A high power continuous wave circulator

Abstract

The application discloses a high-power continuous wave circulator and relates to the technical field of circulators, which comprises a magic T, a phase-shifting unit and a 3dB bridge; the two side ports of the phase-shifting unit are in communication with the connecting ports of the magic T and the 3dB bridge; the first port and the third port form a 500kW power input channel; and the second port and the fourth port form an input channel of reflected microwave signals. The application effectively reduces the risk of ferrite cracking caused by uneven stress due to temperature rise by discretely distributing ferrite inside the phase-shifting unit. At the same time, by reducing the size of the ferrite and chamfering the edges of the ferrite, the local electric field intensity is reduced, the power carrying capacity is improved, and the breakdown phenomenon is inhibited.

Description

Technical Field

[0001] This invention relates to the field of circulator technology, and in particular to a high-power continuous wave circulator. Background Technology

[0002] High-power circulators are widely used in various high-power microwave systems because they can effectively protect microwave sources from damage caused by reflected power. One typical application is in low-mixing-wave current drive (LHCD) systems for tokamak devices, where circulators are used to provide non-inductive plasma current drive at low mixing-wave frequencies.

[0003] Since 2019, to expand the long-pulse operation capability of the EAST tokamak and support the key technology research and development of the China Fusion Engineering Test Reactor (CFETR), a 4MW LHCD system with a rated power of 4.6GHz is under construction. This system consists of eight 500kW continuous wave (CW) dual-window klystron units, equipped with coupling antennas, transmission lines, monitoring and control subsystems, high-voltage power supplies, and a water-cooling system. Currently, each klystron is protected by a 500kW-CW circulator.

[0004] Differential phase-shifted circulators (DPSCs) are commonly used under high-power continuous wave conditions. These structures typically maximize the heat dissipation efficiency of ferrite, thereby improving the thermal stability of the system. Circulators based on ferrite phase shifters rely on the non-reciprocal characteristics of ferrite devices to achieve unidirectional wave propagation. Depending on the biasing method, ferrite phase shifters are generally classified into two operating modes: lower resonance and upper resonance.

[0005] The lower resonant design requires a smaller bias magnetic field, and the bias point is insensitive to temperature-induced changes in ferrite properties, making it suitable for low-power applications. However, in high-power continuous wave operation, the spin wave effect leads to a significant increase in insertion loss, causing the circulator to malfunction.

[0006] In comparison, the upper resonant design has higher permeability, a higher quality factor, and better RF power handling capability. However, it requires a stronger magnetic field to saturate or near-saturate the ferrite and is more susceptible to magnetization changes caused by temperature rise.

[0007] Therefore, there is an urgent need to design a 500 kW continuous wave circulator for LHCD systems. Summary of the Invention

[0008] The purpose of this invention is to provide a high-power continuous wave circulator to solve the problems existing in the prior art.

[0009] To achieve the above objectives, the present invention provides the following technical solution: The present invention provides a high-power continuous wave circulator, comprising: Magic T, phase-shifting unit and 3dB bridge; The Magic T includes a first port, a second port, and a connection port; The phase-shifting unit is formed by combining two non-reciprocal phase shifters; discretely distributed ferrites are disposed within the non-reciprocal phase shifters; the ferrites have a cylindrical structure. The 3dB bridge includes a third port, a fourth port, and a connection port; The two ports of the phase shifting unit are respectively connected to the connection ports of the magic T and the 3dB bridge; so that the first port and the third port form a 500kW power input path; and the second port and the fourth port form an input path for reflected microwave signals.

[0010] The edges of the ferrite are chamfered.

[0011] The connection ports of the Magic T and the 3dB bridge are extended by an impedance transformer to improve the power carrying capacity of the phase shifting unit.

[0012] The dimensions of the waveguide interface at the ends of the Magic T and 3dB bridges are 58.2mm × 36.0mm.

