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Beam Interactions with Surface Waves and Higher-order Modes in Oversized Backward Wave Oscillators
Kazuo Ogura,Akihiko Kojima,Fumiaki Kawabe,Kiyoyuki Yambe,Md. Ruhul Amin 한국물리학회 2014 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.65 No.8
Beam interactions with surface waves and higher-order modes in an oversized backward waveoscillator (BWO) are studied. In addition to the well-known Cherenkov interaction, the slow cyclotroninteraction occurs due to transverse perturbations of the electron beam. The Cherenkovinteraction dominates the slow cyclotron interaction. Growth rates of both the interactions forthe higher order modes are small compared with those for the surface-wave modes in an oversizedBWO. The coaxial slow-wave structure exhibits a reduced number of higher-order modes, whichconsequently reduces the mode competition problem and improves beam interactions with higherordermodes. For higher values of beam currents, the slow cyclotron wave grows at a faster ratethan the Cherenkov waves.
Numerical Study of Slow-wave Instabilities in an Oversized Coaxial Slow-wave Structure
Kazuo Ogura,Shingo Abe,Hiroki Kimura,Kazumasa Yamamoto,Kiyoyuki Yambe,Ruhul Amin 한국물리학회 2011 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.59 No.61
In this paper, slow-wave instabilities in oversized coaxial SWSs are numerically analyzed. An infinitesimally thin annular beam with transverse perturbations and guided by a finite axial magnetic field is considered as the energy source for creating the instabilities. The coaxial SWSs consist of an outer oversized hollow waveguide and a central conductor and have sinusoidal corrugations. An electromagnetic slow-wave is generated by the inner corrugation and is called inner surface wave (ISW). The ISW is a cylindrical surface wave and can exist even if the outer conductor is removed. The higher-order modes are produced by the outer waveguide. The annular beam interacts with the ISW and higher-order modes. Slow cyclotron instability occurs due to the transversely modulated beam boundary, in addition to the conventional Cherenkov instability. The slow-wave instabilities are able to be controlled by the beam radius and the relative position of inner and outer corrugations.
Masatoh Takahashi,Kazuo Ogura,Hiroyuki Yoshimura,Hiroshi Iiduka,Akira Sugawara,Kiyoyuki Yambe,김원섭 한국물리학회 2011 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.59 No.61
Experimental studies of coaxial oversized backward wave oscillators (BWOs) are presented. The beam voltage is weakly relativistic less than 100 kV. The slow-wave structure (SWS) consists of a rectangularly corrugated oversized hollow waveguide and rectangularly corrugated inner conductor, whose target operating frequency due to Cherenkov interaction is in the K-band. The coaxial SWS can have two surface waves caused by the inner and outer corrugations. The oversized BWO operations under the influences of two surface waves are examined. An oscillation starting voltage decreases by introducing the rectangularly corrugated inner conductor. Output powers increase greatly as compared with those without the corrugated inner conductor. The inner corrugation improves the oversized BWO operation
Takayuki Iwasaki,Kazuo Ogura,Shota Magori,Junpei Kojima,Kiyoyuki Yambe 한국물리학회 2014 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.65 No.8
Smith-Purcell (SP) radiations of weakly relativistic oversized backward wave oscillator (BWO)are examined experimentally. A bunching section composed of a coaxial slow wave structure withinner K-band corrugation is placed upstream from the oversized BWO. An annular beam lessthan 100 kV is self-bunched in the bunching section and then excites the oversized BWO. SPradiations are examined by using 25.5- and 45.0-GHz oversized BWOs. The beam is too far awayfrom the walls of the oversized BWO for SP radiation to occur without the self-bunching. Whenthe corrugation parameters of the bunching section are the same as those of the oversized BWO,enhanced SP radiations in the frequency region above the surface wave are observed even when thebeam propagates outside the interaction region of the surface wave.