry caused by manual adjustment in existing technologies.

[0024] In summary, due to the adoption of the above technical solution, the beneficial effects of the present invention are:

[0025] 1. This invention changes the amount of B in the injection channel by adjusting the distance between the long magnets. y The magnetic field components are used to control the focusing of the ribbon stream. Traditional PCM+PQM magnetic focusing methods are difficult to adjust in experimental operations. This invention replaces the dispersed PQM with four elongated magnets, greatly simplifying the magnet structure. Furthermore, replacing them with elongated magnets does not reduce the dynamic flow rate of the ribbon stream. The simplified magnet structure also makes adjusting the magnetic field more convenient during experiments. This invention transforms the previous "adjustable" approach into "easily adjustable."

[0026] 2. This invention uses a synchronization knob to control the simultaneous movement of two long magnets on one side, achieving a synchronized adjustment effect. Simulation revealed that B... y The dynamic flow rate of the electron beam is significantly affected and highly sensitive. When the two long magnets on both sides are out of sync, the dynamic flow rate of the strip beam drops sharply, even to zero. Traditional assembly methods require adjusting each magnet individually, making it difficult to ensure synchronization. However, this invention allows simultaneous control of the movement of the two long magnets by rotating a synchronization knob, moving them closer to the center or further apart, while maintaining symmetry about the central axis of the electron beam channel. This achieves B... y The value was adjusted, and a synchronous adjustment effect was achieved. Attached Figure Description

[0027] Figure 1 This is a schematic diagram of the overall structure of the magnetic focusing system for a terahertz traveling wave tube according to the present invention.

[0028] Figure 2 This is a schematic diagram of the structure of the L-shaped bracket and the flat plate bracket of the present invention;

[0029] (a) is an L-shaped bracket, and (b) is a flat plate bracket.

[0030] Figure 3 This is a schematic diagram showing the position of the long bar magnets before and after the rotating synchronization knob of the magnetic focusing system for a terahertz traveling wave tube according to the present invention.

[0031] Figure 4 This is a structural diagram of the magnet part in the magnetic focusing system of a terahertz traveling wave tube according to the present invention.

[0032] Figure 5 This is a front view of the magnet portion in the magnetic focusing system of the present invention.

[0033] Figure 6 In this invention, when the main magnet comes into contact with the long bar magnet, the magnetic field generated by the magnet at different dx values ​​lies on the straight line B. y Component comparison chart.

[0034] Figure 7 B is the magnetic field generated by the magnet in the magnetic focusing system of this invention on the straight line O. z Components and B on line B y Component curves.

[0035] Figure 8 This is a diagram showing the electron beam trajectory of the strip electron beam passing through the slow-wave structure channel without interception, as described in this invention.

[0036] Figure 9 The magnetic field B generated by the magnet of the present invention at different positions in the channel when dx is asynchronous (i.e., dx1, dx2, dx3, and dx4 are not equal) and synchronous is... y Component comparison chart.

[0037] In the diagram: 1 is the pole shoe, 2 is the main magnet, 3 is the long magnet, 4 is the L-shaped bracket, 5 is the flat bracket, 6 is the pressure bar, 7 is the synchronization knob, 8 is the middle slider of the long magnet, 9 is the side sliders of the long magnet, 10 is the baffle, 11 is the bracket support block, and 12 is the screw. Detailed Implementation

[0038] 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.

[0039] A magnetic focusing system for a terahertz traveling wave tube, the overall structure of which is shown in the schematic diagram below. Figure 1 As shown, the overall structure, except for the support frame, is symmetrical about the central injection channel.

[0040] It includes two pole shoes, a main magnet, two sets of long strip magnets, an L-shaped bracket, a flat bracket, a bracket support block, a pressure bar, and a long strip magnet adjustment device;

[0041] The main magnet includes two magnetic groups, each magnetic group has a pole piece on one vertical side, and the pole piece is located on the side of the main magnet closer to the electron gun; the two magnetic groups are used to transmit electron beams.

