AZIMUTHALLY ASYMMETRIC OSCILLATIONS IN THE DIELECTRIC CHERENKOV MASER

Theoretical and experimental evidences are presented showing that azim uthally asymmetric modes of a dielectric-loaded circular waveguide can also be generated due to the Cherenkov interaction mechanism with sym metric TM modes. A Cherenkov maser configuration with a thin annular r elativistic beam was analysed. Calculations for parameters of recent e xperiments [W. Main et al., IEEE Trans. Plasma Sci. PS-18 (1990) 507] and other experiments we carried out demonstrate the proximity of grow th rates and radiation frequencies. In our experiments we investigated the far field structure, the angular distribution and the spectrum of the output radiation, and we observed qualitatively different far fie ld patterns at various electron beam radii and, moreover, at various d ielectric liner lengths. Also, the possibility of high-order modes gen eration in the experiments of Main et al. is discussed.