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作为一种紧凑型高功率微波器件, 磁绝缘线振荡器在起振过程中容易出现模式竞争现象, 如果不能对其进行有效抑制, 可能导致器件的最终输出性能下降. 由于磁绝缘线振荡器中波束互作用区通常采用同轴盘荷波导作为其慢波结构, 因此本文从同轴盘荷波导中几个可能被相对论电子束激发的低阶本征模与电子束之间的色散关系入手, 分析了三种类型的模式竞争的特点、产生的可能原因以及削弱方法. 基于以上分析, 给出了一种高功率紧凑型L波段磁绝缘线振荡器的物理模型, 并利用全电磁三维粒子程序对其进行了冷腔和热腔的数值模拟. 结果表明, 由于结构不完全对称和电子发射可能存在一定的非均匀性, 器件运行初期互作用区有竞争模式HEM11模出现, 与理论分析一致；起振一小段时间后(10 ns左右), 互作用区基模增长加快, 高阶模被抑制. 进一步优化后器件在基模获得了高效率和高功率微波输出, 饱和时输出功率约为8.1 GW, 输出效率达到了18%, 模式纯度约为97%. 本文研究结果可为磁绝缘线振荡器运行过程中出现的竞争模式的识别和输出性能优化提供理论参考和依据.
As a compact and high power microwave source, the competitions among various modes are prone to appear in the initial stage of the development of the radiated electromagnetic field in a magnetically insulated transmission line oscillator (MILO). If the mode competitions are not controlled effectively, the output characteristics of the MILO may decline in the end. As is well known, the operating mode of MILO is generally designed on the π mode of the TM00 mode and the coaxial disk-loaded waveguide is usually adopted as a slow-wave structure for beam-wave interaction in MILO. Therefore from the dispersion relations between the electron beam and the lower order electromagnetic modes(including TM00, TM01 and HEM11 modes) in the slow-wave structure, the characteristics and possible suppression methods of the three kinds of mode competitions are analyzed simply. The first kind mode competition is between the different axial modes of the fundamental TM00 mode. In this case, the electromagnetic field of the competition mode is also axially symmetric and its frequency is slightly lower than that of the π mode. The second is the competition between the TM00 and higher order TM01 mode. In this case, the competition frequency is rather higher than that of the π mode (TM00). The third is the competitions between the TM00 and low order asymmetric HEM11 modes. In this case, the competition frequency is slightly higher than that of the main mode. Appropriately choosing the radii of the anode vanes, the number of the anode cavity and the load length of the cathode, the corresponding mode competition intensity can be weakened. Based on the obtained results above and the existing model of the MILO, a compact high output power L-band MILO is proposed. Numerical studies of the mode competitions and output characteristics are carried by using the three dimensional particle-in-cell code. Cold-cavity test shows that in the low frequency range, the easily stimulated electromagnetic modes are the π mode of TM00 and HEM11 modes with frequencies of 1.61 GHz and 1.77 GHz, respectively. The numerical results of hot-cavity verify that the competition in the initial stage comes mainly from the asymmetric HEM11 mode due to the fact that there exists the strut in the output region, the Cartesian coordinates are adopted during the simulation, and totally symmetry cannot be guaranteed. In addition, electron beam emission from the cathode is not ideally even. But stable and high output microwave power is obtained in the end in the L-band MILO by being optimized. The output power and efficiency are 8.1 GW and 18% respectively, and the mode purity reaches about 97%. -
Keywords:
- magnetically insulated transmission line oscillator /
- mode competition /
- numerical simulation
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图 1 同轴盘荷波导的结构示意图 (a) 纵向中心截面; (b) 横截面
Fig. 1. Schematic drawings of the coaxial disk-loaded waveguide in (a) Axial and (b) radial cross section
图 2 同轴盘荷波导中TM00模、TM01模、HEM11模以及电子束和光束的色散关系图
Fig. 2. The uncoupled dispersion curves of the coaxial disk-loaded waveguide (TM00, TM01 and HEM11), and the dispersion lines of the electron and light beam.