[0042] The structural diagrams of the flat plate bracket and the L-shaped bracket are as follows: Figure 2As shown, the two supports are fixedly set relative to each other, making the whole rectangular shape. The horizontal arm of the L-shaped support is located inside the rectangle. A boss is set at the center of the horizontal arm of the L-shaped support. The magnetic assemblies of the main magnet are placed on both sides of the boss. The pressure strip is set on the top of the magnetic assembly to fix the main magnet in the vertical direction and prevent the main magnet from being misaligned or sliding out. The flat plate support and the L-shaped support together fix the main magnet in the horizontal direction.

[0043] The bracket support block is located above the pressure strip and is fixedly connected to the flat plate bracket and the L-shaped bracket, so that the vertical arms of the flat plate bracket and the L-shaped bracket remain parallel.

[0044] Both the vertical arm of the L-shaped support and the outer surface of the flat plate support are fixedly equipped with a bar magnet adjustment device and a set of bar magnets. Each set of bar magnets consists of two parallel bar magnets, with their length directions parallel to the electron beam transmission direction. The bar magnet adjustment device is used to adjust the vertical spacing between the two bar magnets and ensure that the two bar magnets are always symmetrical about the central axis of the electron beam channel, thereby generating a B-type focusing effect on the wide side of the strip-shaped beam. y Quantity;

[0045] The elongated magnet adjustment device includes a baffle, a synchronization knob, a fixed slider, and a synchronization knob fixing seat. The baffle includes two sets of baffle strips, one set of which is fixedly and parallel to both sides of the vertical arm of the L-shaped bracket and both sides of the flat bracket. Vertical slides are provided on both sides and at the center of the L-shaped bracket and the flat bracket, and vertical slides are also provided on the baffle strips, with the slides on the baffle strips coinciding with the slides on the two brackets. The synchronization knob fixing seat is fixedly provided at the center of the vertical arm of the L-shaped bracket and the flat bracket, and a synchronization knob is provided on it. The synchronization knob is an elliptical knob, symmetrically arranged on it. Two slides are provided; each bar magnet has a slider fixed at its center and two ends. The slider at the center is positioned within the slide of the synchronization knob, and the sliders at the ends are positioned within the slides of the baffle strips. By rotating the synchronization knob, the slider at the center slides within the slide of the synchronization knob and the slide at the center of the support, while the sliders at the ends slide within the slides of the baffle strips and the slides on both sides of the support. This causes the two bar magnets to move away from or towards each other in the vertical direction, thus adjusting the vertical distance between the two bar magnets. A schematic diagram of the positions of the bar magnets before and after rotating the synchronization knob is shown below. Figure 3 As shown.

[0046] The structural diagram of the magnet part in the magnetic focusing system is as follows: Figure 4 As shown, the main magnet's constituent magnetic assembly consists of several rectangular magnets attracting each other, with each rectangular magnet having a length of m. 1l The height is m 1h Width is m 1t The length of the bar magnet is m 2l The height is m 2h Width is m 2tThe distance between the two rows of main magnets is d, and the pole shoe width is l. p The vertical distance between two parallel bar magnets on a support is dx, and the distance between the bar magnets and the main magnet is h (i.e., the wall thickness of the support).

[0047] A front view of the magnet section in a magnetic focusing system is shown below. Figure 5 As shown, the center points of the wide sides of the strip are marked with lines A and B perpendicular to the paper, the center points of the narrow sides are marked with lines C and D perpendicular to the paper, and the center point of the strip is marked with line O perpendicular to the paper. The distances of the four long magnets from the y-axis are dx1, dx2, dx3 and dx4, respectively.

[0048] Example 1

[0049] Taking a G-band strip-beam traveling wave tube (TWT) as an example, the requirements for the strip beam differ depending on the frequency band of the TWT. For a G-band strip-beam TWT, when the strip beam voltage is typically between 19-25kV, the beam current is usually 30-150mA. The waist size of the strip beam is limited by the channel size of the electron beam, and is usually selected to be around 0.6mm × 0.2mm. In this embodiment, the strip beam voltage is 24.6kV, the beam current is 145mA, the waist size is 0.45mm × 0.1mm, and the channel size is 0.79mm × 0.19mm.

