ENHANCEMENT OF HIGH-POWER MM WAVE RADIATION BY THE BEAM-PLASMA INSTABILITY IN A DIELECTRIC-LOADED WAVEGUIDE

• Project/Area Number: 09680457
• Research Category: Grant-in-Aid for Scientific Research (C)
• Allocation Type: Single-year Grants
• Section: 一般
• Research Field: プラズマ理工学
• Research Institution: KANAZAWA UNIVERSITY
• Principal Investigator: MASUZAKI Masaru KANAZAWA UNIV. PROF., 理学部, 教授 (10110602)
• Co-Investigator(Kenkyū-buntansha): ANDO Ritoku KANAZAWA UNIV. LECTURER, 理学部, 講師 (80212679) ; KAMADA Keiichi KANAZAWA UNIV. ASOC. PROF., 理学部, 助教授 (90143875)
• Project Period (FY): 1997 – 1998
• Project Status: Completed (Fiscal Year 1998)
• Budget Amount: ¥3,000,000 (Direct Cost: ¥3,000,000); Fiscal Year 1998: ¥900,000 (Direct Cost: ¥900,000); Fiscal Year 1997: ¥2,100,000 (Direct Cost: ¥2,100,000)
• Keywords: microwave generation / intense relativistic electron beam / Cherenkov instability / cyclotron-Cherenkov instability / plasma-filled waveguide / beam-plasma instabilities / current amplification / 高出力ミリ波 / 相対論的電子ビーム / プラズマ・チェレンコフ自由電子レーザー / プラズマ・サイクロトロン・チェレンコフ自由電子レーザー

Research Abstract

1. THEORETICAL ANALYSIS
(1) We derived a dispersion relation for waves excited by an intense monoenergetic linear relativistic electron beam (IREB) in a plasma-filled dielectric-lined cylindrical waveguide immersed in a finite magnetic field. Finding is that, in addition to the Cherenkov and cyclotron-Cherenkov instabilities which can be excited in a vacuum waveguide, the beam-plasma instabilities are also excited. These instabilities are due to coupling of slow space-charge waves and slow cyclotron waves on the beam with Trivelpiece-Gould modes in the plasma.
(2) We analyzed numerically the dispersion relation and derived frequencies and growth rates of these instabilities.
(3) When the plasma frequency is lower than the electron cyclotron frequency, enhancement of the growth rates of the Cherenkov and the cyclotron-Cherenkov instabilities due to presence of the plasma are not observed. However, when the plasma frequency is higher than the cyclotron frequency, the growth rates of both in stabilities are enhanced, and, moreover, the growth rates of the beam-plasma instabilities are also much enhanced.
(4) The growth rates of the latter instabilities are much higher than the growth rates of the former instabilities and we can expect high-power radiation based on this mechanism with broad frequency band.
2. EXPERIMENTS
(1) We designed and manufactured an experimental device. A plasma was produced by ionizing argon gas introduced into the device with the injected IREB itself. We studied IREB propagation first, and observed current amplification phenomenon when the argon pressure was less than about 100 mTorr. Taking into account results of radiation measurement. we think that this phenomenon is caused by the beam-plasma instabilities.
(2) We observed broadband microwave radiation. The total power decreased much for the argon pressure higher than about 100 mTorr. The spectrum of the observed radiation shows contribution from the whole instabilities. This supports the idea that decrease of the total power for the argon pressure above 100 mTorr is due to suppression of the beam-plasma instabilities.

Research Products

• [Publications] M.MASUZAKI et al: "Linean analysis of instabilities in a plasma-fieled dielectric-lined circular waveguide immersed in a finite axial magnetic field"to be published in Proc. of the 12th Intern.couf.on High-Power Particle Beams.
  • Description: 「研究成果報告書概要(和文)」より
• [Publications] H.Tsukuda,M.Masuzaki et al.: "Instabilities driven by anintense beam in a plasma-fieled dielectric-lined waveguide immersed in a finite axial magnetic field."Proc.of 21st Intern.Free Electron Laser Conf.. (To be published).
  • Description: 「研究成果報告書概要(和文)」より
• [Publications] M. Masuzaki, H. Tsukuda, N. Toyosugi., K. Kamada, R. Ando, and T. Watanabe.: "Linear analysis of instabilities in a plasma-filled dielectric-lined circular waveguide immersed in a finite axial magnetic field."Proceedings of the 12th International Conference on High-Power Particle Beams (Haifa, Israel,). (To be published). (1998)
  • Description: 「研究成果報告書概要(欧文)」より
• [Publications] H. Tsukuda, M. Masuzaki, M. Matsuoka, N. Toyosygi, C. Y. Lee, R. Ando, K. Kamada, and T. Watanabe: "Instabilities driven by an intense beam in a plasma-filled dielectric-lined waveguide immersed in a finite axial magnetic field."Proceedings of 21st International Free Electron Laser Conference (Hamburg, Germany.). (To be published). (1999)
  • Description: 「研究成果報告書概要(欧文)」より