[0013] The present invention discloses the following technical effects: By designing an enlarged cavity for the phase-shifting unit and a discretely distributed circular chamfered ferrite distribution, the present invention effectively reduces the risk of ferrite cracking caused by uneven stress due to temperature rise, reduces the local electric field intensity, improves the power carrying capacity, and suppresses breakdown phenomena by discretely distributing ferrite inside the phase-shifting unit; the Magic T and 3dB bridge effectively reduce high-order mode excitation and local electric field concentration by enlarging the waveguide port and chamfering the tuning pillar. Attached Figure Description

[0014] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0015] Figure 1 This is a schematic diagram of the complete structure of the high-power continuous wave circulator of the present invention; Figure 2 This is a schematic diagram of the magic T structure of the present invention; Figure 3 This is a schematic diagram of the phase-shifting unit structure of the present invention; Figure 4This is a schematic diagram of the 3dB bridge structure of the present invention; Figure 5 This is a schematic diagram of the magic T-bevel structure of the present invention; Figure 6 A schematic diagram of the chamfered structure of the 3dB bridge for the invention; Figure 7 This is a schematic diagram of the simulation results of the voltage standing wave ratio of the Magic T in this invention; Figure 8 This is a schematic diagram of the simulation results of the Magic-T power division ratio and port phase difference of the present invention; Figure 9 This is a schematic diagram of the simulation results of the phase shifting unit parameters amplitude and port phase difference of the present invention; Figure 10 This is a schematic diagram of the simulation results of the 3dB bridge voltage standing wave ratio of the present invention; Figure 11 This is a schematic diagram of the simulation results of the 3dB bridge power division ratio and port phase difference of the present invention; Figure 12 This is a schematic diagram of the simulation results of the voltage standing wave ratio of the circulator of the present invention; Figure 13 This is a schematic diagram of the simulation results of the S-parameters and isolation of the circulator of the present invention; Figure 14 This is a schematic diagram of the electric field distribution inside the circulator cavity of the present invention; Figure 15 This is a schematic diagram of the electrical breakdown simulation results under different input powers according to the present invention; Figure 16 This is a schematic diagram of the electrical breakdown simulation results under nitrogen filling at different pressures according to the present invention; Figure 17 This is a schematic diagram of the simulation results of ferrite temperature distribution under 500kW input according to the present invention; Figure 18 This is a schematic diagram of the ferrite stress simulation results under 500kW input according to the present invention; Among them, 1. Magic T; 2. Phase shifting unit; 3. 3dB bridge; 11. First port; 12. Second port; 31. Third port; 3. Fourth port. Detailed Implementation

[0016] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0017] To make the above-mentioned objects, features and advantages of the present invention more apparent and understandable, the present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0018] This invention provides a high-power continuous wave circulator, comprising: Magic T1, Phase Shifting Unit 2 and 3dB Bridge 3; The Magic T1 includes a first port 11, a second port 12, and a connection port; Phase shifting unit 2 is formed by combining two non-reciprocal phase shifters; discretely distributed ferrites are arranged inside the non-reciprocal phase shifters; the ferrites have a cylindrical structure. The 3dB bridge 3 includes a third port 31, a fourth port 32, and a connection port; The two ports of the phase shifting unit 2 are connected to the connection ports of the magic T1 and the 3dB bridge 3 respectively, so that the first port 11 and the third port 31 form a 500kW power input path; and the second port 12 and the fourth port 32 form a reflected microwave signal input path.

[0019] The edges of the ferrite are chamfered.

[0020] The connection ports of the Magic T1 and the 3dB bridge 3 are extended through an impedance transformer to improve the power carrying capacity of the phase shifting unit 2.

[0021] The dimensions of the waveguide interface at the end of the Magic T1 and 3dB bridge are 58.2mm × 36mm.

[0022] In one embodiment of the present invention, the magic T1, phase shifting unit 2 and 3dB bridge 3 of the continuous wave circulator are all equipped with independent water cooling systems.