图 3 同轴盘荷波导中TM00(π模)的轴向电场在(a) 纵向中心截面和(b) 横截面的等高图
Fig. 3. The contour plots of Ez of the TM00 (π mode) in the coaxial disk-loaded waveguide in the (a) Axial and (b) radial cross section.
图 4 同轴盘荷波导中TM01的轴向电场在横截面的等高图
Fig. 4. The contour plots of Ez of the TM01 mode in the coaxial disk-loaded waveguide in the radial cross section.
图 5 同轴盘荷波导中HEM11(π模)的轴向电场在 (a) 纵向中心截面和(b)横截面的等高图
Fig. 5. The contour plots of Ez of the HEM11(π mode)in the coaxial disk-loaded waveguide in the (a) Axial and (b) radial cross section.
图 6 紧凑型MILO纵向截面示意图
Fig. 6. Schematic drawing of the compact MILO in the axial cross section.
图 7 短脉冲宽频信号激发后MILO互作用区中点D处电场的频谱图
Fig. 7. The oscillation frequency of the Ez stimulated in cold cavity at point D.
图 8 频率为1.61 GHz的纵向电场在 (a) 纵向和(b) 横向截面等高图
Fig. 8. The contour plots of Ez with the frequency of 1.61 GHz in (a) The axial and (b) the radial cross section.
图 9 频率为1.77 GHz的纵向电场在 (a) 纵向和(b) 横向截面的等高图
Fig. 9. The contour plots of Ez with the frequency of 1.77 GHz in (a) The axial and (b) the radial cross section.
图 10 (a) 阳极腔内观察点D的电场Ez随时间的变化曲线及不同时间窗口(b) 0−50 ns, (c) 8−14 ns和(d) 14−50 ns的FFT变换图
Fig. 10. (a) Variations of Ez with time at the observation point D in the anode cavity; the corresponding Fourier transform with different time intervals: (b) 0−50 ns; (c) 8−14 ns; (d) 14−50 ns.
图 11 (a) 阳极腔内观察点D磁场By随时间的变化曲线及不同时间窗口(b) 0−50 ns, (c) 8−14 ns和(d) 14−50 ns的FFT变换图
Fig. 11. (a) Variations of By with time at the observation point D in the anode cavity, and the corresponding Fourier transform with different time intervals: (b) 0−50 ns, (c) 8−14 ns (d) 14−50 ns.
图 12 初始阶段不同时刻互作用区横截面轴向电场的等高图 (a) t = 12.171 ns; (b) t = 13.094 ns; (c) t = 14.944 ns; (d) t = 16.793 ns
Fig. 12. Contour plots of Ez in the interaction region at different times at the initial stage.
图 13 饱和时互作用区轴向电场在(a) 纵向截面和(b) 横向截面的等高图, t = 45.727 ns
Fig. 13. Contour plots of Ez in the (a) Axial and (b) radial cross section in the interaction region at saturation.
图 14 (a) MILO输出周期平均功率随时间的变化曲线; (b)稳定后输出口电场的FFT变换图
Fig. 14. (a) Time plots of the periodic-average output power of the MILO; (b) the Fourier transform of Ex at the output port.
图 15 电磁场在输出口横向截面分布的箭矢图 (a) 电场; (b)磁场
Fig. 15. The vector plots of the (a) Electric field and (b) magnetic field in the radial cross section at the output port.
