繞軸式電子槍所產生繞軸式的電子束被發展來驅動太赫茲諧波的磁旋裝置，諧波的交互作用能夠降低對磁場的要求，但會產生較嚴重的模式競爭。而繞軸式電子束能夠抑制在交互作用區段所產生的競爭模態。
對於電子動力學所研究的繞軸式電子槍發現在靠近發射帶所設計的電極，能夠產生集中且加速的電場，去平衡掉空間電荷效應的影響，以及磁旋半徑的偏差。在極力的優化之後，能夠用0.53 A的電流在作用區磁場大小3.35 T的強況下，產生一個速度比1.32、軸向速度發散9.98%的低電壓的繞軸式電子槍，這些優勢使得諸如TM11模式的反波振盪器的低電壓磁旋裝置得以開始發展。
在不特別需要特別大功率(>100000 W)的前提下，低電壓所提供的功率已足夠提供給一般使用，且有利於能夠大幅縮減設備價錢及尺寸，以及降低能源成本，將來也可朝桌上型裝置發展。

Axis-encircling gun is being developed to generate an axis-encircling beam to drive the terahertz harmonic gyro-devices. The harmonic interaction is able to mitigate the requirement of the magnetic field but suffer from serious mode competitions. The axis-encircling beam, however, is capable of suppressing the competing modes inside the interaction region. The study of the electron dynamics in the axis-encircling gun reveals that electrodes close to the emitter are employed to construct a focusing-accelerating electric field to balance the space-charge influence and guiding center deviation. Intensive optimization generates a low-voltage axis-encircling gun with a pitch factor of 1.32 and minimum axial velocity spread of 9.98% at a magnetic field of 3.35 T and a beam current of 0.53 A. These merits enable the low-voltage gyro-devices, like the TM11 mode gyrotron backward-wave oscillator to be developed. If the work above can be realized, lowering the voltage while maintaining a good efficiency of electron beam can result in a reduction of the cost of energy and the size of the equipment, that make portable gyrotron possible.

1. W. He, et al., “Axis-encircling electron beam generation using a smooth magnetic cusp for gyrodevices,” Appl. Phys. Lett. 93, pp. 121 501-1–121 501-3 (2008).

2. V. N. Manuilov, S. V. Samsonov, S. V. Mishakin, A. V. Klimov, K. A. Leshcheva , “Cusp guns for helical-waveguide gyro-twts of a high-gain high-power w-band amplifier cascade,” J. Infrared, Millim., Terahertz Waves , vol.39, no.5, pp.447-455 (2018).

3. V.N. Manuilov, “Cusp guns for helical-waveguide Gyro-TWTs of a high-gain high-power w-band amplifier cascade,” J. Infrared, Millim., Terahertz Waves vol. 39, no. 5 (2018).

4. V. L. Bratman, Y. K. Kalynov, and V. N. Manuilov, “Large-orbit gyrotron operation in the terahertz frequency range,” Phys. Rev. Lett., vol. 102, no. 24, pp. 245 101-1–245 101-4 (2009).

5. W.Lawson,“Design of low velocity‐spread cusp guns for axis encircling beams,” Appl. Phys. Lett., vol. 50, no. 21 (1987)

6. C. H. Du, X.B. Qi, B.L. Hao, T.H. Chang, and P.K. Liu, “Development of a magnetic cusp gun for tetrahertz harmonic gyrodevices,” IEEE Trans. Electron Devices, vol. 59, no. 12 (2012).

7. S. B. Harriet, D. B. McDermott, D. A. Gallagher, and N. C. Luhmann, Jr., “Cusp gun TE21 second harmonic Ka band gyro-TWT amplifier,” IEEE
Trans. Plasma Sci., vol. 30, no. 3, pp. 909–914 (2002)

8. S. V. Samsonov, et al., “Ka-Band gyrotron traveling-wave tubes with the highest continuous-wave and average power,” IEEE Trans. Electron Devices. vol. 61, no.12 (2014).

9. W. He, C. R. Donaldson, L. Zhang, K. Ronald, A. D. R. Phelps, and A. W. Cross, “Broadband amplification of low-terahertz signals using axis-encircling electrons in a helically corrugated interaction region,” Phys. Rev. Lett., vol. 119, no. 24, p.184801 (2017).

10. C. R. Donaldson, et al., “A cusp electron gun for millimeter wave gyrodevices,” Appl. Phys. Lett., vol. 96, no. 14, p141501-1–141 501-3 (2010).