[0050] To effectively focus the narrow edge of the banded injection, the longitudinal periodic magnetic field B... z The peak value should be greater than the Brillouin magnetic field, and the formula for calculating the Brillouin magnetic field is:

[0051]

[0052] Where I0 and U0 are the current and voltage of the strip beam, respectively, w0 is the wide side of the strip beam, t0 is the narrow side of the strip beam, ε0 is the vacuum permittivity, η is the charge-to-mass ratio, and γ is the relativistic factor. In practical engineering, in order to effectively focus the strip beam, a longitudinal periodic magnetic field B... z The peak value is typically 1.5 to 2 times that of the Brillouin magnetic field.

[0053] The structural parameters of the magnet are: dx = 6 mm, d = 2.4 mm, l p =0.8mm,m 1t =2.4mm,m 1l =16mm,m 1h =4.8mm,m 2t =45.6mm,m 2l =2mm,m 2h =1.5mm, h=0.4mm.

[0054] The main magnet uses neodymium iron boron (N48SH) rare-earth permanent magnet material. To ensure the long magnet has a certain width to reduce the difficulty of magnetizing it during the experiment, a different neodymium iron boron (N35SH) rare-earth permanent magnet material is used, which has a smaller maximum energy product compared to N48SH. The pole shoes are made of DT8A pure iron. Parts that need to move during the experiment, such as the central fixed slider, the side fixed sliders, and the synchronization knob, are made of high-strength stainless steel (1Cr18Ni9Ti). Parts that do not need to move during the experiment, such as the support, pressure bar, baffle, and support block, are made of lower-strength but lighter LY11 aluminum.

[0055] Depend on Figure 6 When the main magnet comes into contact with the bar magnet, the magnetic field generated by the magnet at different dx values ​​along the line B is... y The component comparison chart shows that as dx increases, the corresponding B... y The component will decrease. Simultaneously, the B generated under different dx values ​​was simulated. y The corresponding dynamic flow rate was observed to increase initially and then decrease as dx increased from 4 mm to 9 mm, at point B. y The dynamic flux reaches its maximum value at approximately 20G. y The value is the optimal value corresponding to a strip injection with an injection voltage of 24.6kV, an injection current of 145mA, and an injection waist size of 0.45mm × 0.1mm.

[0056] However, simulations revealed that when the main magnet comes into contact with the bar magnet, a large B-value is generated along lines O, C, and D. x Components, B on these three straight lines x The trend exhibited by the components is not conducive to the focusing of the strip-shaped beam; this can be greatly reduced by spacing the long strip magnet from the main magnet. x The weight of the magnet increases the electron flow rate. Furthermore, the bar magnet is separated from the main magnet by a support wall. This support wall offers several advantages: firstly, it prevents the bar magnet from contacting the main magnet, thus eliminating some magnetic field interference during movement and making adjustment easier; secondly, the support wall makes the support more stable, and the synchronization knob holder, synchronization knob, the middle slider of the bar magnet, and the sliders on both sides of the bar magnet can be fixed by the support wall.

[0057] The magnetic field generated by the magnet in the magnetic focusing system of the terahertz traveling wave tube of this invention is located on line O at point B. z Components and B on line B y Component curves as shown Figure 7 As shown, the magnetic field generated by the magnet section causes the electron beam trajectory through the slow-wave structure channel to pass through the ribbon-shaped beam without interception. Figure 8As shown, the magnetic field B generated by the magnet at different positions in the channel when dx is asynchronous (i.e., dx1, dx2, dx3, and dx4 are not equal) and synchronous is different. y Component comparison chart as follows Figure 9 As shown.