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[1] Barker R J, Schamiloglu E 2001 High-Power Microwaves Sources and Technologies (New York: Institute of Electrical and Electronic Engineer, Inc.) pp43–53
[2] Eastwood J W, Hawkins K C, Hook M P 1998 IEEE Trans. Plasma Sci. 26 698
Google Scholar
[3] Lemke R W, Calico S E, Clark M C 1997 IEEE Trans. Plasma Sci. 25 364
Google Scholar
[4] Yang W Y 2008 IEEE Trans. Plasma Sci. 36 2801
Google Scholar
[5] Fan Y W, Li S R, Wang X Y, Li A K, Yu Y Q, Liu Z Y 2019 Rev. Sci. Instrum. 90 044704
Google Scholar
[6] 董志伟, 孙会芳, 杨郁林, 杨温渊, 周前红, 张芳, 董烨 2016 强激光与粒子束 28 033023
Google Scholar
Dong Z W, Sun H F, Yang Y L, Yang W Y, Zhou Q H, Zhang F, Dong Y 2016 High Pow. Las. Part. Beam. 28 033023
Google Scholar
[7] Wang X Y, Fan Y W, Shu T, Li A K, Yu Y Q, Liu Z Y 2019 IEEE Trans. Plasma Sci. 47 3974
Google Scholar
[8] Nallasamy V, Datta S K, Reddy S U, Jain P K 2017 J. Electromagn. Waves Appl. 31 1864
Google Scholar
[9] Kumar A, Dwivedi S, Jain P K 2019 IEEE Trans. Plasma Sci. 47 4642
Google Scholar
[10] Kim D H, Jung H C, Min S H, Shin S H, Rhee M J, Park G S, Kim C H, Yim D W 2006 7th IEEE International Vacuum Electronics Conference (IVEC)/6th IEEE International Vacuum Electron Sources Conference (IVESC) Monterey, CA, April 25–27, 2006 p352
[11] Dixit G, Kumar A, Jain P K 2017 Phys. Plasma. 24 013113
Google Scholar
[12] Nallasamy V, Narasimhamurthy C, Geetha B, Gupta S K, Datta S K, Reddy S U, Jain P K 2017 J. Electromagn. Waves Appl. 31 375
Google Scholar
[13] Qin F, Wang D, Xu S, Zhang Y, Fan Z K 2016 Rev. Sci. Instrum. 87 044703
Google Scholar
[14] 孙会芳, 董志伟, 杨郁林 2010 强激光与粒子束 22 303
Google Scholar
Sun H F, Dong Z W, Yang Y L 2010 High Pow. Las. Part. Beam. 22 303
Google Scholar
[15] Kim D H, Jung H C, Min S H, Shin S H, Park G S 2007 Appl. Phys. Lett. 90 124103
Google Scholar
[16] Lemke R W 1989 J. Appl. Phys. 66 1089
Google Scholar
[17] Cousin R, Larour J, Gardelle J, Cassany B, Modin P, Gouard P, Raymond P 2007 IEEE Trans. Plasma Sci. 35 1467
Google Scholar
[18] Cousin R, Larour J, Gouard P, Raymond P 2006 J. Appl. Phys. 100 084512
Google Scholar
[19] 王冬, 陈代兵, 范植开, 邓景康 2008 57 4875
Google Scholar
Wang D, Chen D B, Fan Z K, Deng J K 2008 Acta Phys. Sin. 57 4875
Google Scholar
[20] Jiang T, Zhang J D, He J T, Li Z Q, Ling J P 2016 IEEE Trans. Plasma Sci. 44 755
Google Scholar
[21] 秦奋, 王冬, 陈代兵, 文杰 2012 61 094101
Google Scholar
Qin F, Wang D, Chen D B, Wen J 2012 Acta Phys. Sin. 61 094101
Google Scholar
[22] 董烨, 董志伟, 杨温渊, 周海京 2009 强激光与粒子束 21 1199
Dong Y, Dong Z W, Yang W Y, Zhou H J 2009 High Pow. Las. Part. Beam. 21 1199
[23] 姜利辉, 李浩, 吴泽威 2014 强激光与粒子束 26 063009
Google Scholar
Jiang L H, Li H, Wu Z W 2014 High Pow. Las. Part. Beam. 26 063009
Google Scholar
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