11. C. R. Donaldson, W. He, A. W. Cross, A. D. R. Phelps, F. Li, K. Ronald, C. W. Robertson, C. G. Whyte, and A. R. Young, “Design and numerical optimization of a cusp-gun-based electron beam for millimeter-wave gyro-devices,” IEEE Trans. Plasma Sci., vol. 37, no. 11, pp. 2153–2157, (2009).

12. L. Zhang, C. R. Donaldson, and W. He, “Optimization of a triode-type cusp electron gun for a W-band gyro-TWA,” Phys. Plasmas, vol. 25, no. 4, (2018).

13. T. Idehara, et al.,“A high harmonic gyrotron with an axis-encircling electron beam and a permanent magnet,” IEEE Trans. Plasma Sci., vol. 32, no. 3, pp. 903–909 (2004).

14. S. G. Jeon, C. W. Baik, D. H. Kim, G. S. Park, N. Sato, and K. Yokoo, “Study on velocity spread for axis-encircling electron beams generated by single magnetic cusp,” Appl. Phys. Lett., vol. 80, no. 20, pp. 3703–3705 (2002).

15. S. G. Jeon, C. W. Baik, D. H. Kim, G. S. Park, N. Sato, and K. Yokoo, “Experimental verification of low-velocity spread axis-encircling electron beam,” Appl. Phys. Lett., vol. 84, no. 11, pp. 1994–1996 (2004).

16. W. T. Yang, “Study of Axis-Encircling Electron Beam Under Low Voltage Operation,” National Tsing Hua University, Hsinchu, 2019

17. S. G. Kim, et al., “System development and performance testing of a w-band gyrotron,” J. Infrared, Millim., Terahertz Waves. vol 37, no.3 , pp. 209-229 (2016).

18. Toshitaka Idehara, et al., “Development of frequency tunable, medium power gyrotrons (gyrotron FU series) as submillimeter wave radiation sources,” IEEE Trans. Plasma Sci., vol. 27, no. 2 (1999).

19. Z. H. Geng, et al., “Experiment and simulation of a W-band cw 30 kW low-voltage conventional gyrotron,” IEEE Trans. Electron Devices. vol. 61, no.6 (2014).

20. D. B. McDermott, R. C. Statzman, A.J. Balkcum , and N. C. Luhmann “94-GHz 25-kW cw low-voltage harmonic gyrotron,” IEEE Trans. Plasma Sci., vol. 26, no. 3 (1998).

21. M. Yu. Glyavin, A. G. Luchinin, and G. Yu. Golubiatnikov, “Generation of 1.5-kw, 1-THz coherent radiation from a gyrotron with a pulsed magnetic field,” Phys. Rev. Lett., vol. 100, no. 1 (2008).

22. M. Yu. Glyavin, et al., “Experimental demonstration of the possibility to expand the band of smooth tuning of frequency generation in short-cavity gyrotrons,” Radiophysics and Quantum Electronics , vol.61, no.11 (2019).

23. X.B.Qi, C. H. Du, et al., “Terahertz broadband-tunable minigyrotron with a pulse magnet,” IEEE Trans. Electron Devices. vol. 64, no.2 (2017).

24. T.H.Chang, et al.,“Frequency tunable gyrotron using backward-wave components,”J. Appl. Phys. , vol. 105, no. 6 (2009).

25. C. H. Tsai, T. H. Chang, “Non-Adiabatic Effects on Electron Beam Quality for Frequency-Tunable Gyrotrons,” Plasma Physics, arXiv:1904.12718

26. Andrey Fokin, et al.,”High-power sub-terahertz source with a record frequency stability at up to 1Hz,” scientific reports. vol. 8 (2018).

27. M. Yu. Glyavin, et al., “Experimental tests of a 263 GHz gyrotron for spectroscopic applications and diagnostics of various media,” Rev. Sci. Instrum., vol 86, no.5(2015).

28. Melissa K. Hornstein, et al., “Second harmonic operation at 460 GHz and broadband continuous frequency tuning of a gyrotron oscillator,” IEEE Trans. Electron Devices. vol. 52, no.5 (2005).

29. Toshitaka Idehara, et al., “Gyrotron FU cw VII for 300 MHz and 600 MHz DNP-NMR spectroscopy,” J. Infrared, Millim., Terahertz Waves. vol 31, no.7 (2010).

30. Tao Song, et al., “Study on the effect of electron beam quality on a continuously frequency-tunable 250-GHz gyrotron,” IEEE Trans. Electron Devices. vol. 65, no.4 (2018).