[0058] from Figure 7 As can be seen from this, the main magnet primarily generates a periodic B-shaped beam that has a focusing effect on the narrow edge of the strip. z The magnetic field component has a peak value of approximately 3960 G; while the four elongated magnets mainly produce an approximately constant B that has a focusing effect on the wide side of the strip. y The component, with a value of approximately 20g, corresponds to the optimal B for this band injection. y Value. Additionally, with Figure 6 A comparison of simulation results when the main magnet and the bar magnet are in contact reveals that the spacing between the main magnet and the bar magnet can maintain an approximately constant B. y The ripple of the component decreases, B y It becomes smoother.

[0059] Will Figure 7 The magnetic field shown is introduced into a slow-wave structure model to simulate static flow. The study observes whether an ideal ribbon-like jet can pass through the slow-wave structure channel without interception under the influence of this magnetic field. Figure 8 Simulation results show that a strip-shaped injection beam with a waist size of 0.45mm × 0.1mm and an injection current of 145mA can pass through a slow-wave structure channel with a length of 45mm and a channel cross-sectional size of 0.79mm × 0.19mm without interception. When the long bar magnet is removed, i.e., the approximately constant B is removed... y With all other conditions unchanged, the static flux ratio decreased from 100% to 10.46%, indicating that although B... y The component is much smaller than B z Peak size, but indispensable in band injection focusing.

[0060] To demonstrate the advantages of the magnetic focusing system of this invention, the magnetic field distribution was simulated during synchronous and asynchronous movement of the long strip magnet, with magnetic field B... y Component simulation results are as follows Figure 9 As shown. When the long bar magnets are synchronized (set dx1=dx2=dx3=dx4=3mm), B y The distribution along line O is almost zero. Figure 9 (a) Solid line), meaning that the magnetic field components generated by the four long strip magnets cancel each other out on the straight line O, and do not provide B to the interior of the strip. y Magnetic field to prevent the ribbon-like injection from deforming and diverging; while B y The distributions on lines A and B exhibit equal magnitudes but opposite directions. Figure 9(b) Solid line), providing opposing forces to the wide sides of the strip to keep it balanced and prevent it from becoming divergent and distorted. When the long magnets are not synchronized (setting dx1 = dx3 = 3mm, dx2 = dx4 = 4mm), B y The distribution on line O is no longer zero. Figure 9 (a) dashed line), but approximately a constant, causing the ribbon to be biased to one side and unable to pass smoothly through the channel; B y The distribution along lines A and B is no longer of equal amplitude and opposite direction, but rather of unequal amplitude and same direction. Figure 9 (b) Dashed line), this causes the strip to twist and deform in the channel, which is detrimental to focusing. Ultimately, the dynamic flux decreased from 99.86% when synchronized to 0% when asynchronous (i.e., no flux at all). These results clearly demonstrate the importance of maintaining synchronization when adjusting the bar magnet.

[0061] The above description is merely a specific embodiment of the present invention. Any feature disclosed in this specification may be replaced by other equivalent or similar features unless otherwise specified. All disclosed features, or steps in all methods or processes, may be combined in any way except for mutually exclusive features and / or steps.