[0023] In one embodiment of the present invention, such as Figure 1 As shown, the working path of this continuous wave circulator is as follows: the 3dB bridge 3 splits the 500kW input power from the third port 31 into two signals with equal amplitude and a 90° phase difference, and inputs them to two non-reciprocal phase shifters respectively; after passing through the phase shifting unit 2, the signals achieve equal amplitude and the same phase when entering the port of magic T1, and are then combined and output from the first port 11; the reflected power from the first port 11 is guided to the fourth port 32 after passing through the phase shifting unit, and the reflected power from the fourth port 32 is further guided to the second port 12.

[0024] Furthermore, this structure achieves high isolation between the input and output terminals, thereby effectively protecting the input microwave source from damage caused by high-power reflections.

[0025] In one embodiment of the present invention, such as Figure 2As shown, the Magic T1 adopts an H-plane folded double-T structure; wherein, the H arm serves as the first port 11, the E arm serves as the second port 12, and the connecting ports of the side arms are respectively connected to the two non-reciprocal phase shifters in the phase shifting unit 2.

[0026] Furthermore, since the ferrite-loaded phase-shifting unit 2 is the weakest in terms of power carrying capacity, a Chebyshev impedance transformer is introduced at the side arm output port of the Magic T, expanding the waveguide cross-section from the standard waveguide size BJ40 (58.2mm×29.1mm) to 58.2mm×36.0mm; this design significantly improves the power carrying capacity of the phase-shifting unit without exciting higher-order modes.

[0027] In addition, to further reduce the local electric field intensity and improve the overall power capacity, a chamfered structure was introduced at the edge of the tuning pillar inside the Magic T1.

[0028] The optimized structure was subjected to electromagnetic simulation analysis using HFSS software, and the results are as follows: Figure 5 and Figure 6 As shown in the figure. Simulation results show that, within the frequency range of 4.6 GHz ± 5 MHz, the VSWR of each port is better than 1.08, and the power distribution ratio is better than 3.02 dB, indicating that the structure has excellent RF performance and power characteristics.

[0029] In one embodiment of the present invention, such as Figure 3 As shown, the phase-shifting unit consists of two non-reciprocal ferrite phase shifters. To reduce the electric field strength inside the circulator and improve its power carrying capacity, the phase-shifting unit adopts an enlarged cavity design. Under high-power continuous wave operation conditions, to prevent cracking or breakdown discharge of the ferrite substrate due to uneven thermal stress distribution, a cylindrical ferrite structure is selected in this design, and its specific parameters are listed in the table below. The bias magnetic field required by the ferrite is provided by a permanent magnet with a remanence of Mr = 10.5 kG.

[0030] Ferrite Parameter Table: Furthermore, to reduce the local electric field enhancement at the substrate edge and avoid the risk of breakdown, the edges of the cylindrical ferrite substrate were chamfered.

[0031] like Figure 7 As shown, within a frequency range of 4.6 GHz ± 5 MHz, the transmission coefficient S21 of the phase shifting unit is better than −0.05 dB, and a phase shift performance of 90° ± 0.5° is achieved, indicating that it has excellent transmission characteristics and phase consistency.

[0032] In one embodiment of the present invention, such as Figure 4 As shown, the dB bridge 3 adopts a narrow-side coupling structure, such as... Figure 8As shown, its tuning post and impedance matching design are the same as those of the Magic T1.

[0033] Furthermore, Figure 8 and Figure 9 Simulation results for the 3dB bridge are presented. Within a frequency range of 4.6 GHz ± 5 MHz, the VSWR at each port of the bridge is better than 1.04, the power distribution ratio is better than −3.03 dB, and a phase shift of 90° ± 0.5° is achieved, indicating that the structure has excellent matching performance and phase accuracy.