31. A. L. Goldenberg, M.Yu.Glyavin, N. A. Zavolsky, and V.N.Manuilov , “Technological gyrotron with low accelerating voltage,” Radiophysics and Quantum Electronics , vol.48, no.10-11 (2005).

32. M. K. Hornstein, V. S. Bajaj, R. G. Griffin, and R. J. Temkin,“Efficient Low-Voltage Operation of a CW Gyrotron Oscillator at 233 GHz,” IEEE Trans. Plasma Sci., vol. 35, no. 1 (2007).

33. Sergey A. Kishko, et al.,“Low-voltage cyclotron resonance maser,” IEEE Trans. Plasma Sci., vol. 49, no. 9, pp. 2475–2479 (2013).

34. V. L. Bratman, et al., “Operation of a sub-terahertz CW gyrotron with an extremely low voltage,” Phys. Plasmas, vol. 24, no. 11 (2017).

35. V. L. Bratman, et al., “Smooth Wideband Frequency Tuning in
Low-Voltage Gyrotron With Cathode-End Power Output,” IEEE Trans. Electron Devices. vol. 64, no.12 (2017).

36. B. Y. Wei , “Nonlinear and self-consistent simulation of TM-mode gyrotrons,” National Tsing Hua University, Hsinchu, 2018.

37. T. H. Chang, H.Y. Yao, B.Y. Su, W.C. Chen and B.Y. Wei, “Nonlinear oscillations of TM-mode gyrotrons,” Physics of Plasmas vol. 24,no. 12, p. 122109, 2017.

38. S. H. Kao et al., “Competition between harmonic cyclotron maser interactions in the terahertz regime,” Phys. Rev. Lett., vol. 107, no. 13, p. 135101 (2011).

39. Melissa K. Hornstein, Vikram S. Bajaj, Robert G. Griffin, and Richard J. Temkin, “ Efficient Low-Voltage Operation of a CW Gyrotron Oscillator at 233 GHz,” IEEE Trans. Plasma Sci., vol. 35, no. 1, pp. 27–30 (2007).

40. J.W. Gewartowski, and H.A. Watson, 1965, Principles of electron tubes (Van Nostrand, Princeton, NJ).

41. K. R. Chu, “The electron cyclotron maser,” Rev. Mod. Phys., vol. 76, no. 2, pp. 489–540 (2004).

42. C. P. Yuan, T. H. Chang, N. C. Chen, and Y. S. Yeh, “Magnetron injection gun for a broadband gyrotron backward-wave,” Phys. Plasmas, vol. 16, no. 7, p. 073109 (2009).

43. C. H. Du, et al., “Conformal cross-flow axis-encircling electron beam for driving thz harmonic gyrotron,” IEEE Trans. Electron Devices. vol. 36, no.9 (2015).

44. FS. G. Jeon, C. W. Baik, D. H. Kim, G. S. Park, N. Sato, and K. Yokoo, “Study on velocity spread for axis-encircling electron beams generated by single magnetic cusp,” Appl. Phys. Lett., vol. 80, no. 20, pp. 3703–3705 (2002).

45. S. G. Jeon, C. W. Baik, D. H. Kim, G. S. Park, N. Sato, and K. Yokoo, “Experimental verification of low-velocity spread axis-encircling electron beam,” Appl. Phys. Lett., vol. 84, no. 11, pp. 1994–1996 (2004).

46. C. Q. Jiao, J. R. Luo, “Linear theory of electron cyclotron maser based on TM circular waveguide mode,” Phys. Plasmas, vol. 13, no. 7, p.073104 (2006).

47. C. S. Kou and Fouries Tseng, “ Linear theory of gyrotron traveling wave tubes with nonuniform and lossy interaction structures,” Phys. Plasmas, vol. 5, no.6, p.2454 (1998).

48. C.S. Kou, “Starting oscillation conditions for gyrotron backward wave oscillators,” Phys. Plasmas, vol.1, no.9, p.3093 (1994).

49. Baird, J. Mark, and W.Lawson, “Magnetron injection gun (MIG) design for gyrotron applications,” Int. J.Electronics, vol. 61, no. 6, pp. 953-967 (1986).

50. Sh.E. Tsimring, “On the spread of velocities in helical electron beams,” Radiophysics and Quantum Electronics , vol.15,no.8, pp.952-961 (1972).

51. A. L.Gol’denberg, and M. I.Petelin , “The formation of helical electron beams in an adiabatic gun,” Radiophysics and Quantum Electronics , vol.16, no.1, pp.106-111 (1972).