Claims

1. A magnetic focusing system for a terahertz strip-beam traveling wave tube, characterized in that, It includes two pole shoes, a main magnet, two sets of long bar magnets, an L-shaped bracket, a flat plate bracket, a pressure bar, and a long bar magnet adjustment device; The main magnet includes two magnetic groups, each magnetic group having a pole piece on one vertical side, and the pole piece being located on the side of the main magnet closer to the electron gun; the two magnetic groups are used to transmit electron beams. The flat plate bracket and the L-shaped bracket are fixedly arranged to form a rectangle, with the horizontal arm of the L-shaped bracket located within the rectangle. A boss is set at the center of the horizontal arm of the L-shaped bracket, and magnetic assemblies of the main magnet are placed on both sides of the boss. A pressure strip is set on the top of the magnetic assemblies to fix the main magnet in the vertical direction and prevent the main magnet from being misaligned or sliding out. The flat plate bracket and the L-shaped bracket together fix the main magnet in the horizontal direction. Both the vertical arm of the L-shaped support and the outer surface of the flat plate support are fixedly equipped with a bar magnet adjustment device and a set of bar magnets. Each set of bar magnets consists of two parallel bar magnets, with their length directions parallel to the electron beam transmission direction. The bar magnet adjustment device is used to adjust the vertical spacing between the two bar magnets and ensure that the two bar magnets are always symmetrical about the central axis of the electron beam channel, thereby generating a B-type focusing effect on the wide side of the strip-shaped beam. y Quantity; The long magnet adjustment device includes a baffle, a synchronization knob, a fixed slider, and a synchronization knob fixing seat; The baffle includes two sets of baffle strips. A set of baffle strips is fixedly installed parallel to each other on both sides of the vertical arm of the L-shaped bracket and both sides of the flat plate bracket. Vertical slides are opened at corresponding positions of the baffle strips and the bracket. The synchronization knob fixing seat is fixedly installed at the center of the vertical arm of the L-shaped bracket and the flat plate bracket, and a synchronization knob is installed on it. A slide is set vertically at the center of the two brackets. Two slides are symmetrically arranged on the synchronization knob. A slider is fixed at the center and two ends of each bar magnet. The slider at the center is set in the slide of the synchronization knob, and the slider at the end is set in the slide of the baffle strip. By rotating the synchronization knob, the two bar magnets are moved away from or closer to each other in the vertical direction, thereby adjusting the distance between the two bar magnets in the vertical direction.

2. The magnetic focusing system for a terahertz strip-beam traveling wave tube as described in claim 1, characterized in that, The magnetic focusing system also includes a support block, which is located above the pressure strip and is fixedly connected to the flat plate support and the L-shaped support, so that the vertical arms of the flat plate support and the L-shaped support remain parallel.

3. The magnetic focusing system for a terahertz strip-beam traveling wave tube as described in claim 1, characterized in that, The magnetic focusing system is fixed using a screw and screw hole combination.

4. The magnetic focusing system for a terahertz strip-beam traveling wave tube as described in claim 1, characterized in that, The elongated magnet and the main magnet are separated by a support wall, used to eliminate most of the unwanted B-type magnets near the center of the electron beam channel. x Weight; if the support wall is too thin, the support will not be strong enough; if the support wall is too thick, the B generated by the long bar magnet in the injection channel will be too large. y Too small.

5. The magnetic focusing system for a terahertz strip-beam traveling wave tube as described in claim 1, characterized in that, The main magnet uses neodymium iron boron N48SH rare earth permanent magnet material, the long strip magnet uses neodymium iron boron N35SH rare earth permanent magnet material, the support uses antiferromagnetic material, and the pole shoes use DT8A pure iron material.

6. The magnetic focusing system for a terahertz strip-beam traveling wave tube as described in claim 1, characterized in that, The main magnet is composed of several rectangular magnets that attract each other. The length, width, and height of the main magnet are determined by the required longitudinal periodic magnetic field B. z The peak value and its period are determined; The size of the bar magnet depends on the required B y The size of the component is determined.

7. The magnetic focusing system for a terahertz strip-beam traveling wave tube as described in claim 6, characterized in that, The length direction of the magnetic assembly is the same as the transmission direction of the electron beam.

8. The magnetic focusing system for a terahertz strip-beam traveling wave tube as described in any one of claims 1-7, characterized in that, The specific application process is as follows: the slow wave structure is placed between two rows of magnetic groups. The slow wave structure has four ports, two of which are the input and output ports of the signal to be amplified, and the other two are the input and output ports of the electron beam. By rotating the synchronization knob, the vertical spacing of the long magnets is adjusted, thereby generating a suitable magnetic field distribution in the slow-wave structure channel. This is used to focus the electron beam, prevent it from diverging, and simultaneously perform beam-wave interaction to amplify the input signal.

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