[0034] In one embodiment of the present invention, such as Figure 10 and Figure 11 As shown, within a frequency range of 4.6 GHz ± 5 MHz, all four ports of the circulator achieved a VSWR greater than 1.08, an isolation greater than 47 dB, and an insertion loss less than 0.06 dB, indicating excellent overall RF performance.

[0035] In one embodiment of the present invention, such as Figure 12-14 As shown, a microwave source with an input power of 500kW and a reflectivity of 30% can be used to simulate the continuous wave circulator under an equivalent 650kW condition. The electric field distribution obtained through HFSS and the breakdown simulation results using Spark3D are as follows: Under continuous wave power conditions of 4.6 GHz and 650 kW, the maximum electric field strength inside the circulator reaches 2.61 × 10⁻⁶. 6 V / m, far lower than the breakdown strength of air 3×10 6 V / m.

[0036] In one embodiment of the present invention, a high-efficiency water-cooling system is also incorporated into the entire circulator structure to ensure its temperature stability under long-term high-power operation conditions; such as Figure 15 As shown, the temperature distribution of the ferrite inside the circulator under water cooling conditions, 4.6 GHz, and 500 kW continuous wave input power (obtained through Fluent simulation) is shown. Simulation results indicate that the highest temperature of the ferrite is 59.67°C, far below its normal operating temperature range (<190°C), ensuring long-term thermal stability. Furthermore, the temperature distribution of the ferrite array decreases sequentially from right to left, ensuring the symmetry of the electric field at each cross-section within the cavity.

[0037] Furthermore, such as Figure 16 As shown, the ferrite stress simulation is based on the thermal simulation results. It can be seen that the stress of each ferrite piece expands outward from the center, exhibiting circular symmetry, and the stress is uniform without cracking.

[0038] In summary, the experimental results demonstrate that this circulator achieves excellent performance in the 4.6GHz±5MHz frequency band, with a VSWR of less than 1.1, isolation (simulation results greater than 35dB, experimental results greater than 23dB), and insertion loss of less than 0.1dB. High-power testing verified its stable operation under 500kW input power and 30% reflection conditions, producing only 1.4kW of reflected power, indicating that the circulator possesses reliable power handling capabilities and good stability.

[0039] In the description of this invention, it should be understood that the terms "longitudinal", "lateral", "up", "down", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings, and are only for the convenience of describing this invention, and are not intended to indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of this invention.

[0040] The embodiments described above are merely preferred embodiments of the present invention and are not intended to limit the scope of the present invention. Various modifications and improvements made by those skilled in the art to the technical solutions of the present invention without departing from the spirit of the present invention should fall within the protection scope defined by the claims of the present invention.

Claims

1. A high-power continuous wave circulator, characterized in that, include: Magic T (1), phase shifting unit (2) and 3dB bridge (3); The Magic T (1) includes a first port (11), a second port (12), and a connection port; The phase-shifting unit (2) is formed by combining two non-reciprocal phase shifters; discretely distributed ferrites are provided inside the non-reciprocal phase shifters; the ferrites have a cylindrical structure. The 3dB bridge (3) includes a third port (31), a fourth port (32), and a connection port; The two ports of the phase shifting unit (2) are connected to the connection ports of the magic T (1) and the 3dB bridge (3) respectively; so that the first port (11) and the third port (31) form a 500kW power input path; so that the second port (12) and the fourth port (32) form a reflected microwave signal input path.

2. A high-power continuous wave circulator according to claim 1, characterized in that: The edges of the ferrite are chamfered.

3. A high-power continuous wave circulator according to claim 1, characterized in that: The connection ports of the Magic T (1) and the 3dB bridge (3) are extended by an impedance transformer to improve the power carrying capacity of the phase shifting unit (2).

4. A high-power continuous wave circulator according to claim 1, characterized in that: The dimensions of the end waveguide interface of the Magic T (1) and the 3dB bridge (3) are 58.2mm × 36.0mm.

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