Influence of Reflections of the Output Port on Beam-wave Interaction in Gyrotron Traveling Wave Amplifier
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Influence of Reflections of the Output Port on Beam-wave Interaction in Gyrotron Traveling Wave Amplifier Haiyan Sun & Chongqing Jiao & Jirun Luo
Received: 7 April 2008 / Accepted: 17 April 2008 / Published online: 1 May 2008 # Springer Science + Business Media, LLC 2008
Abstract Based on the nonlinear self-consistent theory of gyrotron traveling wave amplifier (gyro-TWA), the influence of the reflections of the output port with the taper on the beam-wave interaction in the gyro-TWA is studied. The simulation results show that the reflections have great effects on the TE01 mode gyro-TWA operating at the fundamental. The influence of the taper angle and the interaction length on the beamwave interaction and the power profile is discussed and the corresponding physical mechanism is analyzed. The saturated output power keeps same approximately with the increase of the taper angle in the presence of reflection while the saturated gain decreases obviously. Keywords gyro-TWA . Beam-wave interaction . Reflection coefficient
1 Introduction High power and broad bandwidth capability of the gyrotron traveling wave amplifier makes it an attractive source of coherent radiation in the millimeter wavelength range. Gyro-TWA have a broad range of application, especially in radar and communication systems. Steady progress in theory and experiment has been made over an extended period of time. Major advances in gyro-TWA performances have been reported in the review papers. [1–6] The subject of the influence of reflections on gyrotron operation has been studied both theoretically and experimentally. [7–10] Generally, the output port is a matched load as expected, but it is impossible because of the structure, material, technology and so on in H. Sun (*) : J. Luo Institute of Electronics, Chinese Academy of Sciences, Beijing 100190, China e-mail: [email protected] H. Sun Graduate School, Chinese Academy of Sciences, Beijing 100039, China C. Jiao North China Electric Power University, Beijing 102206, China
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Int J Infrared Milli Waves (2008) 29:657–662
practice. Effects like reduction and variation of the output power, frequency pulling, and sequences of discrete frequency jumps as well as excitation of parasitic modes have been observed in the presence of reflections. [11–13] The amplitude and phase of the reflection have effects on beam-wave interaction, analyzing the influence of the reflections of the output port on the beam-wave interaction is useful in studying and designing of gyro-TWA. A nonlinear self-consistent time-independent code, based on a slow-time scale formulation, was developed to evaluate the performance of stable gyro-TWA. Only one TEmn mode is present and the structural nonuniformity is sufficiently weak that mode conversion is negligible in the code. The field equation driven by a current source can be expressed as [5] 2 n vj ð zÞE* rj ; θj ; tj ; z d 8jIb j X 2 f ð z Þ ¼ i þ k W ð1Þ j z x2mn Kmn 5 j¼1 dz2 vzj ðzÞf *ð zÞ Where f (z) is the field profile function along the axis, Ib is the beam c
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