1. 研究方向 Abstract This study proposes Ka-band and W-band harmonic multiplying gyro-TWTs, using distributed wall losses and attenuating severs, to improve the stability of the amplification and the performance of the ampli-fiers. By amplifying a (s=1) drive wave, the second harmonic component (s=2) of the beam cur-rent initiates a wave to be amplified. A nonlinear self-consistent code, based on a slow time scale formulation, is developed to evaluate the performance of stable gyro-TWT amplifiers. The electron beam interacting with multiple waveguide modes ( ) is presumed. Thus the structural nonuniformity must be sufficiently weak to prevent mode conversion. Keywords: harmonic multiplying gyro-TWT, nonlinearly driven oscillation. I. Introduction IV. Oscillator plane A Study of Harmonic Multiplying Gyrotron Traveling-wave Amplifiers with Distributed Wall Losses and Attenuating Severs Y. S. Yeh 1, C. L. Hung 2, T. H. Chang 3, Y. C. Lo 1, C. W. Hung 1 Department of Electro-Optical Engineering, Southern Taiwan University, Tainan 710, Taiwan 2 Department of Communication Engineering, National Penghu University of Science and Technology, Penghu 880, Taiwan 3 Department of Physics, National Tsing Hua University, Hsinchu 300, Taiwan V. Performance of the gyro-TWT 1. T. H. Chang, S. H. Chen, F. H. Cheng, C. S. Kou, and K. R. Chu, “Experimental study of an injection locked Gyro-BWO,” in Proc. 24th IRMMW, 1999, p. M–A2. 2. Y. S. Yeh, T. H. Chang, and Y. C. Yu, "Stability analysis of a gyrotron backward-wave oscillator with an external injection signal ", IEEE Trans. Plasma. Sci., vol. 34, no. 4, pp. 1523-1528, 2006. 3.A. McCurdy, A. Ganguly, and C. Armstrong,"Operation and theory of a driven single mode electron cyclotron maser,” Phys. Rev. A, vol. 44, pp. 1402-1422, 1989. 4.N. Minorsky, "Nonlinear Osicllation,” Van Nostrand, Princeton, NJ, 1962, p.71.  Amplifier mode References II. Computer Models of Nonlinear Simulation Code 6.5 7.5 The authors are also grateful to the National Center for High-Performance Computing (NCHC) for providing computing facilities and technical supports. This work was supported by the National Science Council under Contract No. NSC98-2221-E-218-014. Acknowledgments f (GHz) B 0 =12.7 kG 13.0 kG 12.8 kG  Amplitude-frequency response  Saturation output power The high power and broad bandwidth capabilities of gyrotron traveling-wave amplifiers (gyro-TWTs) make them attractive sources in the millimeter wave range. Harmonic multiplying gyrotron traveling-wave amplifiers (gyro-TWTs) provide the magnetic field reduction and frequency multiplication. However, spurious oscillations may reduce the amplification of the gyro-TWT. Most structures with distributed wall losses are stabilized in gyro-TWTs that operate at low beam currents. Attenuating severs are added to the interaction circuit of a distributed- loss gyro-TWT to prevent high beam currents that result in mode competition. Distributed-loss gyrotron traveling- wave amplifiers with high-gain, broadband, and millimeter-wave capabilities have been demonstrated. Most structures with distributed wall losses are stabilized in gyro-TWTs that operate at low beam currents. Attenuating severs are added to the interaction circuit of a distributed- loss gyro-TWT to prevent high beam currents that result in mode competition [3]. Fields of the circularly polarized TE mn mode Field equation Relativistic equation of motion Fundamental mode ； Harmonic mode ； 4.